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/proc_ns.h>
 65 #include <net/sock.h>
 66 
 67 /*
 68  * pidlists linger the following amount before being destroyed.  The goal
 69  * is avoiding frequent destruction in the middle of consecutive read calls
 70  * Expiring in the middle is a performance problem not a correctness one.
 71  * 1 sec should be enough.
 72  */
 73 #define CGROUP_PIDLIST_DESTROY_DELAY    HZ
 74 
 75 #define CGROUP_FILE_NAME_MAX            (MAX_CGROUP_TYPE_NAMELEN +      \
 76                                          MAX_CFTYPE_NAME + 2)
 77 
 78 /*
 79  * cgroup_mutex is the master lock.  Any modification to cgroup or its
 80  * hierarchy must be performed while holding it.
 81  *
 82  * css_set_lock protects task->cgroups pointer, the list of css_set
 83  * objects, and the chain of tasks off each css_set.
 84  *
 85  * These locks are exported if CONFIG_PROVE_RCU so that accessors in
 86  * cgroup.h can use them for lockdep annotations.
 87  */
 88 #ifdef CONFIG_PROVE_RCU
 89 DEFINE_MUTEX(cgroup_mutex);
 90 DEFINE_SPINLOCK(css_set_lock);
 91 EXPORT_SYMBOL_GPL(cgroup_mutex);
 92 EXPORT_SYMBOL_GPL(css_set_lock);
 93 #else
 94 static DEFINE_MUTEX(cgroup_mutex);
 95 static DEFINE_SPINLOCK(css_set_lock);
 96 #endif
 97 
 98 /*
 99  * Protects cgroup_idr and css_idr so that IDs can be released without
100  * grabbing cgroup_mutex.
101  */
102 static DEFINE_SPINLOCK(cgroup_idr_lock);
103 
104 /*
105  * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
106  * against file removal/re-creation across css hiding.
107  */
108 static DEFINE_SPINLOCK(cgroup_file_kn_lock);
109 
110 /*
111  * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
112  * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
113  */
114 static DEFINE_SPINLOCK(release_agent_path_lock);
115 
116 struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
117 
118 #define cgroup_assert_mutex_or_rcu_locked()                             \
119         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
120                            !lockdep_is_held(&cgroup_mutex),             \
121                            "cgroup_mutex or RCU read lock required");
122 
123 /*
124  * cgroup destruction makes heavy use of work items and there can be a lot
125  * of concurrent destructions.  Use a separate workqueue so that cgroup
126  * destruction work items don't end up filling up max_active of system_wq
127  * which may lead to deadlock.
128  */
129 static struct workqueue_struct *cgroup_destroy_wq;
130 
131 /*
132  * pidlist destructions need to be flushed on cgroup destruction.  Use a
133  * separate workqueue as flush domain.
134  */
135 static struct workqueue_struct *cgroup_pidlist_destroy_wq;
136 
137 /* generate an array of cgroup subsystem pointers */
138 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
139 static struct cgroup_subsys *cgroup_subsys[] = {
140 #include <linux/cgroup_subsys.h>
141 };
142 #undef SUBSYS
143 
144 /* array of cgroup subsystem names */
145 #define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
146 static const char *cgroup_subsys_name[] = {
147 #include <linux/cgroup_subsys.h>
148 };
149 #undef SUBSYS
150 
151 /* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
152 #define SUBSYS(_x)                                                              \
153         DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);                 \
154         DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);                  \
155         EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);                      \
156         EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
157 #include <linux/cgroup_subsys.h>
158 #undef SUBSYS
159 
160 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
161 static struct static_key_true *cgroup_subsys_enabled_key[] = {
162 #include <linux/cgroup_subsys.h>
163 };
164 #undef SUBSYS
165 
166 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
167 static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
168 #include <linux/cgroup_subsys.h>
169 };
170 #undef SUBSYS
171 
172 /*
173  * The default hierarchy, reserved for the subsystems that are otherwise
174  * unattached - it never has more than a single cgroup, and all tasks are
175  * part of that cgroup.
176  */
177 struct cgroup_root cgrp_dfl_root;
178 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
179 
180 /*
181  * The default hierarchy always exists but is hidden until mounted for the
182  * first time.  This is for backward compatibility.
183  */
184 static bool cgrp_dfl_visible;
185 
186 /* Controllers blocked by the commandline in v1 */
187 static u16 cgroup_no_v1_mask;
188 
189 /* some controllers are not supported in the default hierarchy */
190 static u16 cgrp_dfl_inhibit_ss_mask;
191 
192 /* some controllers are implicitly enabled on the default hierarchy */
193 static unsigned long cgrp_dfl_implicit_ss_mask;
194 
195 /* The list of hierarchy roots */
196 
197 static LIST_HEAD(cgroup_roots);
198 static int cgroup_root_count;
199 
200 /* hierarchy ID allocation and mapping, protected by cgroup_mutex */
201 static DEFINE_IDR(cgroup_hierarchy_idr);
202 
203 /*
204  * Assign a monotonically increasing serial number to csses.  It guarantees
205  * cgroups with bigger numbers are newer than those with smaller numbers.
206  * Also, as csses are always appended to the parent's ->children list, it
207  * guarantees that sibling csses are always sorted in the ascending serial
208  * number order on the list.  Protected by cgroup_mutex.
209  */
210 static u64 css_serial_nr_next = 1;
211 
212 /*
213  * These bitmask flags indicate whether tasks in the fork and exit paths have
214  * fork/exit handlers to call. This avoids us having to do extra work in the
215  * fork/exit path to check which subsystems have fork/exit callbacks.
216  */
217 static u16 have_fork_callback __read_mostly;
218 static u16 have_exit_callback __read_mostly;
219 static u16 have_free_callback __read_mostly;
220 
221 /* cgroup namespace for init task */
222 struct cgroup_namespace init_cgroup_ns = {
223         .count          = { .counter = 2, },
224         .user_ns        = &init_user_ns,
225         .ns.ops         = &cgroupns_operations,
226         .ns.inum        = PROC_CGROUP_INIT_INO,
227         .root_cset      = &init_css_set,
228 };
229 
230 /* Ditto for the can_fork callback. */
231 static u16 have_canfork_callback __read_mostly;
232 
233 static struct file_system_type cgroup2_fs_type;
234 static struct cftype cgroup_dfl_base_files[];
235 static struct cftype cgroup_legacy_base_files[];
236 
237 static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
238 static void cgroup_lock_and_drain_offline(struct cgroup *cgrp);
239 static int cgroup_apply_control(struct cgroup *cgrp);
240 static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
241 static void css_task_iter_advance(struct css_task_iter *it);
242 static int cgroup_destroy_locked(struct cgroup *cgrp);
243 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
244                                               struct cgroup_subsys *ss);
245 static void css_release(struct percpu_ref *ref);
246 static void kill_css(struct cgroup_subsys_state *css);
247 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
248                               struct cgroup *cgrp, struct cftype cfts[],
249                               bool is_add);
250 
251 /**
252  * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
253  * @ssid: subsys ID of interest
254  *
255  * cgroup_subsys_enabled() can only be used with literal subsys names which
256  * is fine for individual subsystems but unsuitable for cgroup core.  This
257  * is slower static_key_enabled() based test indexed by @ssid.
258  */
259 static bool cgroup_ssid_enabled(int ssid)
260 {
261         if (CGROUP_SUBSYS_COUNT == 0)
262                 return false;
263 
264         return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
265 }
266 
267 static bool cgroup_ssid_no_v1(int ssid)
268 {
269         return cgroup_no_v1_mask & (1 << ssid);
270 }
271 
272 /**
273  * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
274  * @cgrp: the cgroup of interest
275  *
276  * The default hierarchy is the v2 interface of cgroup and this function
277  * can be used to test whether a cgroup is on the default hierarchy for
278  * cases where a subsystem should behave differnetly depending on the
279  * interface version.
280  *
281  * The set of behaviors which change on the default hierarchy are still
282  * being determined and the mount option is prefixed with __DEVEL__.
283  *
284  * List of changed behaviors:
285  *
286  * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
287  *   and "name" are disallowed.
288  *
289  * - When mounting an existing superblock, mount options should match.
290  *
291  * - Remount is disallowed.
292  *
293  * - rename(2) is disallowed.
294  *
295  * - "tasks" is removed.  Everything should be at process granularity.  Use
296  *   "cgroup.procs" instead.
297  *
298  * - "cgroup.procs" is not sorted.  pids will be unique unless they got
299  *   recycled inbetween reads.
300  *
301  * - "release_agent" and "notify_on_release" are removed.  Replacement
302  *   notification mechanism will be implemented.
303  *
304  * - "cgroup.clone_children" is removed.
305  *
306  * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
307  *   and its descendants contain no task; otherwise, 1.  The file also
308  *   generates kernfs notification which can be monitored through poll and
309  *   [di]notify when the value of the file changes.
310  *
311  * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
312  *   take masks of ancestors with non-empty cpus/mems, instead of being
313  *   moved to an ancestor.
314  *
315  * - cpuset: a task can be moved into an empty cpuset, and again it takes
316  *   masks of ancestors.
317  *
318  * - memcg: use_hierarchy is on by default and the cgroup file for the flag
319  *   is not created.
320  *
321  * - blkcg: blk-throttle becomes properly hierarchical.
322  *
323  * - debug: disallowed on the default hierarchy.
324  */
325 static bool cgroup_on_dfl(const struct cgroup *cgrp)
326 {
327         return cgrp->root == &cgrp_dfl_root;
328 }
329 
330 /* IDR wrappers which synchronize using cgroup_idr_lock */
331 static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
332                             gfp_t gfp_mask)
333 {
334         int ret;
335 
336         idr_preload(gfp_mask);
337         spin_lock_bh(&cgroup_idr_lock);
338         ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
339         spin_unlock_bh(&cgroup_idr_lock);
340         idr_preload_end();
341         return ret;
342 }
343 
344 static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
345 {
346         void *ret;
347 
348         spin_lock_bh(&cgroup_idr_lock);
349         ret = idr_replace(idr, ptr, id);
350         spin_unlock_bh(&cgroup_idr_lock);
351         return ret;
352 }
353 
354 static void cgroup_idr_remove(struct idr *idr, int id)
355 {
356         spin_lock_bh(&cgroup_idr_lock);
357         idr_remove(idr, id);
358         spin_unlock_bh(&cgroup_idr_lock);
359 }
360 
361 static struct cgroup *cgroup_parent(struct cgroup *cgrp)
362 {
363         struct cgroup_subsys_state *parent_css = cgrp->self.parent;
364 
365         if (parent_css)
366                 return container_of(parent_css, struct cgroup, self);
367         return NULL;
368 }
369 
370 /* subsystems visibly enabled on a cgroup */
371 static u16 cgroup_control(struct cgroup *cgrp)
372 {
373         struct cgroup *parent = cgroup_parent(cgrp);
374         u16 root_ss_mask = cgrp->root->subsys_mask;
375 
376         if (parent)
377                 return parent->subtree_control;
378 
379         if (cgroup_on_dfl(cgrp))
380                 root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
381                                   cgrp_dfl_implicit_ss_mask);
382         return root_ss_mask;
383 }
384 
385 /* subsystems enabled on a cgroup */
386 static u16 cgroup_ss_mask(struct cgroup *cgrp)
387 {
388         struct cgroup *parent = cgroup_parent(cgrp);
389 
390         if (parent)
391                 return parent->subtree_ss_mask;
392 
393         return cgrp->root->subsys_mask;
394 }
395 
396 /**
397  * cgroup_css - obtain a cgroup's css for the specified subsystem
398  * @cgrp: the cgroup of interest
399  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
400  *
401  * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
402  * function must be called either under cgroup_mutex or rcu_read_lock() and
403  * the caller is responsible for pinning the returned css if it wants to
404  * keep accessing it outside the said locks.  This function may return
405  * %NULL if @cgrp doesn't have @subsys_id enabled.
406  */
407 static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
408                                               struct cgroup_subsys *ss)
409 {
410         if (ss)
411                 return rcu_dereference_check(cgrp->subsys[ss->id],
412                                         lockdep_is_held(&cgroup_mutex));
413         else
414                 return &cgrp->self;
415 }
416 
417 /**
418  * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
419  * @cgrp: the cgroup of interest
420  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
421  *
422  * Similar to cgroup_css() but returns the effective css, which is defined
423  * as the matching css of the nearest ancestor including self which has @ss
424  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
425  * function is guaranteed to return non-NULL css.
426  */
427 static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
428                                                 struct cgroup_subsys *ss)
429 {
430         lockdep_assert_held(&cgroup_mutex);
431 
432         if (!ss)
433                 return &cgrp->self;
434 
435         /*
436          * This function is used while updating css associations and thus
437          * can't test the csses directly.  Test ss_mask.
438          */
439         while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
440                 cgrp = cgroup_parent(cgrp);
441                 if (!cgrp)
442                         return NULL;
443         }
444 
445         return cgroup_css(cgrp, ss);
446 }
447 
448 /**
449  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
450  * @cgrp: the cgroup of interest
451  * @ss: the subsystem of interest
452  *
453  * Find and get the effective css of @cgrp for @ss.  The effective css is
454  * defined as the matching css of the nearest ancestor including self which
455  * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
456  * the root css is returned, so this function always returns a valid css.
457  * The returned css must be put using css_put().
458  */
459 struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
460                                              struct cgroup_subsys *ss)
461 {
462         struct cgroup_subsys_state *css;
463 
464         rcu_read_lock();
465 
466         do {
467                 css = cgroup_css(cgrp, ss);
468 
469                 if (css && css_tryget_online(css))
470                         goto out_unlock;
471                 cgrp = cgroup_parent(cgrp);
472         } while (cgrp);
473 
474         css = init_css_set.subsys[ss->id];
475         css_get(css);
476 out_unlock:
477         rcu_read_unlock();
478         return css;
479 }
480 
481 /* convenient tests for these bits */
482 static inline bool cgroup_is_dead(const struct cgroup *cgrp)
483 {
484         return !(cgrp->self.flags & CSS_ONLINE);
485 }
486 
487 static void cgroup_get(struct cgroup *cgrp)
488 {
489         WARN_ON_ONCE(cgroup_is_dead(cgrp));
490         css_get(&cgrp->self);
491 }
492 
493 static bool cgroup_tryget(struct cgroup *cgrp)
494 {
495         return css_tryget(&cgrp->self);
496 }
497 
498 struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
499 {
500         struct cgroup *cgrp = of->kn->parent->priv;
501         struct cftype *cft = of_cft(of);
502 
503         /*
504          * This is open and unprotected implementation of cgroup_css().
505          * seq_css() is only called from a kernfs file operation which has
506          * an active reference on the file.  Because all the subsystem
507          * files are drained before a css is disassociated with a cgroup,
508          * the matching css from the cgroup's subsys table is guaranteed to
509          * be and stay valid until the enclosing operation is complete.
510          */
511         if (cft->ss)
512                 return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
513         else
514                 return &cgrp->self;
515 }
516 EXPORT_SYMBOL_GPL(of_css);
517 
518 static int notify_on_release(const struct cgroup *cgrp)
519 {
520         return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
521 }
522 
523 /**
524  * for_each_css - iterate all css's of a cgroup
525  * @css: the iteration cursor
526  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
527  * @cgrp: the target cgroup to iterate css's of
528  *
529  * Should be called under cgroup_[tree_]mutex.
530  */
531 #define for_each_css(css, ssid, cgrp)                                   \
532         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
533                 if (!((css) = rcu_dereference_check(                    \
534                                 (cgrp)->subsys[(ssid)],                 \
535                                 lockdep_is_held(&cgroup_mutex)))) { }   \
536                 else
537 
538 /**
539  * for_each_e_css - iterate all effective css's of a cgroup
540  * @css: the iteration cursor
541  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
542  * @cgrp: the target cgroup to iterate css's of
543  *
544  * Should be called under cgroup_[tree_]mutex.
545  */
546 #define for_each_e_css(css, ssid, cgrp)                                 \
547         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
548                 if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
549                         ;                                               \
550                 else
551 
552 /**
553  * for_each_subsys - iterate all enabled cgroup subsystems
554  * @ss: the iteration cursor
555  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
556  */
557 #define for_each_subsys(ss, ssid)                                       \
558         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&                \
559              (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
560 
561 /**
562  * do_each_subsys_mask - filter for_each_subsys with a bitmask
563  * @ss: the iteration cursor
564  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
565  * @ss_mask: the bitmask
566  *
567  * The block will only run for cases where the ssid-th bit (1 << ssid) of
568  * @ss_mask is set.
569  */
570 #define do_each_subsys_mask(ss, ssid, ss_mask) do {                     \
571         unsigned long __ss_mask = (ss_mask);                            \
572         if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */ \
573                 (ssid) = 0;                                             \
574                 break;                                                  \
575         }                                                               \
576         for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {       \
577                 (ss) = cgroup_subsys[ssid];                             \
578                 {
579 
580 #define while_each_subsys_mask()                                        \
581                 }                                                       \
582         }                                                               \
583 } while (false)
584 
585 /* iterate across the hierarchies */
586 #define for_each_root(root)                                             \
587         list_for_each_entry((root), &cgroup_roots, root_list)
588 
589 /* iterate over child cgrps, lock should be held throughout iteration */
590 #define cgroup_for_each_live_child(child, cgrp)                         \
591         list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
592                 if (({ lockdep_assert_held(&cgroup_mutex);              \
593                        cgroup_is_dead(child); }))                       \
594                         ;                                               \
595                 else
596 
597 /* walk live descendants in preorder */
598 #define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)          \
599         css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))  \
600                 if (({ lockdep_assert_held(&cgroup_mutex);              \
601                        (dsct) = (d_css)->cgroup;                        \
602                        cgroup_is_dead(dsct); }))                        \
603                         ;                                               \
604                 else
605 
606 /* walk live descendants in postorder */
607 #define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)         \
608         css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
609                 if (({ lockdep_assert_held(&cgroup_mutex);              \
610                        (dsct) = (d_css)->cgroup;                        \
611                        cgroup_is_dead(dsct); }))                        \
612                         ;                                               \
613                 else
614 
615 static void cgroup_release_agent(struct work_struct *work);
616 static void check_for_release(struct cgroup *cgrp);
617 
618 /*
619  * A cgroup can be associated with multiple css_sets as different tasks may
620  * belong to different cgroups on different hierarchies.  In the other
621  * direction, a css_set is naturally associated with multiple cgroups.
622  * This M:N relationship is represented by the following link structure
623  * which exists for each association and allows traversing the associations
624  * from both sides.
625  */
626 struct cgrp_cset_link {
627         /* the cgroup and css_set this link associates */
628         struct cgroup           *cgrp;
629         struct css_set          *cset;
630 
631         /* list of cgrp_cset_links anchored at cgrp->cset_links */
632         struct list_head        cset_link;
633 
634         /* list of cgrp_cset_links anchored at css_set->cgrp_links */
635         struct list_head        cgrp_link;
636 };
637 
638 /*
639  * The default css_set - used by init and its children prior to any
640  * hierarchies being mounted. It contains a pointer to the root state
641  * for each subsystem. Also used to anchor the list of css_sets. Not
642  * reference-counted, to improve performance when child cgroups
643  * haven't been created.
644  */
645 struct css_set init_css_set = {
646         .refcount               = ATOMIC_INIT(1),
647         .cgrp_links             = LIST_HEAD_INIT(init_css_set.cgrp_links),
648         .tasks                  = LIST_HEAD_INIT(init_css_set.tasks),
649         .mg_tasks               = LIST_HEAD_INIT(init_css_set.mg_tasks),
650         .mg_preload_node        = LIST_HEAD_INIT(init_css_set.mg_preload_node),
651         .mg_node                = LIST_HEAD_INIT(init_css_set.mg_node),
652         .task_iters             = LIST_HEAD_INIT(init_css_set.task_iters),
653 };
654 
655 static int css_set_count        = 1;    /* 1 for init_css_set */
656 
657 /**
658  * css_set_populated - does a css_set contain any tasks?
659  * @cset: target css_set
660  */
661 static bool css_set_populated(struct css_set *cset)
662 {
663         lockdep_assert_held(&css_set_lock);
664 
665         return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
666 }
667 
668 /**
669  * cgroup_update_populated - updated populated count of a cgroup
670  * @cgrp: the target cgroup
671  * @populated: inc or dec populated count
672  *
673  * One of the css_sets associated with @cgrp is either getting its first
674  * task or losing the last.  Update @cgrp->populated_cnt accordingly.  The
675  * count is propagated towards root so that a given cgroup's populated_cnt
676  * is zero iff the cgroup and all its descendants don't contain any tasks.
677  *
678  * @cgrp's interface file "cgroup.populated" is zero if
679  * @cgrp->populated_cnt is zero and 1 otherwise.  When @cgrp->populated_cnt
680  * changes from or to zero, userland is notified that the content of the
681  * interface file has changed.  This can be used to detect when @cgrp and
682  * its descendants become populated or empty.
683  */
684 static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
685 {
686         lockdep_assert_held(&css_set_lock);
687 
688         do {
689                 bool trigger;
690 
691                 if (populated)
692                         trigger = !cgrp->populated_cnt++;
693                 else
694                         trigger = !--cgrp->populated_cnt;
695 
696                 if (!trigger)
697                         break;
698 
699                 check_for_release(cgrp);
700                 cgroup_file_notify(&cgrp->events_file);
701 
702                 cgrp = cgroup_parent(cgrp);
703         } while (cgrp);
704 }
705 
706 /**
707  * css_set_update_populated - update populated state of a css_set
708  * @cset: target css_set
709  * @populated: whether @cset is populated or depopulated
710  *
711  * @cset is either getting the first task or losing the last.  Update the
712  * ->populated_cnt of all associated cgroups accordingly.
713  */
714 static void css_set_update_populated(struct css_set *cset, bool populated)
715 {
716         struct cgrp_cset_link *link;
717 
718         lockdep_assert_held(&css_set_lock);
719 
720         list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
721                 cgroup_update_populated(link->cgrp, populated);
722 }
723 
724 /**
725  * css_set_move_task - move a task from one css_set to another
726  * @task: task being moved
727  * @from_cset: css_set @task currently belongs to (may be NULL)
728  * @to_cset: new css_set @task is being moved to (may be NULL)
729  * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
730  *
731  * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
732  * css_set, @from_cset can be NULL.  If @task is being disassociated
733  * instead of moved, @to_cset can be NULL.
734  *
735  * This function automatically handles populated_cnt updates and
736  * css_task_iter adjustments but the caller is responsible for managing
737  * @from_cset and @to_cset's reference counts.
738  */
739 static void css_set_move_task(struct task_struct *task,
740                               struct css_set *from_cset, struct css_set *to_cset,
741                               bool use_mg_tasks)
742 {
743         lockdep_assert_held(&css_set_lock);
744 
745         if (to_cset && !css_set_populated(to_cset))
746                 css_set_update_populated(to_cset, true);
747 
748         if (from_cset) {
749                 struct css_task_iter *it, *pos;
750 
751                 WARN_ON_ONCE(list_empty(&task->cg_list));
752 
753                 /*
754                  * @task is leaving, advance task iterators which are
755                  * pointing to it so that they can resume at the next
756                  * position.  Advancing an iterator might remove it from
757                  * the list, use safe walk.  See css_task_iter_advance*()
758                  * for details.
759                  */
760                 list_for_each_entry_safe(it, pos, &from_cset->task_iters,
761                                          iters_node)
762                         if (it->task_pos == &task->cg_list)
763                                 css_task_iter_advance(it);
764 
765                 list_del_init(&task->cg_list);
766                 if (!css_set_populated(from_cset))
767                         css_set_update_populated(from_cset, false);
768         } else {
769                 WARN_ON_ONCE(!list_empty(&task->cg_list));
770         }
771 
772         if (to_cset) {
773                 /*
774                  * We are synchronized through cgroup_threadgroup_rwsem
775                  * against PF_EXITING setting such that we can't race
776                  * against cgroup_exit() changing the css_set to
777                  * init_css_set and dropping the old one.
778                  */
779                 WARN_ON_ONCE(task->flags & PF_EXITING);
780 
781                 rcu_assign_pointer(task->cgroups, to_cset);
782                 list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
783                                                              &to_cset->tasks);
784         }
785 }
786 
787 /*
788  * hash table for cgroup groups. This improves the performance to find
789  * an existing css_set. This hash doesn't (currently) take into
790  * account cgroups in empty hierarchies.
