Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/kernel/cgroup.c

  1 /*
  2  *  Generic process-grouping system.
  3  *
  4  *  Based originally on the cpuset system, extracted by Paul Menage
  5  *  Copyright (C) 2006 Google, Inc
  6  *
  7  *  Notifications support
  8  *  Copyright (C) 2009 Nokia Corporation
  9  *  Author: Kirill A. Shutemov
 10  *
 11  *  Copyright notices from the original cpuset code:
 12  *  --------------------------------------------------
 13  *  Copyright (C) 2003 BULL SA.
 14  *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
 15  *
 16  *  Portions derived from Patrick Mochel's sysfs code.
 17  *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 18  *
 19  *  2003-10-10 Written by Simon Derr.
 20  *  2003-10-22 Updates by Stephen Hemminger.
 21  *  2004 May-July Rework by Paul Jackson.
 22  *  ---------------------------------------------------
 23  *
 24  *  This file is subject to the terms and conditions of the GNU General Public
 25  *  License.  See the file COPYING in the main directory of the Linux
 26  *  distribution for more details.
 27  */
 28 
 29 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 30 
 31 #include <linux/cgroup.h>
 32 #include <linux/cred.h>
 33 #include <linux/ctype.h>
 34 #include <linux/errno.h>
 35 #include <linux/init_task.h>
 36 #include <linux/kernel.h>
 37 #include <linux/list.h>
 38 #include <linux/magic.h>
 39 #include <linux/mm.h>
 40 #include <linux/mutex.h>
 41 #include <linux/mount.h>
 42 #include <linux/pagemap.h>
 43 #include <linux/proc_fs.h>
 44 #include <linux/rcupdate.h>
 45 #include <linux/sched.h>
 46 #include <linux/slab.h>
 47 #include <linux/spinlock.h>
 48 #include <linux/percpu-rwsem.h>
 49 #include <linux/string.h>
 50 #include <linux/sort.h>
 51 #include <linux/kmod.h>
 52 #include <linux/delayacct.h>
 53 #include <linux/cgroupstats.h>
 54 #include <linux/hashtable.h>
 55 #include <linux/pid_namespace.h>
 56 #include <linux/idr.h>
 57 #include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
 58 #include <linux/kthread.h>
 59 #include <linux/delay.h>
 60 #include <linux/atomic.h>
 61 #include <linux/cpuset.h>
 62 #include <linux/proc_ns.h>
 63 #include <linux/nsproxy.h>
 64 #include <linux/file.h>
 65 #include <net/sock.h>
 66 
 67 #define CREATE_TRACE_POINTS
 68 #include <trace/events/cgroup.h>
 69 
 70 /*
 71  * pidlists linger the following amount before being destroyed.  The goal
 72  * is avoiding frequent destruction in the middle of consecutive read calls
 73  * Expiring in the middle is a performance problem not a correctness one.
 74  * 1 sec should be enough.
 75  */
 76 #define CGROUP_PIDLIST_DESTROY_DELAY    HZ
 77 
 78 #define CGROUP_FILE_NAME_MAX            (MAX_CGROUP_TYPE_NAMELEN +      \
 79                                          MAX_CFTYPE_NAME + 2)
 80 
 81 /*
 82  * cgroup_mutex is the master lock.  Any modification to cgroup or its
 83  * hierarchy must be performed while holding it.
 84  *
 85  * css_set_lock protects task->cgroups pointer, the list of css_set
 86  * objects, and the chain of tasks off each css_set.
 87  *
 88  * These locks are exported if CONFIG_PROVE_RCU so that accessors in
 89  * cgroup.h can use them for lockdep annotations.
 90  */
 91 #ifdef CONFIG_PROVE_RCU
 92 DEFINE_MUTEX(cgroup_mutex);
 93 DEFINE_SPINLOCK(css_set_lock);
 94 EXPORT_SYMBOL_GPL(cgroup_mutex);
 95 EXPORT_SYMBOL_GPL(css_set_lock);
 96 #else
 97 static DEFINE_MUTEX(cgroup_mutex);
 98 static DEFINE_SPINLOCK(css_set_lock);
 99 #endif
100 
101 /*
102  * Protects cgroup_idr and css_idr so that IDs can be released without
103  * grabbing cgroup_mutex.
104  */
105 static DEFINE_SPINLOCK(cgroup_idr_lock);
106 
107 /*
108  * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
109  * against file removal/re-creation across css hiding.
110  */
111 static DEFINE_SPINLOCK(cgroup_file_kn_lock);
112 
113 /*
114  * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
115  * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
116  */
117 static DEFINE_SPINLOCK(release_agent_path_lock);
118 
119 struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
120 
121 #define cgroup_assert_mutex_or_rcu_locked()                             \
122         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
123                            !lockdep_is_held(&cgroup_mutex),             \
124                            "cgroup_mutex or RCU read lock required");
125 
126 /*
127  * cgroup destruction makes heavy use of work items and there can be a lot
128  * of concurrent destructions.  Use a separate workqueue so that cgroup
129  * destruction work items don't end up filling up max_active of system_wq
130  * which may lead to deadlock.
131  */
132 static struct workqueue_struct *cgroup_destroy_wq;
133 
134 /*
135  * pidlist destructions need to be flushed on cgroup destruction.  Use a
136  * separate workqueue as flush domain.
137  */
138 static struct workqueue_struct *cgroup_pidlist_destroy_wq;
139 
140 /* generate an array of cgroup subsystem pointers */
141 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
142 static struct cgroup_subsys *cgroup_subsys[] = {
143 #include <linux/cgroup_subsys.h>
144 };
145 #undef SUBSYS
146 
147 /* array of cgroup subsystem names */
148 #define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
149 static const char *cgroup_subsys_name[] = {
150 #include <linux/cgroup_subsys.h>
151 };
152 #undef SUBSYS
153 
154 /* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
155 #define SUBSYS(_x)                                                              \
156         DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);                 \
157         DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);                  \
158         EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);                      \
159         EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
160 #include <linux/cgroup_subsys.h>
161 #undef SUBSYS
162 
163 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
164 static struct static_key_true *cgroup_subsys_enabled_key[] = {
165 #include <linux/cgroup_subsys.h>
166 };
167 #undef SUBSYS
168 
169 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
170 static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
171 #include <linux/cgroup_subsys.h>
172 };
173 #undef SUBSYS
174 
175 /*
176  * The default hierarchy, reserved for the subsystems that are otherwise
177  * unattached - it never has more than a single cgroup, and all tasks are
178  * part of that cgroup.
179  */
180 struct cgroup_root cgrp_dfl_root;
181 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
182 
183 /*
184  * The default hierarchy always exists but is hidden until mounted for the
185  * first time.  This is for backward compatibility.
186  */
187 static bool cgrp_dfl_visible;
188 
189 /* Controllers blocked by the commandline in v1 */
190 static u16 cgroup_no_v1_mask;
191 
192 /* some controllers are not supported in the default hierarchy */
193 static u16 cgrp_dfl_inhibit_ss_mask;
194 
195 /* some controllers are implicitly enabled on the default hierarchy */
196 static unsigned long cgrp_dfl_implicit_ss_mask;
197 
198 /* The list of hierarchy roots */
199 
200 static LIST_HEAD(cgroup_roots);
201 static int cgroup_root_count;
202 
203 /* hierarchy ID allocation and mapping, protected by cgroup_mutex */
204 static DEFINE_IDR(cgroup_hierarchy_idr);
205 
206 /*
207  * Assign a monotonically increasing serial number to csses.  It guarantees
208  * cgroups with bigger numbers are newer than those with smaller numbers.
209  * Also, as csses are always appended to the parent's ->children list, it
210  * guarantees that sibling csses are always sorted in the ascending serial
211  * number order on the list.  Protected by cgroup_mutex.
212  */
213 static u64 css_serial_nr_next = 1;
214 
215 /*
216  * These bitmask flags indicate whether tasks in the fork and exit paths have
217  * fork/exit handlers to call. This avoids us having to do extra work in the
218  * fork/exit path to check which subsystems have fork/exit callbacks.
219  */
220 static u16 have_fork_callback __read_mostly;
221 static u16 have_exit_callback __read_mostly;
222 static u16 have_free_callback __read_mostly;
223 
224 /* cgroup namespace for init task */
225 struct cgroup_namespace init_cgroup_ns = {
226         .count          = { .counter = 2, },
227         .user_ns        = &init_user_ns,
228         .ns.ops         = &cgroupns_operations,
229         .ns.inum        = PROC_CGROUP_INIT_INO,
230         .root_cset      = &init_css_set,
231 };
232 
233 /* Ditto for the can_fork callback. */
234 static u16 have_canfork_callback __read_mostly;
235 
236 static struct file_system_type cgroup2_fs_type;
237 static struct cftype cgroup_dfl_base_files[];
238 static struct cftype cgroup_legacy_base_files[];
239 
240 static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
241 static void cgroup_lock_and_drain_offline(struct cgroup *cgrp);
242 static int cgroup_apply_control(struct cgroup *cgrp);
243 static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
244 static void css_task_iter_advance(struct css_task_iter *it);
245 static int cgroup_destroy_locked(struct cgroup *cgrp);
246 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
247                                               struct cgroup_subsys *ss);
248 static void css_release(struct percpu_ref *ref);
249 static void kill_css(struct cgroup_subsys_state *css);
250 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
251                               struct cgroup *cgrp, struct cftype cfts[],
252                               bool is_add);
253 
254 /**
255  * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
256  * @ssid: subsys ID of interest
257  *
258  * cgroup_subsys_enabled() can only be used with literal subsys names which
259  * is fine for individual subsystems but unsuitable for cgroup core.  This
260  * is slower static_key_enabled() based test indexed by @ssid.
261  */
262 static bool cgroup_ssid_enabled(int ssid)
263 {
264         if (CGROUP_SUBSYS_COUNT == 0)
265                 return false;
266 
267         return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
268 }
269 
270 static bool cgroup_ssid_no_v1(int ssid)
271 {
272         return cgroup_no_v1_mask & (1 << ssid);
273 }
274 
275 /**
276  * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
277  * @cgrp: the cgroup of interest
278  *
279  * The default hierarchy is the v2 interface of cgroup and this function
280  * can be used to test whether a cgroup is on the default hierarchy for
281  * cases where a subsystem should behave differnetly depending on the
282  * interface version.
283  *
284  * The set of behaviors which change on the default hierarchy are still
285  * being determined and the mount option is prefixed with __DEVEL__.
286  *
287  * List of changed behaviors:
288  *
289  * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
290  *   and "name" are disallowed.
291  *
292  * - When mounting an existing superblock, mount options should match.
293  *
294  * - Remount is disallowed.
295  *
296  * - rename(2) is disallowed.
297  *
298  * - "tasks" is removed.  Everything should be at process granularity.  Use
299  *   "cgroup.procs" instead.
300  *
301  * - "cgroup.procs" is not sorted.  pids will be unique unless they got
302  *   recycled inbetween reads.
303  *
304  * - "release_agent" and "notify_on_release" are removed.  Replacement
305  *   notification mechanism will be implemented.
306  *
307  * - "cgroup.clone_children" is removed.
308  *
309  * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
310  *   and its descendants contain no task; otherwise, 1.  The file also
311  *   generates kernfs notification which can be monitored through poll and
312  *   [di]notify when the value of the file changes.
313  *
314  * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
315  *   take masks of ancestors with non-empty cpus/mems, instead of being
316  *   moved to an ancestor.
317  *
318  * - cpuset: a task can be moved into an empty cpuset, and again it takes
319  *   masks of ancestors.
320  *
321  * - memcg: use_hierarchy is on by default and the cgroup file for the flag
322  *   is not created.
323  *
324  * - blkcg: blk-throttle becomes properly hierarchical.
325  *
326  * - debug: disallowed on the default hierarchy.
327  */
328 static bool cgroup_on_dfl(const struct cgroup *cgrp)
329 {
330         return cgrp->root == &cgrp_dfl_root;
331 }
332 
333 /* IDR wrappers which synchronize using cgroup_idr_lock */
334 static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
335                             gfp_t gfp_mask)
336 {
337         int ret;
338 
339         idr_preload(gfp_mask);
340         spin_lock_bh(&cgroup_idr_lock);
341         ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
342         spin_unlock_bh(&cgroup_idr_lock);
343         idr_preload_end();
344         return ret;
345 }
346 
347 static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
348 {
349         void *ret;
350 
351         spin_lock_bh(&cgroup_idr_lock);
352         ret = idr_replace(idr, ptr, id);
353         spin_unlock_bh(&cgroup_idr_lock);
354         return ret;
355 }
356 
357 static void cgroup_idr_remove(struct idr *idr, int id)
358 {
359         spin_lock_bh(&cgroup_idr_lock);
360         idr_remove(idr, id);
361         spin_unlock_bh(&cgroup_idr_lock);
362 }
363 
364 static struct cgroup *cgroup_parent(struct cgroup *cgrp)
365 {
366         struct cgroup_subsys_state *parent_css = cgrp->self.parent;
367 
368         if (parent_css)
369                 return container_of(parent_css, struct cgroup, self);
370         return NULL;
371 }
372 
373 /* subsystems visibly enabled on a cgroup */
374 static u16 cgroup_control(struct cgroup *cgrp)
375 {
376         struct cgroup *parent = cgroup_parent(cgrp);
377         u16 root_ss_mask = cgrp->root->subsys_mask;
378 
379         if (parent)
380                 return parent->subtree_control;
381 
382         if (cgroup_on_dfl(cgrp))
383                 root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
384                                   cgrp_dfl_implicit_ss_mask);
385         return root_ss_mask;
386 }
387 
388 /* subsystems enabled on a cgroup */
389 static u16 cgroup_ss_mask(struct cgroup *cgrp)
390 {
391         struct cgroup *parent = cgroup_parent(cgrp);
392 
393         if (parent)
394                 return parent->subtree_ss_mask;
395 
396         return cgrp->root->subsys_mask;
397 }
398 
399 /**
400  * cgroup_css - obtain a cgroup's css for the specified subsystem
401  * @cgrp: the cgroup of interest
402  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
403  *
404  * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
405  * function must be called either under cgroup_mutex or rcu_read_lock() and
406  * the caller is responsible for pinning the returned css if it wants to
407  * keep accessing it outside the said locks.  This function may return
408  * %NULL if @cgrp doesn't have @subsys_id enabled.
409  */
410 static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
411                                               struct cgroup_subsys *ss)
412 {
413         if (ss)
414                 return rcu_dereference_check(cgrp->subsys[ss->id],
415                                         lockdep_is_held(&cgroup_mutex));
416         else
417                 return &cgrp->self;
418 }
419 
420 /**
421  * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
422  * @cgrp: the cgroup of interest
423  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
424  *
425  * Similar to cgroup_css() but returns the effective css, which is defined
426  * as the matching css of the nearest ancestor including self which has @ss
427  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
428  * function is guaranteed to return non-NULL css.
429  */
430 static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
431                                                 struct cgroup_subsys *ss)
432 {
433         lockdep_assert_held(&cgroup_mutex);
434 
435         if (!ss)
436                 return &cgrp->self;
437 
438         /*
439          * This function is used while updating css associations and thus
440          * can't test the csses directly.  Test ss_mask.
441          */
442         while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
443                 cgrp = cgroup_parent(cgrp);
444                 if (!cgrp)
445                         return NULL;
446         }
447 
448         return cgroup_css(cgrp, ss);
449 }
450 
451 /**
452  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
453  * @cgrp: the cgroup of interest
454  * @ss: the subsystem of interest
455  *
456  * Find and get the effective css of @cgrp for @ss.  The effective css is
457  * defined as the matching css of the nearest ancestor including self which
458  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
459  * the root css is returned, so this function always returns a valid css.
460  * The returned css must be put using css_put().
461  */
462 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
463                                              struct cgroup_subsys *ss)
464 {
465         struct cgroup_subsys_state *css;
466 
467         rcu_read_lock();
468 
469         do {
470                 css = cgroup_css(cgrp, ss);
471 
472                 if (css && css_tryget_online(css))
473                         goto out_unlock;
474                 cgrp = cgroup_parent(cgrp);
475         } while (cgrp);
476 
477         css = init_css_set.subsys[ss->id];
478         css_get(css);
479 out_unlock:
480         rcu_read_unlock();
481         return css;
482 }
483 
484 /* convenient tests for these bits */
485 static inline bool cgroup_is_dead(const struct cgroup *cgrp)
486 {
487         return !(cgrp->self.flags & CSS_ONLINE);
488 }
489 
490 static void cgroup_get(struct cgroup *cgrp)
491 {
492         WARN_ON_ONCE(cgroup_is_dead(cgrp));
493         css_get(&cgrp->self);
494 }
495 
496 static bool cgroup_tryget(struct cgroup *cgrp)
497 {
498         return css_tryget(&cgrp->self);
499 }
500 
501 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
502 {
503         struct cgroup *cgrp = of->kn->parent->priv;
504         struct cftype *cft = of_cft(of);
505 
506         /*
507          * This is open and unprotected implementation of cgroup_css().
508          * seq_css() is only called from a kernfs file operation which has
509          * an active reference on the file.  Because all the subsystem
510          * files are drained before a css is disassociated with a cgroup,
511          * the matching css from the cgroup's subsys table is guaranteed to
512          * be and stay valid until the enclosing operation is complete.
513          */
514         if (cft->ss)
515                 return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
516         else
517                 return &cgrp->self;
518 }
519 EXPORT_SYMBOL_GPL(of_css);
520 
521 static int notify_on_release(const struct cgroup *cgrp)
522 {
523         return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
524 }
525 
526 /**
527  * for_each_css - iterate all css's of a cgroup
528  * @css: the iteration cursor
529  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
530  * @cgrp: the target cgroup to iterate css's of
531  *
532  * Should be called under cgroup_[tree_]mutex.
533  */
534 #define for_each_css(css, ssid, cgrp)                                   \
535         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
536                 if (!((css) = rcu_dereference_check(                    \
537                                 (cgrp)->subsys[(ssid)],                 \
538                                 lockdep_is_held(&cgroup_mutex)))) { }   \
539                 else
540 
541 /**
542  * for_each_e_css - iterate all effective css's of a cgroup
543  * @css: the iteration cursor
544  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
545  * @cgrp: the target cgroup to iterate css's of
546  *
547  * Should be called under cgroup_[tree_]mutex.
548  */
549 #define for_each_e_css(css, ssid, cgrp)                                 \
550         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
551                 if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
552                         ;                                               \
553                 else
554 
555 /**
556  * for_each_subsys - iterate all enabled cgroup subsystems
557  * @ss: the iteration cursor
558  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
559  */
560 #define for_each_subsys(ss, ssid)                                       \
561         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&                \
562              (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
563 
564 /**
565  * do_each_subsys_mask - filter for_each_subsys with a bitmask
566  * @ss: the iteration cursor
567  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
568  * @ss_mask: the bitmask
569  *
570  * The block will only run for cases where the ssid-th bit (1 << ssid) of
571  * @ss_mask is set.
572  */
573 #define do_each_subsys_mask(ss, ssid, ss_mask) do {                     \
574         unsigned long __ss_mask = (ss_mask);                            \
575         if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */ \
576                 (ssid) = 0;                                             \
577                 break;                                                  \
578         }                                                               \
579         for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {       \
580                 (ss) = cgroup_subsys[ssid];                             \
581                 {
582 
583 #define while_each_subsys_mask()                                        \
584                 }                                                       \
585         }                                                               \
586 } while (false)
587 
588 /* iterate across the hierarchies */
589 #define for_each_root(root)                                             \
590         list_for_each_entry((root), &cgroup_roots, root_list)
591 
592 /* iterate over child cgrps, lock should be held throughout iteration */
593 #define cgroup_for_each_live_child(child, cgrp)                         \
594         list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
595                 if (({ lockdep_assert_held(&cgroup_mutex);              \
596                        cgroup_is_dead(child); }))                       \
597                         ;                                               \
598                 else
599 
600 /* walk live descendants in preorder */
601 #define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)          \
602         css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))  \
603                 if (({ lockdep_assert_held(&cgroup_mutex);              \
604                        (dsct) = (d_css)->cgroup;                        \
605                        cgroup_is_dead(dsct); }))                        \
606                         ;                                               \
607                 else
608 
609 /* walk live descendants in postorder */
610 #define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)         \
611         css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
612                 if (({ lockdep_assert_held(&cgroup_mutex);              \
613                        (dsct) = (d_css)->cgroup;                        \
614                        cgroup_is_dead(dsct); }))                        \
615                         ;                                               \
616                 else
617 
618 static void cgroup_release_agent(struct work_struct *work);
619 static void check_for_release(struct cgroup *cgrp);
620 
621 /*
622  * A cgroup can be associated with multiple css_sets as different tasks may
623  * belong to different cgroups on different hierarchies.  In the other
624  * direction, a css_set is naturally associated with multiple cgroups.
625  * This M:N relationship is represented by the following link structure
626  * which exists for each association and allows traversing the associations
627  * from both sides.
628  */
629 struct cgrp_cset_link {
630         /* the cgroup and css_set this link associates */
631         struct cgroup           *cgrp;
632         struct css_set          *cset;
633 
634         /* list of cgrp_cset_links anchored at cgrp->cset_links */
635         struct list_head        cset_link;
636 
637         /* list of cgrp_cset_links anchored at css_set->cgrp_links */
638         struct list_head        cgrp_link;
639 };
640 
641 /*
642  * The default css_set - used by init and its children prior to any
643  * hierarchies being mounted. It contains a pointer to the root state
644  * for each subsystem. Also used to anchor the list of css_sets. Not
645  * reference-counted, to improve performance when child cgroups
646  * haven't been created.
647  */
648 struct css_set init_css_set = {
649         .refcount               = ATOMIC_INIT(1),
650         .cgrp_links             = LIST_HEAD_INIT(init_css_set.cgrp_links),
651         .tasks                  = LIST_HEAD_INIT(init_css_set.tasks),
652         .mg_tasks               = LIST_HEAD_INIT(init_css_set.mg_tasks),
653         .mg_preload_node        = LIST_HEAD_INIT(init_css_set.mg_preload_node),
654         .mg_node                = LIST_HEAD_INIT(init_css_set.mg_node),
655         .task_iters             = LIST_HEAD_INIT(init_css_set.task_iters),
656 };
657 
658 static int css_set_count        = 1;    /* 1 for init_css_set */
659 
660 /**
661  * css_set_populated - does a css_set contain any tasks?
662  * @cset: target css_set
663  */
664 static bool css_set_populated(struct css_set *cset)
665 {
666         lockdep_assert_held(&css_set_lock);
667 
668         return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
669 }
670 
671 /**
672  * cgroup_update_populated - updated populated count of a cgroup
673  * @cgrp: the target cgroup
674  * @populated: inc or dec populated count
675  *
676  * One of the css_sets associated with @cgrp is either getting its first
677  * task or losing the last.  Update @cgrp->populated_cnt accordingly.  The
678  * count is propagated towards root so that a given cgroup's populated_cnt
679  * is zero iff the cgroup and all its descendants don't contain any tasks.
680  *
681  * @cgrp's interface file "cgroup.populated" is zero if
682  * @cgrp->populated_cnt is zero and 1 otherwise.  When @cgrp->populated_cnt
683  * changes from or to zero, userland is notified that the content of the
684  * interface file has changed.  This can be used to detect when @cgrp and
685  * its descendants become populated or empty.
686  */
687 static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
688 {
689         lockdep_assert_held(&css_set_lock);
690 
691         do {
692                 bool trigger;
693 
694                 if (populated)
695                         trigger = !cgrp->populated_cnt++;
696                 else
697                         trigger = !--cgrp->populated_cnt;
698 
699                 if (!trigger)
700                         break;
701 
702                 check_for_release(cgrp);
703                 cgroup_file_notify(&cgrp->events_file);
704 
705                 cgrp = cgroup_parent(cgrp);
706         } while (cgrp);
707 }
708 
709 /**
710  * css_set_update_populated - update populated state of a css_set
711  * @cset: target css_set
712  * @populated: whether @cset is populated or depopulated
713  *
714  * @cset is either getting the first task or losing the last.  Update the
715  * ->populated_cnt of all associated cgroups accordingly.
716  */
717 static void css_set_update_populated(struct css_set *cset, bool populated)
718 {
719         struct cgrp_cset_link *link;
720 
721         lockdep_assert_held(&css_set_lock);
722 
723         list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
724                 cgroup_update_populated(link->cgrp, populated);
725 }
726 
727 /**
728  * css_set_move_task - move a task from one css_set to another
729  * @task: task being moved
730  * @from_cset: css_set @task currently belongs to (may be NULL)
731  * @to_cset: new css_set @task is being moved to (may be NULL)
732  * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
733  *
734  * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
735  * css_set, @from_cset can be NULL.  If @task is being disassociated
736  * instead of moved, @to_cset can be NULL.
737  *
738  * This function automatically handles populated_cnt updates and
739  * css_task_iter adjustments but the caller is responsible for managing
740  * @from_cset and @to_cset's reference counts.
741  */
742 static void css_set_move_task(struct task_struct *task,
743                               struct css_set *from_cset, struct css_set *to_cset,
744                               bool use_mg_tasks)
745 {
746         lockdep_assert_held(&css_set_lock);
747 
748         if (to_cset && !css_set_populated(to_cset))
749                 css_set_update_populated(to_cset, true);
750 
751         if (from_cset) {
752                 struct css_task_iter *it, *pos;
753 
754                 WARN_ON_ONCE(list_empty(&task->cg_list));
755 
756                 /*
757                  * @task is leaving, advance task iterators which are
758                  * pointing to it so that they can resume at the next
759                  * position.  Advancing an iterator might remove it from
760                  * the list, use safe walk.  See css_task_iter_advance*()
761                  * for details.
762                  */
763                 list_for_each_entry_safe(it, pos, &from_cset->task_iters,
764                                          iters_node)
765                         if (it->task_pos == &task->cg_list)
766                                 css_task_iter_advance(it);
767 
768                 list_del_init(&task->cg_list);
769                 if (!css_set_populated(from_cset))
770                         css_set_update_populated(from_cset, false);
771         } else {
772                 WARN_ON_ONCE(!list_empty(&task->cg_list));
773         }
774 
775         if (to_cset) {
776                 /*
777                  * We are synchronized through cgroup_threadgroup_rwsem
778                  * against PF_EXITING setting such that we can't race
779                  * against cgroup_exit() changing the css_set to
780                  * init_css_set and dropping the old one.
781                  */
782                 WARN_ON_ONCE(task->flags & PF_EXITING);
783 
784                 rcu_assign_pointer(task->cgroups, to_cset);
785                 list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
786                                                              &to_cset->tasks);
787         }
788 }
789 
790 /*
791  * hash table for cgroup groups. This improves the performance to find
792  * an existing css_set. This hash doesn't (currently) take into
793  * account cgroups in empty hierarchies.