791  */
792 #define CSS_SET_HASH_BITS       7
793 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
794 
795 static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
796 {
797         unsigned long key = 0UL;
798         struct cgroup_subsys *ss;
799         int i;
800 
801         for_each_subsys(ss, i)
802                 key += (unsigned long)css[i];
803         key = (key >> 16) ^ key;
804 
805         return key;
806 }
807 
808 static void put_css_set_locked(struct css_set *cset)
809 {
810         struct cgrp_cset_link *link, *tmp_link;
811         struct cgroup_subsys *ss;
812         int ssid;
813 
814         lockdep_assert_held(&css_set_lock);
815 
816         if (!atomic_dec_and_test(&cset->refcount))
817                 return;
818 
819         /* This css_set is dead. unlink it and release cgroup and css refs */
820         for_each_subsys(ss, ssid) {
821                 list_del(&cset->e_cset_node[ssid]);
822                 css_put(cset->subsys[ssid]);
823         }
824         hash_del(&cset->hlist);
825         css_set_count--;
826 
827         list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
828                 list_del(&link->cset_link);
829                 list_del(&link->cgrp_link);
830                 if (cgroup_parent(link->cgrp))
831                         cgroup_put(link->cgrp);
832                 kfree(link);
833         }
834 
835         kfree_rcu(cset, rcu_head);
836 }
837 
838 static void put_css_set(struct css_set *cset)
839 {
840         /*
841          * Ensure that the refcount doesn't hit zero while any readers
842          * can see it. Similar to atomic_dec_and_lock(), but for an
843          * rwlock
844          */
845         if (atomic_add_unless(&cset->refcount, -1, 1))
846                 return;
847 
848         spin_lock_bh(&css_set_lock);
849         put_css_set_locked(cset);
850         spin_unlock_bh(&css_set_lock);
851 }
852 
853 /*
854  * refcounted get/put for css_set objects
855  */
856 static inline void get_css_set(struct css_set *cset)
857 {
858         atomic_inc(&cset->refcount);
859 }
860 
861 /**
862  * compare_css_sets - helper function for find_existing_css_set().
863  * @cset: candidate css_set being tested
864  * @old_cset: existing css_set for a task
865  * @new_cgrp: cgroup that's being entered by the task
866  * @template: desired set of css pointers in css_set (pre-calculated)
867  *
868  * Returns true if "cset" matches "old_cset" except for the hierarchy
869  * which "new_cgrp" belongs to, for which it should match "new_cgrp".
870  */
871 static bool compare_css_sets(struct css_set *cset,
872                              struct css_set *old_cset,
873                              struct cgroup *new_cgrp,
874                              struct cgroup_subsys_state *template[])
875 {
876         struct list_head *l1, *l2;
877 
878         /*
879          * On the default hierarchy, there can be csets which are
880          * associated with the same set of cgroups but different csses.
881          * Let's first ensure that csses match.
882          */
883         if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
884                 return false;
885 
886         /*
887          * Compare cgroup pointers in order to distinguish between
888          * different cgroups in hierarchies.  As different cgroups may
889          * share the same effective css, this comparison is always
890          * necessary.
891          */
892         l1 = &cset->cgrp_links;
893         l2 = &old_cset->cgrp_links;
894         while (1) {
895                 struct cgrp_cset_link *link1, *link2;
896                 struct cgroup *cgrp1, *cgrp2;
897 
898                 l1 = l1->next;
899                 l2 = l2->next;
900                 /* See if we reached the end - both lists are equal length. */
901                 if (l1 == &cset->cgrp_links) {
902                         BUG_ON(l2 != &old_cset->cgrp_links);
903                         break;
904                 } else {
905                         BUG_ON(l2 == &old_cset->cgrp_links);
906                 }
907                 /* Locate the cgroups associated with these links. */
908                 link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
909                 link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
910                 cgrp1 = link1->cgrp;
911                 cgrp2 = link2->cgrp;
912                 /* Hierarchies should be linked in the same order. */
913                 BUG_ON(cgrp1->root != cgrp2->root);
914 
915                 /*
916                  * If this hierarchy is the hierarchy of the cgroup
917                  * that's changing, then we need to check that this
918                  * css_set points to the new cgroup; if it's any other
919                  * hierarchy, then this css_set should point to the
920                  * same cgroup as the old css_set.
921                  */
922                 if (cgrp1->root == new_cgrp->root) {
923                         if (cgrp1 != new_cgrp)
924                                 return false;
925                 } else {
926                         if (cgrp1 != cgrp2)
927                                 return false;
928                 }
929         }
930         return true;
931 }
932 
933 /**
934  * find_existing_css_set - init css array and find the matching css_set
935  * @old_cset: the css_set that we're using before the cgroup transition
936  * @cgrp: the cgroup that we're moving into
937  * @template: out param for the new set of csses, should be clear on entry
938  */
939 static struct css_set *find_existing_css_set(struct css_set *old_cset,
940                                         struct cgroup *cgrp,
941                                         struct cgroup_subsys_state *template[])
942 {
943         struct cgroup_root *root = cgrp->root;
944         struct cgroup_subsys *ss;
945         struct css_set *cset;
946         unsigned long key;
947         int i;
948 
949         /*
950          * Build the set of subsystem state objects that we want to see in the
951          * new css_set. while subsystems can change globally, the entries here
952          * won't change, so no need for locking.
953          */
954         for_each_subsys(ss, i) {
955                 if (root->subsys_mask & (1UL << i)) {
956                         /*
957                          * @ss is in this hierarchy, so we want the
958                          * effective css from @cgrp.
959                          */
960                         template[i] = cgroup_e_css(cgrp, ss);
961                 } else {
962                         /*
963                          * @ss is not in this hierarchy, so we don't want
964                          * to change the css.
965                          */
966                         template[i] = old_cset->subsys[i];
967                 }
968         }
969 
970         key = css_set_hash(template);
971         hash_for_each_possible(css_set_table, cset, hlist, key) {
972                 if (!compare_css_sets(cset, old_cset, cgrp, template))
973                         continue;
974 
975                 /* This css_set matches what we need */
976                 return cset;
977         }
978 
979         /* No existing cgroup group matched */
980         return NULL;
981 }
982 
983 static void free_cgrp_cset_links(struct list_head *links_to_free)
984 {
985         struct cgrp_cset_link *link, *tmp_link;
986 
987         list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
988                 list_del(&link->cset_link);
989                 kfree(link);
990         }
991 }
992 
993 /**
994  * allocate_cgrp_cset_links - allocate cgrp_cset_links
995  * @count: the number of links to allocate
996  * @tmp_links: list_head the allocated links are put on
997  *
998  * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
999  * through ->cset_link.  Returns 0 on success or -errno.
1000  */
1001 static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1002 {
1003         struct cgrp_cset_link *link;
1004         int i;
1005 
1006         INIT_LIST_HEAD(tmp_links);
1007 
1008         for (i = 0; i < count; i++) {
1009                 link = kzalloc(sizeof(*link), GFP_KERNEL);
1010                 if (!link) {
1011                         free_cgrp_cset_links(tmp_links);
1012                         return -ENOMEM;
1013                 }
1014                 list_add(&link->cset_link, tmp_links);
1015         }
1016         return 0;
1017 }
1018 
1019 /**
1020  * link_css_set - a helper function to link a css_set to a cgroup
1021  * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1022  * @cset: the css_set to be linked
1023  * @cgrp: the destination cgroup
1024  */
1025 static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1026                          struct cgroup *cgrp)
1027 {
1028         struct cgrp_cset_link *link;
1029 
1030         BUG_ON(list_empty(tmp_links));
1031 
1032         if (cgroup_on_dfl(cgrp))
1033                 cset->dfl_cgrp = cgrp;
1034 
1035         link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1036         link->cset = cset;
1037         link->cgrp = cgrp;
1038 
1039         /*
1040          * Always add links to the tail of the lists so that the lists are
1041          * in choronological order.
1042          */
1043         list_move_tail(&link->cset_link, &cgrp->cset_links);
1044         list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1045 
1046         if (cgroup_parent(cgrp))
1047                 cgroup_get(cgrp);
1048 }
1049 
1050 /**
1051  * find_css_set - return a new css_set with one cgroup updated
1052  * @old_cset: the baseline css_set
1053  * @cgrp: the cgroup to be updated
1054  *
1055  * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1056  * substituted into the appropriate hierarchy.
1057  */
1058 static struct css_set *find_css_set(struct css_set *old_cset,
1059                                     struct cgroup *cgrp)
1060 {
1061         struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1062         struct css_set *cset;
1063         struct list_head tmp_links;
1064         struct cgrp_cset_link *link;
1065         struct cgroup_subsys *ss;
1066         unsigned long key;
1067         int ssid;
1068 
1069         lockdep_assert_held(&cgroup_mutex);
1070 
1071         /* First see if we already have a cgroup group that matches
1072          * the desired set */
1073         spin_lock_bh(&css_set_lock);
1074         cset = find_existing_css_set(old_cset, cgrp, template);
1075         if (cset)
1076                 get_css_set(cset);
1077         spin_unlock_bh(&css_set_lock);
1078 
1079         if (cset)
1080                 return cset;
1081 
1082         cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1083         if (!cset)
1084                 return NULL;
1085 
1086         /* Allocate all the cgrp_cset_link objects that we'll need */
1087         if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1088                 kfree(cset);
1089                 return NULL;
1090         }
1091 
1092         atomic_set(&cset->refcount, 1);
1093         INIT_LIST_HEAD(&cset->cgrp_links);
1094         INIT_LIST_HEAD(&cset->tasks);
1095         INIT_LIST_HEAD(&cset->mg_tasks);
1096         INIT_LIST_HEAD(&cset->mg_preload_node);
1097         INIT_LIST_HEAD(&cset->mg_node);
1098         INIT_LIST_HEAD(&cset->task_iters);
1099         INIT_HLIST_NODE(&cset->hlist);
1100 
1101         /* Copy the set of subsystem state objects generated in
1102          * find_existing_css_set() */
1103         memcpy(cset->subsys, template, sizeof(cset->subsys));
1104 
1105         spin_lock_bh(&css_set_lock);
1106         /* Add reference counts and links from the new css_set. */
1107         list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1108                 struct cgroup *c = link->cgrp;
1109 
1110                 if (c->root == cgrp->root)
1111                         c = cgrp;
1112                 link_css_set(&tmp_links, cset, c);
1113         }
1114 
1115         BUG_ON(!list_empty(&tmp_links));
1116 
1117         css_set_count++;
1118 
1119         /* Add @cset to the hash table */
1120         key = css_set_hash(cset->subsys);
1121         hash_add(css_set_table, &cset->hlist, key);
1122 
1123         for_each_subsys(ss, ssid) {
1124                 struct cgroup_subsys_state *css = cset->subsys[ssid];
1125 
1126                 list_add_tail(&cset->e_cset_node[ssid],
1127                               &css->cgroup->e_csets[ssid]);
1128                 css_get(css);
1129         }
1130 
1131         spin_unlock_bh(&css_set_lock);
1132 
1133         return cset;
1134 }
1135 
1136 static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1137 {
1138         struct cgroup *root_cgrp = kf_root->kn->priv;
1139 
1140         return root_cgrp->root;
1141 }
1142 
1143 static int cgroup_init_root_id(struct cgroup_root *root)
1144 {
1145         int id;
1146 
1147         lockdep_assert_held(&cgroup_mutex);
1148 
1149         id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1150         if (id < 0)
1151                 return id;
1152 
1153         root->hierarchy_id = id;
1154         return 0;
1155 }
1156 
1157 static void cgroup_exit_root_id(struct cgroup_root *root)
1158 {
1159         lockdep_assert_held(&cgroup_mutex);
1160 
1161         if (root->hierarchy_id) {
1162                 idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1163                 root->hierarchy_id = 0;
1164         }
1165 }
1166 
1167 static void cgroup_free_root(struct cgroup_root *root)
1168 {
1169         if (root) {
1170                 /* hierarchy ID should already have been released */
1171                 WARN_ON_ONCE(root->hierarchy_id);
1172 
1173                 idr_destroy(&root->cgroup_idr);
1174                 kfree(root);
1175         }
1176 }
1177 
1178 static void cgroup_destroy_root(struct cgroup_root *root)
1179 {
1180         struct cgroup *cgrp = &root->cgrp;
1181         struct cgrp_cset_link *link, *tmp_link;
1182 
1183         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1184 
1185         BUG_ON(atomic_read(&root->nr_cgrps));
1186         BUG_ON(!list_empty(&cgrp->self.children));
1187 
1188         /* Rebind all subsystems back to the default hierarchy */
1189         WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1190 
1191         /*
1192          * Release all the links from cset_links to this hierarchy's
1193          * root cgroup
1194          */
1195         spin_lock_bh(&css_set_lock);
1196 
1197         list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1198                 list_del(&link->cset_link);
1199                 list_del(&link->cgrp_link);
1200                 kfree(link);
1201         }
1202 
1203         spin_unlock_bh(&css_set_lock);
1204 
1205         if (!list_empty(&root->root_list)) {
1206                 list_del(&root->root_list);
1207                 cgroup_root_count--;
1208         }
1209 
1210         cgroup_exit_root_id(root);
1211 
1212         mutex_unlock(&cgroup_mutex);
1213 
1214         kernfs_destroy_root(root->kf_root);
1215         cgroup_free_root(root);
1216 }
1217 
1218 /*
1219  * look up cgroup associated with current task's cgroup namespace on the
1220  * specified hierarchy
1221  */
1222 static struct cgroup *
1223 current_cgns_cgroup_from_root(struct cgroup_root *root)
1224 {
1225         struct cgroup *res = NULL;
1226         struct css_set *cset;
1227 
1228         lockdep_assert_held(&css_set_lock);
1229 
1230         rcu_read_lock();
1231 
1232         cset = current->nsproxy->cgroup_ns->root_cset;
1233         if (cset == &init_css_set) {
1234                 res = &root->cgrp;
1235         } else {
1236                 struct cgrp_cset_link *link;
1237 
1238                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1239                         struct cgroup *c = link->cgrp;
1240 
1241                         if (c->root == root) {
1242                                 res = c;
1243                                 break;
1244                         }
1245                 }
1246         }
1247         rcu_read_unlock();
1248 
1249         BUG_ON(!res);
1250         return res;
1251 }
1252 
1253 /* look up cgroup associated with given css_set on the specified hierarchy */
1254 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1255                                             struct cgroup_root *root)
1256 {
1257         struct cgroup *res = NULL;
1258 
1259         lockdep_assert_held(&cgroup_mutex);
1260         lockdep_assert_held(&css_set_lock);
1261 
1262         if (cset == &init_css_set) {
1263                 res = &root->cgrp;
1264         } else {
1265                 struct cgrp_cset_link *link;
1266 
1267                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1268                         struct cgroup *c = link->cgrp;
1269 
1270                         if (c->root == root) {
1271                                 res = c;
1272                                 break;
1273                         }
1274                 }
1275         }
1276 
1277         BUG_ON(!res);
1278         return res;
1279 }
1280 
1281 /*
1282  * Return the cgroup for "task" from the given hierarchy. Must be
1283  * called with cgroup_mutex and css_set_lock held.
1284  */
1285 static struct cgroup *task_cgroup_from_root(struct task_struct *task,
1286                                             struct cgroup_root *root)
1287 {
1288         /*
1289          * No need to lock the task - since we hold cgroup_mutex the
1290          * task can't change groups, so the only thing that can happen
1291          * is that it exits and its css is set back to init_css_set.
1292          */
1293         return cset_cgroup_from_root(task_css_set(task), root);
1294 }
1295 
1296 /*
1297  * A task must hold cgroup_mutex to modify cgroups.
1298  *
1299  * Any task can increment and decrement the count field without lock.
1300  * So in general, code holding cgroup_mutex can't rely on the count
1301  * field not changing.  However, if the count goes to zero, then only
1302  * cgroup_attach_task() can increment it again.  Because a count of zero
1303  * means that no tasks are currently attached, therefore there is no
1304  * way a task attached to that cgroup can fork (the other way to
1305  * increment the count).  So code holding cgroup_mutex can safely
1306  * assume that if the count is zero, it will stay zero. Similarly, if
1307  * a task holds cgroup_mutex on a cgroup with zero count, it
1308  * knows that the cgroup won't be removed, as cgroup_rmdir()
1309  * needs that mutex.
1310  *
1311  * A cgroup can only be deleted if both its 'count' of using tasks
1312  * is zero, and its list of 'children' cgroups is empty.  Since all
1313  * tasks in the system use _some_ cgroup, and since there is always at
1314  * least one task in the system (init, pid == 1), therefore, root cgroup
1315  * always has either children cgroups and/or using tasks.  So we don't
1316  * need a special hack to ensure that root cgroup cannot be deleted.
1317  *
1318  * P.S.  One more locking exception.  RCU is used to guard the
1319  * update of a tasks cgroup pointer by cgroup_attach_task()
1320  */
1321 
1322 static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1323 static const struct file_operations proc_cgroupstats_operations;
1324 
1325 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1326                               char *buf)
1327 {
1328         struct cgroup_subsys *ss = cft->ss;
1329 
1330         if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1331             !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
1332                 snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
1333                          cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1334                          cft->name);
1335         else
1336                 strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1337         return buf;
1338 }
1339 
1340 /**
1341  * cgroup_file_mode - deduce file mode of a control file
1342  * @cft: the control file in question
1343  *
1344  * S_IRUGO for read, S_IWUSR for write.
1345  */
1346 static umode_t cgroup_file_mode(const struct cftype *cft)
1347 {
1348         umode_t mode = 0;
1349 
1350         if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1351                 mode |= S_IRUGO;
1352 
1353         if (cft->write_u64 || cft->write_s64 || cft->write) {
1354                 if (cft->flags & CFTYPE_WORLD_WRITABLE)
1355                         mode |= S_IWUGO;
1356                 else
1357                         mode |= S_IWUSR;
1358         }
1359 
1360         return mode;
1361 }
1362 
1363 /**
1364  * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1365  * @subtree_control: the new subtree_control mask to consider
1366  * @this_ss_mask: available subsystems
1367  *
1368  * On the default hierarchy, a subsystem may request other subsystems to be
1369  * enabled together through its ->depends_on mask.  In such cases, more
1370  * subsystems than specified in "cgroup.subtree_control" may be enabled.
1371  *
1372  * This function calculates which subsystems need to be enabled if
1373  * @subtree_control is to be applied while restricted to @this_ss_mask.
1374  */
1375 static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1376 {
1377         u16 cur_ss_mask = subtree_control;
1378         struct cgroup_subsys *ss;
1379         int ssid;
1380 
1381         lockdep_assert_held(&cgroup_mutex);
1382 
1383         cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1384 
1385         while (true) {
1386                 u16 new_ss_mask = cur_ss_mask;
1387 
1388                 do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1389                         new_ss_mask |= ss->depends_on;
1390                 } while_each_subsys_mask();
1391 
1392                 /*
1393                  * Mask out subsystems which aren't available.  This can
1394                  * happen only if some depended-upon subsystems were bound
1395                  * to non-default hierarchies.
1396                  */
1397                 new_ss_mask &= this_ss_mask;
1398 
1399                 if (new_ss_mask == cur_ss_mask)
1400                         break;
1401                 cur_ss_mask = new_ss_mask;
1402         }
1403 
1404         return cur_ss_mask;
1405 }
1406 
1407 /**
1408  * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1409  * @kn: the kernfs_node being serviced
1410  *
1411  * This helper undoes cgroup_kn_lock_live() and should be invoked before
1412  * the method finishes if locking succeeded.  Note that once this function
1413  * returns the cgroup returned by cgroup_kn_lock_live() may become
1414  * inaccessible any time.  If the caller intends to continue to access the
1415  * cgroup, it should pin it before invoking this function.
1416  */
1417 static void cgroup_kn_unlock(struct kernfs_node *kn)
1418 {
1419         struct cgroup *cgrp;
1420 
1421         if (kernfs_type(kn) == KERNFS_DIR)
1422                 cgrp = kn->priv;
1423         else
1424                 cgrp = kn->parent->priv;
1425 
1426         mutex_unlock(&cgroup_mutex);
1427 
1428         kernfs_unbreak_active_protection(kn);
1429         cgroup_put(cgrp);
1430 }
1431 
1432 /**
1433  * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1434  * @kn: the kernfs_node being serviced
1435  * @drain_offline: perform offline draining on the cgroup
1436  *
1437  * This helper is to be used by a cgroup kernfs method currently servicing
1438  * @kn.  It breaks the active protection, performs cgroup locking and
1439  * verifies that the associated cgroup is alive.  Returns the cgroup if
1440  * alive; otherwise, %NULL.  A successful return should be undone by a
1441  * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1442  * cgroup is drained of offlining csses before return.
1443  *
1444  * Any cgroup kernfs method implementation which requires locking the
1445  * associated cgroup should use this helper.  It avoids nesting cgroup
1446  * locking under kernfs active protection and allows all kernfs operations
1447  * including self-removal.
1448  */
1449 static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn,
1450                                           bool drain_offline)
1451 {
1452         struct cgroup *cgrp;
1453 
1454         if (kernfs_type(kn) == KERNFS_DIR)
1455                 cgrp = kn->priv;
1456         else
1457                 cgrp = kn->parent->priv;
1458 
1459         /*
1460          * We're gonna grab cgroup_mutex which nests outside kernfs
1461          * active_ref.  cgroup liveliness check alone provides enough
1462          * protection against removal.  Ensure @cgrp stays accessible and
1463          * break the active_ref protection.
1464          */
1465         if (!cgroup_tryget(cgrp))
1466                 return NULL;
1467         kernfs_break_active_protection(kn);
1468 
1469         if (drain_offline)
1470                 cgroup_lock_and_drain_offline(cgrp);
1471         else
1472                 mutex_lock(&cgroup_mutex);
1473 
1474         if (!cgroup_is_dead(cgrp))
1475                 return cgrp;
1476 
1477         cgroup_kn_unlock(kn);
1478         return NULL;
1479 }
1480 
1481 static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1482 {
1483         char name[CGROUP_FILE_NAME_MAX];
1484 
1485         lockdep_assert_held(&cgroup_mutex);
1486 
1487         if (cft->file_offset) {
1488                 struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1489                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
1490 
1491                 spin_lock_irq(&cgroup_file_kn_lock);
1492                 cfile->kn = NULL;
1493                 spin_unlock_irq(&cgroup_file_kn_lock);
1494         }
1495 
1496         kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1497 }
1498 
1499 /**
1500  * css_clear_dir - remove subsys files in a cgroup directory
1501  * @css: taget css
1502  */
1503 static void css_clear_dir(struct cgroup_subsys_state *css)
1504 {
1505         struct cgroup *cgrp = css->cgroup;
1506         struct cftype *cfts;
1507 
1508         if (!(css->flags & CSS_VISIBLE))
1509                 return;
1510 
1511         css->flags &= ~CSS_VISIBLE;
1512 
1513         list_for_each_entry(cfts, &css->ss->cfts, node)
1514                 cgroup_addrm_files(css, cgrp, cfts, false);
1515 }
1516 
1517 /**
1518  * css_populate_dir - create subsys files in a cgroup directory
1519  * @css: target css
1520  *
1521  * On failure, no file is added.
1522  */
1523 static int css_populate_dir(struct cgroup_subsys_state *css)
1524 {
1525         struct cgroup *cgrp = css->cgroup;
1526         struct cftype *cfts, *failed_cfts;
1527         int ret;
1528 
1529         if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1530                 return 0;
1531 
1532         if (!css->ss) {
1533                 if (cgroup_on_dfl(cgrp))
1534                         cfts = cgroup_dfl_base_files;
1535                 else
1536                         cfts = cgroup_legacy_base_files;
1537 
1538                 return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1539         }
1540 
1541         list_for_each_entry(cfts, &css->ss->cfts, node) {
1542                 ret = cgroup_addrm_files(css, cgrp, cfts, true);
1543                 if (ret < 0) {
1544                         failed_cfts = cfts;
1545                         goto err;
1546                 }
1547         }
1548 
1549         css->flags |= CSS_VISIBLE;
1550 
1551         return 0;
1552 err:
1553         list_for_each_entry(cfts, &css->ss->cfts, node) {
1554                 if (cfts == failed_cfts)
1555                         break;
1556                 cgroup_addrm_files(css, cgrp, cfts, false);
1557         }
1558         return ret;
1559 }
1560 
1561 static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1562 {
1563         struct cgroup *dcgrp = &dst_root->cgrp;
1564         struct cgroup_subsys *ss;
1565         int ssid, i, ret;
1566 
1567         lockdep_assert_held(&cgroup_mutex);
1568 
1569         do_each_subsys_mask(ss, ssid, ss_mask) {
1570                 /*
1571                  * If @ss has non-root csses attached to it, can't move.
1572                  * If @ss is an implicit controller, it is exempt from this
1573                  * rule and can be stolen.
1574                  */
1575                 if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1576                     !ss->implicit_on_dfl)
1577                         return -EBUSY;
1578 
1579                 /* can't move between two non-dummy roots either */
1580                 if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1581                         return -EBUSY;
1582         } while_each_subsys_mask();
1583 
1584         do_each_subsys_mask(ss, ssid, ss_mask) {
1585                 struct cgroup_root *src_root = ss->root;
1586                 struct cgroup *scgrp = &src_root->cgrp;
1587                 struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1588                 struct css_set *cset;
1589 
1590                 WARN_ON(!css || cgroup_css(dcgrp, ss));
1591 
1592                 /* disable from the source */
1593                 src_root->subsys_mask &= ~(1 << ssid);
1594                 WARN_ON(cgroup_apply_control(scgrp));
1595                 cgroup_finalize_control(scgrp, 0);
1596 
1597                 /* rebind */
1598                 RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1599                 rcu_assign_pointer(dcgrp->subsys[ssid], css);
1600                 ss->root = dst_root;
1601                 css->cgroup = dcgrp;
1602 
1603                 spin_lock_bh(&css_set_lock);
1604                 hash_for_each(css_set_table, i, cset, hlist)
1605                         list_move_tail(&cset->e_cset_node[ss->id],
1606                                        &dcgrp->e_csets[ss->id]);
1607                 spin_unlock_bh(&css_set_lock);
1608 
1609                 /* default hierarchy doesn't enable controllers by default */
1610                 dst_root->subsys_mask |= 1 << ssid;
1611                 if (dst_root == &cgrp_dfl_root) {
1612                         static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1613                 } else {
1614                         dcgrp->subtree_control |= 1 << ssid;
1615                         static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1616                 }
1617 
1618                 ret = cgroup_apply_control(dcgrp);
1619                 if (ret)
1620                         pr_warn("partial failure to rebind %s controller (err=%d)\n",
1621                                 ss->name, ret);
1622 
1623                 if (ss->bind)
1624                         ss->bind(css);
1625         } while_each_subsys_mask();
1626 
1627         kernfs_activate(dcgrp->kn);
1628         return 0;
1629 }
1630 
1631 static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1632                             struct kernfs_root *kf_root)
1633 {
1634         int len = 0;
1635         char *buf = NULL;
1636         struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1637         struct cgroup *ns_cgroup;
1638 
1639         buf = kmalloc(PATH_MAX, GFP_KERNEL);
1640         if (!buf)
1641                 return -ENOMEM;
1642 
1643         spin_lock_bh(&css_set_lock);
1644         ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1645         len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1646         spin_unlock_bh(&css_set_lock);
1647 
1648         if (len >= PATH_MAX)
1649                 len = -ERANGE;
1650         else if (len > 0) {
1651                 seq_escape(sf, buf, " \t\n\\");
1652                 len = 0;
1653         }
1654         kfree(buf);
1655         return len;
1656 }
1657 
1658 static int cgroup_show_options(struct seq_file *seq,
1659                                struct kernfs_root *kf_root)
1660 {
1661         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1662         struct cgroup_subsys *ss;
1663         int ssid;
1664 
1665         if (root != &cgrp_dfl_root)
1666                 for_each_subsys(ss, ssid)
1667                         if (root->subsys_mask & (1 << ssid))
1668                                 seq_show_option(seq, ss->legacy_name, NULL);
1669         if (root->flags & CGRP_ROOT_NOPREFIX)
1670                 seq_puts(seq, ",noprefix");
1671         if (root->flags & CGRP_ROOT_XATTR)
1672                 seq_puts(seq, ",xattr");
1673 
1674         spin_lock(&release_agent_path_lock);
1675         if (strlen(root->release_agent_path))
1676                 seq_show_option(seq, "release_agent",
1677                                 root->release_agent_path);
1678         spin_unlock(&release_agent_path_lock);
1679 
1680         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1681                 seq_puts(seq, ",clone_children");
1682         if (strlen(root->name))
1683                 seq_show_option(seq, "name", root->name);
1684         return 0;
1685 }
1686 
1687 struct cgroup_sb_opts {
1688         u16 subsys_mask;
1689         unsigned int flags;
1690         char *release_agent;
1691         bool cpuset_clone_children;
1692         char *name;
1693         /* User explicitly requested empty subsystem */
1694         bool none;
1695 };
1696 
1697 static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1698 {
1699         char *token, *o = data;
1700         bool all_ss = false, one_ss = false;
1701         u16 mask = U16_MAX;
1702         struct cgroup_subsys *ss;
1703         int nr_opts = 0;
1704         int i;
1705 
1706 #ifdef CONFIG_CPUSETS
1707         mask = ~((u16)1 << cpuset_cgrp_id);
1708 #endif
1709 
1710         memset(opts, 0, sizeof(*opts));
1711 
1712         while ((token = strsep(&o, ",")) != NULL) {
1713                 nr_opts++;
1714 
1715                 if (!*token)
1716                         return -EINVAL;
1717                 if (!strcmp(token, "none")) {
1718                         /* Explicitly have no subsystems */
1719                         opts->none = true;
1720                         continue;
1721                 }
1722                 if (!strcmp(token, "all")) {
1723                         /* Mutually exclusive option 'all' + subsystem name */
1724                         if (one_ss)
1725                                 return -EINVAL;
1726                         all_ss = true;
1727                         continue;
1728                 }
1729                 if (!strcmp(token, "noprefix")) {
1730                         opts->flags |= CGRP_ROOT_NOPREFIX;
1731                         continue;
1732                 }
1733                 if (!strcmp(token, "clone_children")) {
1734                         opts->cpuset_clone_children = true;
1735                         continue;
1736                 }
1737                 if (!strcmp(token, "xattr")) {
1738                         opts->flags |= CGRP_ROOT_XATTR;
1739                         continue;
1740                 }
1741                 if (!strncmp(token, "release_agent=", 14)) {
1742                         /* Specifying two release agents is forbidden */
1743                         if (opts->release_agent)
1744                                 return -EINVAL;
1745                         opts->release_agent =
1746                                 kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1747                         if (!opts->release_agent)
1748                                 return -ENOMEM;
1749                         continue;
1750                 }
1751                 if (!strncmp(token, "name=", 5)) {
1752                         const char *name = token + 5;
1753                         /* Can't specify an empty name */
1754                         if (!strlen(name))
1755                                 return -EINVAL;
1756                         /* Must match [\w.-]+ */
1757                         for (i = 0; i < strlen(name); i++) {
1758                                 char c = name[i];
1759                                 if (isalnum(c))
1760                                         continue;
1761                                 if ((c == '.') || (c == '-') || (c == '_'))
1762                                         continue;
1763                                 return -EINVAL;
1764                         }
1765                         /* Specifying two names is forbidden */
1766                         if (opts->name)
1767                                 return -EINVAL;
1768                         opts->name = kstrndup(name,
1769                                               MAX_CGROUP_ROOT_NAMELEN - 1,
1770                                               GFP_KERNEL);
1771                         if (!opts->name)
1772                                 return -ENOMEM;
1773 
1774                         continue;
1775                 }
1776 
1777                 for_each_subsys(ss, i) {
1778                         if (strcmp(token, ss->legacy_name))
1779                                 continue;
1780                         if (!cgroup_ssid_enabled(i))
1781                                 continue;
1782                         if (cgroup_ssid_no_v1(i))
1783                                 continue;
1784 
1785                         /* Mutually exclusive option 'all' + subsystem name */
1786                         if (all_ss)
1787                                 return -EINVAL;
1788                         opts->subsys_mask |= (1 << i);
1789                         one_ss = true;
1790 
1791                         break;
1792                 }
1793                 if (i == CGROUP_SUBSYS_COUNT)
1794                         return -ENOENT;
1795         }
1796 
1797         /*
1798          * If the 'all' option was specified select all the subsystems,
1799          * otherwise if 'none', 'name=' and a subsystem name options were
1800          * not specified, let's default to 'all'
1801          */
1802         if (all_ss || (!one_ss && !opts->none && !opts->name))
1803                 for_each_subsys(ss, i)
1804                         if (cgroup_ssid_enabled(i) && !cgroup_ssid_no_v1(i))
1805                                 opts->subsys_mask |= (1 << i);
1806 
1807         /*
1808          * We either have to specify by name or by subsystems. (So all
1809          * empty hierarchies must have a name).
1810          */
1811         if (!opts->subsys_mask && !opts->name)
1812                 return -EINVAL;
1813 
1814         /*
1815          * Option noprefix was introduced just for backward compatibility
1816          * with the old cpuset, so we allow noprefix only if mounting just
1817          * the cpuset subsystem.
1818          */
1819         if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1820                 return -EINVAL;
1821 
1822         /* Can't specify "none" and some subsystems */
1823         if (opts->subsys_mask && opts->none)
1824                 return -EINVAL;
1825 
1826         return 0;
1827 }
1828 
1829 static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1830 {
1831         int ret = 0;
1832         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1833         struct cgroup_sb_opts opts;
1834         u16 added_mask, removed_mask;
1835 
1836         if (root == &cgrp_dfl_root) {
1837                 pr_err("remount is not allowed\n");
1838                 return -EINVAL;
1839         }
1840 
1841         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1842 
1843         /* See what subsystems are wanted */
1844         ret = parse_cgroupfs_options(data, &opts);
1845         if (ret)
1846                 goto out_unlock;
1847 
1848         if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
1849                 pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
1850                         task_tgid_nr(current), current->comm);
1851 
1852         added_mask = opts.subsys_mask & ~root->subsys_mask;
1853         removed_mask = root->subsys_mask & ~opts.subsys_mask;
1854 
1855         /* Don't allow flags or name to change at remount */
1856         if ((opts.flags ^ root->flags) ||
1857             (opts.name && strcmp(opts.name, root->name))) {
1858                 pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
1859                        opts.flags, opts.name ?: "", root->flags, root->name);
1860                 ret = -EINVAL;
1861                 goto out_unlock;
1862         }
1863 
1864         /* remounting is not allowed for populated hierarchies */
1865         if (!list_empty(&root->cgrp.self.children)) {
1866                 ret = -EBUSY;
1867                 goto out_unlock;
1868         }
1869 
1870         ret = rebind_subsystems(root, added_mask);
1871         if (ret)
1872                 goto out_unlock;
1873 
1874         WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
1875 
1876         if (opts.release_agent) {
1877                 spin_lock(&release_agent_path_lock);
1878                 strcpy(root->release_agent_path, opts.release_agent);
1879                 spin_unlock(&release_agent_path_lock);
1880         }
1881  out_unlock:
1882         kfree(opts.release_agent);
1883         kfree(opts.name);
1884         mutex_unlock(&cgroup_mutex);
1885         return ret;
1886 }
1887 
1888 /*
1889  * To reduce the fork() overhead for systems that are not actually using
1890  * their cgroups capability, we don't maintain the lists running through
1891  * each css_set to its tasks until we see the list actually used - in other
1892  * words after the first mount.
1893  */
1894 static bool use_task_css_set_links __read_mostly;
1895 
1896 static void cgroup_enable_task_cg_lists(void)
1897 {
1898         struct task_struct *p, *g;
1899 
1900         spin_lock_bh(&css_set_lock);
1901 
1902         if (use_task_css_set_links)
1903                 goto out_unlock;
1904 
1905         use_task_css_set_links = true;
1906 
1907         /*
1908          * We need tasklist_lock because RCU is not safe against
1909          * while_each_thread(). Besides, a forking task that has passed
1910          * cgroup_post_fork() without seeing use_task_css_set_links = 1
1911          * is not guaranteed to have its child immediately visible in the
1912          * tasklist if we walk through it with RCU.
1913          */
1914         read_lock(&tasklist_lock);
1915         do_each_thread(g, p) {
1916                 WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1917                              task_css_set(p) != &init_css_set);
1918 
1919                 /*
1920                  * We should check if the process is exiting, otherwise
1921                  * it will race with cgroup_exit() in that the list
1922                  * entry won't be deleted though the process has exited.
1923                  * Do it while holding siglock so that we don't end up
1924                  * racing against cgroup_exit().
1925                  */
1926                 spin_lock_irq(&p->sighand->siglock);
1927                 if (!(p->flags & PF_EXITING)) {
1928                         struct css_set *cset = task_css_set(p);
1929 
1930                         if (!css_set_populated(cset))
1931                                 css_set_update_populated(cset, true);
1932                         list_add_tail(&p->cg_list, &cset->tasks);
1933                         get_css_set(cset);
1934                 }
1935                 spin_unlock_irq(&p->sighand->siglock);
1936         } while_each_thread(g, p);
1937         read_unlock(&tasklist_lock);
1938 out_unlock:
1939         spin_unlock_bh(&css_set_lock);
1940 }
1941 
1942 static void init_cgroup_housekeeping(struct cgroup *cgrp)
1943 {
1944         struct cgroup_subsys *ss;
1945         int ssid;
1946 
1947         INIT_LIST_HEAD(&cgrp->self.sibling);
1948         INIT_LIST_HEAD(&cgrp->self.children);
1949         INIT_LIST_HEAD(&cgrp->cset_links);
1950         INIT_LIST_HEAD(&cgrp->pidlists);
1951         mutex_init(&cgrp->pidlist_mutex);
1952         cgrp->self.cgroup = cgrp;
1953         cgrp->self.flags |= CSS_ONLINE;
1954 
1955         for_each_subsys(ss, ssid)
1956                 INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1957 
1958         init_waitqueue_head(&cgrp->offline_waitq);
1959         INIT_WORK(&cgrp->release_agent_work, cgroup_release_agent);
1960 }
1961 
1962 static void init_cgroup_root(struct cgroup_root *root,
1963                              struct cgroup_sb_opts *opts)
1964 {
1965         struct cgroup *cgrp = &root->cgrp;
1966 
1967         INIT_LIST_HEAD(&root->root_list);
1968         atomic_set(&root->nr_cgrps, 1);
1969         cgrp->root = root;
1970         init_cgroup_housekeeping(cgrp);
1971         idr_init(&root->cgroup_idr);
1972 
1973         root->flags = opts->flags;
1974         if (opts->release_agent)
1975                 strcpy(root->release_agent_path, opts->release_agent);
1976         if (opts->name)
1977                 strcpy(root->name, opts->name);
1978         if (opts->cpuset_clone_children)
1979                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1980 }
1981 
1982 static int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
1983 {
1984         LIST_HEAD(tmp_links);
1985         struct cgroup *root_cgrp = &root->cgrp;
1986         struct css_set *cset;
1987         int i, ret;
1988 
1989         lockdep_assert_held(&cgroup_mutex);
1990 
1991         ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
1992         if (ret < 0)
1993                 goto out;
1994         root_cgrp->id = ret;
1995         root_cgrp->ancestor_ids[0] = ret;
1996 
1997         ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
1998                               GFP_KERNEL);
1999         if (ret)
2000                 goto out;
2001 
2002         /*
2003          * We're accessing css_set_count without locking css_set_lock here,
2004          * but that's OK - it can only be increased by someone holding
2005          * cgroup_lock, and that's us.  Later rebinding may disable
2006          * controllers on the default hierarchy and thus create new csets,
2007          * which can't be more than the existing ones.  Allocate 2x.
2008          */
2009         ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
2010         if (ret)
2011                 goto cancel_ref;
2012 
2013         ret = cgroup_init_root_id(root);
2014         if (ret)
2015                 goto cancel_ref;
2016 
2017         root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
2018                                            KERNFS_ROOT_CREATE_DEACTIVATED,
2019                                            root_cgrp);
2020         if (IS_ERR(root->kf_root)) {
2021                 ret = PTR_ERR(root->kf_root);
2022                 goto exit_root_id;
2023         }
2024         root_cgrp->kn = root->kf_root->kn;
2025 
2026         ret = css_populate_dir(&root_cgrp->self);
2027         if (ret)
2028                 goto destroy_root;
2029 
2030         ret = rebind_subsystems(root, ss_mask);
2031         if (ret)
2032                 goto destroy_root;
2033 
2034         /*
2035          * There must be no failure case after here, since rebinding takes
2036          * care of subsystems' refcounts, which are explicitly dropped in
2037          * the failure exit path.
2038          */
2039         list_add(&root->root_list, &cgroup_roots);
2040         cgroup_root_count++;
2041 
2042         /*
2043          * Link the root cgroup in this hierarchy into all the css_set
2044          * objects.
2045          */
2046         spin_lock_bh(&css_set_lock);
2047         hash_for_each(css_set_table, i, cset, hlist) {
2048                 link_css_set(&tmp_links, cset, root_cgrp);
2049                 if (css_set_populated(cset))
2050                         cgroup_update_populated(root_cgrp, true);
2051         }
2052         spin_unlock_bh(&css_set_lock);
2053 
2054         BUG_ON(!list_empty(&root_cgrp->self.children));
2055         BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2056 
2057         kernfs_activate(root_cgrp->kn);
2058         ret = 0;
2059         goto out;
2060 
2061 destroy_root:
2062         kernfs_destroy_root(root->kf_root);
2063         root->kf_root = NULL;
2064 exit_root_id:
2065         cgroup_exit_root_id(root);
2066 cancel_ref:
2067         percpu_ref_exit(&root_cgrp->self.refcnt);
2068 out:
2069         free_cgrp_cset_links(&tmp_links);
2070         return ret;
2071 }
2072 
2073 static struct dentry *cgroup_mount(struct file_system_type *fs_type,
2074                          int flags, const char *unused_dev_name,
2075                          void *data)
2076 {
2077         bool is_v2 = fs_type == &cgroup2_fs_type;
2078         struct super_block *pinned_sb = NULL;
2079         struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
2080         struct cgroup_subsys *ss;
2081         struct cgroup_root *root;
2082         struct cgroup_sb_opts opts;
2083         struct dentry *dentry;
2084         int ret;
2085         int i;
2086         bool new_sb;
2087 
2088         get_cgroup_ns(ns);
2089 
2090         /* Check if the caller has permission to mount. */
2091         if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
2092                 put_cgroup_ns(ns);
2093                 return ERR_PTR(-EPERM);
2094         }
2095 
2096         /*
2097          * The first time anyone tries to mount a cgroup, enable the list
2098          * linking each css_set to its tasks and fix up all existing tasks.
2099          */
2100         if (!use_task_css_set_links)
2101                 cgroup_enable_task_cg_lists();
2102 
2103         if (is_v2) {
2104                 if (data) {
2105                         pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
2106                         put_cgroup_ns(ns);
2107                         return ERR_PTR(-EINVAL);
2108                 }
2109                 cgrp_dfl_visible = true;
2110                 root = &cgrp_dfl_root;
2111                 cgroup_get(&root->cgrp);
2112                 goto out_mount;
2113         }
2114 
2115         cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
2116 
2117         /* First find the desired set of subsystems */
2118         ret = parse_cgroupfs_options(data, &opts);
2119         if (ret)
2120                 goto out_unlock;
2121 
2122         /*
2123          * Destruction of cgroup root is asynchronous, so subsystems may
2124          * still be dying after the previous unmount.  Let's drain the
2125          * dying subsystems.  We just need to ensure that the ones
2126          * unmounted previously finish dying and don't care about new ones
2127          * starting.  Testing ref liveliness is good enough.
2128          */
2129         for_each_subsys(ss, i) {
2130                 if (!(opts.subsys_mask & (1 << i)) ||
2131                     ss->root == &cgrp_dfl_root)
2132                         continue;
2133 
2134                 if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
2135                         mutex_unlock(&cgroup_mutex);
2136                         msleep(10);
2137                         ret = restart_syscall();
2138                         goto out_free;
2139                 }
2140                 cgroup_put(&ss->root->cgrp);
2141         }
2142 
2143         for_each_root(root) {
2144                 bool name_match = false;
2145 
2146                 if (root == &cgrp_dfl_root)
2147                         continue;
2148 
2149                 /*
2150                  * If we asked for a name then it must match.  Also, if
2151                  * name matches but sybsys_mask doesn't, we should fail.
2152                  * Remember whether name matched.
2153                  */
2154                 if (opts.name) {
2155                         if (strcmp(opts.name, root->name))
2156                                 continue;
2157                         name_match = true;
2158                 }
2159 
2160                 /*
2161                  * If we asked for subsystems (or explicitly for no
2162                  * subsystems) then they must match.
2163                  */
2164                 if ((opts.subsys_mask || opts.none) &&
2165                     (opts.subsys_mask != root->subsys_mask)) {
2166                         if (!name_match)
2167                                 continue;
2168                         ret = -EBUSY;
2169                         goto out_unlock;
2170                 }
2171 
2172                 if (root->flags ^ opts.flags)
2173                         pr_warn("new mount options do not match the existing superblock, will be ignored\n");
2174 
2175                 /*
2176                  * We want to reuse @root whose lifetime is governed by its
2177                  * ->cgrp.  Let's check whether @root is alive and keep it
2178                  * that way.  As cgroup_kill_sb() can happen anytime, we
2179                  * want to block it by pinning the sb so that @root doesn't
2180                  * get killed before mount is complete.
2181                  *
2182                  * With the sb pinned, tryget_live can reliably indicate
2183                  * whether @root can be reused.  If it's being killed,
2184                  * drain it.  We can use wait_queue for the wait but this
2185                  * path is super cold.  Let's just sleep a bit and retry.
2186                  */
2187                 pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
2188                 if (IS_ERR(pinned_sb) ||
2189                     !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
2190                         mutex_unlock(&cgroup_mutex);
2191                         if (!IS_ERR_OR_NULL(pinned_sb))
2192                                 deactivate_super(pinned_sb);
2193                         msleep(10);
2194                         ret = restart_syscall();
2195                         goto out_free;
2196                 }
2197 
2198                 ret = 0;
2199                 goto out_unlock;
2200         }
2201 
2202         /*
2203          * No such thing, create a new one.  name= matching without subsys
2204          * specification is allowed for already existing hierarchies but we
2205          * can't create new one without subsys specification.
2206          */
2207         if (!opts.subsys_mask && !opts.none) {
2208                 ret = -EINVAL;
2209                 goto out_unlock;
2210         }
2211 
2212         /*
2213          * We know this subsystem has not yet been bound.  Users in a non-init
2214          * user namespace may only mount hierarchies with no bound subsystems,
2215          * i.e. 'none,name=user1'
2216          */
2217         if (!opts.none && !capable(CAP_SYS_ADMIN)) {
2218                 ret = -EPERM;
2219                 goto out_unlock;
2220         }
2221 
2222         root = kzalloc(sizeof(*root), GFP_KERNEL);
2223         if (!root) {
2224                 ret = -ENOMEM;
2225                 goto out_unlock;
2226         }
2227 
2228         init_cgroup_root(root, &opts);
2229 
2230         ret = cgroup_setup_root(root, opts.subsys_mask);
2231         if (ret)
2232                 cgroup_free_root(root);
2233 
2234 out_unlock:
2235         mutex_unlock(&cgroup_mutex);
2236 out_free:
2237         kfree(opts.release_agent);
2238         kfree(opts.name);
2239 
2240         if (ret) {
2241                 put_cgroup_ns(ns);
2242                 return ERR_PTR(ret);
2243         }
2244 out_mount:
2245         dentry = kernfs_mount(fs_type, flags, root->kf_root,
2246                               is_v2 ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC,
2247                               &new_sb);
2248 
2249         /*
2250          * In non-init cgroup namespace, instead of root cgroup's
2251          * dentry, we return the dentry corresponding to the
2252          * cgroupns->root_cgrp.
2253          */
2254         if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
2255                 struct dentry *nsdentry;
2256                 struct cgroup *cgrp;
2257 
2258                 mutex_lock(&cgroup_mutex);
2259                 spin_lock_bh(&css_set_lock);
2260 
2261                 cgrp = cset_cgroup_from_root(ns->root_cset, root);
2262 
2263                 spin_unlock_bh(&css_set_lock);
2264                 mutex_unlock(&cgroup_mutex);
2265 
2266                 nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
2267                 dput(dentry);
2268                 dentry = nsdentry;
2269         }
2270 
2271         if (IS_ERR(dentry) || !new_sb)
2272                 cgroup_put(&root->cgrp);
2273 
2274         /*
2275          * If @pinned_sb, we're reusing an existing root and holding an
2276          * extra ref on its sb.  Mount is complete.  Put the extra ref.