794  */
795 #define CSS_SET_HASH_BITS       7
796 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
797 
798 static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
799 {
800         unsigned long key = 0UL;
801         struct cgroup_subsys *ss;
802         int i;
803 
804         for_each_subsys(ss, i)
805                 key += (unsigned long)css[i];
806         key = (key >> 16) ^ key;
807 
808         return key;
809 }
810 
811 static void put_css_set_locked(struct css_set *cset)
812 {
813         struct cgrp_cset_link *link, *tmp_link;
814         struct cgroup_subsys *ss;
815         int ssid;
816 
817         lockdep_assert_held(&css_set_lock);
818 
819         if (!atomic_dec_and_test(&cset->refcount))
820                 return;
821 
822         /* This css_set is dead. unlink it and release cgroup and css refs */
823         for_each_subsys(ss, ssid) {
824                 list_del(&cset->e_cset_node[ssid]);
825                 css_put(cset->subsys[ssid]);
826         }
827         hash_del(&cset->hlist);
828         css_set_count--;
829 
830         list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
831                 list_del(&link->cset_link);
832                 list_del(&link->cgrp_link);
833                 if (cgroup_parent(link->cgrp))
834                         cgroup_put(link->cgrp);
835                 kfree(link);
836         }
837 
838         kfree_rcu(cset, rcu_head);
839 }
840 
841 static void put_css_set(struct css_set *cset)
842 {
843         unsigned long flags;
844 
845         /*
846          * Ensure that the refcount doesn't hit zero while any readers
847          * can see it. Similar to atomic_dec_and_lock(), but for an
848          * rwlock
849          */
850         if (atomic_add_unless(&cset->refcount, -1, 1))
851                 return;
852 
853         spin_lock_irqsave(&css_set_lock, flags);
854         put_css_set_locked(cset);
855         spin_unlock_irqrestore(&css_set_lock, flags);
856 }
857 
858 /*
859  * refcounted get/put for css_set objects
860  */
861 static inline void get_css_set(struct css_set *cset)
862 {
863         atomic_inc(&cset->refcount);
864 }
865 
866 /**
867  * compare_css_sets - helper function for find_existing_css_set().
868  * @cset: candidate css_set being tested
869  * @old_cset: existing css_set for a task
870  * @new_cgrp: cgroup that's being entered by the task
871  * @template: desired set of css pointers in css_set (pre-calculated)
872  *
873  * Returns true if "cset" matches "old_cset" except for the hierarchy
874  * which "new_cgrp" belongs to, for which it should match "new_cgrp".
875  */
876 static bool compare_css_sets(struct css_set *cset,
877                              struct css_set *old_cset,
878                              struct cgroup *new_cgrp,
879                              struct cgroup_subsys_state *template[])
880 {
881         struct list_head *l1, *l2;
882 
883         /*
884          * On the default hierarchy, there can be csets which are
885          * associated with the same set of cgroups but different csses.
886          * Let's first ensure that csses match.
887          */
888         if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
889                 return false;
890 
891         /*
892          * Compare cgroup pointers in order to distinguish between
893          * different cgroups in hierarchies.  As different cgroups may
894          * share the same effective css, this comparison is always
895          * necessary.
896          */
897         l1 = &cset->cgrp_links;
898         l2 = &old_cset->cgrp_links;
899         while (1) {
900                 struct cgrp_cset_link *link1, *link2;
901                 struct cgroup *cgrp1, *cgrp2;
902 
903                 l1 = l1->next;
904                 l2 = l2->next;
905                 /* See if we reached the end - both lists are equal length. */
906                 if (l1 == &cset->cgrp_links) {
907                         BUG_ON(l2 != &old_cset->cgrp_links);
908                         break;
909                 } else {
910                         BUG_ON(l2 == &old_cset->cgrp_links);
911                 }
912                 /* Locate the cgroups associated with these links. */
913                 link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
914                 link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
915                 cgrp1 = link1->cgrp;
916                 cgrp2 = link2->cgrp;
917                 /* Hierarchies should be linked in the same order. */
918                 BUG_ON(cgrp1->root != cgrp2->root);
919 
920                 /*
921                  * If this hierarchy is the hierarchy of the cgroup
922                  * that's changing, then we need to check that this
923                  * css_set points to the new cgroup; if it's any other
924                  * hierarchy, then this css_set should point to the
925                  * same cgroup as the old css_set.
926                  */
927                 if (cgrp1->root == new_cgrp->root) {
928                         if (cgrp1 != new_cgrp)
929                                 return false;
930                 } else {
931                         if (cgrp1 != cgrp2)
932                                 return false;
933                 }
934         }
935         return true;
936 }
937 
938 /**
939  * find_existing_css_set - init css array and find the matching css_set
940  * @old_cset: the css_set that we're using before the cgroup transition
941  * @cgrp: the cgroup that we're moving into
942  * @template: out param for the new set of csses, should be clear on entry
943  */
944 static struct css_set *find_existing_css_set(struct css_set *old_cset,
945                                         struct cgroup *cgrp,
946                                         struct cgroup_subsys_state *template[])
947 {
948         struct cgroup_root *root = cgrp->root;
949         struct cgroup_subsys *ss;
950         struct css_set *cset;
951         unsigned long key;
952         int i;
953 
954         /*
955          * Build the set of subsystem state objects that we want to see in the
956          * new css_set. while subsystems can change globally, the entries here
957          * won't change, so no need for locking.
958          */
959         for_each_subsys(ss, i) {
960                 if (root->subsys_mask & (1UL << i)) {
961                         /*
962                          * @ss is in this hierarchy, so we want the
963                          * effective css from @cgrp.
964                          */
965                         template[i] = cgroup_e_css(cgrp, ss);
966                 } else {
967                         /*
968                          * @ss is not in this hierarchy, so we don't want
969                          * to change the css.
970                          */
971                         template[i] = old_cset->subsys[i];
972                 }
973         }
974 
975         key = css_set_hash(template);
976         hash_for_each_possible(css_set_table, cset, hlist, key) {
977                 if (!compare_css_sets(cset, old_cset, cgrp, template))
978                         continue;
979 
980                 /* This css_set matches what we need */
981                 return cset;
982         }
983 
984         /* No existing cgroup group matched */
985         return NULL;
986 }
987 
988 static void free_cgrp_cset_links(struct list_head *links_to_free)
989 {
990         struct cgrp_cset_link *link, *tmp_link;
991 
992         list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
993                 list_del(&link->cset_link);
994                 kfree(link);
995         }
996 }
997 
998 /**
999  * allocate_cgrp_cset_links - allocate cgrp_cset_links
1000  * @count: the number of links to allocate
1001  * @tmp_links: list_head the allocated links are put on
1002  *
1003  * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1004  * through ->cset_link.  Returns 0 on success or -errno.
1005  */
1006 static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1007 {
1008         struct cgrp_cset_link *link;
1009         int i;
1010 
1011         INIT_LIST_HEAD(tmp_links);
1012 
1013         for (i = 0; i < count; i++) {
1014                 link = kzalloc(sizeof(*link), GFP_KERNEL);
1015                 if (!link) {
1016                         free_cgrp_cset_links(tmp_links);
1017                         return -ENOMEM;
1018                 }
1019                 list_add(&link->cset_link, tmp_links);
1020         }
1021         return 0;
1022 }
1023 
1024 /**
1025  * link_css_set - a helper function to link a css_set to a cgroup
1026  * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1027  * @cset: the css_set to be linked
1028  * @cgrp: the destination cgroup
1029  */
1030 static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1031                          struct cgroup *cgrp)
1032 {
1033         struct cgrp_cset_link *link;
1034 
1035         BUG_ON(list_empty(tmp_links));
1036 
1037         if (cgroup_on_dfl(cgrp))
1038                 cset->dfl_cgrp = cgrp;
1039 
1040         link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1041         link->cset = cset;
1042         link->cgrp = cgrp;
1043 
1044         /*
1045          * Always add links to the tail of the lists so that the lists are
1046          * in choronological order.
1047          */
1048         list_move_tail(&link->cset_link, &cgrp->cset_links);
1049         list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1050 
1051         if (cgroup_parent(cgrp))
1052                 cgroup_get(cgrp);
1053 }
1054 
1055 /**
1056  * find_css_set - return a new css_set with one cgroup updated
1057  * @old_cset: the baseline css_set
1058  * @cgrp: the cgroup to be updated
1059  *
1060  * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1061  * substituted into the appropriate hierarchy.
1062  */
1063 static struct css_set *find_css_set(struct css_set *old_cset,
1064                                     struct cgroup *cgrp)
1065 {
1066         struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1067         struct css_set *cset;
1068         struct list_head tmp_links;
1069         struct cgrp_cset_link *link;
1070         struct cgroup_subsys *ss;
1071         unsigned long key;
1072         int ssid;
1073 
1074         lockdep_assert_held(&cgroup_mutex);
1075 
1076         /* First see if we already have a cgroup group that matches
1077          * the desired set */
1078         spin_lock_irq(&css_set_lock);
1079         cset = find_existing_css_set(old_cset, cgrp, template);
1080         if (cset)
1081                 get_css_set(cset);
1082         spin_unlock_irq(&css_set_lock);
1083 
1084         if (cset)
1085                 return cset;
1086 
1087         cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1088         if (!cset)
1089                 return NULL;
1090 
1091         /* Allocate all the cgrp_cset_link objects that we'll need */
1092         if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1093                 kfree(cset);
1094                 return NULL;
1095         }
1096 
1097         atomic_set(&cset->refcount, 1);
1098         INIT_LIST_HEAD(&cset->cgrp_links);
1099         INIT_LIST_HEAD(&cset->tasks);
1100         INIT_LIST_HEAD(&cset->mg_tasks);
1101         INIT_LIST_HEAD(&cset->mg_preload_node);
1102         INIT_LIST_HEAD(&cset->mg_node);
1103         INIT_LIST_HEAD(&cset->task_iters);
1104         INIT_HLIST_NODE(&cset->hlist);
1105 
1106         /* Copy the set of subsystem state objects generated in
1107          * find_existing_css_set() */
1108         memcpy(cset->subsys, template, sizeof(cset->subsys));
1109 
1110         spin_lock_irq(&css_set_lock);
1111         /* Add reference counts and links from the new css_set. */
1112         list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1113                 struct cgroup *c = link->cgrp;
1114 
1115                 if (c->root == cgrp->root)
1116                         c = cgrp;
1117                 link_css_set(&tmp_links, cset, c);
1118         }
1119 
1120         BUG_ON(!list_empty(&tmp_links));
1121 
1122         css_set_count++;
1123 
1124         /* Add @cset to the hash table */
1125         key = css_set_hash(cset->subsys);
1126         hash_add(css_set_table, &cset->hlist, key);
1127 
1128         for_each_subsys(ss, ssid) {
1129                 struct cgroup_subsys_state *css = cset->subsys[ssid];
1130 
1131                 list_add_tail(&cset->e_cset_node[ssid],
1132                               &css->cgroup->e_csets[ssid]);
1133                 css_get(css);
1134         }
1135 
1136         spin_unlock_irq(&css_set_lock);
1137 
1138         return cset;
1139 }
1140 
1141 static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1142 {
1143         struct cgroup *root_cgrp = kf_root->kn->priv;
1144 
1145         return root_cgrp->root;
1146 }
1147 
1148 static int cgroup_init_root_id(struct cgroup_root *root)
1149 {
1150         int id;
1151 
1152         lockdep_assert_held(&cgroup_mutex);
1153 
1154         id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1155         if (id < 0)
1156                 return id;
1157 
1158         root->hierarchy_id = id;
1159         return 0;
1160 }
1161 
1162 static void cgroup_exit_root_id(struct cgroup_root *root)
1163 {
1164         lockdep_assert_held(&cgroup_mutex);
1165 
1166         idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1167 }
1168 
1169 static void cgroup_free_root(struct cgroup_root *root)
1170 {
1171         if (root) {
1172                 idr_destroy(&root->cgroup_idr);
1173                 kfree(root);
1174         }
1175 }
1176 
1177 static void cgroup_destroy_root(struct cgroup_root *root)
1178 {
1179         struct cgroup *cgrp = &root->cgrp;
1180         struct cgrp_cset_link *link, *tmp_link;
1181 
1182         trace_cgroup_destroy_root(root);
1183 
1184         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1185 
1186         BUG_ON(atomic_read(&root->nr_cgrps));
1187         BUG_ON(!list_empty(&cgrp->self.children));
1188 
1189         /* Rebind all subsystems back to the default hierarchy */
1190         WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1191 
1192         /*
1193          * Release all the links from cset_links to this hierarchy's
1194          * root cgroup
1195          */
1196         spin_lock_irq(&css_set_lock);
1197 
1198         list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1199                 list_del(&link->cset_link);
1200                 list_del(&link->cgrp_link);
1201                 kfree(link);
1202         }
1203 
1204         spin_unlock_irq(&css_set_lock);
1205 
1206         if (!list_empty(&root->root_list)) {
1207                 list_del(&root->root_list);
1208                 cgroup_root_count--;
1209         }
1210 
1211         cgroup_exit_root_id(root);
1212 
1213         mutex_unlock(&cgroup_mutex);
1214 
1215         kernfs_destroy_root(root->kf_root);
1216         cgroup_free_root(root);
1217 }
1218 
1219 /*
1220  * look up cgroup associated with current task's cgroup namespace on the
1221  * specified hierarchy
1222  */
1223 static struct cgroup *
1224 current_cgns_cgroup_from_root(struct cgroup_root *root)
1225 {
1226         struct cgroup *res = NULL;
1227         struct css_set *cset;
1228 
1229         lockdep_assert_held(&css_set_lock);
1230 
1231         rcu_read_lock();
1232 
1233         cset = current->nsproxy->cgroup_ns->root_cset;
1234         if (cset == &init_css_set) {
1235                 res = &root->cgrp;
1236         } else {
1237                 struct cgrp_cset_link *link;
1238 
1239                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1240                         struct cgroup *c = link->cgrp;
1241 
1242                         if (c->root == root) {
1243                                 res = c;
1244                                 break;
1245                         }
1246                 }
1247         }
1248         rcu_read_unlock();
1249 
1250         BUG_ON(!res);
1251         return res;
1252 }
1253 
1254 /* look up cgroup associated with given css_set on the specified hierarchy */
1255 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1256                                             struct cgroup_root *root)
1257 {
1258         struct cgroup *res = NULL;
1259 
1260         lockdep_assert_held(&cgroup_mutex);
1261         lockdep_assert_held(&css_set_lock);
1262 
1263         if (cset == &init_css_set) {
1264                 res = &root->cgrp;
1265         } else {
1266                 struct cgrp_cset_link *link;
1267 
1268                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1269                         struct cgroup *c = link->cgrp;
1270 
1271                         if (c->root == root) {
1272                                 res = c;
1273                                 break;
1274                         }
1275                 }
1276         }
1277 
1278         BUG_ON(!res);
1279         return res;
1280 }
1281 
1282 /*
1283  * Return the cgroup for "task" from the given hierarchy. Must be
1284  * called with cgroup_mutex and css_set_lock held.
1285  */
1286 static struct cgroup *task_cgroup_from_root(struct task_struct *task,
1287                                             struct cgroup_root *root)
1288 {
1289         /*
1290          * No need to lock the task - since we hold cgroup_mutex the
1291          * task can't change groups, so the only thing that can happen
1292          * is that it exits and its css is set back to init_css_set.
1293          */
1294         return cset_cgroup_from_root(task_css_set(task), root);
1295 }
1296 
1297 /*
1298  * A task must hold cgroup_mutex to modify cgroups.
1299  *
1300  * Any task can increment and decrement the count field without lock.
1301  * So in general, code holding cgroup_mutex can't rely on the count
1302  * field not changing.  However, if the count goes to zero, then only
1303  * cgroup_attach_task() can increment it again.  Because a count of zero
1304  * means that no tasks are currently attached, therefore there is no
1305  * way a task attached to that cgroup can fork (the other way to
1306  * increment the count).  So code holding cgroup_mutex can safely
1307  * assume that if the count is zero, it will stay zero. Similarly, if
1308  * a task holds cgroup_mutex on a cgroup with zero count, it
1309  * knows that the cgroup won't be removed, as cgroup_rmdir()
1310  * needs that mutex.
1311  *
1312  * A cgroup can only be deleted if both its 'count' of using tasks
1313  * is zero, and its list of 'children' cgroups is empty.  Since all
1314  * tasks in the system use _some_ cgroup, and since there is always at
1315  * least one task in the system (init, pid == 1), therefore, root cgroup
1316  * always has either children cgroups and/or using tasks.  So we don't
1317  * need a special hack to ensure that root cgroup cannot be deleted.
1318  *
1319  * P.S.  One more locking exception.  RCU is used to guard the
1320  * update of a tasks cgroup pointer by cgroup_attach_task()
1321  */
1322 
1323 static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1324 static const struct file_operations proc_cgroupstats_operations;
1325 
1326 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1327                               char *buf)
1328 {
1329         struct cgroup_subsys *ss = cft->ss;
1330 
1331         if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1332             !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
1333                 snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
1334                          cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1335                          cft->name);
1336         else
1337                 strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1338         return buf;
1339 }
1340 
1341 /**
1342  * cgroup_file_mode - deduce file mode of a control file
1343  * @cft: the control file in question
1344  *
1345  * S_IRUGO for read, S_IWUSR for write.
1346  */
1347 static umode_t cgroup_file_mode(const struct cftype *cft)
1348 {
1349         umode_t mode = 0;
1350 
1351         if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1352                 mode |= S_IRUGO;
1353 
1354         if (cft->write_u64 || cft->write_s64 || cft->write) {
1355                 if (cft->flags & CFTYPE_WORLD_WRITABLE)
1356                         mode |= S_IWUGO;
1357                 else
1358                         mode |= S_IWUSR;
1359         }
1360 
1361         return mode;
1362 }
1363 
1364 /**
1365  * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1366  * @subtree_control: the new subtree_control mask to consider
1367  * @this_ss_mask: available subsystems
1368  *
1369  * On the default hierarchy, a subsystem may request other subsystems to be
1370  * enabled together through its ->depends_on mask.  In such cases, more
1371  * subsystems than specified in "cgroup.subtree_control" may be enabled.
1372  *
1373  * This function calculates which subsystems need to be enabled if
1374  * @subtree_control is to be applied while restricted to @this_ss_mask.
1375  */
1376 static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1377 {
1378         u16 cur_ss_mask = subtree_control;
1379         struct cgroup_subsys *ss;
1380         int ssid;
1381 
1382         lockdep_assert_held(&cgroup_mutex);
1383 
1384         cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1385 
1386         while (true) {
1387                 u16 new_ss_mask = cur_ss_mask;
1388 
1389                 do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1390                         new_ss_mask |= ss->depends_on;
1391                 } while_each_subsys_mask();
1392 
1393                 /*
1394                  * Mask out subsystems which aren't available.  This can
1395                  * happen only if some depended-upon subsystems were bound
1396                  * to non-default hierarchies.
1397                  */
1398                 new_ss_mask &= this_ss_mask;
1399 
1400                 if (new_ss_mask == cur_ss_mask)
1401                         break;
1402                 cur_ss_mask = new_ss_mask;
1403         }
1404 
1405         return cur_ss_mask;
1406 }
1407 
1408 /**
1409  * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1410  * @kn: the kernfs_node being serviced
1411  *
1412  * This helper undoes cgroup_kn_lock_live() and should be invoked before
1413  * the method finishes if locking succeeded.  Note that once this function
1414  * returns the cgroup returned by cgroup_kn_lock_live() may become
1415  * inaccessible any time.  If the caller intends to continue to access the
1416  * cgroup, it should pin it before invoking this function.
1417  */
1418 static void cgroup_kn_unlock(struct kernfs_node *kn)
1419 {
1420         struct cgroup *cgrp;
1421 
1422         if (kernfs_type(kn) == KERNFS_DIR)
1423                 cgrp = kn->priv;
1424         else
1425                 cgrp = kn->parent->priv;
1426 
1427         mutex_unlock(&cgroup_mutex);
1428 
1429         kernfs_unbreak_active_protection(kn);
1430         cgroup_put(cgrp);
1431 }
1432 
1433 /**
1434  * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1435  * @kn: the kernfs_node being serviced
1436  * @drain_offline: perform offline draining on the cgroup
1437  *
1438  * This helper is to be used by a cgroup kernfs method currently servicing
1439  * @kn.  It breaks the active protection, performs cgroup locking and
1440  * verifies that the associated cgroup is alive.  Returns the cgroup if
1441  * alive; otherwise, %NULL.  A successful return should be undone by a
1442  * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1443  * cgroup is drained of offlining csses before return.
1444  *
1445  * Any cgroup kernfs method implementation which requires locking the
1446  * associated cgroup should use this helper.  It avoids nesting cgroup
1447  * locking under kernfs active protection and allows all kernfs operations
1448  * including self-removal.
1449  */
1450 static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn,
1451                                           bool drain_offline)
1452 {
1453         struct cgroup *cgrp;
1454 
1455         if (kernfs_type(kn) == KERNFS_DIR)
1456                 cgrp = kn->priv;
1457         else
1458                 cgrp = kn->parent->priv;
1459 
1460         /*
1461          * We're gonna grab cgroup_mutex which nests outside kernfs
1462          * active_ref.  cgroup liveliness check alone provides enough
1463          * protection against removal.  Ensure @cgrp stays accessible and
1464          * break the active_ref protection.
1465          */
1466         if (!cgroup_tryget(cgrp))
1467                 return NULL;
1468         kernfs_break_active_protection(kn);
1469 
1470         if (drain_offline)
1471                 cgroup_lock_and_drain_offline(cgrp);
1472         else
1473                 mutex_lock(&cgroup_mutex);
1474 
1475         if (!cgroup_is_dead(cgrp))
1476                 return cgrp;
1477 
1478         cgroup_kn_unlock(kn);
1479         return NULL;
1480 }
1481 
1482 static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1483 {
1484         char name[CGROUP_FILE_NAME_MAX];
1485 
1486         lockdep_assert_held(&cgroup_mutex);
1487 
1488         if (cft->file_offset) {
1489                 struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1490                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
1491 
1492                 spin_lock_irq(&cgroup_file_kn_lock);
1493                 cfile->kn = NULL;
1494                 spin_unlock_irq(&cgroup_file_kn_lock);
1495         }
1496 
1497         kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1498 }
1499 
1500 /**
1501  * css_clear_dir - remove subsys files in a cgroup directory
1502  * @css: taget css
1503  */
1504 static void css_clear_dir(struct cgroup_subsys_state *css)
1505 {
1506         struct cgroup *cgrp = css->cgroup;
1507         struct cftype *cfts;
1508 
1509         if (!(css->flags & CSS_VISIBLE))
1510                 return;
1511 
1512         css->flags &= ~CSS_VISIBLE;
1513 
1514         list_for_each_entry(cfts, &css->ss->cfts, node)
1515                 cgroup_addrm_files(css, cgrp, cfts, false);
1516 }
1517 
1518 /**
1519  * css_populate_dir - create subsys files in a cgroup directory
1520  * @css: target css
1521  *
1522  * On failure, no file is added.
1523  */
1524 static int css_populate_dir(struct cgroup_subsys_state *css)
1525 {
1526         struct cgroup *cgrp = css->cgroup;
1527         struct cftype *cfts, *failed_cfts;
1528         int ret;
1529 
1530         if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1531                 return 0;
1532 
1533         if (!css->ss) {
1534                 if (cgroup_on_dfl(cgrp))
1535                         cfts = cgroup_dfl_base_files;
1536                 else
1537                         cfts = cgroup_legacy_base_files;
1538 
1539                 return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1540         }
1541 
1542         list_for_each_entry(cfts, &css->ss->cfts, node) {
1543                 ret = cgroup_addrm_files(css, cgrp, cfts, true);
1544                 if (ret < 0) {
1545                         failed_cfts = cfts;
1546                         goto err;
1547                 }
1548         }
1549 
1550         css->flags |= CSS_VISIBLE;
1551 
1552         return 0;
1553 err:
1554         list_for_each_entry(cfts, &css->ss->cfts, node) {
1555                 if (cfts == failed_cfts)
1556                         break;
1557                 cgroup_addrm_files(css, cgrp, cfts, false);
1558         }
1559         return ret;
1560 }
1561 
1562 static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1563 {
1564         struct cgroup *dcgrp = &dst_root->cgrp;
1565         struct cgroup_subsys *ss;
1566         int ssid, i, ret;
1567 
1568         lockdep_assert_held(&cgroup_mutex);
1569 
1570         do_each_subsys_mask(ss, ssid, ss_mask) {
1571                 /*
1572                  * If @ss has non-root csses attached to it, can't move.
1573                  * If @ss is an implicit controller, it is exempt from this
1574                  * rule and can be stolen.