2277          */
2278         if (pinned_sb) {
2279                 WARN_ON(new_sb);
2280                 deactivate_super(pinned_sb);
2281         }
2282 
2283         put_cgroup_ns(ns);
2284         return dentry;
2285 }
2286 
2287 static void cgroup_kill_sb(struct super_block *sb)
2288 {
2289         struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2290         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2291 
2292         /*
2293          * If @root doesn't have any mounts or children, start killing it.
2294          * This prevents new mounts by disabling percpu_ref_tryget_live().
2295          * cgroup_mount() may wait for @root's release.
2296          *
2297          * And don't kill the default root.
2298          */
2299         if (!list_empty(&root->cgrp.self.children) ||
2300             root == &cgrp_dfl_root)
2301                 cgroup_put(&root->cgrp);
2302         else
2303                 percpu_ref_kill(&root->cgrp.self.refcnt);
2304 
2305         kernfs_kill_sb(sb);
2306 }
2307 
2308 static struct file_system_type cgroup_fs_type = {
2309         .name = "cgroup",
2310         .mount = cgroup_mount,
2311         .kill_sb = cgroup_kill_sb,
2312         .fs_flags = FS_USERNS_MOUNT,
2313 };
2314 
2315 static struct file_system_type cgroup2_fs_type = {
2316         .name = "cgroup2",
2317         .mount = cgroup_mount,
2318         .kill_sb = cgroup_kill_sb,
2319         .fs_flags = FS_USERNS_MOUNT,
2320 };
2321 
2322 static char *cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2323                                    struct cgroup_namespace *ns)
2324 {
2325         struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2326         int ret;
2327 
2328         ret = kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2329         if (ret < 0 || ret >= buflen)
2330                 return NULL;
2331         return buf;
2332 }
2333 
2334 char *cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2335                      struct cgroup_namespace *ns)
2336 {
2337         char *ret;
2338 
2339         mutex_lock(&cgroup_mutex);
2340         spin_lock_bh(&css_set_lock);
2341 
2342         ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2343 
2344         spin_unlock_bh(&css_set_lock);
2345         mutex_unlock(&cgroup_mutex);
2346 
2347         return ret;
2348 }
2349 EXPORT_SYMBOL_GPL(cgroup_path_ns);
2350 
2351 /**
2352  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2353  * @task: target task
2354  * @buf: the buffer to write the path into
2355  * @buflen: the length of the buffer
2356  *
2357  * Determine @task's cgroup on the first (the one with the lowest non-zero
2358  * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2359  * function grabs cgroup_mutex and shouldn't be used inside locks used by
2360  * cgroup controller callbacks.
2361  *
2362  * Return value is the same as kernfs_path().
2363  */
2364 char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2365 {
2366         struct cgroup_root *root;
2367         struct cgroup *cgrp;
2368         int hierarchy_id = 1;
2369         char *path = NULL;
2370 
2371         mutex_lock(&cgroup_mutex);
2372         spin_lock_bh(&css_set_lock);
2373 
2374         root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2375 
2376         if (root) {
2377                 cgrp = task_cgroup_from_root(task, root);
2378                 path = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2379         } else {
2380                 /* if no hierarchy exists, everyone is in "/" */
2381                 if (strlcpy(buf, "/", buflen) < buflen)
2382                         path = buf;
2383         }
2384 
2385         spin_unlock_bh(&css_set_lock);
2386         mutex_unlock(&cgroup_mutex);
2387         return path;
2388 }
2389 EXPORT_SYMBOL_GPL(task_cgroup_path);
2390 
2391 /* used to track tasks and other necessary states during migration */
2392 struct cgroup_taskset {
2393         /* the src and dst cset list running through cset->mg_node */
2394         struct list_head        src_csets;
2395         struct list_head        dst_csets;
2396 
2397         /* the subsys currently being processed */
2398         int                     ssid;
2399 
2400         /*
2401          * Fields for cgroup_taskset_*() iteration.
2402          *
2403          * Before migration is committed, the target migration tasks are on
2404          * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
2405          * the csets on ->dst_csets.  ->csets point to either ->src_csets
2406          * or ->dst_csets depending on whether migration is committed.
2407          *
2408          * ->cur_csets and ->cur_task point to the current task position
2409          * during iteration.
2410          */
2411         struct list_head        *csets;
2412         struct css_set          *cur_cset;
2413         struct task_struct      *cur_task;
2414 };
2415 
2416 #define CGROUP_TASKSET_INIT(tset)       (struct cgroup_taskset){        \
2417         .src_csets              = LIST_HEAD_INIT(tset.src_csets),       \
2418         .dst_csets              = LIST_HEAD_INIT(tset.dst_csets),       \
2419         .csets                  = &tset.src_csets,                      \
2420 }
2421 
2422 /**
2423  * cgroup_taskset_add - try to add a migration target task to a taskset
2424  * @task: target task
2425  * @tset: target taskset
2426  *
2427  * Add @task, which is a migration target, to @tset.  This function becomes
2428  * noop if @task doesn't need to be migrated.  @task's css_set should have
2429  * been added as a migration source and @task->cg_list will be moved from
2430  * the css_set's tasks list to mg_tasks one.
2431  */
2432 static void cgroup_taskset_add(struct task_struct *task,
2433                                struct cgroup_taskset *tset)
2434 {
2435         struct css_set *cset;
2436 
2437         lockdep_assert_held(&css_set_lock);
2438 
2439         /* @task either already exited or can't exit until the end */
2440         if (task->flags & PF_EXITING)
2441                 return;
2442 
2443         /* leave @task alone if post_fork() hasn't linked it yet */
2444         if (list_empty(&task->cg_list))
2445                 return;
2446 
2447         cset = task_css_set(task);
2448         if (!cset->mg_src_cgrp)
2449                 return;
2450 
2451         list_move_tail(&task->cg_list, &cset->mg_tasks);
2452         if (list_empty(&cset->mg_node))
2453                 list_add_tail(&cset->mg_node, &tset->src_csets);
2454         if (list_empty(&cset->mg_dst_cset->mg_node))
2455                 list_move_tail(&cset->mg_dst_cset->mg_node,
2456                                &tset->dst_csets);
2457 }
2458 
2459 /**
2460  * cgroup_taskset_first - reset taskset and return the first task
2461  * @tset: taskset of interest
2462  * @dst_cssp: output variable for the destination css
2463  *
2464  * @tset iteration is initialized and the first task is returned.
2465  */
2466 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2467                                          struct cgroup_subsys_state **dst_cssp)
2468 {
2469         tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2470         tset->cur_task = NULL;
2471 
2472         return cgroup_taskset_next(tset, dst_cssp);
2473 }
2474 
2475 /**
2476  * cgroup_taskset_next - iterate to the next task in taskset
2477  * @tset: taskset of interest
2478  * @dst_cssp: output variable for the destination css
2479  *
2480  * Return the next task in @tset.  Iteration must have been initialized
2481  * with cgroup_taskset_first().
2482  */
2483 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2484                                         struct cgroup_subsys_state **dst_cssp)
2485 {
2486         struct css_set *cset = tset->cur_cset;
2487         struct task_struct *task = tset->cur_task;
2488 
2489         while (&cset->mg_node != tset->csets) {
2490                 if (!task)
2491                         task = list_first_entry(&cset->mg_tasks,
2492                                                 struct task_struct, cg_list);
2493                 else
2494                         task = list_next_entry(task, cg_list);
2495 
2496                 if (&task->cg_list != &cset->mg_tasks) {
2497                         tset->cur_cset = cset;
2498                         tset->cur_task = task;
2499 
2500                         /*
2501                          * This function may be called both before and
2502                          * after cgroup_taskset_migrate().  The two cases
2503                          * can be distinguished by looking at whether @cset
2504                          * has its ->mg_dst_cset set.
2505                          */
2506                         if (cset->mg_dst_cset)
2507                                 *dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2508                         else
2509                                 *dst_cssp = cset->subsys[tset->ssid];
2510 
2511                         return task;
2512                 }
2513 
2514                 cset = list_next_entry(cset, mg_node);
2515                 task = NULL;
2516         }
2517 
2518         return NULL;
2519 }
2520 
2521 /**
2522  * cgroup_taskset_migrate - migrate a taskset
2523  * @tset: taget taskset
2524  * @root: cgroup root the migration is taking place on
2525  *
2526  * Migrate tasks in @tset as setup by migration preparation functions.
2527  * This function fails iff one of the ->can_attach callbacks fails and
2528  * guarantees that either all or none of the tasks in @tset are migrated.
2529  * @tset is consumed regardless of success.
2530  */
2531 static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
2532                                   struct cgroup_root *root)
2533 {
2534         struct cgroup_subsys *ss;
2535         struct task_struct *task, *tmp_task;
2536         struct css_set *cset, *tmp_cset;
2537         int ssid, failed_ssid, ret;
2538 
2539         /* methods shouldn't be called if no task is actually migrating */
2540         if (list_empty(&tset->src_csets))
2541                 return 0;
2542 
2543         /* check that we can legitimately attach to the cgroup */
2544         do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2545                 if (ss->can_attach) {
2546                         tset->ssid = ssid;
2547                         ret = ss->can_attach(tset);
2548                         if (ret) {
2549                                 failed_ssid = ssid;
2550                                 goto out_cancel_attach;
2551                         }
2552                 }
2553         } while_each_subsys_mask();
2554 
2555         /*
2556          * Now that we're guaranteed success, proceed to move all tasks to
2557          * the new cgroup.  There are no failure cases after here, so this
2558          * is the commit point.
2559          */
2560         spin_lock_bh(&css_set_lock);
2561         list_for_each_entry(cset, &tset->src_csets, mg_node) {
2562                 list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2563                         struct css_set *from_cset = task_css_set(task);
2564                         struct css_set *to_cset = cset->mg_dst_cset;
2565 
2566                         get_css_set(to_cset);
2567                         css_set_move_task(task, from_cset, to_cset, true);
2568                         put_css_set_locked(from_cset);
2569                 }
2570         }
2571         spin_unlock_bh(&css_set_lock);
2572 
2573         /*
2574          * Migration is committed, all target tasks are now on dst_csets.
2575          * Nothing is sensitive to fork() after this point.  Notify
2576          * controllers that migration is complete.
2577          */
2578         tset->csets = &tset->dst_csets;
2579 
2580         do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2581                 if (ss->attach) {
2582                         tset->ssid = ssid;
2583                         ss->attach(tset);
2584                 }
2585         } while_each_subsys_mask();
2586 
2587         ret = 0;
2588         goto out_release_tset;
2589 
2590 out_cancel_attach:
2591         do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2592                 if (ssid == failed_ssid)
2593                         break;
2594                 if (ss->cancel_attach) {
2595                         tset->ssid = ssid;
2596                         ss->cancel_attach(tset);
2597                 }
2598         } while_each_subsys_mask();
2599 out_release_tset:
2600         spin_lock_bh(&css_set_lock);
2601         list_splice_init(&tset->dst_csets, &tset->src_csets);
2602         list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2603                 list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2604                 list_del_init(&cset->mg_node);
2605         }
2606         spin_unlock_bh(&css_set_lock);
2607         return ret;
2608 }
2609 
2610 /**
2611  * cgroup_may_migrate_to - verify whether a cgroup can be migration destination
2612  * @dst_cgrp: destination cgroup to test
2613  *
2614  * On the default hierarchy, except for the root, subtree_control must be
2615  * zero for migration destination cgroups with tasks so that child cgroups
2616  * don't compete against tasks.
2617  */
2618 static bool cgroup_may_migrate_to(struct cgroup *dst_cgrp)
2619 {
2620         return !cgroup_on_dfl(dst_cgrp) || !cgroup_parent(dst_cgrp) ||
2621                 !dst_cgrp->subtree_control;
2622 }
2623 
2624 /**
2625  * cgroup_migrate_finish - cleanup after attach
2626  * @preloaded_csets: list of preloaded css_sets
2627  *
2628  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2629  * those functions for details.
2630  */
2631 static void cgroup_migrate_finish(struct list_head *preloaded_csets)
2632 {
2633         struct css_set *cset, *tmp_cset;
2634 
2635         lockdep_assert_held(&cgroup_mutex);
2636 
2637         spin_lock_bh(&css_set_lock);
2638         list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
2639                 cset->mg_src_cgrp = NULL;
2640                 cset->mg_dst_cgrp = NULL;
2641                 cset->mg_dst_cset = NULL;
2642                 list_del_init(&cset->mg_preload_node);
2643                 put_css_set_locked(cset);
2644         }
2645         spin_unlock_bh(&css_set_lock);
2646 }
2647 
2648 /**
2649  * cgroup_migrate_add_src - add a migration source css_set
2650  * @src_cset: the source css_set to add
2651  * @dst_cgrp: the destination cgroup
2652  * @preloaded_csets: list of preloaded css_sets
2653  *
2654  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2655  * @src_cset and add it to @preloaded_csets, which should later be cleaned
2656  * up by cgroup_migrate_finish().
2657  *
2658  * This function may be called without holding cgroup_threadgroup_rwsem
2659  * even if the target is a process.  Threads may be created and destroyed
2660  * but as long as cgroup_mutex is not dropped, no new css_set can be put
2661  * into play and the preloaded css_sets are guaranteed to cover all
2662  * migrations.
2663  */
2664 static void cgroup_migrate_add_src(struct css_set *src_cset,
2665                                    struct cgroup *dst_cgrp,
2666                                    struct list_head *preloaded_csets)
2667 {
2668         struct cgroup *src_cgrp;
2669 
2670         lockdep_assert_held(&cgroup_mutex);
2671         lockdep_assert_held(&css_set_lock);
2672 
2673         /*
2674          * If ->dead, @src_set is associated with one or more dead cgroups
2675          * and doesn't contain any migratable tasks.  Ignore it early so
2676          * that the rest of migration path doesn't get confused by it.
2677          */
2678         if (src_cset->dead)
2679                 return;
2680 
2681         src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2682 
2683         if (!list_empty(&src_cset->mg_preload_node))
2684                 return;
2685 
2686         WARN_ON(src_cset->mg_src_cgrp);
2687         WARN_ON(src_cset->mg_dst_cgrp);
2688         WARN_ON(!list_empty(&src_cset->mg_tasks));
2689         WARN_ON(!list_empty(&src_cset->mg_node));
2690 
2691         src_cset->mg_src_cgrp = src_cgrp;
2692         src_cset->mg_dst_cgrp = dst_cgrp;
2693         get_css_set(src_cset);
2694         list_add(&src_cset->mg_preload_node, preloaded_csets);
2695 }
2696 
2697 /**
2698  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2699  * @preloaded_csets: list of preloaded source css_sets
2700  *
2701  * Tasks are about to be moved and all the source css_sets have been
2702  * preloaded to @preloaded_csets.  This function looks up and pins all
2703  * destination css_sets, links each to its source, and append them to
2704  * @preloaded_csets.
2705  *
2706  * This function must be called after cgroup_migrate_add_src() has been
2707  * called on each migration source css_set.  After migration is performed
2708  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2709  * @preloaded_csets.
2710  */
2711 static int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
2712 {
2713         LIST_HEAD(csets);
2714         struct css_set *src_cset, *tmp_cset;
2715 
2716         lockdep_assert_held(&cgroup_mutex);
2717 
2718         /* look up the dst cset for each src cset and link it to src */
2719         list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
2720                 struct css_set *dst_cset;
2721 
2722                 dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2723                 if (!dst_cset)
2724                         goto err;
2725 
2726                 WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2727 
2728                 /*
2729                  * If src cset equals dst, it's noop.  Drop the src.
2730                  * cgroup_migrate() will skip the cset too.  Note that we
2731                  * can't handle src == dst as some nodes are used by both.
2732                  */
2733                 if (src_cset == dst_cset) {
2734                         src_cset->mg_src_cgrp = NULL;
2735                         src_cset->mg_dst_cgrp = NULL;
2736                         list_del_init(&src_cset->mg_preload_node);
2737                         put_css_set(src_cset);
2738                         put_css_set(dst_cset);
2739                         continue;
2740                 }
2741 
2742                 src_cset->mg_dst_cset = dst_cset;
2743 
2744                 if (list_empty(&dst_cset->mg_preload_node))
2745                         list_add(&dst_cset->mg_preload_node, &csets);
2746                 else
2747                         put_css_set(dst_cset);
2748         }
2749 
2750         list_splice_tail(&csets, preloaded_csets);
2751         return 0;
2752 err:
2753         cgroup_migrate_finish(&csets);
2754         return -ENOMEM;
2755 }
2756 
2757 /**
2758  * cgroup_migrate - migrate a process or task to a cgroup
2759  * @leader: the leader of the process or the task to migrate
2760  * @threadgroup: whether @leader points to the whole process or a single task
2761  * @root: cgroup root migration is taking place on
2762  *
2763  * Migrate a process or task denoted by @leader.  If migrating a process,
2764  * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2765  * responsible for invoking cgroup_migrate_add_src() and
2766  * cgroup_migrate_prepare_dst() on the targets before invoking this
2767  * function and following up with cgroup_migrate_finish().
2768  *
2769  * As long as a controller's ->can_attach() doesn't fail, this function is
2770  * guaranteed to succeed.  This means that, excluding ->can_attach()
2771  * failure, when migrating multiple targets, the success or failure can be
2772  * decided for all targets by invoking group_migrate_prepare_dst() before
2773  * actually starting migrating.
2774  */
2775 static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2776                           struct cgroup_root *root)
2777 {
2778         struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
2779         struct task_struct *task;
2780 
2781         /*
2782          * Prevent freeing of tasks while we take a snapshot. Tasks that are
2783          * already PF_EXITING could be freed from underneath us unless we
2784          * take an rcu_read_lock.
2785          */
2786         spin_lock_bh(&css_set_lock);
2787         rcu_read_lock();
2788         task = leader;
2789         do {
2790                 cgroup_taskset_add(task, &tset);
2791                 if (!threadgroup)
2792                         break;
2793         } while_each_thread(leader, task);
2794         rcu_read_unlock();
2795         spin_unlock_bh(&css_set_lock);
2796 
2797         return cgroup_taskset_migrate(&tset, root);
2798 }
2799 
2800 /**
2801  * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2802  * @dst_cgrp: the cgroup to attach to
2803  * @leader: the task or the leader of the threadgroup to be attached
2804  * @threadgroup: attach the whole threadgroup?
2805  *
2806  * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2807  */
2808 static int cgroup_attach_task(struct cgroup *dst_cgrp,
2809                               struct task_struct *leader, bool threadgroup)
2810 {
2811         LIST_HEAD(preloaded_csets);
2812         struct task_struct *task;
2813         int ret;
2814 
2815         if (!cgroup_may_migrate_to(dst_cgrp))
2816                 return -EBUSY;
2817 
2818         /* look up all src csets */
2819         spin_lock_bh(&css_set_lock);
2820         rcu_read_lock();
2821         task = leader;
2822         do {
2823                 cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
2824                                        &preloaded_csets);
2825                 if (!threadgroup)
2826                         break;
2827         } while_each_thread(leader, task);
2828         rcu_read_unlock();
2829         spin_unlock_bh(&css_set_lock);
2830 
2831         /* prepare dst csets and commit */
2832         ret = cgroup_migrate_prepare_dst(&preloaded_csets);
2833         if (!ret)
2834                 ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
2835 
2836         cgroup_migrate_finish(&preloaded_csets);
2837         return ret;
2838 }
2839 
2840 static int cgroup_procs_write_permission(struct task_struct *task,
2841                                          struct cgroup *dst_cgrp,
2842                                          struct kernfs_open_file *of)
2843 {
2844         const struct cred *cred = current_cred();
2845         const struct cred *tcred = get_task_cred(task);
2846         int ret = 0;
2847 
2848         /*
2849          * even if we're attaching all tasks in the thread group, we only
2850          * need to check permissions on one of them.
2851          */
2852         if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2853             !uid_eq(cred->euid, tcred->uid) &&
2854             !uid_eq(cred->euid, tcred->suid))
2855                 ret = -EACCES;
2856 
2857         if (!ret && cgroup_on_dfl(dst_cgrp)) {
2858                 struct super_block *sb = of->file->f_path.dentry->d_sb;
2859                 struct cgroup *cgrp;
2860                 struct inode *inode;
2861 
2862                 spin_lock_bh(&css_set_lock);
2863                 cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
2864                 spin_unlock_bh(&css_set_lock);
2865 
2866                 while (!cgroup_is_descendant(dst_cgrp, cgrp))
2867                         cgrp = cgroup_parent(cgrp);
2868 
2869                 ret = -ENOMEM;
2870                 inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
2871                 if (inode) {
2872                         ret = inode_permission(inode, MAY_WRITE);
2873                         iput(inode);
2874                 }
2875         }
2876 
2877         put_cred(tcred);
2878         return ret;
2879 }
2880 
2881 /*
2882  * Find the task_struct of the task to attach by vpid and pass it along to the
2883  * function to attach either it or all tasks in its threadgroup. Will lock
2884  * cgroup_mutex and threadgroup.
2885  */
2886 static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
2887                                     size_t nbytes, loff_t off, bool threadgroup)
2888 {
2889         struct task_struct *tsk;
2890         struct cgroup_subsys *ss;
2891         struct cgroup *cgrp;
2892         pid_t pid;
2893         int ssid, ret;
2894 
2895         if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2896                 return -EINVAL;
2897 
2898         cgrp = cgroup_kn_lock_live(of->kn, false);
2899         if (!cgrp)
2900                 return -ENODEV;
2901 
2902         percpu_down_write(&cgroup_threadgroup_rwsem);
2903         rcu_read_lock();
2904         if (pid) {
2905                 tsk = find_task_by_vpid(pid);
2906                 if (!tsk) {
2907                         ret = -ESRCH;
2908                         goto out_unlock_rcu;
2909                 }
2910         } else {
2911                 tsk = current;
2912         }
2913 
2914         if (threadgroup)
2915                 tsk = tsk->group_leader;
2916 
2917         /*
2918          * Workqueue threads may acquire PF_NO_SETAFFINITY and become
2919          * trapped in a cpuset, or RT worker may be born in a cgroup
2920          * with no rt_runtime allocated.  Just say no.
2921          */
2922         if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
2923                 ret = -EINVAL;
2924                 goto out_unlock_rcu;
2925         }
2926 
2927         get_task_struct(tsk);
2928         rcu_read_unlock();
2929 
2930         ret = cgroup_procs_write_permission(tsk, cgrp, of);
2931         if (!ret)
2932                 ret = cgroup_attach_task(cgrp, tsk, threadgroup);
2933 
2934         put_task_struct(tsk);
2935         goto out_unlock_threadgroup;
2936 
2937 out_unlock_rcu:
2938         rcu_read_unlock();
2939 out_unlock_threadgroup:
2940         percpu_up_write(&cgroup_threadgroup_rwsem);
2941         for_each_subsys(ss, ssid)
2942                 if (ss->post_attach)
2943                         ss->post_attach();
2944         cgroup_kn_unlock(of->kn);
2945         return ret ?: nbytes;
2946 }
2947 
2948 /**
2949  * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2950  * @from: attach to all cgroups of a given task
2951  * @tsk: the task to be attached
2952  */
2953 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2954 {
2955         struct cgroup_root *root;
2956         int retval = 0;
2957 
2958         mutex_lock(&cgroup_mutex);
2959         for_each_root(root) {
2960                 struct cgroup *from_cgrp;
2961 
2962                 if (root == &cgrp_dfl_root)
2963                         continue;
2964 
2965                 spin_lock_bh(&css_set_lock);
2966                 from_cgrp = task_cgroup_from_root(from, root);
2967                 spin_unlock_bh(&css_set_lock);
2968 
2969                 retval = cgroup_attach_task(from_cgrp, tsk, false);
2970                 if (retval)
2971                         break;
2972         }
2973         mutex_unlock(&cgroup_mutex);
2974 
2975         return retval;
2976 }
2977 EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2978 
2979 static ssize_t cgroup_tasks_write(struct kernfs_open_file *of,
2980                                   char *buf, size_t nbytes, loff_t off)
2981 {
2982         return __cgroup_procs_write(of, buf, nbytes, off, false);
2983 }
2984 
2985 static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
2986                                   char *buf, size_t nbytes, loff_t off)
2987 {
2988         return __cgroup_procs_write(of, buf, nbytes, off, true);
2989 }
2990 
2991 static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
2992                                           char *buf, size_t nbytes, loff_t off)
2993 {
2994         struct cgroup *cgrp;
2995 
2996         BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
2997 
2998         cgrp = cgroup_kn_lock_live(of->kn, false);
2999         if (!cgrp)
3000                 return -ENODEV;
3001         spin_lock(&release_agent_path_lock);
3002         strlcpy(cgrp->root->release_agent_path, strstrip(buf),
3003                 sizeof(cgrp->root->release_agent_path));
3004         spin_unlock(&release_agent_path_lock);
3005         cgroup_kn_unlock(of->kn);
3006         return nbytes;
3007 }
3008 
3009 static int cgroup_release_agent_show(struct seq_file *seq, void *v)
3010 {
3011         struct cgroup *cgrp = seq_css(seq)->cgroup;
3012 
3013         spin_lock(&release_agent_path_lock);
3014         seq_puts(seq, cgrp->root->release_agent_path);
3015         spin_unlock(&release_agent_path_lock);
3016         seq_putc(seq, '\n');
3017         return 0;
3018 }
3019 
3020 static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
3021 {
3022         seq_puts(seq, "\n");
3023         return 0;
3024 }
3025 
3026 static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
3027 {
3028         struct cgroup_subsys *ss;
3029         bool printed = false;
3030         int ssid;
3031 
3032         do_each_subsys_mask(ss, ssid, ss_mask) {
3033                 if (printed)
3034                         seq_putc(seq, ' ');
3035                 seq_printf(seq, "%s", ss->name);
3036                 printed = true;
3037         } while_each_subsys_mask();
3038         if (printed)
3039                 seq_putc(seq, '\n');
3040 }
3041 
3042 /* show controllers which are enabled from the parent */
3043 static int cgroup_controllers_show(struct seq_file *seq, void *v)
3044 {
3045         struct cgroup *cgrp = seq_css(seq)->cgroup;
3046 
3047         cgroup_print_ss_mask(seq, cgroup_control(cgrp));
3048         return 0;
3049 }
3050 
3051 /* show controllers which are enabled for a given cgroup's children */
3052 static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
3053 {
3054         struct cgroup *cgrp = seq_css(seq)->cgroup;
3055 
3056         cgroup_print_ss_mask(seq, cgrp->subtree_control);
3057         return 0;
3058 }
3059 
3060 /**
3061  * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
3062  * @cgrp: root of the subtree to update csses for
3063  *
3064  * @cgrp's control masks have changed and its subtree's css associations
3065  * need to be updated accordingly.  This function looks up all css_sets
3066  * which are attached to the subtree, creates the matching updated css_sets
3067  * and migrates the tasks to the new ones.
3068  */
3069 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
3070 {
3071         LIST_HEAD(preloaded_csets);
3072         struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
3073         struct cgroup_subsys_state *d_css;
3074         struct cgroup *dsct;
3075         struct css_set *src_cset;
3076         int ret;
3077 
3078         lockdep_assert_held(&cgroup_mutex);
3079 
3080         percpu_down_write(&cgroup_threadgroup_rwsem);
3081 
3082         /* look up all csses currently attached to @cgrp's subtree */
3083         spin_lock_bh(&css_set_lock);
3084         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3085                 struct cgrp_cset_link *link;
3086 
3087                 list_for_each_entry(link, &dsct->cset_links, cset_link)
3088                         cgroup_migrate_add_src(link->cset, dsct,
3089                                                &preloaded_csets);
3090         }
3091         spin_unlock_bh(&css_set_lock);
3092 
3093         /* NULL dst indicates self on default hierarchy */
3094         ret = cgroup_migrate_prepare_dst(&preloaded_csets);
3095         if (ret)
3096                 goto out_finish;
3097 
3098         spin_lock_bh(&css_set_lock);
3099         list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
3100                 struct task_struct *task, *ntask;
3101 
3102                 /* src_csets precede dst_csets, break on the first dst_cset */
3103                 if (!src_cset->mg_src_cgrp)
3104                         break;
3105 
3106                 /* all tasks in src_csets need to be migrated */
3107                 list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
3108                         cgroup_taskset_add(task, &tset);
3109         }
3110         spin_unlock_bh(&css_set_lock);
3111 
3112         ret = cgroup_taskset_migrate(&tset, cgrp->root);
3113 out_finish:
3114         cgroup_migrate_finish(&preloaded_csets);
3115         percpu_up_write(&cgroup_threadgroup_rwsem);
3116         return ret;
3117 }
3118 
3119 /**
3120  * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
3121  * @cgrp: root of the target subtree
3122  *
3123  * Because css offlining is asynchronous, userland may try to re-enable a
3124  * controller while the previous css is still around.  This function grabs
3125  * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
3126  */
3127 static void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
3128         __acquires(&cgroup_mutex)
3129 {
3130         struct cgroup *dsct;
3131         struct cgroup_subsys_state *d_css;
3132         struct cgroup_subsys *ss;
3133         int ssid;
3134 
3135 restart:
3136         mutex_lock(&cgroup_mutex);
3137 
3138         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3139                 for_each_subsys(ss, ssid) {
3140                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3141                         DEFINE_WAIT(wait);
3142 
3143                         if (!css || !percpu_ref_is_dying(&css->refcnt))
3144                                 continue;
3145 
3146                         cgroup_get(dsct);
3147                         prepare_to_wait(&dsct->offline_waitq, &wait,
3148                                         TASK_UNINTERRUPTIBLE);
3149 
3150                         mutex_unlock(&cgroup_mutex);
3151                         schedule();
3152                         finish_wait(&dsct->offline_waitq, &wait);
3153 
3154                         cgroup_put(dsct);
3155                         goto restart;
3156                 }
3157         }
3158 }
3159 
3160 /**
3161  * cgroup_save_control - save control masks of a subtree
3162  * @cgrp: root of the target subtree
3163  *
3164  * Save ->subtree_control and ->subtree_ss_mask to the respective old_
3165  * prefixed fields for @cgrp's subtree including @cgrp itself.
3166  */
3167 static void cgroup_save_control(struct cgroup *cgrp)
3168 {
3169         struct cgroup *dsct;
3170         struct cgroup_subsys_state *d_css;
3171 
3172         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3173                 dsct->old_subtree_control = dsct->subtree_control;
3174                 dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
3175         }
3176 }
3177 
3178 /**
3179  * cgroup_propagate_control - refresh control masks of a subtree
3180  * @cgrp: root of the target subtree
3181  *
3182  * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
3183  * ->subtree_control and propagate controller availability through the
3184  * subtree so that descendants don't have unavailable controllers enabled.
3185  */
3186 static void cgroup_propagate_control(struct cgroup *cgrp)
3187 {
3188         struct cgroup *dsct;
3189         struct cgroup_subsys_state *d_css;
3190 
3191         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3192                 dsct->subtree_control &= cgroup_control(dsct);
3193                 dsct->subtree_ss_mask =
3194                         cgroup_calc_subtree_ss_mask(dsct->subtree_control,
3195                                                     cgroup_ss_mask(dsct));
3196         }
3197 }
3198 
3199 /**
3200  * cgroup_restore_control - restore control masks of a subtree
3201  * @cgrp: root of the target subtree
3202  *
3203  * Restore ->subtree_control and ->subtree_ss_mask from the respective old_
3204  * prefixed fields for @cgrp's subtree including @cgrp itself.
3205  */
3206 static void cgroup_restore_control(struct cgroup *cgrp)
3207 {
3208         struct cgroup *dsct;
3209         struct cgroup_subsys_state *d_css;
3210 
3211         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3212                 dsct->subtree_control = dsct->old_subtree_control;
3213                 dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3214         }
3215 }
3216 
3217 static bool css_visible(struct cgroup_subsys_state *css)
3218 {
3219         struct cgroup_subsys *ss = css->ss;
3220         struct cgroup *cgrp = css->cgroup;
3221 
3222         if (cgroup_control(cgrp) & (1 << ss->id))
3223                 return true;
3224         if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3225                 return false;
3226         return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3227 }
3228 
3229 /**
3230  * cgroup_apply_control_enable - enable or show csses according to control
3231  * @cgrp: root of the target subtree
3232  *
3233  * Walk @cgrp's subtree and create new csses or make the existing ones
3234  * visible.  A css is created invisible if it's being implicitly enabled
3235  * through dependency.  An invisible css is made visible when the userland
3236  * explicitly enables it.
3237  *
3238  * Returns 0 on success, -errno on failure.  On failure, csses which have
3239  * been processed already aren't cleaned up.  The caller is responsible for
3240  * cleaning up with cgroup_apply_control_disble().
3241  */
3242 static int cgroup_apply_control_enable(struct cgroup *cgrp)
3243 {
3244         struct cgroup *dsct;
3245         struct cgroup_subsys_state *d_css;
3246         struct cgroup_subsys *ss;
3247         int ssid, ret;
3248 
3249         cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3250                 for_each_subsys(ss, ssid) {
3251                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3252 
3253                         WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3254 
3255                         if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3256                                 continue;
3257 
3258                         if (!css) {
3259                                 css = css_create(dsct, ss);
3260                                 if (IS_ERR(css))
3261                                         return PTR_ERR(css);
3262                         }
3263 
3264                         if (css_visible(css)) {
3265                                 ret = css_populate_dir(css);
3266                                 if (ret)
3267                                         return ret;
3268                         }
3269                 }
3270         }
3271 
3272         return 0;
3273 }
3274 
3275 /**
3276  * cgroup_apply_control_disable - kill or hide csses according to control
3277  * @cgrp: root of the target subtree
3278  *
3279  * Walk @cgrp's subtree and kill and hide csses so that they match
3280  * cgroup_ss_mask() and cgroup_visible_mask().
3281  *
3282  * A css is hidden when the userland requests it to be disabled while other
3283  * subsystems are still depending on it.  The css must not actively control
3284  * resources and be in the vanilla state if it's made visible again later.
3285  * Controllers which may be depended upon should provide ->css_reset() for
3286  * this purpose.
3287  */
3288 static void cgroup_apply_control_disable(struct cgroup *cgrp)
3289 {
3290         struct cgroup *dsct;
3291         struct cgroup_subsys_state *d_css;
3292         struct cgroup_subsys *ss;
3293         int ssid;
3294 
3295         cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3296                 for_each_subsys(ss, ssid) {
3297                         struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3298 
3299                         WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3300 
3301                         if (!css)
3302                                 continue;
3303 
3304                         if (css->parent &&
3305                             !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3306                                 kill_css(css);
3307                         } else if (!css_visible(css)) {
3308                                 css_clear_dir(css);
3309                                 if (ss->css_reset)
3310                                         ss->css_reset(css);
3311                         }
3312                 }
3313         }
3314 }
3315 
3316 /**
3317  * cgroup_apply_control - apply control mask updates to the subtree
3318  * @cgrp: root of the target subtree
3319  *
3320  * subsystems can be enabled and disabled in a subtree using the following
3321  * steps.
3322  *
3323  * 1. Call cgroup_save_control() to stash the current state.
3324  * 2. Update ->subtree_control masks in the subtree as desired.
3325  * 3. Call cgroup_apply_control() to apply the changes.
3326  * 4. Optionally perform other related operations.
3327  * 5. Call cgroup_finalize_control() to finish up.
3328  *
3329  * This function implements step 3 and propagates the mask changes
3330  * throughout @cgrp's subtree, updates csses accordingly and perform
3331  * process migrations.
3332  */
3333 static int cgroup_apply_control(struct cgroup *cgrp)
3334 {
3335         int ret;
3336 
3337         cgroup_propagate_control(cgrp);
3338 
3339         ret = cgroup_apply_control_enable(cgrp);
3340         if (ret)
3341                 return ret;
3342 
3343         /*
3344          * At this point, cgroup_e_css() results reflect the new csses
3345          * making the following cgroup_update_dfl_csses() properly update
3346          * css associations of all tasks in the subtree.
3347          */
3348         ret = cgroup_update_dfl_csses(cgrp);
3349         if (ret)
3350                 return ret;
3351 
3352         return 0;
3353 }
3354 
3355 /**
3356  * cgroup_finalize_control - finalize control mask update
3357  * @cgrp: root of the target subtree
3358  * @ret: the result of the update
3359  *
3360  * Finalize control mask update.  See cgroup_apply_control() for more info.
3361  */
3362 static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3363 {
3364         if (ret) {
3365                 cgroup_restore_control(cgrp);
3366                 cgroup_propagate_control(cgrp);
3367         }
3368 
3369         cgroup_apply_control_disable(cgrp);
3370 }
3371 
3372 /* change the enabled child controllers for a cgroup in the default hierarchy */
3373 static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3374                                             char *buf, size_t nbytes,
3375                                             loff_t off)
3376 {
3377         u16 enable = 0, disable = 0;
3378         struct cgroup *cgrp, *child;
3379         struct cgroup_subsys *ss;
3380         char *tok;
3381         int ssid, ret;
3382 
3383         /*
3384          * Parse input - space separated list of subsystem names prefixed
3385          * with either + or -.
3386          */
3387         buf = strstrip(buf);
3388         while ((tok = strsep(&buf, " "))) {
3389                 if (tok[0] == '\0')
3390                         continue;
3391                 do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3392                         if (!cgroup_ssid_enabled(ssid) ||
3393                             strcmp(tok + 1, ss->name))
3394                                 continue;
3395 
3396                         if (*tok == '+') {
3397                                 enable |= 1 << ssid;
3398                                 disable &= ~(1 << ssid);
3399                         } else if (*tok == '-') {
3400                                 disable |= 1 << ssid;
3401                                 enable &= ~(1 << ssid);
3402                         } else {
3403                                 return -EINVAL;
3404                         }
3405                         break;
3406                 } while_each_subsys_mask();
3407                 if (ssid == CGROUP_SUBSYS_COUNT)
3408                         return -EINVAL;
3409         }
3410 
3411         cgrp = cgroup_kn_lock_live(of->kn, true);
3412         if (!cgrp)
3413                 return -ENODEV;
3414 
3415         for_each_subsys(ss, ssid) {
3416                 if (enable & (1 << ssid)) {
3417                         if (cgrp->subtree_control & (1 << ssid)) {
3418                                 enable &= ~(1 << ssid);
3419                                 continue;
3420                         }
3421 
3422                         if (!(cgroup_control(cgrp) & (1 << ssid))) {
3423                                 ret = -ENOENT;
3424                                 goto out_unlock;
3425                         }
3426                 } else if (disable & (1 << ssid)) {
3427                         if (!(cgrp->subtree_control & (1 << ssid))) {
3428                                 disable &= ~(1 << ssid);
3429                                 continue;
3430                         }
3431 
3432                         /* a child has it enabled? */
3433                         cgroup_for_each_live_child(child, cgrp) {
3434                                 if (child->subtree_control & (1 << ssid)) {
3435                                         ret = -EBUSY;
3436                                         goto out_unlock;
3437                                 }
3438                         }
3439                 }
3440         }
3441 
3442         if (!enable && !disable) {
3443                 ret = 0;
3444                 goto out_unlock;
3445         }
3446 
3447         /*
3448          * Except for the root, subtree_control must be zero for a cgroup
3449          * with tasks so that child cgroups don't compete against tasks.
3450          */
3451         if (enable && cgroup_parent(cgrp) && !list_empty(&cgrp->cset_links)) {
3452                 ret = -EBUSY;
3453                 goto out_unlock;
3454         }
3455 
3456         /* save and update control masks and prepare csses */
3457         cgroup_save_control(cgrp);
3458 
3459         cgrp->subtree_control |= enable;
3460         cgrp->subtree_control &= ~disable;
3461 
3462         ret = cgroup_apply_control(cgrp);
3463 
3464         cgroup_finalize_control(cgrp, ret);
3465 
3466         kernfs_activate(cgrp->kn);
3467         ret = 0;
3468 out_unlock:
3469         cgroup_kn_unlock(of->kn);
3470         return ret ?: nbytes;
3471 }
3472 
3473 static int cgroup_events_show(struct seq_file *seq, void *v)
3474 {
3475         seq_printf(seq, "populated %d\n",
3476                    cgroup_is_populated(seq_css(seq)->cgroup));
3477         return 0;
3478 }
3479 
3480 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3481                                  size_t nbytes, loff_t off)
3482 {
3483         struct cgroup *cgrp = of->kn->parent->priv;
3484         struct cftype *cft = of->kn->priv;
3485         struct cgroup_subsys_state *css;
3486         int ret;
3487 
3488         if (cft->write)
3489                 return cft->write(of, buf, nbytes, off);
3490 
3491         /*
3492          * kernfs guarantees that a file isn't deleted with operations in
3493          * flight, which means that the matching css is and stays alive and
3494          * doesn't need to be pinned.  The RCU locking is not necessary
3495          * either.  It's just for the convenience of using cgroup_css().
3496          */
3497         rcu_read_lock();
3498         css = cgroup_css(cgrp, cft->ss);
3499         rcu_read_unlock();
3500 
3501         if (cft->write_u64) {
3502                 unsigned long long v;
3503                 ret = kstrtoull(buf, 0, &v);
3504                 if (!ret)
3505                         ret = cft->write_u64(css, cft, v);
3506         } else if (cft->write_s64) {
3507                 long long v;
3508                 ret = kstrtoll(buf, 0, &v);
3509                 if (!ret)
3510                         ret = cft->write_s64(css, cft, v);
3511         } else {
3512                 ret = -EINVAL;
3513         }
3514 
3515         return ret ?: nbytes;
3516 }
3517 
3518 static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3519 {
3520         return seq_cft(seq)->seq_start(seq, ppos);
3521 }
3522 
3523 static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3524 {
3525         return seq_cft(seq)->seq_next(seq, v, ppos);
3526 }
3527 
3528 static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3529 {
3530         seq_cft(seq)->seq_stop(seq, v);
3531 }
3532 
3533 static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3534 {
3535         struct cftype *cft = seq_cft(m);
3536         struct cgroup_subsys_state *css = seq_css(m);
3537 
3538         if (cft->seq_show)
3539                 return cft->seq_show(m, arg);
3540 
3541         if (cft->read_u64)
3542                 seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3543         else if (cft->read_s64)
3544                 seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3545         else
3546                 return -EINVAL;
3547         return 0;
3548 }
3549 
3550 static struct kernfs_ops cgroup_kf_single_ops = {
3551         .atomic_write_len       = PAGE_SIZE,
3552         .write                  = cgroup_file_write,
3553         .seq_show               = cgroup_seqfile_show,
3554 };
3555 
3556 static struct kernfs_ops cgroup_kf_ops = {
3557         .atomic_write_len       = PAGE_SIZE,
3558         .write                  = cgroup_file_write,
3559         .seq_start              = cgroup_seqfile_start,
3560         .seq_next               = cgroup_seqfile_next,
3561         .seq_stop               = cgroup_seqfile_stop,
3562         .seq_show               = cgroup_seqfile_show,
3563 };
3564 
3565 /*
3566  * cgroup_rename - Only allow simple rename of directories in place.
3567  */
3568 static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
3569                          const char *new_name_str)
3570 {
3571         struct cgroup *cgrp = kn->priv;
3572         int ret;
3573 
3574         if (kernfs_type(kn) != KERNFS_DIR)
3575                 return -ENOTDIR;
3576         if (kn->parent != new_parent)
3577                 return -EIO;
3578 
3579         /*
3580          * This isn't a proper migration and its usefulness is very
3581          * limited.  Disallow on the default hierarchy.
3582          */
3583         if (cgroup_on_dfl(cgrp))
3584                 return -EPERM;
3585 
3586         /*
3587          * We're gonna grab cgroup_mutex which nests outside kernfs
3588          * active_ref.  kernfs_rename() doesn't require active_ref
3589          * protection.  Break them before grabbing cgroup_mutex.
3590          */
3591         kernfs_break_active_protection(new_parent);
3592         kernfs_break_active_protection(kn);
3593 
3594         mutex_lock(&cgroup_mutex);
3595 
3596         ret = kernfs_rename(kn, new_parent, new_name_str);
3597 
3598         mutex_unlock(&cgroup_mutex);
3599 
3600         kernfs_unbreak_active_protection(kn);
3601         kernfs_unbreak_active_protection(new_parent);
3602         return ret;
3603 }
3604 
3605 /* set uid and gid of cgroup dirs and files to that of the creator */
3606 static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3607 {
3608         struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3609                                .ia_uid = current_fsuid(),
3610                                .ia_gid = current_fsgid(), };
3611 
3612         if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3613             gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3614                 return 0;
3615 
3616         return kernfs_setattr(kn, &iattr);
3617 }
3618 
3619 static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3620                            struct cftype *cft)
3621 {
3622         char name[CGROUP_FILE_NAME_MAX];
3623         struct kernfs_node *kn;
3624         struct lock_class_key *key = NULL;
3625         int ret;
3626 
3627 #ifdef CONFIG_DEBUG_LOCK_ALLOC
3628         key = &cft->lockdep_key;
3629 #endif
3630         kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3631                                   cgroup_file_mode(cft), 0, cft->kf_ops, cft,
3632                                   NULL, key);
3633         if (IS_ERR(kn))
3634                 return PTR_ERR(kn);
3635 
3636         ret = cgroup_kn_set_ugid(kn);
3637         if (ret) {
3638                 kernfs_remove(kn);
3639                 return ret;
3640         }
3641 
3642         if (cft->file_offset) {
3643                 struct cgroup_file *cfile = (void *)css + cft->file_offset;
3644 
3645                 spin_lock_irq(&cgroup_file_kn_lock);
3646                 cfile->kn = kn;
3647                 spin_unlock_irq(&cgroup_file_kn_lock);
3648         }
3649 
3650         return 0;
3651 }
3652 
3653 /**
3654  * cgroup_addrm_files - add or remove files to a cgroup directory
3655  * @css: the target css
3656  * @cgrp: the target cgroup (usually css->cgroup)
3657  * @cfts: array of cftypes to be added
3658  * @is_add: whether to add or remove
3659  *
3660  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3661  * For removals, this function never fails.
3662  */
3663 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3664                               struct cgroup *cgrp, struct cftype cfts[],
3665                               bool is_add)
3666 {
3667         struct cftype *cft, *cft_end = NULL;
3668         int ret = 0;
3669 
3670         lockdep_assert_held(&cgroup_mutex);
3671 
3672 restart:
3673         for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3674                 /* does cft->flags tell us to skip this file on @cgrp? */
3675                 if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3676                         continue;
3677                 if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3678                         continue;
3679                 if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3680                         continue;
3681                 if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3682                         continue;
3683 
3684                 if (is_add) {
3685                         ret = cgroup_add_file(css, cgrp, cft);
3686                         if (ret) {
3687                                 pr_warn("%s: failed to add %s, err=%d\n",
3688                                         __func__, cft->name, ret);
3689                                 cft_end = cft;
3690                                 is_add = false;
3691                                 goto restart;
3692                         }
3693                 } else {
3694                         cgroup_rm_file(cgrp, cft);
3695                 }
3696         }
3697         return ret;
3698 }
3699 
3700 static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3701 {
3702         LIST_HEAD(pending);
3703         struct cgroup_subsys *ss = cfts[0].ss;
3704         struct cgroup *root = &ss->root->cgrp;
3705         struct cgroup_subsys_state *css;
3706         int ret = 0;
3707 
3708         lockdep_assert_held(&cgroup_mutex);
3709 
3710         /* add/rm files for all cgroups created before */
3711         css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3712                 struct cgroup *cgrp = css->cgroup;
3713 
3714                 if (!(css->flags & CSS_VISIBLE))
3715                         continue;
3716 
3717                 ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3718                 if (ret)
3719                         break;
3720         }
3721 
3722         if (is_add && !ret)
3723                 kernfs_activate(root->kn);
3724         return ret;
3725 }
3726 
3727 static void cgroup_exit_cftypes(struct cftype *cfts)
3728 {
3729         struct cftype *cft;
3730 
3731         for (cft = cfts; cft->name[0] != '\0'; cft++) {
3732                 /* free copy for custom atomic_write_len, see init_cftypes() */
3733                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3734                         kfree(cft->kf_ops);
3735                 cft->kf_ops = NULL;
3736                 cft->ss = NULL;
3737 
3738                 /* revert flags set by cgroup core while adding @cfts */
3739                 cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3740         }
3741 }
3742 
3743 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3744 {
3745         struct cftype *cft;
3746 
3747         for (cft = cfts; cft->name[0] != '\0'; cft++) {
3748                 struct kernfs_ops *kf_ops;
3749 
3750                 WARN_ON(cft->ss || cft->kf_ops);
3751 
3752                 if (cft->seq_start)
3753                         kf_ops = &cgroup_kf_ops;
3754                 else
3755                         kf_ops = &cgroup_kf_single_ops;
3756 
3757                 /*
3758                  * Ugh... if @cft wants a custom max_write_len, we need to
3759                  * make a copy of kf_ops to set its atomic_write_len.