1575                  */
1576                 if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1577                     !ss->implicit_on_dfl)
1578                         return -EBUSY;
1579 
1580                 /* can't move between two non-dummy roots either */
1581                 if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1582                         return -EBUSY;
1583         } while_each_subsys_mask();
1584 
1585         do_each_subsys_mask(ss, ssid, ss_mask) {
1586                 struct cgroup_root *src_root = ss->root;
1587                 struct cgroup *scgrp = &src_root->cgrp;
1588                 struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1589                 struct css_set *cset;
1590 
1591                 WARN_ON(!css || cgroup_css(dcgrp, ss));
1592 
1593                 /* disable from the source */
1594                 src_root->subsys_mask &= ~(1 << ssid);
1595                 WARN_ON(cgroup_apply_control(scgrp));
1596                 cgroup_finalize_control(scgrp, 0);
1597 
1598                 /* rebind */
1599                 RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1600                 rcu_assign_pointer(dcgrp->subsys[ssid], css);
1601                 ss->root = dst_root;
1602                 css->cgroup = dcgrp;
1603 
1604                 spin_lock_irq(&css_set_lock);
1605                 hash_for_each(css_set_table, i, cset, hlist)
1606                         list_move_tail(&cset->e_cset_node[ss->id],
1607                                        &dcgrp->e_csets[ss->id]);
1608                 spin_unlock_irq(&css_set_lock);
1609 
1610                 /* default hierarchy doesn't enable controllers by default */
1611                 dst_root->subsys_mask |= 1 << ssid;
1612                 if (dst_root == &cgrp_dfl_root) {
1613                         static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1614                 } else {
1615                         dcgrp->subtree_control |= 1 << ssid;
1616                         static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1617                 }
1618 
1619                 ret = cgroup_apply_control(dcgrp);
1620                 if (ret)
1621                         pr_warn("partial failure to rebind %s controller (err=%d)\n",
1622                                 ss->name, ret);
1623 
1624                 if (ss->bind)
1625                         ss->bind(css);
1626         } while_each_subsys_mask();
1627 
1628         kernfs_activate(dcgrp->kn);
1629         return 0;
1630 }
1631 
1632 static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1633                             struct kernfs_root *kf_root)
1634 {
1635         int len = 0;
1636         char *buf = NULL;
1637         struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1638         struct cgroup *ns_cgroup;
1639 
1640         buf = kmalloc(PATH_MAX, GFP_KERNEL);
1641         if (!buf)
1642                 return -ENOMEM;
1643 
1644         spin_lock_irq(&css_set_lock);
1645         ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1646         len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1647         spin_unlock_irq(&css_set_lock);
1648 
1649         if (len >= PATH_MAX)
1650                 len = -ERANGE;
1651         else if (len > 0) {
1652                 seq_escape(sf, buf, " \t\n\\");
1653                 len = 0;
1654         }
1655         kfree(buf);
1656         return len;
1657 }
1658 
1659 static int cgroup_show_options(struct seq_file *seq,
1660                                struct kernfs_root *kf_root)
1661 {
1662         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1663         struct cgroup_subsys *ss;
1664         int ssid;
1665 
1666         if (root != &cgrp_dfl_root)
1667                 for_each_subsys(ss, ssid)
1668                         if (root->subsys_mask & (1 << ssid))
1669                                 seq_show_option(seq, ss->legacy_name, NULL);
1670         if (root->flags & CGRP_ROOT_NOPREFIX)
1671                 seq_puts(seq, ",noprefix");
1672         if (root->flags & CGRP_ROOT_XATTR)
1673                 seq_puts(seq, ",xattr");
1674 
1675         spin_lock(&release_agent_path_lock);
1676         if (strlen(root->release_agent_path))
1677                 seq_show_option(seq, "release_agent",
1678                                 root->release_agent_path);
1679         spin_unlock(&release_agent_path_lock);
1680 
1681         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1682                 seq_puts(seq, ",clone_children");
1683         if (strlen(root->name))
1684                 seq_show_option(seq, "name", root->name);
1685         return 0;
1686 }
1687 
1688 struct cgroup_sb_opts {
1689         u16 subsys_mask;
1690         unsigned int flags;
1691         char *release_agent;
1692         bool cpuset_clone_children;
1693         char *name;
1694         /* User explicitly requested empty subsystem */
1695         bool none;
1696 };
1697 
1698 static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1699 {
1700         char *token, *o = data;
1701         bool all_ss = false, one_ss = false;
1702         u16 mask = U16_MAX;
1703         struct cgroup_subsys *ss;
1704         int nr_opts = 0;
1705         int i;
1706 
1707 #ifdef CONFIG_CPUSETS
1708         mask = ~((u16)1 << cpuset_cgrp_id);
1709 #endif
1710 
1711         memset(opts, 0, sizeof(*opts));
1712 
1713         while ((token = strsep(&o, ",")) != NULL) {
1714                 nr_opts++;
1715 
1716                 if (!*token)
1717                         return -EINVAL;
1718                 if (!strcmp(token, "none")) {
1719                         /* Explicitly have no subsystems */
1720                         opts->none = true;
1721                         continue;
1722                 }
1723                 if (!strcmp(token, "all")) {
1724                         /* Mutually exclusive option 'all' + subsystem name */
1725                         if (one_ss)
1726                                 return -EINVAL;
1727                         all_ss = true;
1728                         continue;
1729                 }
1730                 if (!strcmp(token, "noprefix")) {
1731                         opts->flags |= CGRP_ROOT_NOPREFIX;
1732                         continue;
1733                 }
1734                 if (!strcmp(token, "clone_children")) {
1735                         opts->cpuset_clone_children = true;
1736                         continue;
1737                 }
1738                 if (!strcmp(token, "xattr")) {
1739                         opts->flags |= CGRP_ROOT_XATTR;
1740                         continue;
1741                 }
1742                 if (!strncmp(token, "release_agent=", 14)) {
1743                         /* Specifying two release agents is forbidden */
1744                         if (opts->release_agent)
1745                                 return -EINVAL;
1746                         opts->release_agent =
1747                                 kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1748                         if (!opts->release_agent)
1749                                 return -ENOMEM;
1750                         continue;
1751                 }
1752                 if (!strncmp(token, "name=", 5)) {
1753                         const char *name = token + 5;
1754                         /* Can't specify an empty name */
1755                         if (!strlen(name))
1756                                 return -EINVAL;
1757                         /* Must match [\w.-]+ */
1758                         for (i = 0; i < strlen(name); i++) {
1759                                 char c = name[i];
1760                                 if (isalnum(c))
1761                                         continue;
1762                                 if ((c == '.') || (c == '-') || (c == '_'))
1763                                         continue;
1764                                 return -EINVAL;
1765                         }
1766                         /* Specifying two names is forbidden */
1767                         if (opts->name)
1768                                 return -EINVAL;
1769                         opts->name = kstrndup(name,
1770                                               MAX_CGROUP_ROOT_NAMELEN - 1,
1771                                               GFP_KERNEL);
1772                         if (!opts->name)
1773                                 return -ENOMEM;
1774 
1775                         continue;
1776                 }
1777 
1778                 for_each_subsys(ss, i) {
1779                         if (strcmp(token, ss->legacy_name))
1780                                 continue;
1781                         if (!cgroup_ssid_enabled(i))
1782                                 continue;
1783                         if (cgroup_ssid_no_v1(i))
1784                                 continue;
1785 
1786                         /* Mutually exclusive option 'all' + subsystem name */
1787                         if (all_ss)
1788                                 return -EINVAL;
1789                         opts->subsys_mask |= (1 << i);
1790                         one_ss = true;
1791 
1792                         break;
1793                 }
1794                 if (i == CGROUP_SUBSYS_COUNT)
1795                         return -ENOENT;
1796         }
1797 
1798         /*
1799          * If the 'all' option was specified select all the subsystems,
1800          * otherwise if 'none', 'name=' and a subsystem name options were
1801          * not specified, let's default to 'all'
1802          */
1803         if (all_ss || (!one_ss && !opts->none && !opts->name))
1804                 for_each_subsys(ss, i)
1805                         if (cgroup_ssid_enabled(i) && !cgroup_ssid_no_v1(i))
1806                                 opts->subsys_mask |= (1 << i);
1807 
1808         /*
1809          * We either have to specify by name or by subsystems. (So all
1810          * empty hierarchies must have a name).
1811          */
1812         if (!opts->subsys_mask && !opts->name)
1813                 return -EINVAL;
1814 
1815         /*
1816          * Option noprefix was introduced just for backward compatibility
1817          * with the old cpuset, so we allow noprefix only if mounting just
1818          * the cpuset subsystem.
1819          */
1820         if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1821                 return -EINVAL;
1822 
1823         /* Can't specify "none" and some subsystems */
1824         if (opts->subsys_mask && opts->none)
1825                 return -EINVAL;
1826 
1827         return 0;
1828 }
1829 
1830 static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1831 {
1832         int ret = 0;
1833         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1834         struct cgroup_sb_opts opts;
1835         u16 added_mask, removed_mask;
1836 
1837         if (root == &cgrp_dfl_root) {
1838                 pr_err("remount is not allowed\n");
1839                 return -EINVAL;
1840         }
1841 
1842         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1843 
1844         /* See what subsystems are wanted */
1845         ret = parse_cgroupfs_options(data, &opts);
1846         if (ret)
1847                 goto out_unlock;
1848 
1849         if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
1850                 pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
1851                         task_tgid_nr(current), current->comm);
1852 
1853         added_mask = opts.subsys_mask & ~root->subsys_mask;
1854         removed_mask = root->subsys_mask & ~opts.subsys_mask;
1855 
1856         /* Don't allow flags or name to change at remount */
1857         if ((opts.flags ^ root->flags) ||
1858             (opts.name && strcmp(opts.name, root->name))) {
1859                 pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
1860                        opts.flags, opts.name ?: "", root->flags, root->name);
1861                 ret = -EINVAL;
1862                 goto out_unlock;
1863         }
1864 
1865         /* remounting is not allowed for populated hierarchies */
1866         if (!list_empty(&root->cgrp.self.children)) {
1867                 ret = -EBUSY;
1868                 goto out_unlock;
1869         }
1870 
1871         ret = rebind_subsystems(root, added_mask);
1872         if (ret)
1873                 goto out_unlock;
1874 
1875         WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
1876 
1877         if (opts.release_agent) {
1878                 spin_lock(&release_agent_path_lock);
1879                 strcpy(root->release_agent_path, opts.release_agent);
1880                 spin_unlock(&release_agent_path_lock);
1881         }
1882 
1883         trace_cgroup_remount(root);
1884 
1885  out_unlock:
1886         kfree(opts.release_agent);
1887         kfree(opts.name);
1888         mutex_unlock(&cgroup_mutex);
1889         return ret;
1890 }
1891 
1892 /*
1893  * To reduce the fork() overhead for systems that are not actually using
1894  * their cgroups capability, we don't maintain the lists running through
1895  * each css_set to its tasks until we see the list actually used - in other
1896  * words after the first mount.
1897  */
1898 static bool use_task_css_set_links __read_mostly;
1899 
1900 static void cgroup_enable_task_cg_lists(void)
1901 {
1902         struct task_struct *p, *g;
1903 
1904         spin_lock_irq(&css_set_lock);
1905 
1906         if (use_task_css_set_links)
1907                 goto out_unlock;
1908 
1909         use_task_css_set_links = true;
1910 
1911         /*
1912          * We need tasklist_lock because RCU is not safe against
1913          * while_each_thread(). Besides, a forking task that has passed
1914          * cgroup_post_fork() without seeing use_task_css_set_links = 1
1915          * is not guaranteed to have its child immediately visible in the
1916          * tasklist if we walk through it with RCU.
1917          */
1918         read_lock(&tasklist_lock);
1919         do_each_thread(g, p) {
1920                 WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1921                              task_css_set(p) != &init_css_set);
1922 
1923                 /*
1924                  * We should check if the process is exiting, otherwise
1925                  * it will race with cgroup_exit() in that the list
1926                  * entry won't be deleted though the process has exited.
1927                  * Do it while holding siglock so that we don't end up
1928                  * racing against cgroup_exit().
1929                  *
1930                  * Interrupts were already disabled while acquiring
1931                  * the css_set_lock, so we do not need to disable it
1932                  * again when acquiring the sighand->siglock here.
1933                  */
1934                 spin_lock(&p->sighand->siglock);
1935                 if (!(p->flags & PF_EXITING)) {
1936                         struct css_set *cset = task_css_set(p);
1937 
1938                         if (!css_set_populated(cset))
1939                                 css_set_update_populated(cset, true);
1940                         list_add_tail(&p->cg_list, &cset->tasks);
1941                         get_css_set(cset);
1942                 }
1943                 spin_unlock(&p->sighand->siglock);
1944         } while_each_thread(g, p);
1945         read_unlock(&tasklist_lock);
1946 out_unlock:
1947         spin_unlock_irq(&css_set_lock);
1948 }
1949 
1950 static void init_cgroup_housekeeping(struct cgroup *cgrp)
1951 {
1952         struct cgroup_subsys *ss;
1953         int ssid;
1954 
1955         INIT_LIST_HEAD(&cgrp->self.sibling);
1956         INIT_LIST_HEAD(&cgrp->self.children);
1957         INIT_LIST_HEAD(&cgrp->cset_links);
1958         INIT_LIST_HEAD(&cgrp->pidlists);
1959         mutex_init(&cgrp->pidlist_mutex);
1960         cgrp->self.cgroup = cgrp;
1961         cgrp->self.flags |= CSS_ONLINE;
1962 
1963         for_each_subsys(ss, ssid)
1964                 INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1965 
1966         init_waitqueue_head(&cgrp->offline_waitq);
1967         INIT_WORK(&cgrp->release_agent_work, cgroup_release_agent);
1968 }
1969 
1970 static void init_cgroup_root(struct cgroup_root *root,
1971                              struct cgroup_sb_opts *opts)
1972 {
1973         struct cgroup *cgrp = &root->cgrp;
1974 
1975         INIT_LIST_HEAD(&root->root_list);
1976         atomic_set(&root->nr_cgrps, 1);
1977         cgrp->root = root;
1978         init_cgroup_housekeeping(cgrp);
1979         idr_init(&root->cgroup_idr);
1980 
1981         root->flags = opts->flags;
1982         if (opts->release_agent)
1983                 strcpy(root->release_agent_path, opts->release_agent);
1984         if (opts->name)
1985                 strcpy(root->name, opts->name);
1986         if (opts->cpuset_clone_children)
1987                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1988 }
1989 
1990 static int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
1991 {
1992         LIST_HEAD(tmp_links);
1993         struct cgroup *root_cgrp = &root->cgrp;
1994         struct css_set *cset;
1995         int i, ret;
1996 
1997         lockdep_assert_held(&cgroup_mutex);
1998 
1999         ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
2000         if (ret < 0)
2001                 goto out;
2002         root_cgrp->id = ret;
2003         root_cgrp->ancestor_ids[0] = ret;
2004 
2005         ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
2006                               GFP_KERNEL);
2007         if (ret)
2008                 goto out;
2009 
2010         /*
2011          * We're accessing css_set_count without locking css_set_lock here,
2012          * but that's OK - it can only be increased by someone holding
2013          * cgroup_lock, and that's us.  Later rebinding may disable
2014          * controllers on the default hierarchy and thus create new csets,
2015          * which can't be more than the existing ones.  Allocate 2x.
2016          */
2017         ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
2018         if (ret)
2019                 goto cancel_ref;
2020 
2021         ret = cgroup_init_root_id(root);
2022         if (ret)
2023                 goto cancel_ref;
2024 
2025         root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
2026                                            KERNFS_ROOT_CREATE_DEACTIVATED,
2027                                            root_cgrp);
2028         if (IS_ERR(root->kf_root)) {
2029                 ret = PTR_ERR(root->kf_root);
2030                 goto exit_root_id;
2031         }
2032         root_cgrp->kn = root->kf_root->kn;
2033 
2034         ret = css_populate_dir(&root_cgrp->self);
2035         if (ret)
2036                 goto destroy_root;
2037 
2038         ret = rebind_subsystems(root, ss_mask);
2039         if (ret)
2040                 goto destroy_root;
2041 
2042         trace_cgroup_setup_root(root);
2043 
2044         /*
2045          * There must be no failure case after here, since rebinding takes
2046          * care of subsystems' refcounts, which are explicitly dropped in
2047          * the failure exit path.
2048          */
2049         list_add(&root->root_list, &cgroup_roots);
2050         cgroup_root_count++;
2051 
2052         /*
2053          * Link the root cgroup in this hierarchy into all the css_set
2054          * objects.
2055          */
2056         spin_lock_irq(&css_set_lock);
2057         hash_for_each(css_set_table, i, cset, hlist) {
2058                 link_css_set(&tmp_links, cset, root_cgrp);
2059                 if (css_set_populated(cset))
2060                         cgroup_update_populated(root_cgrp, true);
2061         }
2062         spin_unlock_irq(&css_set_lock);
2063 
2064         BUG_ON(!list_empty(&root_cgrp->self.children));
2065         BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2066 
2067         kernfs_activate(root_cgrp->kn);
2068         ret = 0;
2069         goto out;
2070 
2071 destroy_root:
2072         kernfs_destroy_root(root->kf_root);
2073         root->kf_root = NULL;
2074 exit_root_id:
2075         cgroup_exit_root_id(root);
2076 cancel_ref:
2077         percpu_ref_exit(&root_cgrp->self.refcnt);
2078 out:
2079         free_cgrp_cset_links(&tmp_links);
2080         return ret;
2081 }
2082 
2083 static struct dentry *cgroup_mount(struct file_system_type *fs_type,
2084                          int flags, const char *unused_dev_name,
2085                          void *data)
2086 {
2087         bool is_v2 = fs_type == &cgroup2_fs_type;
2088         struct super_block *pinned_sb = NULL;
2089         struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
2090         struct cgroup_subsys *ss;
2091         struct cgroup_root *root;
2092         struct cgroup_sb_opts opts;
2093         struct dentry *dentry;
2094         int ret;
2095         int i;
2096         bool new_sb;
2097 
2098         get_cgroup_ns(ns);
2099 
2100         /* Check if the caller has permission to mount. */
2101         if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
2102                 put_cgroup_ns(ns);
2103                 return ERR_PTR(-EPERM);
2104         }
2105 
2106         /*
2107          * The first time anyone tries to mount a cgroup, enable the list
2108          * linking each css_set to its tasks and fix up all existing tasks.
2109          */
2110         if (!use_task_css_set_links)
2111                 cgroup_enable_task_cg_lists();
2112 
2113         if (is_v2) {
2114                 if (data) {
2115                         pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
2116                         put_cgroup_ns(ns);
2117                         return ERR_PTR(-EINVAL);
2118                 }
2119                 cgrp_dfl_visible = true;
2120                 root = &cgrp_dfl_root;
2121                 cgroup_get(&root->cgrp);
2122                 goto out_mount;
2123         }
2124 
2125         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
2126 
2127         /* First find the desired set of subsystems */
2128         ret = parse_cgroupfs_options(data, &opts);
2129         if (ret)
2130                 goto out_unlock;
2131 
2132         /*
2133          * Destruction of cgroup root is asynchronous, so subsystems may
2134          * still be dying after the previous unmount.  Let's drain the
2135          * dying subsystems.  We just need to ensure that the ones
2136          * unmounted previously finish dying and don't care about new ones
2137          * starting.  Testing ref liveliness is good enough.
2138          */
2139         for_each_subsys(ss, i) {
2140                 if (!(opts.subsys_mask & (1 << i)) ||
2141                     ss->root == &cgrp_dfl_root)
2142                         continue;
2143 
2144                 if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
2145                         mutex_unlock(&cgroup_mutex);
2146                         msleep(10);
2147                         ret = restart_syscall();
2148                         goto out_free;
2149                 }
2150                 cgroup_put(&ss->root->cgrp);
2151         }
2152 
2153         for_each_root(root) {
2154                 bool name_match = false;
2155 
2156                 if (root == &cgrp_dfl_root)
2157                         continue;
2158 
2159                 /*
2160                  * If we asked for a name then it must match.  Also, if
2161                  * name matches but sybsys_mask doesn't, we should fail.
2162                  * Remember whether name matched.
2163                  */
2164                 if (opts.name) {
2165                         if (strcmp(opts.name, root->name))
2166                                 continue;
2167                         name_match = true;
2168                 }
2169 
2170                 /*
2171                  * If we asked for subsystems (or explicitly for no
2172                  * subsystems) then they must match.
2173                  */
2174                 if ((opts.subsys_mask || opts.none) &&
2175                     (opts.subsys_mask != root->subsys_mask)) {
2176                         if (!name_match)
2177                                 continue;
2178                         ret = -EBUSY;
2179                         goto out_unlock;
2180                 }
2181 
2182                 if (root->flags ^ opts.flags)
2183                         pr_warn("new mount options do not match the existing superblock, will be ignored\n");
2184 
2185                 /*
2186                  * We want to reuse @root whose lifetime is governed by its
2187                  * ->cgrp.  Let's check whether @root is alive and keep it
2188                  * that way.  As cgroup_kill_sb() can happen anytime, we
2189                  * want to block it by pinning the sb so that @root doesn't
2190                  * get killed before mount is complete.
2191                  *
2192                  * With the sb pinned, tryget_live can reliably indicate
2193                  * whether @root can be reused.  If it's being killed,
2194                  * drain it.  We can use wait_queue for the wait but this
2195                  * path is super cold.  Let's just sleep a bit and retry.
2196                  */
2197                 pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
2198                 if (IS_ERR(pinned_sb) ||
2199                     !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
2200                         mutex_unlock(&cgroup_mutex);
2201                         if (!IS_ERR_OR_NULL(pinned_sb))
2202                                 deactivate_super(pinned_sb);
2203                         msleep(10);
2204                         ret = restart_syscall();
2205                         goto out_free;
2206                 }
2207 
2208                 ret = 0;
2209                 goto out_unlock;
2210         }
2211 
2212         /*
2213          * No such thing, create a new one.  name= matching without subsys
2214          * specification is allowed for already existing hierarchies but we
2215          * can't create new one without subsys specification.
2216          */
2217         if (!opts.subsys_mask && !opts.none) {
2218                 ret = -EINVAL;
2219                 goto out_unlock;
2220         }
2221 
2222         /* Hierarchies may only be created in the initial cgroup namespace. */
2223         if (ns != &init_cgroup_ns) {
2224                 ret = -EPERM;
2225                 goto out_unlock;
2226         }
2227 
2228         root = kzalloc(sizeof(*root), GFP_KERNEL);
2229         if (!root) {
2230                 ret = -ENOMEM;
2231                 goto out_unlock;
2232         }
2233 
2234         init_cgroup_root(root, &opts);
2235 
2236         ret = cgroup_setup_root(root, opts.subsys_mask);
2237         if (ret)
2238                 cgroup_free_root(root);
2239 
2240 out_unlock:
2241         mutex_unlock(&cgroup_mutex);
2242 out_free:
2243         kfree(opts.release_agent);
2244         kfree(opts.name);
2245 
2246         if (ret) {
2247                 put_cgroup_ns(ns);
2248                 return ERR_PTR(ret);
2249         }
2250 out_mount:
2251         dentry = kernfs_mount(fs_type, flags, root->kf_root,
2252                               is_v2 ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC,
2253                               &new_sb);
2254 
2255         /*
2256          * In non-init cgroup namespace, instead of root cgroup's
2257          * dentry, we return the dentry corresponding to the
2258          * cgroupns->root_cgrp.
2259          */
2260         if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
2261                 struct dentry *nsdentry;
2262                 struct cgroup *cgrp;
2263 
2264                 mutex_lock(&cgroup_mutex);
2265                 spin_lock_irq(&css_set_lock);
2266 
2267                 cgrp = cset_cgroup_from_root(ns->root_cset, root);
2268 
2269                 spin_unlock_irq(&css_set_lock);
2270                 mutex_unlock(&cgroup_mutex);
2271 
2272                 nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
2273                 dput(dentry);
2274                 dentry = nsdentry;
2275         }
2276 
2277         if (IS_ERR(dentry) || !new_sb)
2278                 cgroup_put(&root->cgrp);
2279 
2280         /*
2281          * If @pinned_sb, we're reusing an existing root and holding an
2282          * extra ref on its sb.  Mount is complete.  Put the extra ref.
2283          */
2284         if (pinned_sb) {
2285                 WARN_ON(new_sb);
2286                 deactivate_super(pinned_sb);
2287         }
2288 
2289         put_cgroup_ns(ns);
2290         return dentry;
2291 }
2292 
2293 static void cgroup_kill_sb(struct super_block *sb)
2294 {
2295         struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2296         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2297 
2298         /*
2299          * If @root doesn't have any mounts or children, start killing it.
2300          * This prevents new mounts by disabling percpu_ref_tryget_live().
2301          * cgroup_mount() may wait for @root's release.
2302          *
2303          * And don't kill the default root.
2304          */
2305         if (!list_empty(&root->cgrp.self.children) ||
2306             root == &cgrp_dfl_root)
2307                 cgroup_put(&root->cgrp);
2308         else
2309                 percpu_ref_kill(&root->cgrp.self.refcnt);
2310 
2311         kernfs_kill_sb(sb);
2312 }
2313 
2314 static struct file_system_type cgroup_fs_type = {
2315         .name = "cgroup",
2316         .mount = cgroup_mount,
2317         .kill_sb = cgroup_kill_sb,
2318         .fs_flags = FS_USERNS_MOUNT,
2319 };
2320 
2321 static struct file_system_type cgroup2_fs_type = {
2322         .name = "cgroup2",
2323         .mount = cgroup_mount,
2324         .kill_sb = cgroup_kill_sb,
2325         .fs_flags = FS_USERNS_MOUNT,
2326 };
2327 
2328 static int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2329                                  struct cgroup_namespace *ns)
2330 {
2331         struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2332 
2333         return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2334 }
2335 
2336 int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2337                    struct cgroup_namespace *ns)
2338 {
2339         int ret;
2340 
2341         mutex_lock(&cgroup_mutex);
2342         spin_lock_irq(&css_set_lock);
2343 
2344         ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2345 
2346         spin_unlock_irq(&css_set_lock);
2347         mutex_unlock(&cgroup_mutex);
2348 
2349         return ret;
2350 }
2351 EXPORT_SYMBOL_GPL(cgroup_path_ns);
2352 
2353 /**
2354  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2355  * @task: target task
2356  * @buf: the buffer to write the path into
2357  * @buflen: the length of the buffer
2358  *
2359  * Determine @task's cgroup on the first (the one with the lowest non-zero
2360  * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2361  * function grabs cgroup_mutex and shouldn't be used inside locks used by
2362  * cgroup controller callbacks.
2363  *
2364  * Return value is the same as kernfs_path().
2365  */
2366 int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2367 {
2368         struct cgroup_root *root;
2369         struct cgroup *cgrp;
2370         int hierarchy_id = 1;
2371         int ret;
2372 
2373         mutex_lock(&cgroup_mutex);
2374         spin_lock_irq(&css_set_lock);
2375 
2376         root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2377 
2378         if (root) {
2379                 cgrp = task_cgroup_from_root(task, root);
2380                 ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2381         } else {
2382                 /* if no hierarchy exists, everyone is in "/" */
2383                 ret = strlcpy(buf, "/", buflen);
2384         }
2385 
2386         spin_unlock_irq(&css_set_lock);
2387         mutex_unlock(&cgroup_mutex);
2388         return ret;
2389 }
2390 EXPORT_SYMBOL_GPL(task_cgroup_path);
2391 
2392 /* used to track tasks and other necessary states during migration */
2393 struct cgroup_taskset {
2394         /* the src and dst cset list running through cset->mg_node */
2395         struct list_head        src_csets;
2396         struct list_head        dst_csets;
2397 
2398         /* the subsys currently being processed */
2399         int                     ssid;
2400 
2401         /*
2402          * Fields for cgroup_taskset_*() iteration.
2403          *
2404          * Before migration is committed, the target migration tasks are on
2405          * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
2406          * the csets on ->dst_csets.  ->csets point to either ->src_csets
2407          * or ->dst_csets depending on whether migration is committed.
2408          *
2409          * ->cur_csets and ->cur_task point to the current task position
2410          * during iteration.
2411          */
2412         struct list_head        *csets;
2413         struct css_set          *cur_cset;
2414         struct task_struct      *cur_task;
2415 };
2416 
2417 #define CGROUP_TASKSET_INIT(tset)       (struct cgroup_taskset){        \
2418         .src_csets              = LIST_HEAD_INIT(tset.src_csets),       \
2419         .dst_csets              = LIST_HEAD_INIT(tset.dst_csets),       \
2420         .csets                  = &tset.src_csets,                      \
2421 }
2422 
2423 /**
2424  * cgroup_taskset_add - try to add a migration target task to a taskset
2425  * @task: target task
2426  * @tset: target taskset
2427  *
2428  * Add @task, which is a migration target, to @tset.  This function becomes
2429  * noop if @task doesn't need to be migrated.  @task's css_set should have
2430  * been added as a migration source and @task->cg_list will be moved from
2431  * the css_set's tasks list to mg_tasks one.
2432  */
2433 static void cgroup_taskset_add(struct task_struct *task,
2434                                struct cgroup_taskset *tset)
2435 {
2436         struct css_set *cset;
2437 
2438         lockdep_assert_held(&css_set_lock);
2439 
2440         /* @task either already exited or can't exit until the end */
2441         if (task->flags & PF_EXITING)
2442                 return;
2443 
2444         /* leave @task alone if post_fork() hasn't linked it yet */
2445         if (list_empty(&task->cg_list))
2446                 return;
2447 
2448         cset = task_css_set(task);
2449         if (!cset->mg_src_cgrp)
2450                 return;
2451 
2452         list_move_tail(&task->cg_list, &cset->mg_tasks);
2453         if (list_empty(&cset->mg_node))
2454                 list_add_tail(&cset->mg_node, &tset->src_csets);
2455         if (list_empty(&cset->mg_dst_cset->mg_node))
2456                 list_move_tail(&cset->mg_dst_cset->mg_node,
2457                                &tset->dst_csets);
2458 }
2459 
2460 /**
2461  * cgroup_taskset_first - reset taskset and return the first task
2462  * @tset: taskset of interest
2463  * @dst_cssp: output variable for the destination css
2464  *
2465  * @tset iteration is initialized and the first task is returned.
2466  */
2467 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2468                                          struct cgroup_subsys_state **dst_cssp)
2469 {
2470         tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2471         tset->cur_task = NULL;
2472 
2473         return cgroup_taskset_next(tset, dst_cssp);
2474 }
2475 
2476 /**
2477  * cgroup_taskset_next - iterate to the next task in taskset
2478  * @tset: taskset of interest
2479  * @dst_cssp: output variable for the destination css
2480  *
2481  * Return the next task in @tset.  Iteration must have been initialized
2482  * with cgroup_taskset_first().