3760                  */
3761                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3762                         kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3763                         if (!kf_ops) {
3764                                 cgroup_exit_cftypes(cfts);
3765                                 return -ENOMEM;
3766                         }
3767                         kf_ops->atomic_write_len = cft->max_write_len;
3768                 }
3769 
3770                 cft->kf_ops = kf_ops;
3771                 cft->ss = ss;
3772         }
3773 
3774         return 0;
3775 }
3776 
3777 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
3778 {
3779         lockdep_assert_held(&cgroup_mutex);
3780 
3781         if (!cfts || !cfts[0].ss)
3782                 return -ENOENT;
3783 
3784         list_del(&cfts->node);
3785         cgroup_apply_cftypes(cfts, false);
3786         cgroup_exit_cftypes(cfts);
3787         return 0;
3788 }
3789 
3790 /**
3791  * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
3792  * @cfts: zero-length name terminated array of cftypes
3793  *
3794  * Unregister @cfts.  Files described by @cfts are removed from all
3795  * existing cgroups and all future cgroups won't have them either.  This
3796  * function can be called anytime whether @cfts' subsys is attached or not.
3797  *
3798  * Returns 0 on successful unregistration, -ENOENT if @cfts is not
3799  * registered.
3800  */
3801 int cgroup_rm_cftypes(struct cftype *cfts)
3802 {
3803         int ret;
3804 
3805         mutex_lock(&cgroup_mutex);
3806         ret = cgroup_rm_cftypes_locked(cfts);
3807         mutex_unlock(&cgroup_mutex);
3808         return ret;
3809 }
3810 
3811 /**
3812  * cgroup_add_cftypes - add an array of cftypes to a subsystem
3813  * @ss: target cgroup subsystem
3814  * @cfts: zero-length name terminated array of cftypes
3815  *
3816  * Register @cfts to @ss.  Files described by @cfts are created for all
3817  * existing cgroups to which @ss is attached and all future cgroups will
3818  * have them too.  This function can be called anytime whether @ss is
3819  * attached or not.
3820  *
3821  * Returns 0 on successful registration, -errno on failure.  Note that this
3822  * function currently returns 0 as long as @cfts registration is successful
3823  * even if some file creation attempts on existing cgroups fail.
3824  */
3825 static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3826 {
3827         int ret;
3828 
3829         if (!cgroup_ssid_enabled(ss->id))
3830                 return 0;
3831 
3832         if (!cfts || cfts[0].name[0] == '\0')
3833                 return 0;
3834 
3835         ret = cgroup_init_cftypes(ss, cfts);
3836         if (ret)
3837                 return ret;
3838 
3839         mutex_lock(&cgroup_mutex);
3840 
3841         list_add_tail(&cfts->node, &ss->cfts);
3842         ret = cgroup_apply_cftypes(cfts, true);
3843         if (ret)
3844                 cgroup_rm_cftypes_locked(cfts);
3845 
3846         mutex_unlock(&cgroup_mutex);
3847         return ret;
3848 }
3849 
3850 /**
3851  * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
3852  * @ss: target cgroup subsystem
3853  * @cfts: zero-length name terminated array of cftypes
3854  *
3855  * Similar to cgroup_add_cftypes() but the added files are only used for
3856  * the default hierarchy.
3857  */
3858 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3859 {
3860         struct cftype *cft;
3861 
3862         for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3863                 cft->flags |= __CFTYPE_ONLY_ON_DFL;
3864         return cgroup_add_cftypes(ss, cfts);
3865 }
3866 
3867 /**
3868  * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
3869  * @ss: target cgroup subsystem
3870  * @cfts: zero-length name terminated array of cftypes
3871  *
3872  * Similar to cgroup_add_cftypes() but the added files are only used for
3873  * the legacy hierarchies.
3874  */
3875 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3876 {
3877         struct cftype *cft;
3878 
3879         for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3880                 cft->flags |= __CFTYPE_NOT_ON_DFL;
3881         return cgroup_add_cftypes(ss, cfts);
3882 }
3883 
3884 /**
3885  * cgroup_file_notify - generate a file modified event for a cgroup_file
3886  * @cfile: target cgroup_file
3887  *
3888  * @cfile must have been obtained by setting cftype->file_offset.
3889  */
3890 void cgroup_file_notify(struct cgroup_file *cfile)
3891 {
3892         unsigned long flags;
3893 
3894         spin_lock_irqsave(&cgroup_file_kn_lock, flags);
3895         if (cfile->kn)
3896                 kernfs_notify(cfile->kn);
3897         spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
3898 }
3899 
3900 /**
3901  * cgroup_task_count - count the number of tasks in a cgroup.
3902  * @cgrp: the cgroup in question
3903  *
3904  * Return the number of tasks in the cgroup.
3905  */
3906 static int cgroup_task_count(const struct cgroup *cgrp)
3907 {
3908         int count = 0;
3909         struct cgrp_cset_link *link;
3910 
3911         spin_lock_bh(&css_set_lock);
3912         list_for_each_entry(link, &cgrp->cset_links, cset_link)
3913                 count += atomic_read(&link->cset->refcount);
3914         spin_unlock_bh(&css_set_lock);
3915         return count;
3916 }
3917 
3918 /**
3919  * css_next_child - find the next child of a given css
3920  * @pos: the current position (%NULL to initiate traversal)
3921  * @parent: css whose children to walk
3922  *
3923  * This function returns the next child of @parent and should be called
3924  * under either cgroup_mutex or RCU read lock.  The only requirement is
3925  * that @parent and @pos are accessible.  The next sibling is guaranteed to
3926  * be returned regardless of their states.
3927  *
3928  * If a subsystem synchronizes ->css_online() and the start of iteration, a
3929  * css which finished ->css_online() is guaranteed to be visible in the
3930  * future iterations and will stay visible until the last reference is put.
3931  * A css which hasn't finished ->css_online() or already finished
3932  * ->css_offline() may show up during traversal.  It's each subsystem's
3933  * responsibility to synchronize against on/offlining.
3934  */
3935 struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
3936                                            struct cgroup_subsys_state *parent)
3937 {
3938         struct cgroup_subsys_state *next;
3939 
3940         cgroup_assert_mutex_or_rcu_locked();
3941 
3942         /*
3943          * @pos could already have been unlinked from the sibling list.
3944          * Once a cgroup is removed, its ->sibling.next is no longer
3945          * updated when its next sibling changes.  CSS_RELEASED is set when
3946          * @pos is taken off list, at which time its next pointer is valid,
3947          * and, as releases are serialized, the one pointed to by the next
3948          * pointer is guaranteed to not have started release yet.  This
3949          * implies that if we observe !CSS_RELEASED on @pos in this RCU
3950          * critical section, the one pointed to by its next pointer is
3951          * guaranteed to not have finished its RCU grace period even if we
3952          * have dropped rcu_read_lock() inbetween iterations.
3953          *
3954          * If @pos has CSS_RELEASED set, its next pointer can't be
3955          * dereferenced; however, as each css is given a monotonically
3956          * increasing unique serial number and always appended to the
3957          * sibling list, the next one can be found by walking the parent's
3958          * children until the first css with higher serial number than
3959          * @pos's.  While this path can be slower, it happens iff iteration
3960          * races against release and the race window is very small.
3961          */
3962         if (!pos) {
3963                 next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
3964         } else if (likely(!(pos->flags & CSS_RELEASED))) {
3965                 next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
3966         } else {
3967                 list_for_each_entry_rcu(next, &parent->children, sibling)
3968                         if (next->serial_nr > pos->serial_nr)
3969                                 break;
3970         }
3971 
3972         /*
3973          * @next, if not pointing to the head, can be dereferenced and is
3974          * the next sibling.
3975          */
3976         if (&next->sibling != &parent->children)
3977                 return next;
3978         return NULL;
3979 }
3980 
3981 /**
3982  * css_next_descendant_pre - find the next descendant for pre-order walk
3983  * @pos: the current position (%NULL to initiate traversal)
3984  * @root: css whose descendants to walk
3985  *
3986  * To be used by css_for_each_descendant_pre().  Find the next descendant
3987  * to visit for pre-order traversal of @root's descendants.  @root is
3988  * included in the iteration and the first node to be visited.
3989  *
3990  * While this function requires cgroup_mutex or RCU read locking, it
3991  * doesn't require the whole traversal to be contained in a single critical
3992  * section.  This function will return the correct next descendant as long
3993  * as both @pos and @root are accessible and @pos is a descendant of @root.
3994  *
3995  * If a subsystem synchronizes ->css_online() and the start of iteration, a
3996  * css which finished ->css_online() is guaranteed to be visible in the
3997  * future iterations and will stay visible until the last reference is put.
3998  * A css which hasn't finished ->css_online() or already finished
3999  * ->css_offline() may show up during traversal.  It's each subsystem's
4000  * responsibility to synchronize against on/offlining.
4001  */
4002 struct cgroup_subsys_state *
4003 css_next_descendant_pre(struct cgroup_subsys_state *pos,
4004                         struct cgroup_subsys_state *root)
4005 {
4006         struct cgroup_subsys_state *next;
4007 
4008         cgroup_assert_mutex_or_rcu_locked();
4009 
4010         /* if first iteration, visit @root */
4011         if (!pos)
4012                 return root;
4013 
4014         /* visit the first child if exists */
4015         next = css_next_child(NULL, pos);
4016         if (next)
4017                 return next;
4018 
4019         /* no child, visit my or the closest ancestor's next sibling */
4020         while (pos != root) {
4021                 next = css_next_child(pos, pos->parent);
4022                 if (next)
4023                         return next;
4024                 pos = pos->parent;
4025         }
4026 
4027         return NULL;
4028 }
4029 
4030 /**
4031  * css_rightmost_descendant - return the rightmost descendant of a css
4032  * @pos: css of interest
4033  *
4034  * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4035  * is returned.  This can be used during pre-order traversal to skip
4036  * subtree of @pos.
4037  *
4038  * While this function requires cgroup_mutex or RCU read locking, it
4039  * doesn't require the whole traversal to be contained in a single critical
4040  * section.  This function will return the correct rightmost descendant as
4041  * long as @pos is accessible.
4042  */
4043 struct cgroup_subsys_state *
4044 css_rightmost_descendant(struct cgroup_subsys_state *pos)
4045 {
4046         struct cgroup_subsys_state *last, *tmp;
4047 
4048         cgroup_assert_mutex_or_rcu_locked();
4049 
4050         do {
4051                 last = pos;
4052                 /* ->prev isn't RCU safe, walk ->next till the end */
4053                 pos = NULL;
4054                 css_for_each_child(tmp, last)
4055                         pos = tmp;
4056         } while (pos);
4057 
4058         return last;
4059 }
4060 
4061 static struct cgroup_subsys_state *
4062 css_leftmost_descendant(struct cgroup_subsys_state *pos)
4063 {
4064         struct cgroup_subsys_state *last;
4065 
4066         do {
4067                 last = pos;
4068                 pos = css_next_child(NULL, pos);
4069         } while (pos);
4070 
4071         return last;
4072 }
4073 
4074 /**
4075  * css_next_descendant_post - find the next descendant for post-order walk
4076  * @pos: the current position (%NULL to initiate traversal)
4077  * @root: css whose descendants to walk
4078  *
4079  * To be used by css_for_each_descendant_post().  Find the next descendant
4080  * to visit for post-order traversal of @root's descendants.  @root is
4081  * included in the iteration and the last node to be visited.
4082  *
4083  * While this function requires cgroup_mutex or RCU read locking, it
4084  * doesn't require the whole traversal to be contained in a single critical
4085  * section.  This function will return the correct next descendant as long
4086  * as both @pos and @cgroup are accessible and @pos is a descendant of
4087  * @cgroup.
4088  *
4089  * If a subsystem synchronizes ->css_online() and the start of iteration, a
4090  * css which finished ->css_online() is guaranteed to be visible in the
4091  * future iterations and will stay visible until the last reference is put.
4092  * A css which hasn't finished ->css_online() or already finished
4093  * ->css_offline() may show up during traversal.  It's each subsystem's
4094  * responsibility to synchronize against on/offlining.
4095  */
4096 struct cgroup_subsys_state *
4097 css_next_descendant_post(struct cgroup_subsys_state *pos,
4098                          struct cgroup_subsys_state *root)
4099 {
4100         struct cgroup_subsys_state *next;
4101 
4102         cgroup_assert_mutex_or_rcu_locked();
4103 
4104         /* if first iteration, visit leftmost descendant which may be @root */
4105         if (!pos)
4106                 return css_leftmost_descendant(root);
4107 
4108         /* if we visited @root, we're done */
4109         if (pos == root)
4110                 return NULL;
4111 
4112         /* if there's an unvisited sibling, visit its leftmost descendant */
4113         next = css_next_child(pos, pos->parent);
4114         if (next)
4115                 return css_leftmost_descendant(next);
4116 
4117         /* no sibling left, visit parent */
4118         return pos->parent;
4119 }
4120 
4121 /**
4122  * css_has_online_children - does a css have online children
4123  * @css: the target css
4124  *
4125  * Returns %true if @css has any online children; otherwise, %false.  This
4126  * function can be called from any context but the caller is responsible
4127  * for synchronizing against on/offlining as necessary.
4128  */
4129 bool css_has_online_children(struct cgroup_subsys_state *css)
4130 {
4131         struct cgroup_subsys_state *child;
4132         bool ret = false;
4133 
4134         rcu_read_lock();
4135         css_for_each_child(child, css) {
4136                 if (child->flags & CSS_ONLINE) {
4137                         ret = true;
4138                         break;
4139                 }
4140         }
4141         rcu_read_unlock();
4142         return ret;
4143 }
4144 
4145 /**
4146  * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4147  * @it: the iterator to advance
4148  *
4149  * Advance @it to the next css_set to walk.
4150  */
4151 static void css_task_iter_advance_css_set(struct css_task_iter *it)
4152 {
4153         struct list_head *l = it->cset_pos;
4154         struct cgrp_cset_link *link;
4155         struct css_set *cset;
4156 
4157         lockdep_assert_held(&css_set_lock);
4158 
4159         /* Advance to the next non-empty css_set */
4160         do {
4161                 l = l->next;
4162                 if (l == it->cset_head) {
4163                         it->cset_pos = NULL;
4164                         it->task_pos = NULL;
4165                         return;
4166                 }
4167 
4168                 if (it->ss) {
4169                         cset = container_of(l, struct css_set,
4170                                             e_cset_node[it->ss->id]);
4171                 } else {
4172                         link = list_entry(l, struct cgrp_cset_link, cset_link);
4173                         cset = link->cset;
4174                 }
4175         } while (!css_set_populated(cset));
4176 
4177         it->cset_pos = l;
4178 
4179         if (!list_empty(&cset->tasks))
4180                 it->task_pos = cset->tasks.next;
4181         else
4182                 it->task_pos = cset->mg_tasks.next;
4183 
4184         it->tasks_head = &cset->tasks;
4185         it->mg_tasks_head = &cset->mg_tasks;
4186 
4187         /*
4188          * We don't keep css_sets locked across iteration steps and thus
4189          * need to take steps to ensure that iteration can be resumed after
4190          * the lock is re-acquired.  Iteration is performed at two levels -
4191          * css_sets and tasks in them.
4192          *
4193          * Once created, a css_set never leaves its cgroup lists, so a
4194          * pinned css_set is guaranteed to stay put and we can resume
4195          * iteration afterwards.
4196          *
4197          * Tasks may leave @cset across iteration steps.  This is resolved
4198          * by registering each iterator with the css_set currently being
4199          * walked and making css_set_move_task() advance iterators whose
4200          * next task is leaving.
4201          */
4202         if (it->cur_cset) {
4203                 list_del(&it->iters_node);
4204                 put_css_set_locked(it->cur_cset);
4205         }
4206         get_css_set(cset);
4207         it->cur_cset = cset;
4208         list_add(&it->iters_node, &cset->task_iters);
4209 }
4210 
4211 static void css_task_iter_advance(struct css_task_iter *it)
4212 {
4213         struct list_head *l = it->task_pos;
4214 
4215         lockdep_assert_held(&css_set_lock);
4216         WARN_ON_ONCE(!l);
4217 
4218         /*
4219          * Advance iterator to find next entry.  cset->tasks is consumed
4220          * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
4221          * next cset.
4222          */
4223         l = l->next;
4224 
4225         if (l == it->tasks_head)
4226                 l = it->mg_tasks_head->next;
4227 
4228         if (l == it->mg_tasks_head)
4229                 css_task_iter_advance_css_set(it);
4230         else
4231                 it->task_pos = l;
4232 }
4233 
4234 /**
4235  * css_task_iter_start - initiate task iteration
4236  * @css: the css to walk tasks of
4237  * @it: the task iterator to use
4238  *
4239  * Initiate iteration through the tasks of @css.  The caller can call
4240  * css_task_iter_next() to walk through the tasks until the function
4241  * returns NULL.  On completion of iteration, css_task_iter_end() must be
4242  * called.
4243  */
4244 void css_task_iter_start(struct cgroup_subsys_state *css,
4245                          struct css_task_iter *it)
4246 {
4247         /* no one should try to iterate before mounting cgroups */
4248         WARN_ON_ONCE(!use_task_css_set_links);
4249 
4250         memset(it, 0, sizeof(*it));
4251 
4252         spin_lock_bh(&css_set_lock);
4253 
4254         it->ss = css->ss;
4255 
4256         if (it->ss)
4257                 it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4258         else
4259                 it->cset_pos = &css->cgroup->cset_links;
4260 
4261         it->cset_head = it->cset_pos;
4262 
4263         css_task_iter_advance_css_set(it);
4264 
4265         spin_unlock_bh(&css_set_lock);
4266 }
4267 
4268 /**
4269  * css_task_iter_next - return the next task for the iterator
4270  * @it: the task iterator being iterated
4271  *
4272  * The "next" function for task iteration.  @it should have been
4273  * initialized via css_task_iter_start().  Returns NULL when the iteration
4274  * reaches the end.
4275  */
4276 struct task_struct *css_task_iter_next(struct css_task_iter *it)
4277 {
4278         if (it->cur_task) {
4279                 put_task_struct(it->cur_task);
4280                 it->cur_task = NULL;
4281         }
4282 
4283         spin_lock_bh(&css_set_lock);
4284 
4285         if (it->task_pos) {
4286                 it->cur_task = list_entry(it->task_pos, struct task_struct,
4287                                           cg_list);
4288                 get_task_struct(it->cur_task);
4289                 css_task_iter_advance(it);
4290         }
4291 
4292         spin_unlock_bh(&css_set_lock);
4293 
4294         return it->cur_task;
4295 }
4296 
4297 /**
4298  * css_task_iter_end - finish task iteration
4299  * @it: the task iterator to finish
4300  *
4301  * Finish task iteration started by css_task_iter_start().
4302  */
4303 void css_task_iter_end(struct css_task_iter *it)
4304 {
4305         if (it->cur_cset) {
4306                 spin_lock_bh(&css_set_lock);
4307                 list_del(&it->iters_node);
4308                 put_css_set_locked(it->cur_cset);
4309                 spin_unlock_bh(&css_set_lock);
4310         }
4311 
4312         if (it->cur_task)
4313                 put_task_struct(it->cur_task);
4314 }
4315 
4316 /**
4317  * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
4318  * @to: cgroup to which the tasks will be moved
4319  * @from: cgroup in which the tasks currently reside
4320  *
4321  * Locking rules between cgroup_post_fork() and the migration path
4322  * guarantee that, if a task is forking while being migrated, the new child
4323  * is guaranteed to be either visible in the source cgroup after the
4324  * parent's migration is complete or put into the target cgroup.  No task
4325  * can slip out of migration through forking.
4326  */
4327 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
4328 {
4329         LIST_HEAD(preloaded_csets);
4330         struct cgrp_cset_link *link;
4331         struct css_task_iter it;
4332         struct task_struct *task;
4333         int ret;
4334 
4335         if (!cgroup_may_migrate_to(to))
4336                 return -EBUSY;
4337 
4338         mutex_lock(&cgroup_mutex);
4339 
4340         /* all tasks in @from are being moved, all csets are source */
4341         spin_lock_bh(&css_set_lock);
4342         list_for_each_entry(link, &from->cset_links, cset_link)
4343                 cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
4344         spin_unlock_bh(&css_set_lock);
4345 
4346         ret = cgroup_migrate_prepare_dst(&preloaded_csets);
4347         if (ret)
4348                 goto out_err;
4349 
4350         /*
4351          * Migrate tasks one-by-one until @from is empty.  This fails iff
4352          * ->can_attach() fails.
4353          */
4354         do {
4355                 css_task_iter_start(&from->self, &it);
4356                 task = css_task_iter_next(&it);
4357                 if (task)
4358                         get_task_struct(task);
4359                 css_task_iter_end(&it);
4360 
4361                 if (task) {
4362                         ret = cgroup_migrate(task, false, to->root);
4363                         put_task_struct(task);
4364                 }
4365         } while (task && !ret);
4366 out_err:
4367         cgroup_migrate_finish(&preloaded_csets);
4368         mutex_unlock(&cgroup_mutex);
4369         return ret;
4370 }
4371 
4372 /*
4373  * Stuff for reading the 'tasks'/'procs' files.
4374  *
4375  * Reading this file can return large amounts of data if a cgroup has
4376  * *lots* of attached tasks. So it may need several calls to read(),
4377  * but we cannot guarantee that the information we produce is correct
4378  * unless we produce it entirely atomically.
4379  *
4380  */
4381 
4382 /* which pidlist file are we talking about? */
4383 enum cgroup_filetype {
4384         CGROUP_FILE_PROCS,
4385         CGROUP_FILE_TASKS,
4386 };
4387 
4388 /*
4389  * A pidlist is a list of pids that virtually represents the contents of one
4390  * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
4391  * a pair (one each for procs, tasks) for each pid namespace that's relevant
4392  * to the cgroup.
4393  */
4394 struct cgroup_pidlist {
4395         /*
4396          * used to find which pidlist is wanted. doesn't change as long as
4397          * this particular list stays in the list.
4398         */
4399         struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
4400         /* array of xids */
4401         pid_t *list;
4402         /* how many elements the above list has */
4403         int length;
4404         /* each of these stored in a list by its cgroup */
4405         struct list_head links;
4406         /* pointer to the cgroup we belong to, for list removal purposes */
4407         struct cgroup *owner;
4408         /* for delayed destruction */
4409         struct delayed_work destroy_dwork;
4410 };
4411 
4412 /*
4413  * The following two functions "fix" the issue where there are more pids
4414  * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
4415  * TODO: replace with a kernel-wide solution to this problem
4416  */
4417 #define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
4418 static void *pidlist_allocate(int count)
4419 {
4420         if (PIDLIST_TOO_LARGE(count))
4421                 return vmalloc(count * sizeof(pid_t));
4422         else
4423                 return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
4424 }
4425 
4426 static void pidlist_free(void *p)
4427 {
4428         kvfree(p);
4429 }
4430 
4431 /*
4432  * Used to destroy all pidlists lingering waiting for destroy timer.  None
4433  * should be left afterwards.
4434  */
4435 static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
4436 {
4437         struct cgroup_pidlist *l, *tmp_l;
4438 
4439         mutex_lock(&cgrp->pidlist_mutex);
4440         list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
4441                 mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
4442         mutex_unlock(&cgrp->pidlist_mutex);
4443 
4444         flush_workqueue(cgroup_pidlist_destroy_wq);
4445         BUG_ON(!list_empty(&cgrp->pidlists));
4446 }
4447 
4448 static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
4449 {
4450         struct delayed_work *dwork = to_delayed_work(work);
4451         struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
4452                                                 destroy_dwork);
4453         struct cgroup_pidlist *tofree = NULL;
4454 
4455         mutex_lock(&l->owner->pidlist_mutex);
4456 
4457         /*
4458          * Destroy iff we didn't get queued again.  The state won't change
4459          * as destroy_dwork can only be queued while locked.
4460          */
4461         if (!delayed_work_pending(dwork)) {
4462                 list_del(&l->links);
4463                 pidlist_free(l->list);
4464                 put_pid_ns(l->key.ns);
4465                 tofree = l;
4466         }
4467 
4468         mutex_unlock(&l->owner->pidlist_mutex);
4469         kfree(tofree);
4470 }
4471 
4472 /*
4473  * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
4474  * Returns the number of unique elements.