2483  */
2484 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2485                                         struct cgroup_subsys_state **dst_cssp)
2486 {
2487         struct css_set *cset = tset->cur_cset;
2488         struct task_struct *task = tset->cur_task;
2489 
2490         while (&cset->mg_node != tset->csets) {
2491                 if (!task)
2492                         task = list_first_entry(&cset->mg_tasks,
2493                                                 struct task_struct, cg_list);
2494                 else
2495                         task = list_next_entry(task, cg_list);
2496 
2497                 if (&task->cg_list != &cset->mg_tasks) {
2498                         tset->cur_cset = cset;
2499                         tset->cur_task = task;
2500 
2501                         /*
2502                          * This function may be called both before and
2503                          * after cgroup_taskset_migrate().  The two cases
2504                          * can be distinguished by looking at whether @cset
2505                          * has its ->mg_dst_cset set.
2506                          */
2507                         if (cset->mg_dst_cset)
2508                                 *dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2509                         else
2510                                 *dst_cssp = cset->subsys[tset->ssid];
2511 
2512                         return task;
2513                 }
2514 
2515                 cset = list_next_entry(cset, mg_node);
2516                 task = NULL;
2517         }
2518 
2519         return NULL;
2520 }
2521 
2522 /**
2523  * cgroup_taskset_migrate - migrate a taskset
2524  * @tset: taget taskset
2525  * @root: cgroup root the migration is taking place on
2526  *
2527  * Migrate tasks in @tset as setup by migration preparation functions.
2528  * This function fails iff one of the ->can_attach callbacks fails and
2529  * guarantees that either all or none of the tasks in @tset are migrated.
2530  * @tset is consumed regardless of success.
2531  */
2532 static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
2533                                   struct cgroup_root *root)
2534 {
2535         struct cgroup_subsys *ss;
2536         struct task_struct *task, *tmp_task;
2537         struct css_set *cset, *tmp_cset;
2538         int ssid, failed_ssid, ret;
2539 
2540         /* methods shouldn't be called if no task is actually migrating */
2541         if (list_empty(&tset->src_csets))
2542                 return 0;
2543 
2544         /* check that we can legitimately attach to the cgroup */
2545         do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2546                 if (ss->can_attach) {
2547                         tset->ssid = ssid;
2548                         ret = ss->can_attach(tset);
2549                         if (ret) {
2550                                 failed_ssid = ssid;
2551                                 goto out_cancel_attach;
2552                         }
2553                 }
2554         } while_each_subsys_mask();
2555 
2556         /*
2557          * Now that we're guaranteed success, proceed to move all tasks to
2558          * the new cgroup.  There are no failure cases after here, so this
2559          * is the commit point.
2560          */
2561         spin_lock_irq(&css_set_lock);
2562         list_for_each_entry(cset, &tset->src_csets, mg_node) {
2563                 list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2564                         struct css_set *from_cset = task_css_set(task);
2565                         struct css_set *to_cset = cset->mg_dst_cset;
2566 
2567                         get_css_set(to_cset);
2568                         css_set_move_task(task, from_cset, to_cset, true);
2569                         put_css_set_locked(from_cset);
2570                 }
2571         }
2572         spin_unlock_irq(&css_set_lock);
2573 
2574         /*
2575          * Migration is committed, all target tasks are now on dst_csets.
2576          * Nothing is sensitive to fork() after this point.  Notify
2577          * controllers that migration is complete.
2578          */
2579         tset->csets = &tset->dst_csets;
2580 
2581         do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2582                 if (ss->attach) {
2583                         tset->ssid = ssid;
2584                         ss->attach(tset);
2585                 }
2586         } while_each_subsys_mask();
2587 
2588         ret = 0;
2589         goto out_release_tset;
2590 
2591 out_cancel_attach:
2592         do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2593                 if (ssid == failed_ssid)
2594                         break;
2595                 if (ss->cancel_attach) {
2596                         tset->ssid = ssid;
2597                         ss->cancel_attach(tset);
2598                 }
2599         } while_each_subsys_mask();
2600 out_release_tset:
2601         spin_lock_irq(&css_set_lock);
2602         list_splice_init(&tset->dst_csets, &tset->src_csets);
2603         list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2604                 list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2605                 list_del_init(&cset->mg_node);
2606         }
2607         spin_unlock_irq(&css_set_lock);
2608         return ret;
2609 }
2610 
2611 /**
2612  * cgroup_may_migrate_to - verify whether a cgroup can be migration destination
2613  * @dst_cgrp: destination cgroup to test
2614  *
2615  * On the default hierarchy, except for the root, subtree_control must be
2616  * zero for migration destination cgroups with tasks so that child cgroups
2617  * don't compete against tasks.
2618  */
2619 static bool cgroup_may_migrate_to(struct cgroup *dst_cgrp)
2620 {
2621         return !cgroup_on_dfl(dst_cgrp) || !cgroup_parent(dst_cgrp) ||
2622                 !dst_cgrp->subtree_control;
2623 }
2624 
2625 /**
2626  * cgroup_migrate_finish - cleanup after attach
2627  * @preloaded_csets: list of preloaded css_sets
2628  *
2629  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2630  * those functions for details.
2631  */
2632 static void cgroup_migrate_finish(struct list_head *preloaded_csets)
2633 {
2634         struct css_set *cset, *tmp_cset;
2635 
2636         lockdep_assert_held(&cgroup_mutex);
2637 
2638         spin_lock_irq(&css_set_lock);
2639         list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
2640                 cset->mg_src_cgrp = NULL;
2641                 cset->mg_dst_cgrp = NULL;
2642                 cset->mg_dst_cset = NULL;
2643                 list_del_init(&cset->mg_preload_node);
2644                 put_css_set_locked(cset);
2645         }
2646         spin_unlock_irq(&css_set_lock);
2647 }
2648 
2649 /**
2650  * cgroup_migrate_add_src - add a migration source css_set
2651  * @src_cset: the source css_set to add
2652  * @dst_cgrp: the destination cgroup
2653  * @preloaded_csets: list of preloaded css_sets
2654  *
2655  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2656  * @src_cset and add it to @preloaded_csets, which should later be cleaned
2657  * up by cgroup_migrate_finish().
2658  *
2659  * This function may be called without holding cgroup_threadgroup_rwsem
2660  * even if the target is a process.  Threads may be created and destroyed
2661  * but as long as cgroup_mutex is not dropped, no new css_set can be put
2662  * into play and the preloaded css_sets are guaranteed to cover all
2663  * migrations.
2664  */
2665 static void cgroup_migrate_add_src(struct css_set *src_cset,
2666                                    struct cgroup *dst_cgrp,
2667                                    struct list_head *preloaded_csets)
2668 {
2669         struct cgroup *src_cgrp;
2670 
2671         lockdep_assert_held(&cgroup_mutex);
2672         lockdep_assert_held(&css_set_lock);
2673 
2674         /*
2675          * If ->dead, @src_set is associated with one or more dead cgroups
2676          * and doesn't contain any migratable tasks.  Ignore it early so
2677          * that the rest of migration path doesn't get confused by it.
2678          */
2679         if (src_cset->dead)
2680                 return;
2681 
2682         src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2683 
2684         if (!list_empty(&src_cset->mg_preload_node))
2685                 return;
2686 
2687         WARN_ON(src_cset->mg_src_cgrp);
2688         WARN_ON(src_cset->mg_dst_cgrp);
2689         WARN_ON(!list_empty(&src_cset->mg_tasks));
2690         WARN_ON(!list_empty(&src_cset->mg_node));
2691 
2692         src_cset->mg_src_cgrp = src_cgrp;
2693         src_cset->mg_dst_cgrp = dst_cgrp;
2694         get_css_set(src_cset);
2695         list_add(&src_cset->mg_preload_node, preloaded_csets);
2696 }
2697 
2698 /**
2699  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2700  * @preloaded_csets: list of preloaded source css_sets
2701  *
2702  * Tasks are about to be moved and all the source css_sets have been
2703  * preloaded to @preloaded_csets.  This function looks up and pins all
2704  * destination css_sets, links each to its source, and append them to
2705  * @preloaded_csets.
2706  *
2707  * This function must be called after cgroup_migrate_add_src() has been
2708  * called on each migration source css_set.  After migration is performed
2709  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2710  * @preloaded_csets.
2711  */
2712 static int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
2713 {
2714         LIST_HEAD(csets);
2715         struct css_set *src_cset, *tmp_cset;
2716 
2717         lockdep_assert_held(&cgroup_mutex);
2718 
2719         /* look up the dst cset for each src cset and link it to src */
2720         list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
2721                 struct css_set *dst_cset;
2722 
2723                 dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2724                 if (!dst_cset)
2725                         goto err;
2726 
2727                 WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2728 
2729                 /*
2730                  * If src cset equals dst, it's noop.  Drop the src.
2731                  * cgroup_migrate() will skip the cset too.  Note that we
2732                  * can't handle src == dst as some nodes are used by both.
2733                  */
2734                 if (src_cset == dst_cset) {
2735                         src_cset->mg_src_cgrp = NULL;
2736                         src_cset->mg_dst_cgrp = NULL;
2737                         list_del_init(&src_cset->mg_preload_node);
2738                         put_css_set(src_cset);
2739                         put_css_set(dst_cset);
2740                         continue;
2741                 }
2742 
2743                 src_cset->mg_dst_cset = dst_cset;
2744 
2745                 if (list_empty(&dst_cset->mg_preload_node))
2746                         list_add(&dst_cset->mg_preload_node, &csets);
2747                 else
2748                         put_css_set(dst_cset);
2749         }
2750 
2751         list_splice_tail(&csets, preloaded_csets);
2752         return 0;
2753 err:
2754         cgroup_migrate_finish(&csets);
2755         return -ENOMEM;
2756 }
2757 
2758 /**
2759  * cgroup_migrate - migrate a process or task to a cgroup
2760  * @leader: the leader of the process or the task to migrate
2761  * @threadgroup: whether @leader points to the whole process or a single task
2762  * @root: cgroup root migration is taking place on
2763  *
2764  * Migrate a process or task denoted by @leader.  If migrating a process,
2765  * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2766  * responsible for invoking cgroup_migrate_add_src() and
2767  * cgroup_migrate_prepare_dst() on the targets before invoking this
2768  * function and following up with cgroup_migrate_finish().
2769  *
2770  * As long as a controller's ->can_attach() doesn't fail, this function is
2771  * guaranteed to succeed.  This means that, excluding ->can_attach()
2772  * failure, when migrating multiple targets, the success or failure can be
2773  * decided for all targets by invoking group_migrate_prepare_dst() before
2774  * actually starting migrating.
2775  */
2776 static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2777                           struct cgroup_root *root)
2778 {
2779         struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
2780         struct task_struct *task;
2781 
2782         /*
2783          * Prevent freeing of tasks while we take a snapshot. Tasks that are
2784          * already PF_EXITING could be freed from underneath us unless we
2785          * take an rcu_read_lock.
2786          */
2787         spin_lock_irq(&css_set_lock);
2788         rcu_read_lock();
2789         task = leader;
2790         do {
2791                 cgroup_taskset_add(task, &tset);
2792                 if (!threadgroup)
2793                         break;
2794         } while_each_thread(leader, task);
2795         rcu_read_unlock();
2796         spin_unlock_irq(&css_set_lock);
2797 
2798         return cgroup_taskset_migrate(&tset, root);
2799 }
2800 
2801 /**
2802  * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2803  * @dst_cgrp: the cgroup to attach to
2804  * @leader: the task or the leader of the threadgroup to be attached
2805  * @threadgroup: attach the whole threadgroup?
2806  *
2807  * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2808  */
2809 static int cgroup_attach_task(struct cgroup *dst_cgrp,
2810                               struct task_struct *leader, bool threadgroup)
2811 {
2812         LIST_HEAD(preloaded_csets);
2813         struct task_struct *task;
2814         int ret;
2815 
2816         if (!cgroup_may_migrate_to(dst_cgrp))
2817                 return -EBUSY;
2818 
2819         /* look up all src csets */
2820         spin_lock_irq(&css_set_lock);
2821         rcu_read_lock();
2822         task = leader;
2823         do {
2824                 cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
2825                                        &preloaded_csets);
2826                 if (!threadgroup)
2827                         break;
2828         } while_each_thread(leader, task);
2829         rcu_read_unlock();
2830         spin_unlock_irq(&css_set_lock);
2831 
2832         /* prepare dst csets and commit */
2833         ret = cgroup_migrate_prepare_dst(&preloaded_csets);
2834         if (!ret)
2835                 ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
2836 
2837         cgroup_migrate_finish(&preloaded_csets);
2838 
2839         if (!ret)
2840                 trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
2841 
2842         return ret;
2843 }
2844 
2845 static int cgroup_procs_write_permission(struct task_struct *task,
2846                                          struct cgroup *dst_cgrp,
2847                                          struct kernfs_open_file *of)
2848 {
2849         const struct cred *cred = current_cred();
2850         const struct cred *tcred = get_task_cred(task);
2851         int ret = 0;
2852 
2853         /*
2854          * even if we're attaching all tasks in the thread group, we only
2855          * need to check permissions on one of them.
2856          */
2857         if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2858             !uid_eq(cred->euid, tcred->uid) &&
2859             !uid_eq(cred->euid, tcred->suid))
2860                 ret = -EACCES;
2861 
2862         if (!ret && cgroup_on_dfl(dst_cgrp)) {
2863                 struct super_block *sb = of->file->f_path.dentry->d_sb;
2864                 struct cgroup *cgrp;
2865                 struct inode *inode;
2866 
2867                 spin_lock_irq(&css_set_lock);
2868                 cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
2869                 spin_unlock_irq(&css_set_lock);
2870 
2871                 while (!cgroup_is_descendant(dst_cgrp, cgrp))
2872                         cgrp = cgroup_parent(cgrp);
2873 
2874                 ret = -ENOMEM;
2875                 inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
2876                 if (inode) {
2877                         ret = inode_permission(inode, MAY_WRITE);
2878                         iput(inode);
2879                 }
2880         }
2881 
2882         put_cred(tcred);
2883         return ret;
2884 }
2885 
2886 /*
2887  * Find the task_struct of the task to attach by vpid and pass it along to the
2888  * function to attach either it or all tasks in its threadgroup. Will lock
2889  * cgroup_mutex and threadgroup.
2890  */
2891 static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
2892                                     size_t nbytes, loff_t off, bool threadgroup)
2893 {
2894         struct task_struct *tsk;
2895         struct cgroup_subsys *ss;
2896         struct cgroup *cgrp;
2897         pid_t pid;
2898         int ssid, ret;
2899 
2900         if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2901                 return -EINVAL;
2902 
2903         cgrp = cgroup_kn_lock_live(of->kn, false);
2904         if (!cgrp)
2905                 return -ENODEV;
2906 
2907         percpu_down_write(&cgroup_threadgroup_rwsem);
2908         rcu_read_lock();
2909         if (pid) {
2910                 tsk = find_task_by_vpid(pid);
2911                 if (!tsk) {
2912                         ret = -ESRCH;
2913                         goto out_unlock_rcu;
2914                 }
2915         } else {
2916                 tsk = current;
2917         }
2918 
2919         if (threadgroup)
2920                 tsk = tsk->group_leader;
2921 
2922         /*
2923          * Workqueue threads may acquire PF_NO_SETAFFINITY and become
2924          * trapped in a cpuset, or RT worker may be born in a cgroup
2925          * with no rt_runtime allocated.  Just say no.
2926          */
2927         if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
2928                 ret = -EINVAL;
2929                 goto out_unlock_rcu;
2930         }
2931 
2932         get_task_struct(tsk);
2933         rcu_read_unlock();
2934 
2935         ret = cgroup_procs_write_permission(tsk, cgrp, of);
2936         if (!ret)
2937                 ret = cgroup_attach_task(cgrp, tsk, threadgroup);
2938 
2939         put_task_struct(tsk);
2940         goto out_unlock_threadgroup;
2941 
2942 out_unlock_rcu:
2943         rcu_read_unlock();
2944 out_unlock_threadgroup:
2945         percpu_up_write(&cgroup_threadgroup_rwsem);
2946         for_each_subsys(ss, ssid)
2947                 if (ss->post_attach)
2948                         ss->post_attach();
2949         cgroup_kn_unlock(of->kn);
2950         return ret ?: nbytes;
2951 }
2952 
2953 /**
2954  * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2955  * @from: attach to all cgroups of a given task
2956  * @tsk: the task to be attached
2957  */
2958 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2959 {
2960         struct cgroup_root *root;
2961         int retval = 0;
2962 
2963         mutex_lock(&cgroup_mutex);
2964         percpu_down_write(&cgroup_threadgroup_rwsem);
2965         for_each_root(root) {
2966                 struct cgroup *from_cgrp;
2967 
2968                 if (root == &cgrp_dfl_root)
2969                         continue;
2970 
2971                 spin_lock_irq(&css_set_lock);
2972                 from_cgrp = task_cgroup_from_root(from, root);
2973                 spin_unlock_irq(&css_set_lock);
2974 
2975                 retval = cgroup_attach_task(from_cgrp, tsk, false);
2976                 if (retval)
2977                         break;
2978         }
2979         percpu_up_write(&cgroup_threadgroup_rwsem);
2980         mutex_unlock(&cgroup_mutex);
2981 
2982         return retval;
2983 }
2984 EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2985 
2986 static ssize_t cgroup_tasks_write(struct kernfs_open_file *of,
2987                                   char *buf, size_t nbytes, loff_t off)
2988 {
2989         return __cgroup_procs_write(of, buf, nbytes, off, false);
2990 }
2991 
2992 static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
2993                                   char *buf, size_t nbytes, loff_t off)
2994 {
2995         return __cgroup_procs_write(of, buf, nbytes, off, true);
2996 }
2997 
2998 static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
2999                                           char *buf, size_t nbytes, loff_t off)
3000 {
3001         struct cgroup *cgrp;
3002 
3003         BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
3004 
3005         cgrp = cgroup_kn_lock_live(of->kn, false);
3006         if (!cgrp)
3007                 return -ENODEV;
3008         spin_lock(&release_agent_path_lock);
3009         strlcpy(cgrp->root->release_agent_path, strstrip(buf),
3010                 sizeof(cgrp->root->release_agent_path));
3011         spin_unlock(&release_agent_path_lock);
3012         cgroup_kn_unlock(of->kn);
3013         return nbytes;
3014 }
3015 
3016 static int cgroup_release_agent_show(struct seq_file *seq, void *v)
3017 {
3018         struct cgroup *cgrp = seq_css(seq)->cgroup;
3019 
3020         spin_lock(&release_agent_path_lock);
3021         seq_puts(seq, cgrp->root->release_agent_path);
3022         spin_unlock(&release_agent_path_lock);
3023         seq_putc(seq, '\n');
3024         return 0;
3025 }
3026 
3027 static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
3028 {
3029         seq_puts(seq, "\n");
3030         return 0;
3031 }
3032 
3033 static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
3034 {
3035         struct cgroup_subsys *ss;
3036         bool printed = false;
3037         int ssid;
3038 
3039         do_each_subsys_mask(ss, ssid, ss_mask) {
3040                 if (printed)
3041                         seq_putc(seq, ' ');
3042                 seq_printf(seq, "%s", ss->name);
3043                 printed = true;
3044         } while_each_subsys_mask();
3045         if (printed)
3046                 seq_putc(seq, '\n');
3047 }
3048 
3049 /* show controllers which are enabled from the parent */
3050 static int cgroup_controllers_show(struct seq_file *seq, void *v)
3051 {
3052         struct cgroup *cgrp = seq_css(seq)->cgroup;
3053 
3054         cgroup_print_ss_mask(seq, cgroup_control(cgrp));
3055         return 0;
3056 }
3057 
3058 /* show controllers which are enabled for a given cgroup's children */
3059 static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
3060 {
3061         struct cgroup *cgrp = seq_css(seq)->cgroup;
3062 
3063         cgroup_print_ss_mask(seq, cgrp->subtree_control);
3064         return 0;
3065 }
3066 
3067 /**
3068  * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
3069  * @cgrp: root of the subtree to update csses for
3070  *
3071  * @cgrp's control masks have changed and its subtree's css associations
3072  * need to be updated accordingly.  This function looks up all css_sets
3073  * which are attached to the subtree, creates the matching updated css_sets
3074  * and migrates the tasks to the new ones.
3075  */
3076 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
3077 {
3078         LIST_HEAD(preloaded_csets);
3079         struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
3080         struct cgroup_subsys_state *d_css;
3081         struct cgroup *dsct;
3082         struct css_set *src_cset;
3083         int ret;
3084 
3085         lockdep_assert_held(&cgroup_mutex);
3086 
3087         percpu_down_write(&cgroup_threadgroup_rwsem);
3088 
3089         /* look up all csses currently attached to @cgrp's subtree */
3090         spin_lock_irq(&css_set_lock);
3091         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3092                 struct cgrp_cset_link *link;
3093 
3094                 list_for_each_entry(link, &dsct->cset_links, cset_link)
3095                         cgroup_migrate_add_src(link->cset, dsct,
3096                                                &preloaded_csets);
3097         }
3098         spin_unlock_irq(&css_set_lock);
3099 
3100         /* NULL dst indicates self on default hierarchy */
3101         ret = cgroup_migrate_prepare_dst(&preloaded_csets);
3102         if (ret)
3103                 goto out_finish;
3104 
3105         spin_lock_irq(&css_set_lock);
3106         list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
3107                 struct task_struct *task, *ntask;
3108 
3109                 /* src_csets precede dst_csets, break on the first dst_cset */
3110                 if (!src_cset->mg_src_cgrp)
3111                         break;
3112 
3113                 /* all tasks in src_csets need to be migrated */
3114                 list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
3115                         cgroup_taskset_add(task, &tset);
3116         }
3117         spin_unlock_irq(&css_set_lock);
3118 
3119         ret = cgroup_taskset_migrate(&tset, cgrp->root);
3120 out_finish:
3121         cgroup_migrate_finish(&preloaded_csets);
3122         percpu_up_write(&cgroup_threadgroup_rwsem);
3123         return ret;
3124 }
3125 
3126 /**
3127  * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
3128  * @cgrp: root of the target subtree
3129  *
3130  * Because css offlining is asynchronous, userland may try to re-enable a
3131  * controller while the previous css is still around.  This function grabs
3132  * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
3133  */
3134 static void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
3135         __acquires(&cgroup_mutex)
3136 {
3137         struct cgroup *dsct;
3138         struct cgroup_subsys_state *d_css;
3139         struct cgroup_subsys *ss;
3140         int ssid;
3141 
3142 restart:
3143         mutex_lock(&cgroup_mutex);
3144 
3145         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3146                 for_each_subsys(ss, ssid) {
3147                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3148                         DEFINE_WAIT(wait);
3149 
3150                         if (!css || !percpu_ref_is_dying(&css->refcnt))
3151                                 continue;
3152 
3153                         cgroup_get(dsct);
3154                         prepare_to_wait(&dsct->offline_waitq, &wait,
3155                                         TASK_UNINTERRUPTIBLE);
3156 
3157                         mutex_unlock(&cgroup_mutex);
3158                         schedule();
3159                         finish_wait(&dsct->offline_waitq, &wait);
3160 
3161                         cgroup_put(dsct);
3162                         goto restart;
3163                 }
3164         }
3165 }
3166 
3167 /**
3168  * cgroup_save_control - save control masks of a subtree
3169  * @cgrp: root of the target subtree
3170  *
3171  * Save ->subtree_control and ->subtree_ss_mask to the respective old_
3172  * prefixed fields for @cgrp's subtree including @cgrp itself.
3173  */
3174 static void cgroup_save_control(struct cgroup *cgrp)
3175 {
3176         struct cgroup *dsct;
3177         struct cgroup_subsys_state *d_css;
3178 
3179         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3180                 dsct->old_subtree_control = dsct->subtree_control;
3181                 dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
3182         }
3183 }
3184 
3185 /**
3186  * cgroup_propagate_control - refresh control masks of a subtree
3187  * @cgrp: root of the target subtree
3188  *
3189  * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
3190  * ->subtree_control and propagate controller availability through the
3191  * subtree so that descendants don't have unavailable controllers enabled.
3192  */
3193 static void cgroup_propagate_control(struct cgroup *cgrp)
3194 {
3195         struct cgroup *dsct;
3196         struct cgroup_subsys_state *d_css;
3197 
3198         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3199                 dsct->subtree_control &= cgroup_control(dsct);
3200                 dsct->subtree_ss_mask =
3201                         cgroup_calc_subtree_ss_mask(dsct->subtree_control,
3202                                                     cgroup_ss_mask(dsct));
3203         }
3204 }
3205 
3206 /**
3207  * cgroup_restore_control - restore control masks of a subtree
3208  * @cgrp: root of the target subtree
3209  *
3210  * Restore ->subtree_control and ->subtree_ss_mask from the respective old_
3211  * prefixed fields for @cgrp's subtree including @cgrp itself.
3212  */
3213 static void cgroup_restore_control(struct cgroup *cgrp)
3214 {
3215         struct cgroup *dsct;
3216         struct cgroup_subsys_state *d_css;
3217 
3218         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3219                 dsct->subtree_control = dsct->old_subtree_control;
3220                 dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3221         }
3222 }
3223 
3224 static bool css_visible(struct cgroup_subsys_state *css)
3225 {
3226         struct cgroup_subsys *ss = css->ss;
3227         struct cgroup *cgrp = css->cgroup;
3228 
3229         if (cgroup_control(cgrp) & (1 << ss->id))
3230                 return true;
3231         if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3232                 return false;
3233         return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3234 }
3235 
3236 /**
3237  * cgroup_apply_control_enable - enable or show csses according to control
3238  * @cgrp: root of the target subtree
3239  *
3240  * Walk @cgrp's subtree and create new csses or make the existing ones
3241  * visible.  A css is created invisible if it's being implicitly enabled
3242  * through dependency.  An invisible css is made visible when the userland
3243  * explicitly enables it.
3244  *
3245  * Returns 0 on success, -errno on failure.  On failure, csses which have
3246  * been processed already aren't cleaned up.  The caller is responsible for
3247  * cleaning up with cgroup_apply_control_disble().
3248  */
3249 static int cgroup_apply_control_enable(struct cgroup *cgrp)
3250 {
3251         struct cgroup *dsct;
3252         struct cgroup_subsys_state *d_css;
3253         struct cgroup_subsys *ss;
3254         int ssid, ret;
3255 
3256         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3257                 for_each_subsys(ss, ssid) {
3258                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3259 
3260                         WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3261 
3262                         if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3263                                 continue;
3264 
3265                         if (!css) {
3266                                 css = css_create(dsct, ss);
3267                                 if (IS_ERR(css))
3268                                         return PTR_ERR(css);
3269                         }
3270 
3271                         if (css_visible(css)) {
3272                                 ret = css_populate_dir(css);
3273                                 if (ret)
3274                                         return ret;
3275                         }
3276                 }
3277         }
3278 
3279         return 0;
3280 }
3281 
3282 /**
3283  * cgroup_apply_control_disable - kill or hide csses according to control
3284  * @cgrp: root of the target subtree
3285  *
3286  * Walk @cgrp's subtree and kill and hide csses so that they match
3287  * cgroup_ss_mask() and cgroup_visible_mask().
3288  *
3289  * A css is hidden when the userland requests it to be disabled while other
3290  * subsystems are still depending on it.  The css must not actively control
3291  * resources and be in the vanilla state if it's made visible again later.
3292  * Controllers which may be depended upon should provide ->css_reset() for
3293  * this purpose.
3294  */
3295 static void cgroup_apply_control_disable(struct cgroup *cgrp)
3296 {
3297         struct cgroup *dsct;
3298         struct cgroup_subsys_state *d_css;
3299         struct cgroup_subsys *ss;
3300         int ssid;
3301 
3302         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3303                 for_each_subsys(ss, ssid) {
3304                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3305 
3306                         WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3307 
3308                         if (!css)
3309                                 continue;
3310 
3311                         if (css->parent &&
3312                             !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3313                                 kill_css(css);
3314                         } else if (!css_visible(css)) {
3315                                 css_clear_dir(css);
3316                                 if (ss->css_reset)
3317                                         ss->css_reset(css);
3318                         }
3319                 }
3320         }
3321 }
3322 
3323 /**
3324  * cgroup_apply_control - apply control mask updates to the subtree
3325  * @cgrp: root of the target subtree
3326  *
3327  * subsystems can be enabled and disabled in a subtree using the following
3328  * steps.
3329  *
3330  * 1. Call cgroup_save_control() to stash the current state.
3331  * 2. Update ->subtree_control masks in the subtree as desired.
3332  * 3. Call cgroup_apply_control() to apply the changes.
3333  * 4. Optionally perform other related operations.
3334  * 5. Call cgroup_finalize_control() to finish up.
3335  *
3336  * This function implements step 3 and propagates the mask changes
3337  * throughout @cgrp's subtree, updates csses accordingly and perform
3338  * process migrations.
3339  */
3340 static int cgroup_apply_control(struct cgroup *cgrp)
3341 {
3342         int ret;
3343 
3344         cgroup_propagate_control(cgrp);
3345 
3346         ret = cgroup_apply_control_enable(cgrp);
3347         if (ret)
3348                 return ret;
3349 
3350         /*
3351          * At this point, cgroup_e_css() results reflect the new csses
3352          * making the following cgroup_update_dfl_csses() properly update
3353          * css associations of all tasks in the subtree.
3354          */
3355         ret = cgroup_update_dfl_csses(cgrp);
3356         if (ret)
3357                 return ret;
3358 
3359         return 0;
3360 }
3361 
3362 /**
3363  * cgroup_finalize_control - finalize control mask update
3364  * @cgrp: root of the target subtree
3365  * @ret: the result of the update
3366  *
3367  * Finalize control mask update.  See cgroup_apply_control() for more info.
3368  */
3369 static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3370 {
3371         if (ret) {
3372                 cgroup_restore_control(cgrp);
3373                 cgroup_propagate_control(cgrp);
3374         }
3375 
3376         cgroup_apply_control_disable(cgrp);
3377 }
3378 
3379 /* change the enabled child controllers for a cgroup in the default hierarchy */
3380 static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3381                                             char *buf, size_t nbytes,
3382                                             loff_t off)
3383 {
3384         u16 enable = 0, disable = 0;
3385         struct cgroup *cgrp, *child;
3386         struct cgroup_subsys *ss;
3387         char *tok;
3388         int ssid, ret;
3389 
3390         /*
3391          * Parse input - space separated list of subsystem names prefixed
3392          * with either + or -.
3393          */
3394         buf = strstrip(buf);
3395         while ((tok = strsep(&buf, " "))) {
3396                 if (tok[0] == '\0')
3397                         continue;
3398                 do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3399                         if (!cgroup_ssid_enabled(ssid) ||
3400                             strcmp(tok + 1, ss->name))
3401                                 continue;
3402 
3403                         if (*tok == '+') {
3404                                 enable |= 1 << ssid;
3405                                 disable &= ~(1 << ssid);
3406                         } else if (*tok == '-') {
3407                                 disable |= 1 << ssid;
3408                                 enable &= ~(1 << ssid);
3409                         } else {
3410                                 return -EINVAL;
3411                         }
3412                         break;
3413                 } while_each_subsys_mask();
3414                 if (ssid == CGROUP_SUBSYS_COUNT)
3415                         return -EINVAL;
3416         }
3417 
3418         cgrp = cgroup_kn_lock_live(of->kn, true);
3419         if (!cgrp)
3420                 return -ENODEV;
3421 
3422         for_each_subsys(ss, ssid) {
3423                 if (enable & (1 << ssid)) {
3424                         if (cgrp->subtree_control & (1 << ssid)) {
3425                                 enable &= ~(1 << ssid);
3426                                 continue;
3427                         }
3428 
3429                         if (!(cgroup_control(cgrp) & (1 << ssid))) {
3430                                 ret = -ENOENT;
3431                                 goto out_unlock;
3432                         }
3433                 } else if (disable & (1 << ssid)) {
3434                         if (!(cgrp->subtree_control & (1 << ssid))) {
3435                                 disable &= ~(1 << ssid);
3436                                 continue;
3437                         }
3438 
3439                         /* a child has it enabled? */
3440                         cgroup_for_each_live_child(child, cgrp) {
3441                                 if (child->subtree_control & (1 << ssid)) {
3442                                         ret = -EBUSY;
3443                                         goto out_unlock;
3444                                 }
3445                         }
3446                 }
3447         }
3448 
3449         if (!enable && !disable) {
3450                 ret = 0;
3451                 goto out_unlock;
3452         }
3453 
3454         /*
3455          * Except for the root, subtree_control must be zero for a cgroup
3456          * with tasks so that child cgroups don't compete against tasks.
3457          */
3458         if (enable && cgroup_parent(cgrp)) {
3459                 struct cgrp_cset_link *link;
3460 
3461                 /*
3462                  * Because namespaces pin csets too, @cgrp->cset_links
3463                  * might not be empty even when @cgrp is empty.  Walk and
3464                  * verify each cset.
3465                  */
3466                 spin_lock_irq(&css_set_lock);
3467 
3468                 ret = 0;
3469                 list_for_each_entry(link, &cgrp->cset_links, cset_link) {
3470                         if (css_set_populated(link->cset)) {
3471                                 ret = -EBUSY;
3472                                 break;
3473                         }
3474                 }
3475 
3476                 spin_unlock_irq(&css_set_lock);
3477 
3478                 if (ret)
3479                         goto out_unlock;
3480         }
3481 
3482         /* save and update control masks and prepare csses */
3483         cgroup_save_control(cgrp);
3484 
3485         cgrp->subtree_control |= enable;
3486         cgrp->subtree_control &= ~disable;
3487 
3488         ret = cgroup_apply_control(cgrp);
3489 
3490         cgroup_finalize_control(cgrp, ret);
3491 
3492         kernfs_activate(cgrp->kn);
3493         ret = 0;
3494 out_unlock:
3495         cgroup_kn_unlock(of->kn);
3496         return ret ?: nbytes;
3497 }
3498 
3499 static int cgroup_events_show(struct seq_file *seq, void *v)
3500 {
3501         seq_printf(seq, "populated %d\n",
3502                    cgroup_is_populated(seq_css(seq)->cgroup));
3503         return 0;
3504 }
3505 
3506 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3507                                  size_t nbytes, loff_t off)
3508 {
3509         struct cgroup *cgrp = of->kn->parent->priv;
3510         struct cftype *cft = of->kn->priv;
3511         struct cgroup_subsys_state *css;
3512         int ret;
3513 
3514         if (cft->write)
3515                 return cft->write(of, buf, nbytes, off);
3516 
3517         /*
3518          * kernfs guarantees that a file isn't deleted with operations in
3519          * flight, which means that the matching css is and stays alive and
3520          * doesn't need to be pinned.  The RCU locking is not necessary
3521          * either.  It's just for the convenience of using cgroup_css().
3522          */
3523         rcu_read_lock();
3524         css = cgroup_css(cgrp, cft->ss);
3525         rcu_read_unlock();
3526 
3527         if (cft->write_u64) {
3528                 unsigned long long v;
3529                 ret = kstrtoull(buf, 0, &v);
3530                 if (!ret)
3531                         ret = cft->write_u64(css, cft, v);
3532         } else if (cft->write_s64) {
3533                 long long v;
3534                 ret = kstrtoll(buf, 0, &v);
3535                 if (!ret)
3536                         ret = cft->write_s64(css, cft, v);
3537         } else {
3538                 ret = -EINVAL;
3539         }
3540 
3541         return ret ?: nbytes;
3542 }
3543 
3544 static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3545 {
3546         return seq_cft(seq)->seq_start(seq, ppos);
3547 }
3548 
3549 static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3550 {
3551         return seq_cft(seq)->seq_next(seq, v, ppos);
3552 }
3553 
3554 static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3555 {
3556         seq_cft(seq)->seq_stop(seq, v);
3557 }
3558 
3559 static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3560 {
3561         struct cftype *cft = seq_cft(m);
3562         struct cgroup_subsys_state *css = seq_css(m);
3563 
3564         if (cft->seq_show)
3565                 return cft->seq_show(m, arg);
3566 
3567         if (cft->read_u64)
3568                 seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3569         else if (cft->read_s64)
3570                 seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3571         else
3572                 return -EINVAL;
3573         return 0;
3574 }
3575 
3576 static struct kernfs_ops cgroup_kf_single_ops = {
3577         .atomic_write_len       = PAGE_SIZE,
3578         .write                  = cgroup_file_write,
3579         .seq_show               = cgroup_seqfile_show,
3580 };
3581 
3582 static struct kernfs_ops cgroup_kf_ops = {
3583         .atomic_write_len       = PAGE_SIZE,
3584         .write                  = cgroup_file_write,
3585         .seq_start              = cgroup_seqfile_start,
3586         .seq_next               = cgroup_seqfile_next,
3587         .seq_stop               = cgroup_seqfile_stop,
3588         .seq_show               = cgroup_seqfile_show,
3589 };
3590 
3591 /*
3592  * cgroup_rename - Only allow simple rename of directories in place.
3593  */
3594 static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
3595                          const char *new_name_str)
3596 {
3597         struct cgroup *cgrp = kn->priv;
3598         int ret;
3599 
3600         if (kernfs_type(kn) != KERNFS_DIR)
3601                 return -ENOTDIR;
3602         if (kn->parent != new_parent)
3603                 return -EIO;
3604 
3605         /*
3606          * This isn't a proper migration and its usefulness is very
3607          * limited.  Disallow on the default hierarchy.
3608          */
3609         if (cgroup_on_dfl(cgrp))
3610                 return -EPERM;
3611 
3612         /*
3613          * We're gonna grab cgroup_mutex which nests outside kernfs
3614          * active_ref.  kernfs_rename() doesn't require active_ref
3615          * protection.  Break them before grabbing cgroup_mutex.
3616          */
3617         kernfs_break_active_protection(new_parent);
3618         kernfs_break_active_protection(kn);
3619 
3620         mutex_lock(&cgroup_mutex);
3621 
3622         ret = kernfs_rename(kn, new_parent, new_name_str);
3623         if (!ret)
3624                 trace_cgroup_rename(cgrp);
3625 
3626         mutex_unlock(&cgroup_mutex);
3627 
3628         kernfs_unbreak_active_protection(kn);
3629         kernfs_unbreak_active_protection(new_parent);
3630         return ret;
3631 }
3632 
3633 /* set uid and gid of cgroup dirs and files to that of the creator */
3634 static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3635 {
3636         struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3637                                .ia_uid = current_fsuid(),
3638                                .ia_gid = current_fsgid(), };
3639 
3640         if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3641             gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3642                 return 0;
3643 
3644         return kernfs_setattr(kn, &iattr);
3645 }
3646 
3647 static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3648                            struct cftype *cft)
3649 {
3650         char name[CGROUP_FILE_NAME_MAX];
3651         struct kernfs_node *kn;
3652         struct lock_class_key *key = NULL;
3653         int ret;
3654 
3655 #ifdef CONFIG_DEBUG_LOCK_ALLOC
3656         key = &cft->lockdep_key;
3657 #endif
3658         kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3659                                   cgroup_file_mode(cft), 0, cft->kf_ops, cft,
3660                                   NULL, key);
3661         if (IS_ERR(kn))
3662                 return PTR_ERR(kn);
3663 
3664         ret = cgroup_kn_set_ugid(kn);
3665         if (ret) {
3666                 kernfs_remove(kn);
3667                 return ret;
3668         }
3669 
3670         if (cft->file_offset) {
3671                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
3672 
3673                 spin_lock_irq(&cgroup_file_kn_lock);
3674                 cfile->kn = kn;
3675                 spin_unlock_irq(&cgroup_file_kn_lock);
3676         }
3677 
3678         return 0;
3679 }
3680 
3681 /**
3682  * cgroup_addrm_files - add or remove files to a cgroup directory
3683  * @css: the target css
3684  * @cgrp: the target cgroup (usually css->cgroup)
3685  * @cfts: array of cftypes to be added
3686  * @is_add: whether to add or remove
3687  *
3688  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3689  * For removals, this function never fails.
3690  */
3691 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3692                               struct cgroup *cgrp, struct cftype cfts[],
3693                               bool is_add)
3694 {
3695         struct cftype *cft, *cft_end = NULL;
3696         int ret = 0;
3697 
3698         lockdep_assert_held(&cgroup_mutex);
3699 
3700 restart:
3701         for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3702                 /* does cft->flags tell us to skip this file on @cgrp? */
3703                 if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3704                         continue;
3705                 if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3706                         continue;
3707                 if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3708                         continue;
3709                 if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3710                         continue;
3711 
3712                 if (is_add) {
3713                         ret = cgroup_add_file(css, cgrp, cft);
3714                         if (ret) {
3715                                 pr_warn("%s: failed to add %s, err=%d\n",
3716                                         __func__, cft->name, ret);
3717                                 cft_end = cft;
3718                                 is_add = false;
3719                                 goto restart;
3720                         }
3721                 } else {
3722                         cgroup_rm_file(cgrp, cft);
3723                 }
3724         }
3725         return ret;
3726 }
3727 
3728 static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3729 {
3730         LIST_HEAD(pending);
3731         struct cgroup_subsys *ss = cfts[0].ss;
3732         struct cgroup *root = &ss->root->cgrp;
3733         struct cgroup_subsys_state *css;
3734         int ret = 0;
3735 
3736         lockdep_assert_held(&cgroup_mutex);
3737 
3738         /* add/rm files for all cgroups created before */
3739         css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3740                 struct cgroup *cgrp = css->cgroup;
3741 
3742                 if (!(css->flags & CSS_VISIBLE))
3743                         continue;
3744 
3745                 ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3746                 if (ret)
3747                         break;
3748         }
3749 
3750         if (is_add && !ret)
3751                 kernfs_activate(root->kn);
3752         return ret;
3753 }
3754 
3755 static void cgroup_exit_cftypes(struct cftype *cfts)
3756 {
3757         struct cftype *cft;
3758 
3759         for (cft = cfts; cft->name[0] != '\0'; cft++) {
3760                 /* free copy for custom atomic_write_len, see init_cftypes() */
3761                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3762                         kfree(cft->kf_ops);
3763                 cft->kf_ops = NULL;
3764                 cft->ss = NULL;
3765 
3766                 /* revert flags set by cgroup core while adding @cfts */
3767                 cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3768         }
3769 }
3770 
3771 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3772 {
3773         struct cftype *cft;
3774 
3775         for (cft = cfts; cft->name[0] != '\0'; cft++) {
3776                 struct kernfs_ops *kf_ops;
3777 
3778                 WARN_ON(cft->ss || cft->kf_ops);
3779 
3780                 if (cft->seq_start)
3781                         kf_ops = &cgroup_kf_ops;
3782                 else
3783                         kf_ops = &cgroup_kf_single_ops;
3784 
3785                 /*
3786                  * Ugh... if @cft wants a custom max_write_len, we need to
3787                  * make a copy of kf_ops to set its atomic_write_len.
3788                  */
3789                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3790                         kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3791                         if (!kf_ops) {
3792                                 cgroup_exit_cftypes(cfts);
3793                                 return -ENOMEM;
3794                         }
3795                         kf_ops->atomic_write_len = cft->max_write_len;
3796                 }
3797 
3798                 cft->kf_ops = kf_ops;
3799                 cft->ss = ss;
3800         }
3801 
3802         return 0;
3803 }
3804 
3805 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
3806 {
3807         lockdep_assert_held(&cgroup_mutex);
3808 
3809         if (!cfts || !cfts[0].ss)
3810                 return -ENOENT;
3811 
3812         list_del(&cfts->node);
3813         cgroup_apply_cftypes(cfts, false);
3814         cgroup_exit_cftypes(cfts);
3815         return 0;
3816 }
3817 
3818 /**
3819  * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
3820  * @cfts: zero-length name terminated array of cftypes
3821  *
3822  * Unregister @cfts.  Files described by @cfts are removed from all
3823  * existing cgroups and all future cgroups won't have them either.  This
3824  * function can be called anytime whether @cfts' subsys is attached or not.
3825  *
3826  * Returns 0 on successful unregistration, -ENOENT if @cfts is not
3827  * registered.
3828  */
3829 int cgroup_rm_cftypes(struct cftype *cfts)
3830 {
3831         int ret;
3832 
3833         mutex_lock(&cgroup_mutex);
3834         ret = cgroup_rm_cftypes_locked(cfts);
3835         mutex_unlock(&cgroup_mutex);
3836         return ret;
3837 }
3838 
3839 /**
3840  * cgroup_add_cftypes - add an array of cftypes to a subsystem
3841  * @ss: target cgroup subsystem
3842  * @cfts: zero-length name terminated array of cftypes
3843  *
3844  * Register @cfts to @ss.  Files described by @cfts are created for all
3845  * existing cgroups to which @ss is attached and all future cgroups will
3846  * have them too.  This function can be called anytime whether @ss is
3847  * attached or not.
3848  *
3849  * Returns 0 on successful registration, -errno on failure.  Note that this
3850  * function currently returns 0 as long as @cfts registration is successful
3851  * even if some file creation attempts on existing cgroups fail.
3852  */
3853 static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3854 {
3855         int ret;
3856 
3857         if (!cgroup_ssid_enabled(ss->id))
3858                 return 0;
3859 
3860         if (!cfts || cfts[0].name[0] == '\0')
3861                 return 0;
3862 
3863         ret = cgroup_init_cftypes(ss, cfts);
3864         if (ret)
3865                 return ret;
3866 
3867         mutex_lock(&cgroup_mutex);
3868 
3869         list_add_tail(&cfts->node, &ss->cfts);
3870         ret = cgroup_apply_cftypes(cfts, true);
3871         if (ret)
3872                 cgroup_rm_cftypes_locked(cfts);
3873 
3874         mutex_unlock(&cgroup_mutex);
3875         return ret;
3876 }
3877 
3878 /**
3879  * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
3880  * @ss: target cgroup subsystem
3881  * @cfts: zero-length name terminated array of cftypes
3882  *
3883  * Similar to cgroup_add_cftypes() but the added files are only used for
3884  * the default hierarchy.
3885  */
3886 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3887 {
3888         struct cftype *cft;
3889 
3890         for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3891                 cft->flags |= __CFTYPE_ONLY_ON_DFL;
3892         return cgroup_add_cftypes(ss, cfts);
3893 }
3894 
3895 /**
3896  * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
3897  * @ss: target cgroup subsystem
3898  * @cfts: zero-length name terminated array of cftypes
3899  *
3900  * Similar to cgroup_add_cftypes() but the added files are only used for
3901  * the legacy hierarchies.
3902  */
3903 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3904 {
3905         struct cftype *cft;
3906 
3907         for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3908                 cft->flags |= __CFTYPE_NOT_ON_DFL;
3909         return cgroup_add_cftypes(ss, cfts);
3910 }
3911 
3912 /**
3913  * cgroup_file_notify - generate a file modified event for a cgroup_file
3914  * @cfile: target cgroup_file
3915  *
3916  * @cfile must have been obtained by setting cftype->file_offset.
3917  */
3918 void cgroup_file_notify(struct cgroup_file *cfile)
3919 {
3920         unsigned long flags;
3921 
3922         spin_lock_irqsave(&cgroup_file_kn_lock, flags);
3923         if (cfile->kn)
3924                 kernfs_notify(cfile->kn);
3925         spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
3926 }
3927 
3928 /**
3929  * cgroup_task_count - count the number of tasks in a cgroup.
3930  * @cgrp: the cgroup in question
3931  *
3932  * Return the number of tasks in the cgroup.  The returned number can be
3933  * higher than the actual number of tasks due to css_set references from
3934  * namespace roots and temporary usages.
3935  */
3936 static int cgroup_task_count(const struct cgroup *cgrp)
3937 {
3938         int count = 0;
3939         struct cgrp_cset_link *link;
3940 
3941         spin_lock_irq(&css_set_lock);
3942         list_for_each_entry(link, &cgrp->cset_links, cset_link)
3943                 count += atomic_read(&link->cset->refcount);
3944         spin_unlock_irq(&css_set_lock);
3945         return count;
3946 }
3947 
3948 /**
3949  * css_next_child - find the next child of a given css
3950  * @pos: the current position (%NULL to initiate traversal)
3951  * @parent: css whose children to walk
3952  *
3953  * This function returns the next child of @parent and should be called
3954  * under either cgroup_mutex or RCU read lock.  The only requirement is
3955  * that @parent and @pos are accessible.  The next sibling is guaranteed to
3956  * be returned regardless of their states.
3957  *
3958  * If a subsystem synchronizes ->css_online() and the start of iteration, a
3959  * css which finished ->css_online() is guaranteed to be visible in the
3960  * future iterations and will stay visible until the last reference is put.
3961  * A css which hasn't finished ->css_online() or already finished
3962  * ->css_offline() may show up during traversal.  It's each subsystem's
3963  * responsibility to synchronize against on/offlining.
3964  */
3965 struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
3966                                            struct cgroup_subsys_state *parent)
3967 {
3968         struct cgroup_subsys_state *next;
3969 
3970         cgroup_assert_mutex_or_rcu_locked();
3971 
3972         /*
3973          * @pos could already have been unlinked from the sibling list.
3974          * Once a cgroup is removed, its ->sibling.next is no longer
3975          * updated when its next sibling changes.  CSS_RELEASED is set when
3976          * @pos is taken off list, at which time its next pointer is valid,
3977          * and, as releases are serialized, the one pointed to by the next
3978          * pointer is guaranteed to not have started release yet.  This
3979          * implies that if we observe !CSS_RELEASED on @pos in this RCU
3980          * critical section, the one pointed to by its next pointer is
3981          * guaranteed to not have finished its RCU grace period even if we
3982          * have dropped rcu_read_lock() inbetween iterations.
3983          *
3984          * If @pos has CSS_RELEASED set, its next pointer can't be
3985          * dereferenced; however, as each css is given a monotonically
3986          * increasing unique serial number and always appended to the
3987          * sibling list, the next one can be found by walking the parent's
3988          * children until the first css with higher serial number than
3989          * @pos's.  While this path can be slower, it happens iff iteration
3990          * races against release and the race window is very small.
3991          */
3992         if (!pos) {
3993                 next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
3994         } else if (likely(!(pos->flags & CSS_RELEASED))) {
3995                 next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
3996         } else {
3997                 list_for_each_entry_rcu(next, &parent->children, sibling)
3998                         if (next->serial_nr > pos->serial_nr)
3999                                 break;
4000         }
4001 
4002         /*
4003          * @next, if not pointing to the head, can be dereferenced and is
4004          * the next sibling.
4005          */
4006         if (&next->sibling != &parent->children)
4007                 return next;
4008         return NULL;
4009 }
4010 
4011 /**
4012  * css_next_descendant_pre - find the next descendant for pre-order walk
4013  * @pos: the current position (%NULL to initiate traversal)
4014  * @root: css whose descendants to walk
4015  *
4016  * To be used by css_for_each_descendant_pre().  Find the next descendant
4017  * to visit for pre-order traversal of @root's descendants.  @root is
4018  * included in the iteration and the first node to be visited.
4019  *
4020  * While this function requires cgroup_mutex or RCU read locking, it
4021  * doesn't require the whole traversal to be contained in a single critical
4022  * section.  This function will return the correct next descendant as long
4023  * as both @pos and @root are accessible and @pos is a descendant of @root.
4024  *
4025  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4026  * css which finished ->css_online() is guaranteed to be visible in the
4027  * future iterations and will stay visible until the last reference is put.
4028  * A css which hasn't finished ->css_online() or already finished
4029  * ->css_offline() may show up during traversal.  It's each subsystem's
4030  * responsibility to synchronize against on/offlining.
4031  */
4032 struct cgroup_subsys_state *
4033 css_next_descendant_pre(struct cgroup_subsys_state *pos,
4034                         struct cgroup_subsys_state *root)
4035 {
4036         struct cgroup_subsys_state *next;
4037 
4038         cgroup_assert_mutex_or_rcu_locked();
4039 
4040         /* if first iteration, visit @root */
4041         if (!pos)
4042                 return root;
4043 
4044         /* visit the first child if exists */
4045         next = css_next_child(NULL, pos);
4046         if (next)
4047                 return next;
4048 
4049         /* no child, visit my or the closest ancestor's next sibling */
4050         while (pos != root) {
4051                 next = css_next_child(pos, pos->parent);
4052                 if (next)
4053                         return next;
4054                 pos = pos->parent;
4055         }
4056 
4057         return NULL;
4058 }
4059 
4060 /**
4061  * css_rightmost_descendant - return the rightmost descendant of a css
4062  * @pos: css of interest
4063  *
4064  * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4065  * is returned.  This can be used during pre-order traversal to skip
4066  * subtree of @pos.
4067  *
4068  * While this function requires cgroup_mutex or RCU read locking, it
4069  * doesn't require the whole traversal to be contained in a single critical
4070  * section.  This function will return the correct rightmost descendant as
4071  * long as @pos is accessible.
4072  */
4073 struct cgroup_subsys_state *
4074 css_rightmost_descendant(struct cgroup_subsys_state *pos)
4075 {
4076         struct cgroup_subsys_state *last, *tmp;
4077 
4078         cgroup_assert_mutex_or_rcu_locked();
4079 
4080         do {
4081                 last = pos;
4082                 /* ->prev isn't RCU safe, walk ->next till the end */
4083                 pos = NULL;
4084                 css_for_each_child(tmp, last)
4085                         pos = tmp;
4086         } while (pos);
4087 
4088         return last;
4089 }
4090 
4091 static struct cgroup_subsys_state *
4092 css_leftmost_descendant(struct cgroup_subsys_state *pos)
4093 {
4094         struct cgroup_subsys_state *last;
4095 
4096         do {
4097                 last = pos;
4098                 pos = css_next_child(NULL, pos);
4099         } while (pos);
4100 
4101         return last;
4102 }
4103 
4104 /**
4105  * css_next_descendant_post - find the next descendant for post-order walk
4106  * @pos: the current position (%NULL to initiate traversal)
4107  * @root: css whose descendants to walk
4108  *
4109  * To be used by css_for_each_descendant_post().  Find the next descendant
4110  * to visit for post-order traversal of @root's descendants.  @root is
4111  * included in the iteration and the last node to be visited.
4112  *
4113  * While this function requires cgroup_mutex or RCU read locking, it
4114  * doesn't require the whole traversal to be contained in a single critical
4115  * section.  This function will return the correct next descendant as long
4116  * as both @pos and @cgroup are accessible and @pos is a descendant of
4117  * @cgroup.
4118  *
4119  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4120  * css which finished ->css_online() is guaranteed to be visible in the
4121  * future iterations and will stay visible until the last reference is put.
4122  * A css which hasn't finished ->css_online() or already finished
4123  * ->css_offline() may show up during traversal.  It's each subsystem's
4124  * responsibility to synchronize against on/offlining.