4475  */
4476 static int pidlist_uniq(pid_t *list, int length)
4477 {
4478         int src, dest = 1;
4479 
4480         /*
4481          * we presume the 0th element is unique, so i starts at 1. trivial
4482          * edge cases first; no work needs to be done for either
4483          */
4484         if (length == 0 || length == 1)
4485                 return length;
4486         /* src and dest walk down the list; dest counts unique elements */
4487         for (src = 1; src < length; src++) {
4488                 /* find next unique element */
4489                 while (list[src] == list[src-1]) {
4490                         src++;
4491                         if (src == length)
4492                                 goto after;
4493                 }
4494                 /* dest always points to where the next unique element goes */
4495                 list[dest] = list[src];
4496                 dest++;
4497         }
4498 after:
4499         return dest;
4500 }
4501 
4502 /*
4503  * The two pid files - task and cgroup.procs - guaranteed that the result
4504  * is sorted, which forced this whole pidlist fiasco.  As pid order is
4505  * different per namespace, each namespace needs differently sorted list,
4506  * making it impossible to use, for example, single rbtree of member tasks
4507  * sorted by task pointer.  As pidlists can be fairly large, allocating one
4508  * per open file is dangerous, so cgroup had to implement shared pool of
4509  * pidlists keyed by cgroup and namespace.
4510  *
4511  * All this extra complexity was caused by the original implementation
4512  * committing to an entirely unnecessary property.  In the long term, we
4513  * want to do away with it.  Explicitly scramble sort order if on the
4514  * default hierarchy so that no such expectation exists in the new
4515  * interface.
4516  *
4517  * Scrambling is done by swapping every two consecutive bits, which is
4518  * non-identity one-to-one mapping which disturbs sort order sufficiently.
4519  */
4520 static pid_t pid_fry(pid_t pid)
4521 {
4522         unsigned a = pid & 0x55555555;
4523         unsigned b = pid & 0xAAAAAAAA;
4524 
4525         return (a << 1) | (b >> 1);
4526 }
4527 
4528 static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
4529 {
4530         if (cgroup_on_dfl(cgrp))
4531                 return pid_fry(pid);
4532         else
4533                 return pid;
4534 }
4535 
4536 static int cmppid(const void *a, const void *b)
4537 {
4538         return *(pid_t *)a - *(pid_t *)b;
4539 }
4540 
4541 static int fried_cmppid(const void *a, const void *b)
4542 {
4543         return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b);
4544 }
4545 
4546 static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
4547                                                   enum cgroup_filetype type)
4548 {
4549         struct cgroup_pidlist *l;
4550         /* don't need task_nsproxy() if we're looking at ourself */
4551         struct pid_namespace *ns = task_active_pid_ns(current);
4552 
4553         lockdep_assert_held(&cgrp->pidlist_mutex);
4554 
4555         list_for_each_entry(l, &cgrp->pidlists, links)
4556                 if (l->key.type == type && l->key.ns == ns)
4557                         return l;
4558         return NULL;
4559 }
4560 
4561 /*
4562  * find the appropriate pidlist for our purpose (given procs vs tasks)
4563  * returns with the lock on that pidlist already held, and takes care
4564  * of the use count, or returns NULL with no locks held if we're out of
4565  * memory.
4566  */
4567 static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
4568                                                 enum cgroup_filetype type)
4569 {
4570         struct cgroup_pidlist *l;
4571 
4572         lockdep_assert_held(&cgrp->pidlist_mutex);
4573 
4574         l = cgroup_pidlist_find(cgrp, type);
4575         if (l)
4576                 return l;
4577 
4578         /* entry not found; create a new one */
4579         l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
4580         if (!l)
4581                 return l;
4582 
4583         INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
4584         l->key.type = type;
4585         /* don't need task_nsproxy() if we're looking at ourself */
4586         l->key.ns = get_pid_ns(task_active_pid_ns(current));
4587         l->owner = cgrp;
4588         list_add(&l->links, &cgrp->pidlists);
4589         return l;
4590 }
4591 
4592 /*
4593  * Load a cgroup's pidarray with either procs' tgids or tasks' pids
4594  */
4595 static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
4596                               struct cgroup_pidlist **lp)
4597 {
4598         pid_t *array;
4599         int length;
4600         int pid, n = 0; /* used for populating the array */
4601         struct css_task_iter it;
4602         struct task_struct *tsk;
4603         struct cgroup_pidlist *l;
4604 
4605         lockdep_assert_held(&cgrp->pidlist_mutex);
4606 
4607         /*
4608          * If cgroup gets more users after we read count, we won't have
4609          * enough space - tough.  This race is indistinguishable to the
4610          * caller from the case that the additional cgroup users didn't
4611          * show up until sometime later on.
4612          */
4613         length = cgroup_task_count(cgrp);
4614         array = pidlist_allocate(length);
4615         if (!array)
4616                 return -ENOMEM;
4617         /* now, populate the array */
4618         css_task_iter_start(&cgrp->self, &it);
4619         while ((tsk = css_task_iter_next(&it))) {
4620                 if (unlikely(n == length))
4621                         break;
4622                 /* get tgid or pid for procs or tasks file respectively */
4623                 if (type == CGROUP_FILE_PROCS)
4624                         pid = task_tgid_vnr(tsk);
4625                 else
4626                         pid = task_pid_vnr(tsk);
4627                 if (pid > 0) /* make sure to only use valid results */
4628                         array[n++] = pid;
4629         }
4630         css_task_iter_end(&it);
4631         length = n;
4632         /* now sort & (if procs) strip out duplicates */
4633         if (cgroup_on_dfl(cgrp))
4634                 sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
4635         else
4636                 sort(array, length, sizeof(pid_t), cmppid, NULL);
4637         if (type == CGROUP_FILE_PROCS)
4638                 length = pidlist_uniq(array, length);
4639 
4640         l = cgroup_pidlist_find_create(cgrp, type);
4641         if (!l) {
4642                 pidlist_free(array);
4643                 return -ENOMEM;
4644         }
4645 
4646         /* store array, freeing old if necessary */
4647         pidlist_free(l->list);
4648         l->list = array;
4649         l->length = length;
4650         *lp = l;
4651         return 0;
4652 }
4653 
4654 /**
4655  * cgroupstats_build - build and fill cgroupstats
4656  * @stats: cgroupstats to fill information into
4657  * @dentry: A dentry entry belonging to the cgroup for which stats have
4658  * been requested.
4659  *
4660  * Build and fill cgroupstats so that taskstats can export it to user
4661  * space.
4662  */
4663 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
4664 {
4665         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
4666         struct cgroup *cgrp;
4667         struct css_task_iter it;
4668         struct task_struct *tsk;
4669 
4670         /* it should be kernfs_node belonging to cgroupfs and is a directory */
4671         if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
4672             kernfs_type(kn) != KERNFS_DIR)
4673                 return -EINVAL;
4674 
4675         mutex_lock(&cgroup_mutex);
4676 
4677         /*
4678          * We aren't being called from kernfs and there's no guarantee on
4679          * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
4680          * @kn->priv is RCU safe.  Let's do the RCU dancing.
4681          */
4682         rcu_read_lock();
4683         cgrp = rcu_dereference(kn->priv);
4684         if (!cgrp || cgroup_is_dead(cgrp)) {
4685                 rcu_read_unlock();
4686                 mutex_unlock(&cgroup_mutex);
4687                 return -ENOENT;
4688         }
4689         rcu_read_unlock();
4690 
4691         css_task_iter_start(&cgrp->self, &it);
4692         while ((tsk = css_task_iter_next(&it))) {
4693                 switch (tsk->state) {
4694                 case TASK_RUNNING:
4695                         stats->nr_running++;
4696                         break;
4697                 case TASK_INTERRUPTIBLE:
4698                         stats->nr_sleeping++;
4699                         break;
4700                 case TASK_UNINTERRUPTIBLE:
4701                         stats->nr_uninterruptible++;
4702                         break;
4703                 case TASK_STOPPED:
4704                         stats->nr_stopped++;
4705                         break;
4706                 default:
4707                         if (delayacct_is_task_waiting_on_io(tsk))
4708                                 stats->nr_io_wait++;
4709                         break;
4710                 }
4711         }
4712         css_task_iter_end(&it);
4713 
4714         mutex_unlock(&cgroup_mutex);
4715         return 0;
4716 }
4717 
4718 
4719 /*
4720  * seq_file methods for the tasks/procs files. The seq_file position is the
4721  * next pid to display; the seq_file iterator is a pointer to the pid
4722  * in the cgroup->l->list array.
4723  */
4724 
4725 static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
4726 {
4727         /*
4728          * Initially we receive a position value that corresponds to
4729          * one more than the last pid shown (or 0 on the first call or
4730          * after a seek to the start). Use a binary-search to find the
4731          * next pid to display, if any
4732          */
4733         struct kernfs_open_file *of = s->private;
4734         struct cgroup *cgrp = seq_css(s)->cgroup;
4735         struct cgroup_pidlist *l;
4736         enum cgroup_filetype type = seq_cft(s)->private;
4737         int index = 0, pid = *pos;
4738         int *iter, ret;
4739 
4740         mutex_lock(&cgrp->pidlist_mutex);
4741 
4742         /*
4743          * !NULL @of->priv indicates that this isn't the first start()
4744          * after open.  If the matching pidlist is around, we can use that.
4745          * Look for it.  Note that @of->priv can't be used directly.  It
4746          * could already have been destroyed.
4747          */
4748         if (of->priv)
4749                 of->priv = cgroup_pidlist_find(cgrp, type);
4750 
4751         /*
4752          * Either this is the first start() after open or the matching
4753          * pidlist has been destroyed inbetween.  Create a new one.
4754          */
4755         if (!of->priv) {
4756                 ret = pidlist_array_load(cgrp, type,
4757                                          (struct cgroup_pidlist **)&of->priv);
4758                 if (ret)
4759                         return ERR_PTR(ret);
4760         }
4761         l = of->priv;
4762 
4763         if (pid) {
4764                 int end = l->length;
4765 
4766                 while (index < end) {
4767                         int mid = (index + end) / 2;
4768                         if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
4769                                 index = mid;
4770                                 break;
4771                         } else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
4772                                 index = mid + 1;
4773                         else
4774                                 end = mid;
4775                 }
4776         }
4777         /* If we're off the end of the array, we're done */
4778         if (index >= l->length)
4779                 return NULL;
4780         /* Update the abstract position to be the actual pid that we found */
4781         iter = l->list + index;
4782         *pos = cgroup_pid_fry(cgrp, *iter);
4783         return iter;
4784 }
4785 
4786 static void cgroup_pidlist_stop(struct seq_file *s, void *v)
4787 {
4788         struct kernfs_open_file *of = s->private;
4789         struct cgroup_pidlist *l = of->priv;
4790 
4791         if (l)
4792                 mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
4793                                  CGROUP_PIDLIST_DESTROY_DELAY);
4794         mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
4795 }
4796 
4797 static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
4798 {
4799         struct kernfs_open_file *of = s->private;
4800         struct cgroup_pidlist *l = of->priv;
4801         pid_t *p = v;
4802         pid_t *end = l->list + l->length;
4803         /*
4804          * Advance to the next pid in the array. If this goes off the
4805          * end, we're done
4806          */
4807         p++;
4808         if (p >= end) {
4809                 return NULL;
4810         } else {
4811                 *pos = cgroup_pid_fry(seq_css(s)->cgroup, *p);
4812                 return p;
4813         }
4814 }
4815 
4816 static int cgroup_pidlist_show(struct seq_file *s, void *v)
4817 {
4818         seq_printf(s, "%d\n", *(int *)v);
4819 
4820         return 0;
4821 }
4822 
4823 static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
4824                                          struct cftype *cft)
4825 {
4826         return notify_on_release(css->cgroup);
4827 }
4828 
4829 static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
4830                                           struct cftype *cft, u64 val)
4831 {
4832         if (val)
4833                 set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4834         else
4835                 clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4836         return 0;
4837 }
4838 
4839 static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
4840                                       struct cftype *cft)
4841 {
4842         return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4843 }
4844 
4845 static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
4846                                        struct cftype *cft, u64 val)
4847 {
4848         if (val)
4849                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4850         else
4851                 clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4852         return 0;
4853 }
4854 
4855 /* cgroup core interface files for the default hierarchy */
4856 static struct cftype cgroup_dfl_base_files[] = {
4857         {
4858                 .name = "cgroup.procs",
4859                 .file_offset = offsetof(struct cgroup, procs_file),
4860                 .seq_start = cgroup_pidlist_start,
4861                 .seq_next = cgroup_pidlist_next,
4862                 .seq_stop = cgroup_pidlist_stop,
4863                 .seq_show = cgroup_pidlist_show,
4864                 .private = CGROUP_FILE_PROCS,
4865                 .write = cgroup_procs_write,
4866         },
4867         {
4868                 .name = "cgroup.controllers",
4869                 .seq_show = cgroup_controllers_show,
4870         },
4871         {
4872                 .name = "cgroup.subtree_control",
4873                 .seq_show = cgroup_subtree_control_show,
4874                 .write = cgroup_subtree_control_write,
4875         },
4876         {
4877                 .name = "cgroup.events",
4878                 .flags = CFTYPE_NOT_ON_ROOT,
4879                 .file_offset = offsetof(struct cgroup, events_file),
4880                 .seq_show = cgroup_events_show,
4881         },
4882         { }     /* terminate */
4883 };
4884 
4885 /* cgroup core interface files for the legacy hierarchies */
4886 static struct cftype cgroup_legacy_base_files[] = {
4887         {
4888                 .name = "cgroup.procs",
4889                 .seq_start = cgroup_pidlist_start,
4890                 .seq_next = cgroup_pidlist_next,
4891                 .seq_stop = cgroup_pidlist_stop,
4892                 .seq_show = cgroup_pidlist_show,
4893                 .private = CGROUP_FILE_PROCS,
4894                 .write = cgroup_procs_write,
4895         },
4896         {
4897                 .name = "cgroup.clone_children",
4898                 .read_u64 = cgroup_clone_children_read,
4899                 .write_u64 = cgroup_clone_children_write,
4900         },
4901         {
4902                 .name = "cgroup.sane_behavior",
4903                 .flags = CFTYPE_ONLY_ON_ROOT,
4904                 .seq_show = cgroup_sane_behavior_show,
4905         },
4906         {
4907                 .name = "tasks",
4908                 .seq_start = cgroup_pidlist_start,
4909                 .seq_next = cgroup_pidlist_next,
4910                 .seq_stop = cgroup_pidlist_stop,
4911                 .seq_show = cgroup_pidlist_show,
4912                 .private = CGROUP_FILE_TASKS,
4913                 .write = cgroup_tasks_write,
4914         },
4915         {
4916                 .name = "notify_on_release",
4917                 .read_u64 = cgroup_read_notify_on_release,
4918                 .write_u64 = cgroup_write_notify_on_release,
4919         },
4920         {
4921                 .name = "release_agent",
4922                 .flags = CFTYPE_ONLY_ON_ROOT,
4923                 .seq_show = cgroup_release_agent_show,
4924                 .write = cgroup_release_agent_write,
4925                 .max_write_len = PATH_MAX - 1,
4926         },
4927         { }     /* terminate */
4928 };
4929 
4930 /*
4931  * css destruction is four-stage process.
4932  *
4933  * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4934  *    Implemented in kill_css().
4935  *
4936  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4937  *    and thus css_tryget_online() is guaranteed to fail, the css can be
4938  *    offlined by invoking offline_css().  After offlining, the base ref is
4939  *    put.  Implemented in css_killed_work_fn().
4940  *
4941  * 3. When the percpu_ref reaches zero, the only possible remaining
4942  *    accessors are inside RCU read sections.  css_release() schedules the
4943  *    RCU callback.
4944  *
4945  * 4. After the grace period, the css can be freed.  Implemented in
4946  *    css_free_work_fn().
4947  *
4948  * It is actually hairier because both step 2 and 4 require process context
4949  * and thus involve punting to css->destroy_work adding two additional
4950  * steps to the already complex sequence.
4951  */
4952 static void css_free_work_fn(struct work_struct *work)
4953 {
4954         struct cgroup_subsys_state *css =
4955                 container_of(work, struct cgroup_subsys_state, destroy_work);
4956         struct cgroup_subsys *ss = css->ss;
4957         struct cgroup *cgrp = css->cgroup;
4958 
4959         percpu_ref_exit(&css->refcnt);
4960 
4961         if (ss) {
4962                 /* css free path */
4963                 struct cgroup_subsys_state *parent = css->parent;
4964                 int id = css->id;
4965 
4966                 ss->css_free(css);
4967                 cgroup_idr_remove(&ss->css_idr, id);
4968                 cgroup_put(cgrp);
4969 
4970                 if (parent)
4971                         css_put(parent);
4972         } else {
4973                 /* cgroup free path */
4974                 atomic_dec(&cgrp->root->nr_cgrps);
4975                 cgroup_pidlist_destroy_all(cgrp);
4976                 cancel_work_sync(&cgrp->release_agent_work);
4977 
4978                 if (cgroup_parent(cgrp)) {
4979                         /*
4980                          * We get a ref to the parent, and put the ref when
4981                          * this cgroup is being freed, so it's guaranteed
4982                          * that the parent won't be destroyed before its
4983                          * children.
4984                          */
4985                         cgroup_put(cgroup_parent(cgrp));
4986                         kernfs_put(cgrp->kn);
4987                         kfree(cgrp);
4988                 } else {
4989                         /*
4990                          * This is root cgroup's refcnt reaching zero,
4991                          * which indicates that the root should be
4992                          * released.
4993                          */
4994                         cgroup_destroy_root(cgrp->root);
4995                 }
4996         }
4997 }
4998 
4999 static void css_free_rcu_fn(struct rcu_head *rcu_head)
5000 {
5001         struct cgroup_subsys_state *css =
5002                 container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
5003 
5004         INIT_WORK(&css->destroy_work, css_free_work_fn);
5005         queue_work(cgroup_destroy_wq, &css->destroy_work);
5006 }
5007 
5008 static void css_release_work_fn(struct work_struct *work)
5009 {
5010         struct cgroup_subsys_state *css =
5011                 container_of(work, struct cgroup_subsys_state, destroy_work);
5012         struct cgroup_subsys *ss = css->ss;
5013         struct cgroup *cgrp = css->cgroup;
5014 
5015         mutex_lock(&cgroup_mutex);
5016 
5017         css->flags |= CSS_RELEASED;
5018         list_del_rcu(&css->sibling);
5019 
5020         if (ss) {
5021                 /* css release path */
5022                 cgroup_idr_replace(&ss->css_idr, NULL, css->id);
5023                 if (ss->css_released)
5024                         ss->css_released(css);
5025         } else {
5026                 /* cgroup release path */
5027                 cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
5028                 cgrp->id = -1;
5029 
5030                 /*
5031                  * There are two control paths which try to determine
5032                  * cgroup from dentry without going through kernfs -
5033                  * cgroupstats_build() and css_tryget_online_from_dir().
5034                  * Those are supported by RCU protecting clearing of
5035                  * cgrp->kn->priv backpointer.
5036                  */
5037                 if (cgrp->kn)
5038                         RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
5039                                          NULL);
5040         }
5041 
5042         mutex_unlock(&cgroup_mutex);
5043 
5044         call_rcu(&css->rcu_head, css_free_rcu_fn);
5045 }
5046 
5047 static void css_release(struct percpu_ref *ref)
5048 {
5049         struct cgroup_subsys_state *css =
5050                 container_of(ref, struct cgroup_subsys_state, refcnt);
5051 
5052         INIT_WORK(&css->destroy_work, css_release_work_fn);
5053         queue_work(cgroup_destroy_wq, &css->destroy_work);
5054 }
5055 
5056 static void init_and_link_css(struct cgroup_subsys_state *css,
5057                               struct cgroup_subsys *ss, struct cgroup *cgrp)
5058 {
5059         lockdep_assert_held(&cgroup_mutex);
5060 
5061         cgroup_get(cgrp);
5062 
5063         memset(css, 0, sizeof(*css));
5064         css->cgroup = cgrp;
5065         css->ss = ss;
5066         INIT_LIST_HEAD(&css->sibling);
5067         INIT_LIST_HEAD(&css->children);
5068         css->serial_nr = css_serial_nr_next++;
5069         atomic_set(&css->online_cnt, 0);
5070 
5071         if (cgroup_parent(cgrp)) {
5072                 css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5073                 css_get(css->parent);
5074         }
5075 
5076         BUG_ON(cgroup_css(cgrp, ss));
5077 }
5078 
5079 /* invoke ->css_online() on a new CSS and mark it online if successful */
5080 static int online_css(struct cgroup_subsys_state *css)
5081 {
5082         struct cgroup_subsys *ss = css->ss;
5083         int ret = 0;
5084 
5085         lockdep_assert_held(&cgroup_mutex);
5086 
5087         if (ss->css_online)
5088                 ret = ss->css_online(css);
5089         if (!ret) {
5090                 css->flags |= CSS_ONLINE;
5091                 rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5092 
5093                 atomic_inc(&css->online_cnt);
5094                 if (css->parent)
5095                         atomic_inc(&css->parent->online_cnt);
5096         }
5097         return ret;
5098 }
5099 
5100 /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5101 static void offline_css(struct cgroup_subsys_state *css)
5102 {
5103         struct cgroup_subsys *ss = css->ss;
5104 
5105         lockdep_assert_held(&cgroup_mutex);
5106 
5107         if (!(css->flags & CSS_ONLINE))
5108                 return;
5109 
5110         if (ss->css_reset)
5111                 ss->css_reset(css);
5112 
5113         if (ss->css_offline)
5114                 ss->css_offline(css);
5115 
5116         css->flags &= ~CSS_ONLINE;
5117         RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5118 
5119         wake_up_all(&css->cgroup->offline_waitq);
5120 }
5121 
5122 /**
5123  * css_create - create a cgroup_subsys_state
5124  * @cgrp: the cgroup new css will be associated with
5125  * @ss: the subsys of new css
5126  *
5127  * Create a new css associated with @cgrp - @ss pair.  On success, the new
5128  * css is online and installed in @cgrp.  This function doesn't create the
5129  * interface files.  Returns 0 on success, -errno on failure.
5130  */
5131 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5132                                               struct cgroup_subsys *ss)
5133 {
5134         struct cgroup *parent = cgroup_parent(cgrp);
5135         struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5136         struct cgroup_subsys_state *css;
5137         int err;
5138 
5139         lockdep_assert_held(&cgroup_mutex);
5140 
5141         css = ss->css_alloc(parent_css);
5142         if (IS_ERR(css))
5143                 return css;
5144 
5145         init_and_link_css(css, ss, cgrp);
5146 
5147         err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5148         if (err)
5149                 goto err_free_css;
5150 
5151         err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5152         if (err < 0)
5153                 goto err_free_percpu_ref;
5154         css->id = err;
5155 
5156         /* @css is ready to be brought online now, make it visible */
5157         list_add_tail_rcu(&css->sibling, &parent_css->children);
5158         cgroup_idr_replace(&ss->css_idr, css, css->id);
5159 
5160         err = online_css(css);
5161         if (err)
5162                 goto err_list_del;
5163 
5164         if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
5165             cgroup_parent(parent)) {
5166                 pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
5167                         current->comm, current->pid, ss->name);
5168                 if (!strcmp(ss->name, "memory"))
5169                         pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
5170                 ss->warned_broken_hierarchy = true;
5171         }
5172 
5173         return css;
5174 
5175 err_list_del:
5176         list_del_rcu(&css->sibling);
5177         cgroup_idr_remove(&ss->css_idr, css->id);
5178 err_free_percpu_ref:
5179         percpu_ref_exit(&css->refcnt);
5180 err_free_css:
5181         call_rcu(&css->rcu_head, css_free_rcu_fn);
5182         return ERR_PTR(err);
5183 }
5184 
5185 static struct cgroup *cgroup_create(struct cgroup *parent)
5186 {
5187         struct cgroup_root *root = parent->root;
5188         struct cgroup *cgrp, *tcgrp;
5189         int level = parent->level + 1;
5190         int ret;
5191 
5192         /* allocate the cgroup and its ID, 0 is reserved for the root */
5193         cgrp = kzalloc(sizeof(*cgrp) +
5194                        sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
5195         if (!cgrp)
5196                 return ERR_PTR(-ENOMEM);
5197 
5198         ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5199         if (ret)
5200                 goto out_free_cgrp;
5201 
5202         /*
5203          * Temporarily set the pointer to NULL, so idr_find() won't return
5204          * a half-baked cgroup.
5205          */
5206         cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
5207         if (cgrp->id < 0) {
5208                 ret = -ENOMEM;
5209                 goto out_cancel_ref;
5210         }
5211 
5212         init_cgroup_housekeeping(cgrp);
5213 
5214         cgrp->self.parent = &parent->self;
5215         cgrp->root = root;
5216         cgrp->level = level;
5217 
5218         for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp))
5219                 cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
5220 
5221         if (notify_on_release(parent))
5222                 set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5223 
5224         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5225                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5226 
5227         cgrp->self.serial_nr = css_serial_nr_next++;
5228 
5229         /* allocation complete, commit to creation */
5230         list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5231         atomic_inc(&root->nr_cgrps);
5232         cgroup_get(parent);
5233 
5234         /*
5235          * @cgrp is now fully operational.  If something fails after this
5236          * point, it'll be released via the normal destruction path.