4125  */
4126 struct cgroup_subsys_state *
4127 css_next_descendant_post(struct cgroup_subsys_state *pos,
4128                          struct cgroup_subsys_state *root)
4129 {
4130         struct cgroup_subsys_state *next;
4131 
4132         cgroup_assert_mutex_or_rcu_locked();
4133 
4134         /* if first iteration, visit leftmost descendant which may be @root */
4135         if (!pos)
4136                 return css_leftmost_descendant(root);
4137 
4138         /* if we visited @root, we're done */
4139         if (pos == root)
4140                 return NULL;
4141 
4142         /* if there's an unvisited sibling, visit its leftmost descendant */
4143         next = css_next_child(pos, pos->parent);
4144         if (next)
4145                 return css_leftmost_descendant(next);
4146 
4147         /* no sibling left, visit parent */
4148         return pos->parent;
4149 }
4150 
4151 /**
4152  * css_has_online_children - does a css have online children
4153  * @css: the target css
4154  *
4155  * Returns %true if @css has any online children; otherwise, %false.  This
4156  * function can be called from any context but the caller is responsible
4157  * for synchronizing against on/offlining as necessary.
4158  */
4159 bool css_has_online_children(struct cgroup_subsys_state *css)
4160 {
4161         struct cgroup_subsys_state *child;
4162         bool ret = false;
4163 
4164         rcu_read_lock();
4165         css_for_each_child(child, css) {
4166                 if (child->flags & CSS_ONLINE) {
4167                         ret = true;
4168                         break;
4169                 }
4170         }
4171         rcu_read_unlock();
4172         return ret;
4173 }
4174 
4175 /**
4176  * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4177  * @it: the iterator to advance
4178  *
4179  * Advance @it to the next css_set to walk.
4180  */
4181 static void css_task_iter_advance_css_set(struct css_task_iter *it)
4182 {
4183         struct list_head *l = it->cset_pos;
4184         struct cgrp_cset_link *link;
4185         struct css_set *cset;
4186 
4187         lockdep_assert_held(&css_set_lock);
4188 
4189         /* Advance to the next non-empty css_set */
4190         do {
4191                 l = l->next;
4192                 if (l == it->cset_head) {
4193                         it->cset_pos = NULL;
4194                         it->task_pos = NULL;
4195                         return;
4196                 }
4197 
4198                 if (it->ss) {
4199                         cset = container_of(l, struct css_set,
4200                                             e_cset_node[it->ss->id]);
4201                 } else {
4202                         link = list_entry(l, struct cgrp_cset_link, cset_link);
4203                         cset = link->cset;
4204                 }
4205         } while (!css_set_populated(cset));
4206 
4207         it->cset_pos = l;
4208 
4209         if (!list_empty(&cset->tasks))
4210                 it->task_pos = cset->tasks.next;
4211         else
4212                 it->task_pos = cset->mg_tasks.next;
4213 
4214         it->tasks_head = &cset->tasks;
4215         it->mg_tasks_head = &cset->mg_tasks;
4216 
4217         /*
4218          * We don't keep css_sets locked across iteration steps and thus
4219          * need to take steps to ensure that iteration can be resumed after
4220          * the lock is re-acquired.  Iteration is performed at two levels -
4221          * css_sets and tasks in them.
4222          *
4223          * Once created, a css_set never leaves its cgroup lists, so a
4224          * pinned css_set is guaranteed to stay put and we can resume
4225          * iteration afterwards.
4226          *
4227          * Tasks may leave @cset across iteration steps.  This is resolved
4228          * by registering each iterator with the css_set currently being
4229          * walked and making css_set_move_task() advance iterators whose
4230          * next task is leaving.
4231          */
4232         if (it->cur_cset) {
4233                 list_del(&it->iters_node);
4234                 put_css_set_locked(it->cur_cset);
4235         }
4236         get_css_set(cset);
4237         it->cur_cset = cset;
4238         list_add(&it->iters_node, &cset->task_iters);
4239 }
4240 
4241 static void css_task_iter_advance(struct css_task_iter *it)
4242 {
4243         struct list_head *l = it->task_pos;
4244 
4245         lockdep_assert_held(&css_set_lock);
4246         WARN_ON_ONCE(!l);
4247 
4248         /*
4249          * Advance iterator to find next entry.  cset->tasks is consumed
4250          * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
4251          * next cset.
4252          */
4253         l = l->next;
4254 
4255         if (l == it->tasks_head)
4256                 l = it->mg_tasks_head->next;
4257 
4258         if (l == it->mg_tasks_head)
4259                 css_task_iter_advance_css_set(it);
4260         else
4261                 it->task_pos = l;
4262 }
4263 
4264 /**
4265  * css_task_iter_start - initiate task iteration
4266  * @css: the css to walk tasks of
4267  * @it: the task iterator to use
4268  *
4269  * Initiate iteration through the tasks of @css.  The caller can call
4270  * css_task_iter_next() to walk through the tasks until the function
4271  * returns NULL.  On completion of iteration, css_task_iter_end() must be
4272  * called.
4273  */
4274 void css_task_iter_start(struct cgroup_subsys_state *css,
4275                          struct css_task_iter *it)
4276 {
4277         /* no one should try to iterate before mounting cgroups */
4278         WARN_ON_ONCE(!use_task_css_set_links);
4279 
4280         memset(it, 0, sizeof(*it));
4281 
4282         spin_lock_irq(&css_set_lock);
4283 
4284         it->ss = css->ss;
4285 
4286         if (it->ss)
4287                 it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4288         else
4289                 it->cset_pos = &css->cgroup->cset_links;
4290 
4291         it->cset_head = it->cset_pos;
4292 
4293         css_task_iter_advance_css_set(it);
4294 
4295         spin_unlock_irq(&css_set_lock);
4296 }
4297 
4298 /**
4299  * css_task_iter_next - return the next task for the iterator
4300  * @it: the task iterator being iterated
4301  *
4302  * The "next" function for task iteration.  @it should have been
4303  * initialized via css_task_iter_start().  Returns NULL when the iteration
4304  * reaches the end.
4305  */
4306 struct task_struct *css_task_iter_next(struct css_task_iter *it)
4307 {
4308         if (it->cur_task) {
4309                 put_task_struct(it->cur_task);
4310                 it->cur_task = NULL;
4311         }
4312 
4313         spin_lock_irq(&css_set_lock);
4314 
4315         if (it->task_pos) {
4316                 it->cur_task = list_entry(it->task_pos, struct task_struct,
4317                                           cg_list);
4318                 get_task_struct(it->cur_task);
4319                 css_task_iter_advance(it);
4320         }
4321 
4322         spin_unlock_irq(&css_set_lock);
4323 
4324         return it->cur_task;
4325 }
4326 
4327 /**
4328  * css_task_iter_end - finish task iteration
4329  * @it: the task iterator to finish
4330  *
4331  * Finish task iteration started by css_task_iter_start().
4332  */
4333 void css_task_iter_end(struct css_task_iter *it)
4334 {
4335         if (it->cur_cset) {
4336                 spin_lock_irq(&css_set_lock);
4337                 list_del(&it->iters_node);
4338                 put_css_set_locked(it->cur_cset);
4339                 spin_unlock_irq(&css_set_lock);
4340         }
4341 
4342         if (it->cur_task)
4343                 put_task_struct(it->cur_task);
4344 }
4345 
4346 /**
4347  * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
4348  * @to: cgroup to which the tasks will be moved
4349  * @from: cgroup in which the tasks currently reside
4350  *
4351  * Locking rules between cgroup_post_fork() and the migration path
4352  * guarantee that, if a task is forking while being migrated, the new child
4353  * is guaranteed to be either visible in the source cgroup after the
4354  * parent's migration is complete or put into the target cgroup.  No task
4355  * can slip out of migration through forking.
4356  */
4357 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
4358 {
4359         LIST_HEAD(preloaded_csets);
4360         struct cgrp_cset_link *link;
4361         struct css_task_iter it;
4362         struct task_struct *task;
4363         int ret;
4364 
4365         if (!cgroup_may_migrate_to(to))
4366                 return -EBUSY;
4367 
4368         mutex_lock(&cgroup_mutex);
4369 
4370         percpu_down_write(&cgroup_threadgroup_rwsem);
4371 
4372         /* all tasks in @from are being moved, all csets are source */
4373         spin_lock_irq(&css_set_lock);
4374         list_for_each_entry(link, &from->cset_links, cset_link)
4375                 cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
4376         spin_unlock_irq(&css_set_lock);
4377 
4378         ret = cgroup_migrate_prepare_dst(&preloaded_csets);
4379         if (ret)
4380                 goto out_err;
4381 
4382         /*
4383          * Migrate tasks one-by-one until @from is empty.  This fails iff
4384          * ->can_attach() fails.
4385          */
4386         do {
4387                 css_task_iter_start(&from->self, &it);
4388                 task = css_task_iter_next(&it);
4389                 if (task)
4390                         get_task_struct(task);
4391                 css_task_iter_end(&it);
4392 
4393                 if (task) {
4394                         ret = cgroup_migrate(task, false, to->root);
4395                         if (!ret)
4396                                 trace_cgroup_transfer_tasks(to, task, false);
4397                         put_task_struct(task);
4398                 }
4399         } while (task && !ret);
4400 out_err:
4401         cgroup_migrate_finish(&preloaded_csets);
4402         percpu_up_write(&cgroup_threadgroup_rwsem);
4403         mutex_unlock(&cgroup_mutex);
4404         return ret;
4405 }
4406 
4407 /*
4408  * Stuff for reading the 'tasks'/'procs' files.
4409  *
4410  * Reading this file can return large amounts of data if a cgroup has
4411  * *lots* of attached tasks. So it may need several calls to read(),
4412  * but we cannot guarantee that the information we produce is correct
4413  * unless we produce it entirely atomically.
4414  *
4415  */
4416 
4417 /* which pidlist file are we talking about? */
4418 enum cgroup_filetype {
4419         CGROUP_FILE_PROCS,
4420         CGROUP_FILE_TASKS,
4421 };
4422 
4423 /*
4424  * A pidlist is a list of pids that virtually represents the contents of one
4425  * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
4426  * a pair (one each for procs, tasks) for each pid namespace that's relevant
4427  * to the cgroup.
4428  */
4429 struct cgroup_pidlist {
4430         /*
4431          * used to find which pidlist is wanted. doesn't change as long as
4432          * this particular list stays in the list.
4433         */
4434         struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
4435         /* array of xids */
4436         pid_t *list;
4437         /* how many elements the above list has */
4438         int length;
4439         /* each of these stored in a list by its cgroup */
4440         struct list_head links;
4441         /* pointer to the cgroup we belong to, for list removal purposes */
4442         struct cgroup *owner;
4443         /* for delayed destruction */
4444         struct delayed_work destroy_dwork;
4445 };
4446 
4447 /*
4448  * The following two functions "fix" the issue where there are more pids
4449  * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
4450  * TODO: replace with a kernel-wide solution to this problem
4451  */
4452 #define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
4453 static void *pidlist_allocate(int count)
4454 {
4455         if (PIDLIST_TOO_LARGE(count))
4456                 return vmalloc(count * sizeof(pid_t));
4457         else
4458                 return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
4459 }
4460 
4461 static void pidlist_free(void *p)
4462 {
4463         kvfree(p);
4464 }
4465 
4466 /*
4467  * Used to destroy all pidlists lingering waiting for destroy timer.  None
4468  * should be left afterwards.
4469  */
4470 static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
4471 {
4472         struct cgroup_pidlist *l, *tmp_l;
4473 
4474         mutex_lock(&cgrp->pidlist_mutex);
4475         list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
4476                 mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
4477         mutex_unlock(&cgrp->pidlist_mutex);
4478 
4479         flush_workqueue(cgroup_pidlist_destroy_wq);
4480         BUG_ON(!list_empty(&cgrp->pidlists));
4481 }
4482 
4483 static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
4484 {
4485         struct delayed_work *dwork = to_delayed_work(work);
4486         struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
4487                                                 destroy_dwork);
4488         struct cgroup_pidlist *tofree = NULL;
4489 
4490         mutex_lock(&l->owner->pidlist_mutex);
4491 
4492         /*
4493          * Destroy iff we didn't get queued again.  The state won't change
4494          * as destroy_dwork can only be queued while locked.
4495          */
4496         if (!delayed_work_pending(dwork)) {
4497                 list_del(&l->links);
4498                 pidlist_free(l->list);
4499                 put_pid_ns(l->key.ns);
4500                 tofree = l;
4501         }
4502 
4503         mutex_unlock(&l->owner->pidlist_mutex);
4504         kfree(tofree);
4505 }
4506 
4507 /*
4508  * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
4509  * Returns the number of unique elements.
4510  */
4511 static int pidlist_uniq(pid_t *list, int length)
4512 {
4513         int src, dest = 1;
4514 
4515         /*
4516          * we presume the 0th element is unique, so i starts at 1. trivial
4517          * edge cases first; no work needs to be done for either
4518          */
4519         if (length == 0 || length == 1)
4520                 return length;
4521         /* src and dest walk down the list; dest counts unique elements */
4522         for (src = 1; src < length; src++) {
4523                 /* find next unique element */
4524                 while (list[src] == list[src-1]) {
4525                         src++;
4526                         if (src == length)
4527                                 goto after;
4528                 }
4529                 /* dest always points to where the next unique element goes */
4530                 list[dest] = list[src];
4531                 dest++;
4532         }
4533 after:
4534         return dest;
4535 }
4536 
4537 /*
4538  * The two pid files - task and cgroup.procs - guaranteed that the result
4539  * is sorted, which forced this whole pidlist fiasco.  As pid order is
4540  * different per namespace, each namespace needs differently sorted list,
4541  * making it impossible to use, for example, single rbtree of member tasks
4542  * sorted by task pointer.  As pidlists can be fairly large, allocating one
4543  * per open file is dangerous, so cgroup had to implement shared pool of
4544  * pidlists keyed by cgroup and namespace.
4545  *
4546  * All this extra complexity was caused by the original implementation
4547  * committing to an entirely unnecessary property.  In the long term, we
4548  * want to do away with it.  Explicitly scramble sort order if on the
4549  * default hierarchy so that no such expectation exists in the new
4550  * interface.
4551  *
4552  * Scrambling is done by swapping every two consecutive bits, which is
4553  * non-identity one-to-one mapping which disturbs sort order sufficiently.
4554  */
4555 static pid_t pid_fry(pid_t pid)
4556 {
4557         unsigned a = pid & 0x55555555;
4558         unsigned b = pid & 0xAAAAAAAA;
4559 
4560         return (a << 1) | (b >> 1);
4561 }
4562 
4563 static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
4564 {
4565         if (cgroup_on_dfl(cgrp))
4566                 return pid_fry(pid);
4567         else
4568                 return pid;
4569 }
4570 
4571 static int cmppid(const void *a, const void *b)
4572 {
4573         return *(pid_t *)a - *(pid_t *)b;
4574 }
4575 
4576 static int fried_cmppid(const void *a, const void *b)
4577 {
4578         return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b);
4579 }
4580 
4581 static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
4582                                                   enum cgroup_filetype type)
4583 {
4584         struct cgroup_pidlist *l;
4585         /* don't need task_nsproxy() if we're looking at ourself */
4586         struct pid_namespace *ns = task_active_pid_ns(current);
4587 
4588         lockdep_assert_held(&cgrp->pidlist_mutex);
4589 
4590         list_for_each_entry(l, &cgrp->pidlists, links)
4591                 if (l->key.type == type && l->key.ns == ns)
4592                         return l;
4593         return NULL;
4594 }
4595 
4596 /*
4597  * find the appropriate pidlist for our purpose (given procs vs tasks)
4598  * returns with the lock on that pidlist already held, and takes care
4599  * of the use count, or returns NULL with no locks held if we're out of
4600  * memory.
4601  */
4602 static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
4603                                                 enum cgroup_filetype type)
4604 {
4605         struct cgroup_pidlist *l;
4606 
4607         lockdep_assert_held(&cgrp->pidlist_mutex);
4608 
4609         l = cgroup_pidlist_find(cgrp, type);
4610         if (l)
4611                 return l;
4612 
4613         /* entry not found; create a new one */
4614         l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
4615         if (!l)
4616                 return l;
4617 
4618         INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
4619         l->key.type = type;
4620         /* don't need task_nsproxy() if we're looking at ourself */
4621         l->key.ns = get_pid_ns(task_active_pid_ns(current));
4622         l->owner = cgrp;
4623         list_add(&l->links, &cgrp->pidlists);
4624         return l;
4625 }
4626 
4627 /*
4628  * Load a cgroup's pidarray with either procs' tgids or tasks' pids
4629  */
4630 static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
4631                               struct cgroup_pidlist **lp)
4632 {
4633         pid_t *array;
4634         int length;
4635         int pid, n = 0; /* used for populating the array */
4636         struct css_task_iter it;
4637         struct task_struct *tsk;
4638         struct cgroup_pidlist *l;
4639 
4640         lockdep_assert_held(&cgrp->pidlist_mutex);
4641 
4642         /*
4643          * If cgroup gets more users after we read count, we won't have
4644          * enough space - tough.  This race is indistinguishable to the
4645          * caller from the case that the additional cgroup users didn't
4646          * show up until sometime later on.
4647          */
4648         length = cgroup_task_count(cgrp);
4649         array = pidlist_allocate(length);
4650         if (!array)
4651                 return -ENOMEM;
4652         /* now, populate the array */
4653         css_task_iter_start(&cgrp->self, &it);
4654         while ((tsk = css_task_iter_next(&it))) {
4655                 if (unlikely(n == length))
4656                         break;
4657                 /* get tgid or pid for procs or tasks file respectively */
4658                 if (type == CGROUP_FILE_PROCS)
4659                         pid = task_tgid_vnr(tsk);
4660                 else
4661                         pid = task_pid_vnr(tsk);
4662                 if (pid > 0) /* make sure to only use valid results */
4663                         array[n++] = pid;
4664         }
4665         css_task_iter_end(&it);
4666         length = n;
4667         /* now sort & (if procs) strip out duplicates */
4668         if (cgroup_on_dfl(cgrp))
4669                 sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
4670         else
4671                 sort(array, length, sizeof(pid_t), cmppid, NULL);
4672         if (type == CGROUP_FILE_PROCS)
4673                 length = pidlist_uniq(array, length);
4674 
4675         l = cgroup_pidlist_find_create(cgrp, type);
4676         if (!l) {
4677                 pidlist_free(array);
4678                 return -ENOMEM;
4679         }
4680 
4681         /* store array, freeing old if necessary */
4682         pidlist_free(l->list);
4683         l->list = array;
4684         l->length = length;
4685         *lp = l;
4686         return 0;
4687 }
4688 
4689 /**
4690  * cgroupstats_build - build and fill cgroupstats
4691  * @stats: cgroupstats to fill information into
4692  * @dentry: A dentry entry belonging to the cgroup for which stats have
4693  * been requested.
4694  *
4695  * Build and fill cgroupstats so that taskstats can export it to user
4696  * space.
4697  */
4698 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
4699 {
4700         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
4701         struct cgroup *cgrp;
4702         struct css_task_iter it;
4703         struct task_struct *tsk;
4704 
4705         /* it should be kernfs_node belonging to cgroupfs and is a directory */
4706         if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
4707             kernfs_type(kn) != KERNFS_DIR)
4708                 return -EINVAL;
4709 
4710         mutex_lock(&cgroup_mutex);
4711 
4712         /*
4713          * We aren't being called from kernfs and there's no guarantee on
4714          * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
4715          * @kn->priv is RCU safe.  Let's do the RCU dancing.
4716          */
4717         rcu_read_lock();
4718         cgrp = rcu_dereference(kn->priv);
4719         if (!cgrp || cgroup_is_dead(cgrp)) {
4720                 rcu_read_unlock();
4721                 mutex_unlock(&cgroup_mutex);
4722                 return -ENOENT;
4723         }
4724         rcu_read_unlock();
4725 
4726         css_task_iter_start(&cgrp->self, &it);
4727         while ((tsk = css_task_iter_next(&it))) {
4728                 switch (tsk->state) {
4729                 case TASK_RUNNING:
4730                         stats->nr_running++;
4731                         break;
4732                 case TASK_INTERRUPTIBLE:
4733                         stats->nr_sleeping++;
4734                         break;
4735                 case TASK_UNINTERRUPTIBLE:
4736                         stats->nr_uninterruptible++;
4737                         break;
4738                 case TASK_STOPPED:
4739                         stats->nr_stopped++;
4740                         break;
4741                 default:
4742                         if (delayacct_is_task_waiting_on_io(tsk))
4743                                 stats->nr_io_wait++;
4744                         break;
4745                 }
4746         }
4747         css_task_iter_end(&it);
4748 
4749         mutex_unlock(&cgroup_mutex);
4750         return 0;
4751 }
4752 
4753 
4754 /*
4755  * seq_file methods for the tasks/procs files. The seq_file position is the
4756  * next pid to display; the seq_file iterator is a pointer to the pid
4757  * in the cgroup->l->list array.
4758  */
4759 
4760 static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
4761 {
4762         /*
4763          * Initially we receive a position value that corresponds to
4764          * one more than the last pid shown (or 0 on the first call or
4765          * after a seek to the start). Use a binary-search to find the
4766          * next pid to display, if any
4767          */
4768         struct kernfs_open_file *of = s->private;
4769         struct cgroup *cgrp = seq_css(s)->cgroup;
4770         struct cgroup_pidlist *l;
4771         enum cgroup_filetype type = seq_cft(s)->private;
4772         int index = 0, pid = *pos;
4773         int *iter, ret;
4774 
4775         mutex_lock(&cgrp->pidlist_mutex);
4776 
4777         /*
4778          * !NULL @of->priv indicates that this isn't the first start()
4779          * after open.  If the matching pidlist is around, we can use that.
4780          * Look for it.  Note that @of->priv can't be used directly.  It
4781          * could already have been destroyed.
4782          */
4783         if (of->priv)
4784                 of->priv = cgroup_pidlist_find(cgrp, type);
4785 
4786         /*
4787          * Either this is the first start() after open or the matching
4788          * pidlist has been destroyed inbetween.  Create a new one.
4789          */
4790         if (!of->priv) {
4791                 ret = pidlist_array_load(cgrp, type,
4792                                          (struct cgroup_pidlist **)&of->priv);
4793                 if (ret)
4794                         return ERR_PTR(ret);
4795         }
4796         l = of->priv;
4797 
4798         if (pid) {
4799                 int end = l->length;
4800 
4801                 while (index < end) {
4802                         int mid = (index + end) / 2;
4803                         if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
4804                                 index = mid;
4805                                 break;
4806                         } else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
4807                                 index = mid + 1;
4808                         else
4809                                 end = mid;
4810                 }
4811         }
4812         /* If we're off the end of the array, we're done */
4813         if (index >= l->length)
4814                 return NULL;
4815         /* Update the abstract position to be the actual pid that we found */
4816         iter = l->list + index;
4817         *pos = cgroup_pid_fry(cgrp, *iter);
4818         return iter;
4819 }
4820 
4821 static void cgroup_pidlist_stop(struct seq_file *s, void *v)
4822 {
4823         struct kernfs_open_file *of = s->private;
4824         struct cgroup_pidlist *l = of->priv;
4825 
4826         if (l)
4827                 mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
4828                                  CGROUP_PIDLIST_DESTROY_DELAY);
4829         mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
4830 }
4831 
4832 static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
4833 {
4834         struct kernfs_open_file *of = s->private;
4835         struct cgroup_pidlist *l = of->priv;
4836         pid_t *p = v;
4837         pid_t *end = l->list + l->length;
4838         /*
4839          * Advance to the next pid in the array. If this goes off the
4840          * end, we're done
4841          */
4842         p++;
4843         if (p >= end) {
4844                 return NULL;
4845         } else {
4846                 *pos = cgroup_pid_fry(seq_css(s)->cgroup, *p);
4847                 return p;
4848         }
4849 }
4850 
4851 static int cgroup_pidlist_show(struct seq_file *s, void *v)
4852 {
4853         seq_printf(s, "%d\n", *(int *)v);
4854 
4855         return 0;
4856 }
4857 
4858 static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
4859                                          struct cftype *cft)
4860 {
4861         return notify_on_release(css->cgroup);
4862 }
4863 
4864 static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
4865                                           struct cftype *cft, u64 val)
4866 {
4867         if (val)
4868                 set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4869         else
4870                 clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4871         return 0;
4872 }
4873 
4874 static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
4875                                       struct cftype *cft)
4876 {
4877         return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4878 }
4879 
4880 static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
4881                                        struct cftype *cft, u64 val)
4882 {
4883         if (val)
4884                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4885         else
4886                 clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4887         return 0;
4888 }
4889 
4890 /* cgroup core interface files for the default hierarchy */
4891 static struct cftype cgroup_dfl_base_files[] = {
4892         {
4893                 .name = "cgroup.procs",
4894                 .file_offset = offsetof(struct cgroup, procs_file),
4895                 .seq_start = cgroup_pidlist_start,
4896                 .seq_next = cgroup_pidlist_next,
4897                 .seq_stop = cgroup_pidlist_stop,
4898                 .seq_show = cgroup_pidlist_show,
4899                 .private = CGROUP_FILE_PROCS,
4900                 .write = cgroup_procs_write,
4901         },
4902         {
4903                 .name = "cgroup.controllers",
4904                 .seq_show = cgroup_controllers_show,
4905         },
4906         {
4907                 .name = "cgroup.subtree_control",
4908                 .seq_show = cgroup_subtree_control_show,
4909                 .write = cgroup_subtree_control_write,
4910         },
4911         {
4912                 .name = "cgroup.events",
4913                 .flags = CFTYPE_NOT_ON_ROOT,
4914                 .file_offset = offsetof(struct cgroup, events_file),
4915                 .seq_show = cgroup_events_show,
4916         },
4917         { }     /* terminate */
4918 };
4919 
4920 /* cgroup core interface files for the legacy hierarchies */
4921 static struct cftype cgroup_legacy_base_files[] = {
4922         {
4923                 .name = "cgroup.procs",
4924                 .seq_start = cgroup_pidlist_start,
4925                 .seq_next = cgroup_pidlist_next,
4926                 .seq_stop = cgroup_pidlist_stop,
4927                 .seq_show = cgroup_pidlist_show,
4928                 .private = CGROUP_FILE_PROCS,
4929                 .write = cgroup_procs_write,
4930         },
4931         {
4932                 .name = "cgroup.clone_children",
4933                 .read_u64 = cgroup_clone_children_read,
4934                 .write_u64 = cgroup_clone_children_write,
4935         },
4936         {
4937                 .name = "cgroup.sane_behavior",
4938                 .flags = CFTYPE_ONLY_ON_ROOT,
4939                 .seq_show = cgroup_sane_behavior_show,
4940         },
4941         {
4942                 .name = "tasks",
4943                 .seq_start = cgroup_pidlist_start,
4944                 .seq_next = cgroup_pidlist_next,
4945                 .seq_stop = cgroup_pidlist_stop,
4946                 .seq_show = cgroup_pidlist_show,
4947                 .private = CGROUP_FILE_TASKS,
4948                 .write = cgroup_tasks_write,
4949         },
4950         {
4951                 .name = "notify_on_release",
4952                 .read_u64 = cgroup_read_notify_on_release,
4953                 .write_u64 = cgroup_write_notify_on_release,
4954         },
4955         {
4956                 .name = "release_agent",
4957                 .flags = CFTYPE_ONLY_ON_ROOT,
4958                 .seq_show = cgroup_release_agent_show,
4959                 .write = cgroup_release_agent_write,
4960                 .max_write_len = PATH_MAX - 1,
4961         },
4962         { }     /* terminate */
4963 };
4964 
4965 /*
4966  * css destruction is four-stage process.
4967  *
4968  * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4969  *    Implemented in kill_css().
4970  *
4971  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4972  *    and thus css_tryget_online() is guaranteed to fail, the css can be
4973  *    offlined by invoking offline_css().  After offlining, the base ref is
4974  *    put.  Implemented in css_killed_work_fn().
4975  *
4976  * 3. When the percpu_ref reaches zero, the only possible remaining
4977  *    accessors are inside RCU read sections.  css_release() schedules the
4978  *    RCU callback.
4979  *
4980  * 4. After the grace period, the css can be freed.  Implemented in
4981  *    css_free_work_fn().
4982  *
4983  * It is actually hairier because both step 2 and 4 require process context
4984  * and thus involve punting to css->destroy_work adding two additional
4985  * steps to the already complex sequence.
4986  */
4987 static void css_free_work_fn(struct work_struct *work)
4988 {
4989         struct cgroup_subsys_state *css =
4990                 container_of(work, struct cgroup_subsys_state, destroy_work);
4991         struct cgroup_subsys *ss = css->ss;
4992         struct cgroup *cgrp = css->cgroup;
4993 
4994         percpu_ref_exit(&css->refcnt);
4995 
4996         if (ss) {
4997                 /* css free path */
4998                 struct cgroup_subsys_state *parent = css->parent;
4999                 int id = css->id;
5000 
5001                 ss->css_free(css);
5002                 cgroup_idr_remove(&ss->css_idr, id);
5003                 cgroup_put(cgrp);
5004 
5005                 if (parent)
5006                         css_put(parent);
5007         } else {
5008                 /* cgroup free path */
5009                 atomic_dec(&cgrp->root->nr_cgrps);
5010                 cgroup_pidlist_destroy_all(cgrp);
5011                 cancel_work_sync(&cgrp->release_agent_work);
5012 
5013                 if (cgroup_parent(cgrp)) {
5014                         /*
5015                          * We get a ref to the parent, and put the ref when
5016                          * this cgroup is being freed, so it's guaranteed
5017                          * that the parent won't be destroyed before its
5018                          * children.
5019                          */
5020                         cgroup_put(cgroup_parent(cgrp));
5021                         kernfs_put(cgrp->kn);
5022                         kfree(cgrp);
5023                 } else {
5024                         /*
5025                          * This is root cgroup's refcnt reaching zero,
5026                          * which indicates that the root should be
5027                          * released.
5028                          */
5029                         cgroup_destroy_root(cgrp->root);
5030                 }
5031         }
5032 }
5033 
5034 static void css_free_rcu_fn(struct rcu_head *rcu_head)
5035 {
5036         struct cgroup_subsys_state *css =
5037                 container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
5038 
5039         INIT_WORK(&css->destroy_work, css_free_work_fn);
5040         queue_work(cgroup_destroy_wq, &css->destroy_work);
5041 }
5042 
5043 static void css_release_work_fn(struct work_struct *work)
5044 {
5045         struct cgroup_subsys_state *css =
5046                 container_of(work, struct cgroup_subsys_state, destroy_work);
5047         struct cgroup_subsys *ss = css->ss;
5048         struct cgroup *cgrp = css->cgroup;
5049 
5050         mutex_lock(&cgroup_mutex);
5051 
5052         css->flags |= CSS_RELEASED;
5053         list_del_rcu(&css->sibling);
5054 
5055         if (ss) {
5056                 /* css release path */
5057                 cgroup_idr_replace(&ss->css_idr, NULL, css->id);
5058                 if (ss->css_released)
5059                         ss->css_released(css);
5060         } else {
5061                 /* cgroup release path */
5062                 trace_cgroup_release(cgrp);
5063 
5064                 cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
5065                 cgrp->id = -1;
5066 
5067                 /*
5068                  * There are two control paths which try to determine
5069                  * cgroup from dentry without going through kernfs -
5070                  * cgroupstats_build() and css_tryget_online_from_dir().
5071                  * Those are supported by RCU protecting clearing of
5072                  * cgrp->kn->priv backpointer.
5073                  */
5074                 if (cgrp->kn)
5075                         RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
5076                                          NULL);
5077         }
5078 
5079         mutex_unlock(&cgroup_mutex);
5080 
5081         call_rcu(&css->rcu_head, css_free_rcu_fn);
5082 }
5083 
5084 static void css_release(struct percpu_ref *ref)
5085 {
5086         struct cgroup_subsys_state *css =
5087                 container_of(ref, struct cgroup_subsys_state, refcnt);
5088 
5089         INIT_WORK(&css->destroy_work, css_release_work_fn);
5090         queue_work(cgroup_destroy_wq, &css->destroy_work);
5091 }
5092 
5093 static void init_and_link_css(struct cgroup_subsys_state *css,
5094                               struct cgroup_subsys *ss, struct cgroup *cgrp)
5095 {
5096         lockdep_assert_held(&cgroup_mutex);
5097 
5098         cgroup_get(cgrp);
5099 
5100         memset(css, 0, sizeof(*css));
5101         css->cgroup = cgrp;
5102         css->ss = ss;
5103         css->id = -1;
5104         INIT_LIST_HEAD(&css->sibling);
5105         INIT_LIST_HEAD(&css->children);
5106         css->serial_nr = css_serial_nr_next++;
5107         atomic_set(&css->online_cnt, 0);
5108 
5109         if (cgroup_parent(cgrp)) {
5110                 css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5111                 css_get(css->parent);
5112         }
5113 
5114         BUG_ON(cgroup_css(cgrp, ss));
5115 }
5116 
5117 /* invoke ->css_online() on a new CSS and mark it online if successful */
5118 static int online_css(struct cgroup_subsys_state *css)
5119 {
5120         struct cgroup_subsys *ss = css->ss;
5121         int ret = 0;
5122 
5123         lockdep_assert_held(&cgroup_mutex);
5124 
5125         if (ss->css_online)
5126                 ret = ss->css_online(css);
5127         if (!ret) {
5128                 css->flags |= CSS_ONLINE;
5129                 rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5130 
5131                 atomic_inc(&css->online_cnt);
5132                 if (css->parent)
5133                         atomic_inc(&css->parent->online_cnt);
5134         }
5135         return ret;
5136 }
5137 
5138 /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5139 static void offline_css(struct cgroup_subsys_state *css)
5140 {
5141         struct cgroup_subsys *ss = css->ss;
5142 
5143         lockdep_assert_held(&cgroup_mutex);
5144 
5145         if (!(css->flags & CSS_ONLINE))
5146                 return;
5147 
5148         if (ss->css_reset)
5149                 ss->css_reset(css);
5150 
5151         if (ss->css_offline)
5152                 ss->css_offline(css);
5153 
5154         css->flags &= ~CSS_ONLINE;
5155         RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5156 
5157         wake_up_all(&css->cgroup->offline_waitq);
5158 }
5159 
5160 /**
5161  * css_create - create a cgroup_subsys_state
5162  * @cgrp: the cgroup new css will be associated with
5163  * @ss: the subsys of new css
5164  *
5165  * Create a new css associated with @cgrp - @ss pair.  On success, the new
5166  * css is online and installed in @cgrp.  This function doesn't create the
5167  * interface files.  Returns 0 on success, -errno on failure.
5168  */
5169 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5170                                               struct cgroup_subsys *ss)
5171 {
5172         struct cgroup *parent = cgroup_parent(cgrp);
5173         struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5174         struct cgroup_subsys_state *css;
5175         int err;
5176 
5177         lockdep_assert_held(&cgroup_mutex);
5178 
5179         css = ss->css_alloc(parent_css);
5180         if (!css)
5181                 css = ERR_PTR(-ENOMEM);
5182         if (IS_ERR(css))
5183                 return css;
5184 
5185         init_and_link_css(css, ss, cgrp);
5186 
5187         err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5188         if (err)
5189                 goto err_free_css;
5190 
5191         err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5192         if (err < 0)
5193                 goto err_free_css;
5194         css->id = err;
5195 
5196         /* @css is ready to be brought online now, make it visible */
5197         list_add_tail_rcu(&css->sibling, &parent_css->children);
5198         cgroup_idr_replace(&ss->css_idr, css, css->id);
5199 
5200         err = online_css(css);
5201         if (err)
5202                 goto err_list_del;
5203 
5204         if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
5205             cgroup_parent(parent)) {
5206                 pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
5207                         current->comm, current->pid, ss->name);
5208                 if (!strcmp(ss->name, "memory"))
5209                         pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
5210                 ss->warned_broken_hierarchy = true;
5211         }
5212 
5213         return css;
5214 
5215 err_list_del:
5216         list_del_rcu(&css->sibling);
5217 err_free_css:
5218         call_rcu(&css->rcu_head, css_free_rcu_fn);
5219         return ERR_PTR(err);
5220 }
5221 
5222 static struct cgroup *cgroup_create(struct cgroup *parent)
5223 {
5224         struct cgroup_root *root = parent->root;
5225         struct cgroup *cgrp, *tcgrp;
5226         int level = parent->level + 1;
5227         int ret;
5228 
5229         /* allocate the cgroup and its ID, 0 is reserved for the root */
5230         cgrp = kzalloc(sizeof(*cgrp) +
5231                        sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
5232         if (!cgrp)
5233                 return ERR_PTR(-ENOMEM);
5234 
5235         ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5236         if (ret)
5237                 goto out_free_cgrp;
5238 
5239         /*
5240          * Temporarily set the pointer to NULL, so idr_find() won't return
5241          * a half-baked cgroup.
5242          */
5243         cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
5244         if (cgrp->id < 0) {
5245                 ret = -ENOMEM;
5246                 goto out_cancel_ref;
5247         }
5248 
5249         init_cgroup_housekeeping(cgrp);
5250 
5251         cgrp->self.parent = &parent->self;
5252         cgrp->root = root;
5253         cgrp->level = level;
5254 
5255         for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp))
5256                 cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
5257 
5258         if (notify_on_release(parent))
5259                 set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5260 
5261         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5262                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5263 
5264         cgrp->self.serial_nr = css_serial_nr_next++;
5265 
5266         /* allocation complete, commit to creation */
5267         list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5268         atomic_inc(&root->nr_cgrps);
5269         cgroup_get(parent);
5270 
5271         /*
5272          * @cgrp is now fully operational.  If something fails after this
5273          * point, it'll be released via the normal destruction path.
5274          */
5275         cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
5276 
5277         /*
5278          * On the default hierarchy, a child doesn't automatically inherit
5279          * subtree_control from the parent.  Each is configured manually.
5280          */
5281         if (!cgroup_on_dfl(cgrp))
5282                 cgrp->subtree_control = cgroup_control(cgrp);
5283 
5284         cgroup_propagate_control(cgrp);
5285 
5286         /* @cgrp doesn't have dir yet so the following will only create csses */
5287         ret = cgroup_apply_control_enable(cgrp);
5288         if (ret)
5289                 goto out_destroy;
5290 
5291         return cgrp;
5292 
5293 out_cancel_ref:
5294         percpu_ref_exit(&cgrp->self.refcnt);
5295 out_free_cgrp:
5296         kfree(cgrp);
5297         return ERR_PTR(ret);
5298 out_destroy:
5299         cgroup_destroy_locked(cgrp);
5300         return ERR_PTR(ret);
5301 }
5302 
5303 static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
5304                         umode_t mode)
5305 {
5306         struct cgroup *parent, *cgrp;
5307         struct kernfs_node *kn;
5308         int ret;
5309 
5310         /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5311         if (strchr(name, '\n'))
5312                 return -EINVAL;
5313 
5314         parent = cgroup_kn_lock_live(parent_kn, false);
5315         if (!parent)
5316                 return -ENODEV;
5317 
5318         cgrp = cgroup_create(parent);
5319         if (IS_ERR(cgrp)) {
5320                 ret = PTR_ERR(cgrp);
5321                 goto out_unlock;
5322         }
5323 
5324         /* create the directory */
5325         kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5326         if (IS_ERR(kn)) {
5327                 ret = PTR_ERR(kn);
5328                 goto out_destroy;
5329         }
5330         cgrp->kn = kn;
5331 
5332         /*
5333          * This extra ref will be put in cgroup_free_fn() and guarantees
5334          * that @cgrp->kn is always accessible.
5335          */
5336         kernfs_get(kn);
5337 
5338         ret = cgroup_kn_set_ugid(kn);
5339         if (ret)
5340                 goto out_destroy;
5341 
5342         ret = css_populate_dir(&cgrp->self);
5343         if (ret)
5344                 goto out_destroy;
5345 
5346         ret = cgroup_apply_control_enable(cgrp);
5347         if (ret)
5348                 goto out_destroy;
5349 
5350         trace_cgroup_mkdir(cgrp);
5351 
5352         /* let's create and online css's */
5353         kernfs_activate(kn);
5354 
5355         ret = 0;
5356         goto out_unlock;
5357 
5358 out_destroy:
5359         cgroup_destroy_locked(cgrp);
5360 out_unlock:
5361         cgroup_kn_unlock(parent_kn);
5362         return ret;
5363 }
5364 
5365 /*
5366  * This is called when the refcnt of a css is confirmed to be killed.
5367  * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5368  * initate destruction and put the css ref from kill_css().
5369  */
5370 static void css_killed_work_fn(struct work_struct *work)
5371 {
5372         struct cgroup_subsys_state *css =
5373                 container_of(work, struct cgroup_subsys_state, destroy_work);
5374 
5375         mutex_lock(&cgroup_mutex);
5376 
5377         do {
5378                 offline_css(css);
5379                 css_put(css);
5380                 /* @css can't go away while we're holding cgroup_mutex */
5381                 css = css->parent;
5382         } while (css && atomic_dec_and_test(&css->online_cnt));
5383 
5384         mutex_unlock(&cgroup_mutex);
5385 }
5386 
5387 /* css kill confirmation processing requires process context, bounce */
5388 static void css_killed_ref_fn(struct percpu_ref *ref)
5389 {
5390         struct cgroup_subsys_state *css =
5391                 container_of(ref, struct cgroup_subsys_state, refcnt);
5392 
5393         if (atomic_dec_and_test(&css->online_cnt)) {
5394                 INIT_WORK(&css->destroy_work, css_killed_work_fn);
5395                 queue_work(cgroup_destroy_wq, &css->destroy_work);
5396         }
5397 }
5398 
5399 /**
5400  * kill_css - destroy a css
5401  * @css: css to destroy
5402  *
5403  * This function initiates destruction of @css by removing cgroup interface
5404  * files and putting its base reference.  ->css_offline() will be invoked
5405  * asynchronously once css_tryget_online() is guaranteed to fail and when
5406  * the reference count reaches zero, @css will be released.
5407  */
5408 static void kill_css(struct cgroup_subsys_state *css)
5409 {
5410         lockdep_assert_held(&cgroup_mutex);
5411 
5412         /*
5413          * This must happen before css is disassociated with its cgroup.
5414          * See seq_css() for details.
5415          */
5416         css_clear_dir(css);
5417 
5418         /*
5419          * Killing would put the base ref, but we need to keep it alive
5420          * until after ->css_offline().
5421          */
5422         css_get(css);
5423 
5424         /*
5425          * cgroup core guarantees that, by the time ->css_offline() is
5426          * invoked, no new css reference will be given out via
5427          * css_tryget_online().  We can't simply call percpu_ref_kill() and
5428          * proceed to offlining css's because percpu_ref_kill() doesn't
5429          * guarantee that the ref is seen as killed on all CPUs on return.
5430          *
5431          * Use percpu_ref_kill_and_confirm() to get notifications as each
5432          * css is confirmed to be seen as killed on all CPUs.
5433          */
5434         percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5435 }
5436 
5437 /**
5438  * cgroup_destroy_locked - the first stage of cgroup destruction
5439  * @cgrp: cgroup to be destroyed
5440  *
5441  * css's make use of percpu refcnts whose killing latency shouldn't be
5442  * exposed to userland and are RCU protected.  Also, cgroup core needs to
5443  * guarantee that css_tryget_online() won't succeed by the time
5444  * ->css_offline() is invoked.  To satisfy all the requirements,
5445  * destruction is implemented in the following two steps.
5446  *
5447  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5448  *     userland visible parts and start killing the percpu refcnts of
5449  *     css's.  Set up so that the next stage will be kicked off once all
5450  *     the percpu refcnts are confirmed to be killed.
5451  *
5452  * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5453  *     rest of destruction.  Once all cgroup references are gone, the
5454  *     cgroup is RCU-freed.
5455  *
5456  * This function implements s1.  After this step, @cgrp is gone as far as
5457  * the userland is concerned and a new cgroup with the same name may be
5458  * created.  As cgroup doesn't care about the names internally, this
5459  * doesn't cause any problem.
5460  */
5461 static int cgroup_destroy_locked(struct cgroup *cgrp)
5462         __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5463 {
5464         struct cgroup_subsys_state *css;
5465         struct cgrp_cset_link *link;
5466         int ssid;
5467 
5468         lockdep_assert_held(&cgroup_mutex);
5469 
5470         /*
5471          * Only migration can raise populated from zero and we're already
5472          * holding cgroup_mutex.
5473          */
5474         if (cgroup_is_populated(cgrp))
5475                 return -EBUSY;
5476 
5477         /*
5478          * Make sure there's no live children.  We can't test emptiness of
5479          * ->self.children as dead children linger on it while being
5480          * drained; otherwise, "rmdir parent/child parent" may fail.
5481          */
5482         if (css_has_online_children(&cgrp->self))
5483                 return -EBUSY;
5484 
5485         /*
5486          * Mark @cgrp and the associated csets dead.  The former prevents
5487          * further task migration and child creation by disabling
5488          * cgroup_lock_live_group().  The latter makes the csets ignored by
5489          * the migration path.
5490          */
5491         cgrp->self.flags &= ~CSS_ONLINE;
5492 
5493         spin_lock_irq(&css_set_lock);
5494         list_for_each_entry(link, &cgrp->cset_links, cset_link)
5495                 link->cset->dead = true;
5496         spin_unlock_irq(&css_set_lock);
5497 
5498         /* initiate massacre of all css's */
5499         for_each_css(css, ssid, cgrp)
5500                 kill_css(css);
5501 
5502         /*
5503          * Remove @cgrp directory along with the base files.  @cgrp has an
5504          * extra ref on its kn.
5505          */
5506         kernfs_remove(cgrp->kn);
5507 
5508         check_for_release(cgroup_parent(cgrp));
5509 
5510         /* put the base reference */
5511         percpu_ref_kill(&cgrp->self.refcnt);
5512 
5513         return 0;
5514 };
5515 
5516 static int cgroup_rmdir(struct kernfs_node *kn)
5517 {
5518         struct cgroup *cgrp;
5519         int ret = 0;
5520 
5521         cgrp = cgroup_kn_lock_live(kn, false);
5522         if (!cgrp)
5523                 return 0;
5524 
5525         ret = cgroup_destroy_locked(cgrp);
5526 
5527         if (!ret)
5528                 trace_cgroup_rmdir(cgrp);
5529 
5530         cgroup_kn_unlock(kn);
5531         return ret;
5532 }
5533 
5534 static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5535         .remount_fs             = cgroup_remount,
5536         .show_options           = cgroup_show_options,
5537         .mkdir                  = cgroup_mkdir,
5538         .rmdir                  = cgroup_rmdir,
5539         .rename                 = cgroup_rename,
5540         .show_path              = cgroup_show_path,
5541 };
5542 
5543 static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5544 {
5545         struct cgroup_subsys_state *css;
5546 
5547         pr_debug("Initializing cgroup subsys %s\n", ss->name);
5548 
5549         mutex_lock(&cgroup_mutex);
5550 
5551         idr_init(&ss->css_idr);
5552         INIT_LIST_HEAD(&ss->cfts);
5553 
5554         /* Create the root cgroup state for this subsystem */
5555         ss->root = &cgrp_dfl_root;
5556         css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5557         /* We don't handle early failures gracefully */
5558         BUG_ON(IS_ERR(css));
5559         init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5560 
5561         /*
5562          * Root csses are never destroyed and we can't initialize
5563          * percpu_ref during early init.  Disable refcnting.
5564          */
5565         css->flags |= CSS_NO_REF;
5566 
5567         if (early) {
5568                 /* allocation can't be done safely during early init */
5569                 css->id = 1;
5570         } else {
5571                 css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5572                 BUG_ON(css->id < 0);
5573         }
5574 
5575         /* Update the init_css_set to contain a subsys
5576          * pointer to this state - since the subsystem is
5577          * newly registered, all tasks and hence the
5578          * init_css_set is in the subsystem's root cgroup. */
5579         init_css_set.subsys[ss->id] = css;
5580 
5581         have_fork_callback |= (bool)ss->fork << ss->id;
5582         have_exit_callback |= (bool)ss->exit << ss->id;
5583         have_free_callback |= (bool)ss->free << ss->id;
5584         have_canfork_callback |= (bool)ss->can_fork << ss->id;
5585 
5586         /* At system boot, before all subsystems have been
5587          * registered, no tasks have been forked, so we don't
5588          * need to invoke fork callbacks here. */
5589         BUG_ON(!list_empty(&init_task.tasks));
5590 
5591         BUG_ON(online_css(css));
5592 
5593         mutex_unlock(&cgroup_mutex);
5594 }
5595 
5596 /**
5597  * cgroup_init_early - cgroup initialization at system boot
5598  *
5599  * Initialize cgroups at system boot, and initialize any
5600  * subsystems that request early init.
5601  */
5602 int __init cgroup_init_early(void)
5603 {
5604         static struct cgroup_sb_opts __initdata opts;
5605         struct cgroup_subsys *ss;
5606         int i;
5607 
5608         init_cgroup_root(&cgrp_dfl_root, &opts);
5609         cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5610 
5611         RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5612 
5613         for_each_subsys(ss, i) {
5614                 WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5615                      "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5616                      i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5617                      ss->id, ss->name);
5618                 WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5619                      "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5620 
5621                 ss->id = i;
5622                 ss->name = cgroup_subsys_name[i];
5623                 if (!ss->legacy_name)
5624                         ss->legacy_name = cgroup_subsys_name[i];
5625 
5626                 if (ss->early_init)
5627                         cgroup_init_subsys(ss, true);
5628         }
5629         return 0;
5630 }
5631 
5632 static u16 cgroup_disable_mask __initdata;
5633 
5634 /**
5635  * cgroup_init - cgroup initialization
5636  *
5637  * Register cgroup filesystem and /proc file, and initialize
5638  * any subsystems that didn't request early init.
5639  */
5640 int __init cgroup_init(void)
5641 {
5642         struct cgroup_subsys *ss;
5643         int ssid;
5644 
5645         BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5646         BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
5647         BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
5648         BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
5649 
5650         /*
5651          * The latency of the synchronize_sched() is too high for cgroups,
5652          * avoid it at the cost of forcing all readers into the slow path.
5653          */
5654         rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5655 
5656         get_user_ns(init_cgroup_ns.user_ns);
5657 
5658         mutex_lock(&cgroup_mutex);
5659 
5660         /*
5661          * Add init_css_set to the hash table so that dfl_root can link to
5662          * it during init.
5663          */
5664         hash_add(css_set_table, &init_css_set.hlist,
5665                  css_set_hash(init_css_set.subsys));
5666 
5667         BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5668 
5669         mutex_unlock(&cgroup_mutex);
5670 
5671         for_each_subsys(ss, ssid) {
5672                 if (ss->early_init) {
5673                         struct cgroup_subsys_state *css =
5674                                 init_css_set.subsys[ss->id];
5675 
5676                         css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5677                                                    GFP_KERNEL);
5678                         BUG_ON(css->id < 0);
5679                 } else {
5680                         cgroup_init_subsys(ss, false);
5681                 }
5682 
5683                 list_add_tail(&init_css_set.e_cset_node[ssid],
5684                               &cgrp_dfl_root.cgrp.e_csets[ssid]);
5685 
5686                 /*
5687                  * Setting dfl_root subsys_mask needs to consider the
5688                  * disabled flag and cftype registration needs kmalloc,
5689                  * both of which aren't available during early_init.
5690                  */
5691                 if (cgroup_disable_mask & (1 << ssid)) {
5692                         static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5693                         printk(KERN_INFO "Disabling %s control group subsystem\n",
5694                                ss->name);
5695                         continue;
5696                 }
5697 
5698                 if (cgroup_ssid_no_v1(ssid))
5699                         printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5700                                ss->name);
5701 
5702                 cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5703 
5704                 if (ss->implicit_on_dfl)
5705                         cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5706                 else if (!ss->dfl_cftypes)
5707                         cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5708 
5709                 if (ss->dfl_cftypes == ss->legacy_cftypes) {
5710                         WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5711                 } else {
5712                         WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5713                         WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5714                 }
5715 
5716                 if (ss->bind)
5717                         ss->bind(init_css_set.subsys[ssid]);
5718         }
5719 
5720         /* init_css_set.subsys[] has been updated, re-hash */
5721         hash_del(&init_css_set.hlist);
5722         hash_add(css_set_table, &init_css_set.hlist,
5723                  css_set_hash(init_css_set.subsys));
5724 
5725         WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5726         WARN_ON(register_filesystem(&cgroup_fs_type));
5727         WARN_ON(register_filesystem(&cgroup2_fs_type));
5728         WARN_ON(!proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations));
5729 
5730         return 0;
5731 }
5732 
5733 static int __init cgroup_wq_init(void)
5734 {
5735         /*
5736          * There isn't much point in executing destruction path in
5737          * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5738          * Use 1 for @max_active.
5739          *
5740          * We would prefer to do this in cgroup_init() above, but that
5741          * is called before init_workqueues(): so leave this until after.
5742          */
5743         cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5744         BUG_ON(!cgroup_destroy_wq);
5745 
5746         /*
5747          * Used to destroy pidlists and separate to serve as flush domain.
5748          * Cap @max_active to 1 too.
5749          */
5750         cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
5751                                                     0, 1);
5752         BUG_ON(!cgroup_pidlist_destroy_wq);
5753 
5754         return 0;
5755 }
5756 core_initcall(cgroup_wq_init);
5757 
5758 /*
5759  * proc_cgroup_show()
5760  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5761  *  - Used for /proc/<pid>/cgroup.
5762  */
5763 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5764                      struct pid *pid, struct task_struct *tsk)
5765 {
5766         char *buf;
5767         int retval;
5768         struct cgroup_root *root;
5769 
5770         retval = -ENOMEM;
5771         buf = kmalloc(PATH_MAX, GFP_KERNEL);
5772         if (!buf)
5773                 goto out;
5774 
5775         mutex_lock(&cgroup_mutex);
5776         spin_lock_irq(&css_set_lock);
5777 
5778         for_each_root(root) {
5779                 struct cgroup_subsys *ss;
5780                 struct cgroup *cgrp;
5781                 int ssid, count = 0;
5782 
5783                 if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5784                         continue;
5785 
5786                 seq_printf(m, "%d:", root->hierarchy_id);
5787                 if (root != &cgrp_dfl_root)
5788                         for_each_subsys(ss, ssid)
5789                                 if (root->subsys_mask & (1 << ssid))
5790                                         seq_printf(m, "%s%s", count++ ? "," : "",
5791                                                    ss->legacy_name);
5792                 if (strlen(root->name))
5793                         seq_printf(m, "%sname=%s", count ? "," : "",
5794                                    root->name);
5795                 seq_putc(m, ':');
5796 
5797                 cgrp = task_cgroup_from_root(tsk, root);
5798 
5799                 /*
5800                  * On traditional hierarchies, all zombie tasks show up as
5801                  * belonging to the root cgroup.  On the default hierarchy,
5802                  * while a zombie doesn't show up in "cgroup.procs" and
5803                  * thus can't be migrated, its /proc/PID/cgroup keeps
5804                  * reporting the cgroup it belonged to before exiting.  If
5805                  * the cgroup is removed before the zombie is reaped,
5806                  * " (deleted)" is appended to the cgroup path.
5807                  */
5808                 if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5809                         retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5810                                                 current->nsproxy->cgroup_ns);
5811                         if (retval >= PATH_MAX)
5812                                 retval = -ENAMETOOLONG;
5813                         if (retval < 0)
5814                                 goto out_unlock;
5815 
5816                         seq_puts(m, buf);
5817                 } else {
5818                         seq_puts(m, "/");
5819                 }
5820 
5821                 if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5822                         seq_puts(m, " (deleted)\n");
5823                 else
5824                         seq_putc(m, '\n');
5825         }
5826 
5827         retval = 0;
5828 out_unlock:
5829         spin_unlock_irq(&css_set_lock);
5830         mutex_unlock(&cgroup_mutex);
5831         kfree(buf);
5832 out:
5833         return retval;
5834 }
5835 
5836 /* Display information about each subsystem and each hierarchy */
5837 static int proc_cgroupstats_show(struct seq_file *m, void *v)
5838 {
5839         struct cgroup_subsys *ss;
5840         int i;
5841 
5842         seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
5843         /*
5844          * ideally we don't want subsystems moving around while we do this.
5845          * cgroup_mutex is also necessary to guarantee an atomic snapshot of
5846          * subsys/hierarchy state.
5847          */
5848         mutex_lock(&cgroup_mutex);
5849 
5850         for_each_subsys(ss, i)
5851                 seq_printf(m, "%s\t%d\t%d\t%d\n",
5852                            ss->legacy_name, ss->root->hierarchy_id,
5853                            atomic_read(&ss->root->nr_cgrps),
5854                            cgroup_ssid_enabled(i));
5855 
5856         mutex_unlock(&cgroup_mutex);
5857         return 0;
5858 }
5859 
5860 static int cgroupstats_open(struct inode *inode, struct file *file)
5861 {
5862         return single_open(file, proc_cgroupstats_show, NULL);
5863 }
5864 
5865 static const struct file_operations proc_cgroupstats_operations = {
5866         .open = cgroupstats_open,
5867         .read = seq_read,
5868         .llseek = seq_lseek,
5869         .release = single_release,
5870 };
5871 
5872 /**
5873  * cgroup_fork - initialize cgroup related fields during copy_process()
5874  * @child: pointer to task_struct of forking parent process.
5875  *
5876  * A task is associated with the init_css_set until cgroup_post_fork()
5877  * attaches it to the parent's css_set.  Empty cg_list indicates that
5878  * @child isn't holding reference to its css_set.
5879  */
5880 void cgroup_fork(struct task_struct *child)
5881 {
5882         RCU_INIT_POINTER(child->cgroups, &init_css_set);
5883         INIT_LIST_HEAD(&child->cg_list);
5884 }
5885 
5886 /**
5887  * cgroup_can_fork - called on a new task before the process is exposed
5888  * @child: the task in question.
5889  *
5890  * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5891  * returns an error, the fork aborts with that error code. This allows for
5892  * a cgroup subsystem to conditionally allow or deny new forks.
5893  */
5894 int cgroup_can_fork(struct task_struct *child)
5895 {
5896         struct cgroup_subsys *ss;
5897         int i, j, ret;
5898 
5899         do_each_subsys_mask(ss, i, have_canfork_callback) {
5900                 ret = ss->can_fork(child);
5901                 if (ret)
5902                         goto out_revert;
5903         } while_each_subsys_mask();
5904 
5905         return 0;
5906 
5907 out_revert:
5908         for_each_subsys(ss, j) {
5909                 if (j >= i)
5910                         break;
5911                 if (ss->cancel_fork)
5912                         ss->cancel_fork(child);
5913         }
5914 
5915         return ret;
5916 }
5917 
5918 /**
5919  * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5920  * @child: the task in question
5921  *
5922  * This calls the cancel_fork() callbacks if a fork failed *after*
5923  * cgroup_can_fork() succeded.
5924  */
5925 void cgroup_cancel_fork(struct task_struct *child)
5926 {
5927         struct cgroup_subsys *ss;
5928         int i;
5929 
5930         for_each_subsys(ss, i)
5931                 if (ss->cancel_fork)
5932                         ss->cancel_fork(child);
5933 }
5934 
5935 /**
5936  * cgroup_post_fork - called on a new task after adding it to the task list
5937  * @child: the task in question
5938  *
5939  * Adds the task to the list running through its css_set if necessary and
5940  * call the subsystem fork() callbacks.  Has to be after the task is
5941  * visible on the task list in case we race with the first call to
5942  * cgroup_task_iter_start() - to guarantee that the new task ends up on its
5943  * list.
5944  */
5945 void cgroup_post_fork(struct task_struct *child)
5946 {
5947         struct cgroup_subsys *ss;
5948         int i;
5949 
5950         /*
5951          * This may race against cgroup_enable_task_cg_lists().  As that
5952          * function sets use_task_css_set_links before grabbing
5953          * tasklist_lock and we just went through tasklist_lock to add
5954          * @child, it's guaranteed that either we see the set
5955          * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
5956          * @child during its iteration.
5957          *
5958          * If we won the race, @child is associated with %current's
5959          * css_set.  Grabbing css_set_lock guarantees both that the
5960          * association is stable, and, on completion of the parent's
5961          * migration, @child is visible in the source of migration or
5962          * already in the destination cgroup.  This guarantee is necessary
5963          * when implementing operations which need to migrate all tasks of
5964          * a cgroup to another.
5965          *
5966          * Note that if we lose to cgroup_enable_task_cg_lists(), @child
5967          * will remain in init_css_set.  This is safe because all tasks are
5968          * in the init_css_set before cg_links is enabled and there's no
5969          * operation which transfers all tasks out of init_css_set.
5970          */
5971         if (use_task_css_set_links) {
5972                 struct css_set *cset;
5973 
5974                 spin_lock_irq(&css_set_lock);
5975                 cset = task_css_set(current);
5976                 if (list_empty(&child->cg_list)) {
5977                         get_css_set(cset);
5978                         css_set_move_task(child, NULL, cset, false);
5979                 }
5980                 spin_unlock_irq(&css_set_lock);
5981         }
5982 
5983         /*
5984          * Call ss->fork().  This must happen after @child is linked on
5985          * css_set; otherwise, @child might change state between ->fork()
5986          * and addition to css_set.
5987          */
5988         do_each_subsys_mask(ss, i, have_fork_callback) {
5989                 ss->fork(child);
5990         } while_each_subsys_mask();
5991 }
5992 
5993 /**
5994  * cgroup_exit - detach cgroup from exiting task
5995  * @tsk: pointer to task_struct of exiting process
5996  *
5997  * Description: Detach cgroup from @tsk and release it.
5998  *
5999  * Note that cgroups marked notify_on_release force every task in
6000  * them to take the global cgroup_mutex mutex when exiting.
6001  * This could impact scaling on very large systems.  Be reluctant to
6002  * use notify_on_release cgroups where very high task exit scaling
6003  * is required on large systems.
6004  *
6005  * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
6006  * call cgroup_exit() while the task is still competent to handle
6007  * notify_on_release(), then leave the task attached to the root cgroup in
6008  * each hierarchy for the remainder of its exit.  No need to bother with
6009  * init_css_set refcnting.  init_css_set never goes away and we can't race
6010  * with migration path - PF_EXITING is visible to migration path.
6011  */
6012 void cgroup_exit(struct task_struct *tsk)
6013 {
6014         struct cgroup_subsys *ss;
6015         struct css_set *cset;
6016         int i;
6017 
6018         /*
6019          * Unlink from @tsk from its css_set.  As migration path can't race
6020          * with us, we can check css_set and cg_list without synchronization.
6021          */
6022         cset = task_css_set(tsk);
6023 
6024         if (!list_empty(&tsk->cg_list)) {
6025                 spin_lock_irq(&css_set_lock);
6026                 css_set_move_task(tsk, cset, NULL, false);
6027                 spin_unlock_irq(&css_set_lock);
6028         } else {
6029                 get_css_set(cset);
6030         }
6031 
6032         /* see cgroup_post_fork() for details */
6033         do_each_subsys_mask(ss, i, have_exit_callback) {
6034                 ss->exit(tsk);
6035         } while_each_subsys_mask();
6036 }
6037 
6038 void cgroup_free(struct task_struct *task)
6039 {
6040         struct css_set *cset = task_css_set(task);
6041         struct cgroup_subsys *ss;
6042         int ssid;
6043 
6044         do_each_subsys_mask(ss, ssid, have_free_callback) {
6045                 ss->free(task);
6046         } while_each_subsys_mask();
6047 
6048         put_css_set(cset);
6049 }
6050 
6051 static void check_for_release(struct cgroup *cgrp)
6052 {
6053         if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) &&
6054             !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
6055                 schedule_work(&cgrp->release_agent_work);
6056 }
6057 
6058 /*
6059  * Notify userspace when a cgroup is released, by running the
6060  * configured release agent with the name of the cgroup (path
6061  * relative to the root of cgroup file system) as the argument.
6062  *
6063  * Most likely, this user command will try to rmdir this cgroup.
6064  *
6065  * This races with the possibility that some other task will be
6066  * attached to this cgroup before it is removed, or that some other
6067  * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
6068  * The presumed 'rmdir' will fail quietly if this cgroup is no longer
6069  * unused, and this cgroup will be reprieved from its death sentence,
6070  * to continue to serve a useful existence.  Next time it's released,
6071  * we will get notified again, if it still has 'notify_on_release' set.
6072  *
6073  * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
6074  * means only wait until the task is successfully execve()'d.  The
6075  * separate release agent task is forked by call_usermodehelper(),
6076  * then control in this thread returns here, without waiting for the
6077  * release agent task.  We don't bother to wait because the caller of
6078  * this routine has no use for the exit status of the release agent
6079  * task, so no sense holding our caller up for that.
6080  */
6081 static void cgroup_release_agent(struct work_struct *work)
6082 {
6083         struct cgroup *cgrp =
6084                 container_of(work, struct cgroup, release_agent_work);
6085         char *pathbuf = NULL, *agentbuf = NULL;
6086         char *argv[3], *envp[3];
6087         int ret;
6088 
6089         mutex_lock(&cgroup_mutex);
6090 
6091         pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
6092         agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
6093         if (!pathbuf || !agentbuf)
6094                 goto out;
6095 
6096         spin_lock_irq(&css_set_lock);
6097         ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
6098         spin_unlock_irq(&css_set_lock);
6099         if (ret < 0 || ret >= PATH_MAX)
6100                 goto out;
6101 
6102         argv[0] = agentbuf;
6103         argv[1] = pathbuf;
6104         argv[2] = NULL;
6105 
6106         /* minimal command environment */
6107         envp[0] = "HOME=/";
6108         envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
6109         envp[2] = NULL;
6110 
6111         mutex_unlock(&cgroup_mutex);
6112         call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
6113         goto out_free;
6114 out:
6115         mutex_unlock(&cgroup_mutex);
6116 out_free:
6117         kfree(agentbuf);
6118         kfree(pathbuf);
6119 }
6120 
6121 static int __init cgroup_disable(char *str)
6122 {
6123         struct cgroup_subsys *ss;
6124         char *token;
6125         int i;
6126 
6127         while ((token = strsep(&str, ",")) != NULL) {
6128                 if (!*token)
6129                         continue;
6130 
6131                 for_each_subsys(ss, i) {
6132                         if (strcmp(token, ss->name) &&
6133                             strcmp(token, ss->legacy_name))
6134                                 continue;
6135                         cgroup_disable_mask |= 1 << i;
6136                 }
6137         }
6138         return 1;
6139 }
6140 __setup("cgroup_disable=", cgroup_disable);
6141 
6142 static int __init cgroup_no_v1(char *str)
6143 {
6144         struct cgroup_subsys *ss;
6145         char *token;
6146         int i;
6147 
6148         while ((token = strsep(&str, ",")) != NULL) {
6149                 if (!*token)
6150                         continue;
6151 
6152                 if (!strcmp(token, "all")) {
6153                         cgroup_no_v1_mask = U16_MAX;
6154                         break;
6155                 }
6156 
6157                 for_each_subsys(ss, i) {
6158                         if (strcmp(token, ss->name) &&
6159                             strcmp(token, ss->legacy_name))
6160                                 continue;
6161 
6162                         cgroup_no_v1_mask |= 1 << i;
6163                 }
6164         }
6165         return 1;
6166 }
6167 __setup("cgroup_no_v1=", cgroup_no_v1);
6168 
6169 /**
6170  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
6171  * @dentry: directory dentry of interest
6172  * @ss: subsystem of interest
6173  *
6174  * If @dentry is a directory for a cgroup which has @ss enabled on it, try
6175  * to get the corresponding css and return it.  If such css doesn't exist
6176  * or can't be pinned, an ERR_PTR value is returned.
6177  */
6178 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
6179                                                        struct cgroup_subsys *ss)
6180 {
6181         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
6182         struct file_system_type *s_type = dentry->d_sb->s_type;
6183         struct cgroup_subsys_state *css = NULL;
6184         struct cgroup *cgrp;
6185 
6186         /* is @dentry a cgroup dir? */
6187         if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
6188             !kn || kernfs_type(kn) != KERNFS_DIR)
6189                 return ERR_PTR(-EBADF);
6190 
6191         rcu_read_lock();
6192 
6193         /*
6194          * This path doesn't originate from kernfs and @kn could already
6195          * have been or be removed at any point.  @kn->priv is RCU
6196          * protected for this access.  See css_release_work_fn() for details.
6197          */
6198         cgrp = rcu_dereference(kn->priv);
6199         if (cgrp)
6200                 css = cgroup_css(cgrp, ss);
6201 
6202         if (!css || !css_tryget_online(css))
6203                 css = ERR_PTR(-ENOENT);
6204 
6205         rcu_read_unlock();
6206         return css;
6207 }
6208 
6209 /**
6210  * css_from_id - lookup css by id
6211  * @id: the cgroup id
6212  * @ss: cgroup subsys to be looked into
6213  *
6214  * Returns the css if there's valid one with @id, otherwise returns NULL.
6215  * Should be called under rcu_read_lock().
6216  */
6217 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
6218 {
6219         WARN_ON_ONCE(!rcu_read_lock_held());
6220         return idr_find(&ss->css_idr, id);
6221 }
6222 
6223 /**
6224  * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
6225  * @path: path on the default hierarchy
6226  *
6227  * Find the cgroup at @path on the default hierarchy, increment its
6228  * reference count and return it.  Returns pointer to the found cgroup on
6229  * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
6230  * if @path points to a non-directory.
6231  */
6232 struct cgroup *cgroup_get_from_path(const char *path)
6233 {
6234         struct kernfs_node *kn;
6235         struct cgroup *cgrp;
6236 
6237         mutex_lock(&cgroup_mutex);
6238 
6239         kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
6240         if (kn) {
6241                 if (kernfs_type(kn) == KERNFS_DIR) {
6242                         cgrp = kn->priv;
6243                         cgroup_get(cgrp);
6244                 } else {
6245                         cgrp = ERR_PTR(-ENOTDIR);
6246                 }
6247                 kernfs_put(kn);
6248         } else {
6249                 cgrp = ERR_PTR(-ENOENT);
6250         }
6251 
6252         mutex_unlock(&cgroup_mutex);
6253         return cgrp;
6254 }
6255 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
6256 
6257 /**
6258  * cgroup_get_from_fd - get a cgroup pointer from a fd
6259  * @fd: fd obtained by open(cgroup2_dir)
6260  *
6261  * Find the cgroup from a fd which should be obtained
6262  * by opening a cgroup directory.  Returns a pointer to the
6263  * cgroup on success. ERR_PTR is returned if the cgroup
6264  * cannot be found.
6265  */
6266 struct cgroup *cgroup_get_from_fd(int fd)
6267 {
6268         struct cgroup_subsys_state *css;
6269         struct cgroup *cgrp;
6270         struct file *f;
6271 
6272         f = fget_raw(fd);
6273         if (!f)
6274                 return ERR_PTR(-EBADF);
6275 
6276         css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
6277         fput(f);
6278         if (IS_ERR(css))
6279                 return ERR_CAST(css);
6280 
6281         cgrp = css->cgroup;
6282         if (!cgroup_on_dfl(cgrp)) {
6283                 cgroup_put(cgrp);
6284                 return ERR_PTR(-EBADF);
6285         }
6286 
6287         return cgrp;
6288 }
6289 EXPORT_SYMBOL_GPL(cgroup_get_from_fd);
6290 
6291 /*
6292  * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
6293  * definition in cgroup-defs.h.
6294  */
6295 #ifdef CONFIG_SOCK_CGROUP_DATA
6296 
6297 #if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
6298 
6299 DEFINE_SPINLOCK(cgroup_sk_update_lock);
6300 static bool cgroup_sk_alloc_disabled __read_mostly;
6301 
6302 void cgroup_sk_alloc_disable(void)
6303 {
6304         if (cgroup_sk_alloc_disabled)
6305                 return;
6306         pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
6307         cgroup_sk_alloc_disabled = true;
6308 }
6309 
6310 #else
6311 
6312 #define cgroup_sk_alloc_disabled        false
6313 
6314 #endif
6315 
6316 void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
6317 {
6318         if (cgroup_sk_alloc_disabled)
6319                 return;
6320 
6321         /* Socket clone path */
6322         if (skcd->val) {
6323                 cgroup_get(sock_cgroup_ptr(skcd));
6324                 return;
6325         }
6326 
6327         rcu_read_lock();
6328 
6329         while (true) {
6330                 struct css_set *cset;
6331 
6332                 cset = task_css_set(current);
6333                 if (likely(cgroup_tryget(cset->dfl_cgrp))) {
6334                         skcd->val = (unsigned long)cset->dfl_cgrp;
6335                         break;
6336                 }
6337                 cpu_relax();
6338         }
6339 
6340         rcu_read_unlock();
6341 }
6342 
6343 void cgroup_sk_free(struct sock_cgroup_data *skcd)
6344 {
6345         cgroup_put(sock_cgroup_ptr(skcd));
6346 }
6347 
6348 #endif  /* CONFIG_SOCK_CGROUP_DATA */
6349 
6350 /* cgroup namespaces */
6351 
6352 static struct ucounts *inc_cgroup_namespaces(struct user_namespace *ns)
6353 {
6354         return inc_ucount(ns, current_euid(), UCOUNT_CGROUP_NAMESPACES);
6355 }
6356 
6357 static void dec_cgroup_namespaces(struct ucounts *ucounts)
6358 {
6359         dec_ucount(ucounts, UCOUNT_CGROUP_NAMESPACES);
6360 }
6361 
6362 static struct cgroup_namespace *alloc_cgroup_ns(void)
6363 {
6364         struct cgroup_namespace *new_ns;
6365         int ret;
6366 
6367         new_ns = kzalloc(sizeof(struct cgroup_namespace), GFP_KERNEL);
6368         if (!new_ns)
6369                 return ERR_PTR(-ENOMEM);
6370         ret = ns_alloc_inum(&new_ns->ns);
6371         if (ret) {
6372                 kfree(new_ns);
6373                 return ERR_PTR(ret);
6374         }
6375         atomic_set(&new_ns->count, 1);
6376         new_ns->ns.ops = &cgroupns_operations;
6377         return new_ns;
6378 }
6379 
6380 void free_cgroup_ns(struct cgroup_namespace *ns)
6381 {
6382         put_css_set(ns->root_cset);
6383         dec_cgroup_namespaces(ns->ucounts);
6384         put_user_ns(ns->user_ns);
6385         ns_free_inum(&ns->ns);
6386         kfree(ns);
6387 }
6388 EXPORT_SYMBOL(free_cgroup_ns);
6389 
6390 struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
6391                                         struct user_namespace *user_ns,
6392                                         struct cgroup_namespace *old_ns)
6393 {
6394         struct cgroup_namespace *new_ns;
6395         struct ucounts *ucounts;
6396         struct css_set *cset;
6397 
6398         BUG_ON(!old_ns);
6399 
6400         if (!(flags & CLONE_NEWCGROUP)) {
6401                 get_cgroup_ns(old_ns);
6402                 return old_ns;
6403         }
6404 
6405         /* Allow only sysadmin to create cgroup namespace. */
6406         if (!ns_capable(user_ns, CAP_SYS_ADMIN))
6407                 return ERR_PTR(-EPERM);
6408 
6409         ucounts = inc_cgroup_namespaces(user_ns);
6410         if (!ucounts)
6411                 return ERR_PTR(-ENOSPC);
6412 
6413         /* It is not safe to take cgroup_mutex here */
6414         spin_lock_irq(&css_set_lock);
6415         cset = task_css_set(current);
6416         get_css_set(cset);
6417         spin_unlock_irq(&css_set_lock);
6418 
6419         new_ns = alloc_cgroup_ns();
6420         if (IS_ERR(new_ns)) {
6421                 put_css_set(cset);
6422                 dec_cgroup_namespaces(ucounts);
6423                 return new_ns;
6424         }
6425 
6426         new_ns->user_ns = get_user_ns(user_ns);
6427         new_ns->ucounts = ucounts;
6428         new_ns->root_cset = cset;
6429 
6430         return new_ns;
6431 }
6432 
6433 static inline struct cgroup_namespace *to_cg_ns(struct ns_common *ns)
6434 {
6435         return container_of(ns, struct cgroup_namespace, ns);
6436 }
6437 
6438 static int cgroupns_install(struct nsproxy *nsproxy, struct ns_common *ns)
6439 {
6440         struct cgroup_namespace *cgroup_ns = to_cg_ns(ns);
6441 
6442         if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN) ||
6443             !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
6444                 return -EPERM;
6445 
6446         /* Don't need to do anything if we are attaching to our own cgroupns. */
6447         if (cgroup_ns == nsproxy->cgroup_ns)
6448                 return 0;
6449 
6450         get_cgroup_ns(cgroup_ns);
6451         put_cgroup_ns(nsproxy->cgroup_ns);
6452         nsproxy->cgroup_ns = cgroup_ns;
6453 
6454         return 0;
6455 }
6456 
6457 static struct ns_common *cgroupns_get(struct task_struct *task)
6458 {
6459         struct cgroup_namespace *ns = NULL;
6460         struct nsproxy *nsproxy;
6461 
6462         task_lock(task);
6463         nsproxy = task->nsproxy;
6464         if (nsproxy) {
6465                 ns = nsproxy->cgroup_ns;
6466                 get_cgroup_ns(ns);
6467         }
6468         task_unlock(task);
6469 
6470         return ns ? &ns->ns : NULL;
6471 }
6472 
6473 static void cgroupns_put(struct ns_common *ns)
6474 {
6475         put_cgroup_ns(to_cg_ns(ns));
6476 }
6477 
6478 static struct user_namespace *cgroupns_owner(struct ns_common *ns)
6479 {
6480         return to_cg_ns(ns)->user_ns;
6481 }
6482 
6483 const struct proc_ns_operations cgroupns_operations = {
6484         .name           = "cgroup",
6485         .type           = CLONE_NEWCGROUP,
6486         .get            = cgroupns_get,
6487         .put            = cgroupns_put,
6488         .install        = cgroupns_install,
6489         .owner          = cgroupns_owner,
6490 };
6491 
6492 static __init int cgroup_namespaces_init(void)
6493 {
6494         return 0;
6495 }
6496 subsys_initcall(cgroup_namespaces_init);
6497 
6498 #ifdef CONFIG_CGROUP_DEBUG
6499 static struct cgroup_subsys_state *
6500 debug_css_alloc(struct cgroup_subsys_state *parent_css)
6501 {
6502         struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
6503 
6504         if (!css)
6505                 return ERR_PTR(-ENOMEM);
6506 
6507         return css;
6508 }
6509 
6510 static void debug_css_free(struct cgroup_subsys_state *css)
6511 {
6512         kfree(css);
6513 }
6514 
6515 static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
6516                                 struct cftype *cft)
6517 {
6518         return cgroup_task_count(css->cgroup);
6519 }
6520 
6521 static u64 current_css_set_read(struct cgroup_subsys_state *css,
6522                                 struct cftype *cft)
6523 {
6524         return (u64)(unsigned long)current->cgroups;
6525 }
6526 
6527 static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
6528                                          struct cftype *cft)
6529 {
6530         u64 count;
6531 
6532         rcu_read_lock();
6533         count = atomic_read(&task_css_set(current)->refcount);
6534         rcu_read_unlock();
6535         return count;
6536 }
6537 
6538 static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
6539 {
6540         struct cgrp_cset_link *link;
6541         struct css_set *cset;
6542         char *name_buf;
6543 
6544         name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
6545         if (!name_buf)
6546                 return -ENOMEM;
6547 
6548         spin_lock_irq(&css_set_lock);
6549         rcu_read_lock();
6550         cset = rcu_dereference(current->cgroups);
6551         list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
6552                 struct cgroup *c = link->cgrp;
6553 
6554                 cgroup_name(c, name_buf, NAME_MAX + 1);
6555                 seq_printf(seq, "Root %d group %s\n",
6556                            c->root->hierarchy_id, name_buf);
6557         }
6558         rcu_read_unlock();
6559         spin_unlock_irq(&css_set_lock);
6560         kfree(name_buf);
6561         return 0;
6562 }
6563 
6564 #define MAX_TASKS_SHOWN_PER_CSS 25
6565 static int cgroup_css_links_read(struct seq_file *seq, void *v)
6566 {
6567         struct cgroup_subsys_state *css = seq_css(seq);
6568         struct cgrp_cset_link *link;
6569 
6570         spin_lock_irq(&css_set_lock);
6571         list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
6572                 struct css_set *cset = link->cset;
6573                 struct task_struct *task;
6574                 int count = 0;
6575 
6576                 seq_printf(seq, "css_set %p\n", cset);
6577 
6578                 list_for_each_entry(task, &cset->tasks, cg_list) {
6579                         if (count++ > MAX_TASKS_SHOWN_PER_CSS)
6580                                 goto overflow;
6581                         seq_printf(seq, "  task %d\n", task_pid_vnr(task));
6582                 }
6583 
6584                 list_for_each_entry(task, &cset->mg_tasks, cg_list) {
6585                         if (count++ > MAX_TASKS_SHOWN_PER_CSS)
6586                                 goto overflow;
6587                         seq_printf(seq, "  task %d\n", task_pid_vnr(task));
6588                 }
6589                 continue;
6590         overflow:
6591                 seq_puts(seq, "  ...\n");
6592         }
6593         spin_unlock_irq(&css_set_lock);
6594         return 0;
6595 }
6596 
6597 static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
6598 {
6599         return (!cgroup_is_populated(css->cgroup) &&
6600                 !css_has_online_children(&css->cgroup->self));
6601 }
6602 
6603 static struct cftype debug_files[] =  {
6604         {
6605                 .name = "taskcount",
6606                 .read_u64 = debug_taskcount_read,
6607         },
6608 
6609         {
6610                 .name = "current_css_set",
6611                 .read_u64 = current_css_set_read,
6612         },
6613 
6614         {
6615                 .name = "current_css_set_refcount",
6616                 .read_u64 = current_css_set_refcount_read,
6617         },
6618 
6619         {
6620                 .name = "current_css_set_cg_links",
6621                 .seq_show = current_css_set_cg_links_read,
6622         },
6623 
6624         {
6625                 .name = "cgroup_css_links",
6626                 .seq_show = cgroup_css_links_read,
6627         },
6628 
6629         {
6630                 .name = "releasable",
6631                 .read_u64 = releasable_read,
6632         },
6633 
6634         { }     /* terminate */
6635 };
6636 
6637 struct cgroup_subsys debug_cgrp_subsys = {
6638         .css_alloc = debug_css_alloc,
6639         .css_free = debug_css_free,
6640         .legacy_cftypes = debug_files,
6641 };
6642 #endif /* CONFIG_CGROUP_DEBUG */
6643 

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