5237          */
5238         cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
5239 
5240         /*
5241          * On the default hierarchy, a child doesn't automatically inherit
5242          * subtree_control from the parent.  Each is configured manually.
5243          */
5244         if (!cgroup_on_dfl(cgrp))
5245                 cgrp->subtree_control = cgroup_control(cgrp);
5246 
5247         cgroup_propagate_control(cgrp);
5248 
5249         /* @cgrp doesn't have dir yet so the following will only create csses */
5250         ret = cgroup_apply_control_enable(cgrp);
5251         if (ret)
5252                 goto out_destroy;
5253 
5254         return cgrp;
5255 
5256 out_cancel_ref:
5257         percpu_ref_exit(&cgrp->self.refcnt);
5258 out_free_cgrp:
5259         kfree(cgrp);
5260         return ERR_PTR(ret);
5261 out_destroy:
5262         cgroup_destroy_locked(cgrp);
5263         return ERR_PTR(ret);
5264 }
5265 
5266 static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
5267                         umode_t mode)
5268 {
5269         struct cgroup *parent, *cgrp;
5270         struct kernfs_node *kn;
5271         int ret;
5272 
5273         /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5274         if (strchr(name, '\n'))
5275                 return -EINVAL;
5276 
5277         parent = cgroup_kn_lock_live(parent_kn, false);
5278         if (!parent)
5279                 return -ENODEV;
5280 
5281         cgrp = cgroup_create(parent);
5282         if (IS_ERR(cgrp)) {
5283                 ret = PTR_ERR(cgrp);
5284                 goto out_unlock;
5285         }
5286 
5287         /* create the directory */
5288         kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5289         if (IS_ERR(kn)) {
5290                 ret = PTR_ERR(kn);
5291                 goto out_destroy;
5292         }
5293         cgrp->kn = kn;
5294 
5295         /*
5296          * This extra ref will be put in cgroup_free_fn() and guarantees
5297          * that @cgrp->kn is always accessible.
5298          */
5299         kernfs_get(kn);
5300 
5301         ret = cgroup_kn_set_ugid(kn);
5302         if (ret)
5303                 goto out_destroy;
5304 
5305         ret = css_populate_dir(&cgrp->self);
5306         if (ret)
5307                 goto out_destroy;
5308 
5309         ret = cgroup_apply_control_enable(cgrp);
5310         if (ret)
5311                 goto out_destroy;
5312 
5313         /* let's create and online css's */
5314         kernfs_activate(kn);
5315 
5316         ret = 0;
5317         goto out_unlock;
5318 
5319 out_destroy:
5320         cgroup_destroy_locked(cgrp);
5321 out_unlock:
5322         cgroup_kn_unlock(parent_kn);
5323         return ret;
5324 }
5325 
5326 /*
5327  * This is called when the refcnt of a css is confirmed to be killed.
5328  * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5329  * initate destruction and put the css ref from kill_css().
5330  */
5331 static void css_killed_work_fn(struct work_struct *work)
5332 {
5333         struct cgroup_subsys_state *css =
5334                 container_of(work, struct cgroup_subsys_state, destroy_work);
5335 
5336         mutex_lock(&cgroup_mutex);
5337 
5338         do {
5339                 offline_css(css);
5340                 css_put(css);
5341                 /* @css can't go away while we're holding cgroup_mutex */
5342                 css = css->parent;
5343         } while (css && atomic_dec_and_test(&css->online_cnt));
5344 
5345         mutex_unlock(&cgroup_mutex);
5346 }
5347 
5348 /* css kill confirmation processing requires process context, bounce */
5349 static void css_killed_ref_fn(struct percpu_ref *ref)
5350 {
5351         struct cgroup_subsys_state *css =
5352                 container_of(ref, struct cgroup_subsys_state, refcnt);
5353 
5354         if (atomic_dec_and_test(&css->online_cnt)) {
5355                 INIT_WORK(&css->destroy_work, css_killed_work_fn);
5356                 queue_work(cgroup_destroy_wq, &css->destroy_work);
5357         }
5358 }
5359 
5360 /**
5361  * kill_css - destroy a css
5362  * @css: css to destroy
5363  *
5364  * This function initiates destruction of @css by removing cgroup interface
5365  * files and putting its base reference.  ->css_offline() will be invoked
5366  * asynchronously once css_tryget_online() is guaranteed to fail and when
5367  * the reference count reaches zero, @css will be released.
5368  */
5369 static void kill_css(struct cgroup_subsys_state *css)
5370 {
5371         lockdep_assert_held(&cgroup_mutex);
5372 
5373         /*
5374          * This must happen before css is disassociated with its cgroup.
5375          * See seq_css() for details.
5376          */
5377         css_clear_dir(css);
5378 
5379         /*
5380          * Killing would put the base ref, but we need to keep it alive
5381          * until after ->css_offline().
5382          */
5383         css_get(css);
5384 
5385         /*
5386          * cgroup core guarantees that, by the time ->css_offline() is
5387          * invoked, no new css reference will be given out via
5388          * css_tryget_online().  We can't simply call percpu_ref_kill() and
5389          * proceed to offlining css's because percpu_ref_kill() doesn't
5390          * guarantee that the ref is seen as killed on all CPUs on return.
5391          *
5392          * Use percpu_ref_kill_and_confirm() to get notifications as each
5393          * css is confirmed to be seen as killed on all CPUs.
5394          */
5395         percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5396 }
5397 
5398 /**
5399  * cgroup_destroy_locked - the first stage of cgroup destruction
5400  * @cgrp: cgroup to be destroyed
5401  *
5402  * css's make use of percpu refcnts whose killing latency shouldn't be
5403  * exposed to userland and are RCU protected.  Also, cgroup core needs to
5404  * guarantee that css_tryget_online() won't succeed by the time
5405  * ->css_offline() is invoked.  To satisfy all the requirements,
5406  * destruction is implemented in the following two steps.
5407  *
5408  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5409  *     userland visible parts and start killing the percpu refcnts of
5410  *     css's.  Set up so that the next stage will be kicked off once all
5411  *     the percpu refcnts are confirmed to be killed.
5412  *
5413  * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5414  *     rest of destruction.  Once all cgroup references are gone, the
5415  *     cgroup is RCU-freed.
5416  *
5417  * This function implements s1.  After this step, @cgrp is gone as far as
5418  * the userland is concerned and a new cgroup with the same name may be
5419  * created.  As cgroup doesn't care about the names internally, this
5420  * doesn't cause any problem.
5421  */
5422 static int cgroup_destroy_locked(struct cgroup *cgrp)
5423         __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5424 {
5425         struct cgroup_subsys_state *css;
5426         struct cgrp_cset_link *link;
5427         int ssid;
5428 
5429         lockdep_assert_held(&cgroup_mutex);
5430 
5431         /*
5432          * Only migration can raise populated from zero and we're already
5433          * holding cgroup_mutex.
5434          */
5435         if (cgroup_is_populated(cgrp))
5436                 return -EBUSY;
5437 
5438         /*
5439          * Make sure there's no live children.  We can't test emptiness of
5440          * ->self.children as dead children linger on it while being
5441          * drained; otherwise, "rmdir parent/child parent" may fail.
5442          */
5443         if (css_has_online_children(&cgrp->self))
5444                 return -EBUSY;
5445 
5446         /*
5447          * Mark @cgrp and the associated csets dead.  The former prevents
5448          * further task migration and child creation by disabling
5449          * cgroup_lock_live_group().  The latter makes the csets ignored by
5450          * the migration path.
5451          */
5452         cgrp->self.flags &= ~CSS_ONLINE;
5453 
5454         spin_lock_bh(&css_set_lock);
5455         list_for_each_entry(link, &cgrp->cset_links, cset_link)
5456                 link->cset->dead = true;
5457         spin_unlock_bh(&css_set_lock);
5458 
5459         /* initiate massacre of all css's */
5460         for_each_css(css, ssid, cgrp)
5461                 kill_css(css);
5462 
5463         /*
5464          * Remove @cgrp directory along with the base files.  @cgrp has an
5465          * extra ref on its kn.
5466          */
5467         kernfs_remove(cgrp->kn);
5468 
5469         check_for_release(cgroup_parent(cgrp));
5470 
5471         /* put the base reference */
5472         percpu_ref_kill(&cgrp->self.refcnt);
5473 
5474         return 0;
5475 };
5476 
5477 static int cgroup_rmdir(struct kernfs_node *kn)
5478 {
5479         struct cgroup *cgrp;
5480         int ret = 0;
5481 
5482         cgrp = cgroup_kn_lock_live(kn, false);
5483         if (!cgrp)
5484                 return 0;
5485 
5486         ret = cgroup_destroy_locked(cgrp);
5487 
5488         cgroup_kn_unlock(kn);
5489         return ret;
5490 }
5491 
5492 static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5493         .remount_fs             = cgroup_remount,
5494         .show_options           = cgroup_show_options,
5495         .mkdir                  = cgroup_mkdir,
5496         .rmdir                  = cgroup_rmdir,
5497         .rename                 = cgroup_rename,
5498         .show_path              = cgroup_show_path,
5499 };
5500 
5501 static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5502 {
5503         struct cgroup_subsys_state *css;
5504 
5505         pr_debug("Initializing cgroup subsys %s\n", ss->name);
5506 
5507         mutex_lock(&cgroup_mutex);
5508 
5509         idr_init(&ss->css_idr);
5510         INIT_LIST_HEAD(&ss->cfts);
5511 
5512         /* Create the root cgroup state for this subsystem */
5513         ss->root = &cgrp_dfl_root;
5514         css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5515         /* We don't handle early failures gracefully */
5516         BUG_ON(IS_ERR(css));
5517         init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5518 
5519         /*
5520          * Root csses are never destroyed and we can't initialize
5521          * percpu_ref during early init.  Disable refcnting.
5522          */
5523         css->flags |= CSS_NO_REF;
5524 
5525         if (early) {
5526                 /* allocation can't be done safely during early init */
5527                 css->id = 1;
5528         } else {
5529                 css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5530                 BUG_ON(css->id < 0);
5531         }
5532 
5533         /* Update the init_css_set to contain a subsys
5534          * pointer to this state - since the subsystem is
5535          * newly registered, all tasks and hence the
5536          * init_css_set is in the subsystem's root cgroup. */
5537         init_css_set.subsys[ss->id] = css;
5538 
5539         have_fork_callback |= (bool)ss->fork << ss->id;
5540         have_exit_callback |= (bool)ss->exit << ss->id;
5541         have_free_callback |= (bool)ss->free << ss->id;
5542         have_canfork_callback |= (bool)ss->can_fork << ss->id;
5543 
5544         /* At system boot, before all subsystems have been
5545          * registered, no tasks have been forked, so we don't
5546          * need to invoke fork callbacks here. */
5547         BUG_ON(!list_empty(&init_task.tasks));
5548 
5549         BUG_ON(online_css(css));
5550 
5551         mutex_unlock(&cgroup_mutex);
5552 }
5553 
5554 /**
5555  * cgroup_init_early - cgroup initialization at system boot
5556  *
5557  * Initialize cgroups at system boot, and initialize any
5558  * subsystems that request early init.
5559  */
5560 int __init cgroup_init_early(void)
5561 {
5562         static struct cgroup_sb_opts __initdata opts;
5563         struct cgroup_subsys *ss;
5564         int i;
5565 
5566         init_cgroup_root(&cgrp_dfl_root, &opts);
5567         cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5568 
5569         RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5570 
5571         for_each_subsys(ss, i) {
5572                 WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5573                      "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5574                      i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5575                      ss->id, ss->name);
5576                 WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5577                      "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5578 
5579                 ss->id = i;
5580                 ss->name = cgroup_subsys_name[i];
5581                 if (!ss->legacy_name)
5582                         ss->legacy_name = cgroup_subsys_name[i];
5583 
5584                 if (ss->early_init)
5585                         cgroup_init_subsys(ss, true);
5586         }
5587         return 0;
5588 }
5589 
5590 static u16 cgroup_disable_mask __initdata;
5591 
5592 /**
5593  * cgroup_init - cgroup initialization
5594  *
5595  * Register cgroup filesystem and /proc file, and initialize
5596  * any subsystems that didn't request early init.
5597  */
5598 int __init cgroup_init(void)
5599 {
5600         struct cgroup_subsys *ss;
5601         int ssid;
5602 
5603         BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5604         BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
5605         BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
5606         BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
5607 
5608         get_user_ns(init_cgroup_ns.user_ns);
5609 
5610         mutex_lock(&cgroup_mutex);
5611 
5612         /*
5613          * Add init_css_set to the hash table so that dfl_root can link to
5614          * it during init.
5615          */
5616         hash_add(css_set_table, &init_css_set.hlist,
5617                  css_set_hash(init_css_set.subsys));
5618 
5619         BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5620 
5621         mutex_unlock(&cgroup_mutex);
5622 
5623         for_each_subsys(ss, ssid) {
5624                 if (ss->early_init) {
5625                         struct cgroup_subsys_state *css =
5626                                 init_css_set.subsys[ss->id];
5627 
5628                         css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5629                                                    GFP_KERNEL);
5630                         BUG_ON(css->id < 0);
5631                 } else {
5632                         cgroup_init_subsys(ss, false);
5633                 }
5634 
5635                 list_add_tail(&init_css_set.e_cset_node[ssid],
5636                               &cgrp_dfl_root.cgrp.e_csets[ssid]);
5637 
5638                 /*
5639                  * Setting dfl_root subsys_mask needs to consider the
5640                  * disabled flag and cftype registration needs kmalloc,
5641                  * both of which aren't available during early_init.
5642                  */
5643                 if (cgroup_disable_mask & (1 << ssid)) {
5644                         static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5645                         printk(KERN_INFO "Disabling %s control group subsystem\n",
5646                                ss->name);
5647                         continue;
5648                 }
5649 
5650                 if (cgroup_ssid_no_v1(ssid))
5651                         printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5652                                ss->name);
5653 
5654                 cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5655 
5656                 if (ss->implicit_on_dfl)
5657                         cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5658                 else if (!ss->dfl_cftypes)
5659                         cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5660 
5661                 if (ss->dfl_cftypes == ss->legacy_cftypes) {
5662                         WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5663                 } else {
5664                         WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5665                         WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5666                 }
5667 
5668                 if (ss->bind)
5669                         ss->bind(init_css_set.subsys[ssid]);
5670         }
5671 
5672         /* init_css_set.subsys[] has been updated, re-hash */
5673         hash_del(&init_css_set.hlist);
5674         hash_add(css_set_table, &init_css_set.hlist,
5675                  css_set_hash(init_css_set.subsys));
5676 
5677         WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5678         WARN_ON(register_filesystem(&cgroup_fs_type));
5679         WARN_ON(register_filesystem(&cgroup2_fs_type));
5680         WARN_ON(!proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations));
5681 
5682         return 0;
5683 }
5684 
5685 static int __init cgroup_wq_init(void)
5686 {
5687         /*
5688          * There isn't much point in executing destruction path in
5689          * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5690          * Use 1 for @max_active.
5691          *
5692          * We would prefer to do this in cgroup_init() above, but that
5693          * is called before init_workqueues(): so leave this until after.
5694          */
5695         cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5696         BUG_ON(!cgroup_destroy_wq);
5697 
5698         /*
5699          * Used to destroy pidlists and separate to serve as flush domain.
5700          * Cap @max_active to 1 too.
5701          */
5702         cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
5703                                                     0, 1);
5704         BUG_ON(!cgroup_pidlist_destroy_wq);
5705 
5706         return 0;
5707 }
5708 core_initcall(cgroup_wq_init);
5709 
5710 /*
5711  * proc_cgroup_show()
5712  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5713  *  - Used for /proc/<pid>/cgroup.
5714  */
5715 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5716                      struct pid *pid, struct task_struct *tsk)
5717 {
5718         char *buf, *path;
5719         int retval;
5720         struct cgroup_root *root;
5721 
5722         retval = -ENOMEM;
5723         buf = kmalloc(PATH_MAX, GFP_KERNEL);
5724         if (!buf)
5725                 goto out;
5726 
5727         mutex_lock(&cgroup_mutex);
5728         spin_lock_bh(&css_set_lock);
5729 
5730         for_each_root(root) {
5731                 struct cgroup_subsys *ss;
5732                 struct cgroup *cgrp;
5733                 int ssid, count = 0;
5734 
5735                 if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5736                         continue;
5737 
5738                 seq_printf(m, "%d:", root->hierarchy_id);
5739                 if (root != &cgrp_dfl_root)
5740                         for_each_subsys(ss, ssid)
5741                                 if (root->subsys_mask & (1 << ssid))
5742                                         seq_printf(m, "%s%s", count++ ? "," : "",
5743                                                    ss->legacy_name);
5744                 if (strlen(root->name))
5745                         seq_printf(m, "%sname=%s", count ? "," : "",
5746                                    root->name);
5747                 seq_putc(m, ':');
5748 
5749                 cgrp = task_cgroup_from_root(tsk, root);
5750 
5751                 /*
5752                  * On traditional hierarchies, all zombie tasks show up as
5753                  * belonging to the root cgroup.  On the default hierarchy,
5754                  * while a zombie doesn't show up in "cgroup.procs" and
5755                  * thus can't be migrated, its /proc/PID/cgroup keeps
5756                  * reporting the cgroup it belonged to before exiting.  If
5757                  * the cgroup is removed before the zombie is reaped,
5758                  * " (deleted)" is appended to the cgroup path.
5759                  */
5760                 if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5761                         path = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5762                                                 current->nsproxy->cgroup_ns);
5763                         if (!path) {
5764                                 retval = -ENAMETOOLONG;
5765                                 goto out_unlock;
5766                         }
5767                 } else {
5768                         path = "/";
5769                 }
5770 
5771                 seq_puts(m, path);
5772 
5773                 if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5774                         seq_puts(m, " (deleted)\n");
5775                 else
5776                         seq_putc(m, '\n');
5777         }
5778 
5779         retval = 0;
5780 out_unlock:
5781         spin_unlock_bh(&css_set_lock);
5782         mutex_unlock(&cgroup_mutex);
5783         kfree(buf);
5784 out:
5785         return retval;
5786 }
5787 
5788 /* Display information about each subsystem and each hierarchy */
5789 static int proc_cgroupstats_show(struct seq_file *m, void *v)
5790 {
5791         struct cgroup_subsys *ss;
5792         int i;
5793 
5794         seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
5795         /*
5796          * ideally we don't want subsystems moving around while we do this.
5797          * cgroup_mutex is also necessary to guarantee an atomic snapshot of
5798          * subsys/hierarchy state.
5799          */
5800         mutex_lock(&cgroup_mutex);
5801 
5802         for_each_subsys(ss, i)
5803                 seq_printf(m, "%s\t%d\t%d\t%d\n",
5804                            ss->legacy_name, ss->root->hierarchy_id,
5805                            atomic_read(&ss->root->nr_cgrps),
5806                            cgroup_ssid_enabled(i));
5807 
5808         mutex_unlock(&cgroup_mutex);
5809         return 0;
5810 }
5811 
5812 static int cgroupstats_open(struct inode *inode, struct file *file)
5813 {
5814         return single_open(file, proc_cgroupstats_show, NULL);
5815 }
5816 
5817 static const struct file_operations proc_cgroupstats_operations = {
5818         .open = cgroupstats_open,
5819         .read = seq_read,
5820         .llseek = seq_lseek,
5821         .release = single_release,
5822 };
5823 
5824 /**
5825  * cgroup_fork - initialize cgroup related fields during copy_process()
5826  * @child: pointer to task_struct of forking parent process.
5827  *
5828  * A task is associated with the init_css_set until cgroup_post_fork()
5829  * attaches it to the parent's css_set.  Empty cg_list indicates that
5830  * @child isn't holding reference to its css_set.
5831  */
5832 void cgroup_fork(struct task_struct *child)
5833 {
5834         RCU_INIT_POINTER(child->cgroups, &init_css_set);
5835         INIT_LIST_HEAD(&child->cg_list);
5836 }
5837 
5838 /**
5839  * cgroup_can_fork - called on a new task before the process is exposed
5840  * @child: the task in question.
5841  *
5842  * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5843  * returns an error, the fork aborts with that error code. This allows for
5844  * a cgroup subsystem to conditionally allow or deny new forks.
5845  */
5846 int cgroup_can_fork(struct task_struct *child)
5847 {
5848         struct cgroup_subsys *ss;
5849         int i, j, ret;
5850 
5851         do_each_subsys_mask(ss, i, have_canfork_callback) {
5852                 ret = ss->can_fork(child);
5853                 if (ret)
5854                         goto out_revert;
5855         } while_each_subsys_mask();
5856 
5857         return 0;
5858 
5859 out_revert:
5860         for_each_subsys(ss, j) {
5861                 if (j >= i)
5862                         break;
5863                 if (ss->cancel_fork)
5864                         ss->cancel_fork(child);
5865         }
5866 
5867         return ret;
5868 }
5869 
5870 /**
5871  * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5872  * @child: the task in question
5873  *
5874  * This calls the cancel_fork() callbacks if a fork failed *after*
5875  * cgroup_can_fork() succeded.
5876  */
5877 void cgroup_cancel_fork(struct task_struct *child)
5878 {
5879         struct cgroup_subsys *ss;
5880         int i;
5881 
5882         for_each_subsys(ss, i)
5883                 if (ss->cancel_fork)
5884                         ss->cancel_fork(child);
5885 }
5886 
5887 /**
5888  * cgroup_post_fork - called on a new task after adding it to the task list
5889  * @child: the task in question
5890  *
5891  * Adds the task to the list running through its css_set if necessary and
5892  * call the subsystem fork() callbacks.  Has to be after the task is
5893  * visible on the task list in case we race with the first call to
5894  * cgroup_task_iter_start() - to guarantee that the new task ends up on its
5895  * list.
5896  */
5897 void cgroup_post_fork(struct task_struct *child)
5898 {
5899         struct cgroup_subsys *ss;
5900         int i;
5901 
5902         /*
5903          * This may race against cgroup_enable_task_cg_lists().  As that
5904          * function sets use_task_css_set_links before grabbing
5905          * tasklist_lock and we just went through tasklist_lock to add
5906          * @child, it's guaranteed that either we see the set
5907          * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
5908          * @child during its iteration.
5909          *
5910          * If we won the race, @child is associated with %current's
5911          * css_set.  Grabbing css_set_lock guarantees both that the
5912          * association is stable, and, on completion of the parent's
5913          * migration, @child is visible in the source of migration or
5914          * already in the destination cgroup.  This guarantee is necessary
5915          * when implementing operations which need to migrate all tasks of
5916          * a cgroup to another.
5917          *
5918          * Note that if we lose to cgroup_enable_task_cg_lists(), @child
5919          * will remain in init_css_set.  This is safe because all tasks are
5920          * in the init_css_set before cg_links is enabled and there's no
5921          * operation which transfers all tasks out of init_css_set.
5922          */
5923         if (use_task_css_set_links) {
5924                 struct css_set *cset;
5925 
5926                 spin_lock_bh(&css_set_lock);
5927                 cset = task_css_set(current);
5928                 if (list_empty(&child->cg_list)) {
5929                         get_css_set(cset);
5930                         css_set_move_task(child, NULL, cset, false);
5931                 }
5932                 spin_unlock_bh(&css_set_lock);
5933         }
5934 
5935         /*
5936          * Call ss->fork().  This must happen after @child is linked on
5937          * css_set; otherwise, @child might change state between ->fork()
5938          * and addition to css_set.
5939          */
5940         do_each_subsys_mask(ss, i, have_fork_callback) {
5941                 ss->fork(child);
5942         } while_each_subsys_mask();
5943 }
5944 
5945 /**
5946  * cgroup_exit - detach cgroup from exiting task
5947  * @tsk: pointer to task_struct of exiting process
5948  *
5949  * Description: Detach cgroup from @tsk and release it.
5950  *
5951  * Note that cgroups marked notify_on_release force every task in
5952  * them to take the global cgroup_mutex mutex when exiting.
5953  * This could impact scaling on very large systems.  Be reluctant to
5954  * use notify_on_release cgroups where very high task exit scaling
5955  * is required on large systems.
5956  *
5957  * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
5958  * call cgroup_exit() while the task is still competent to handle
5959  * notify_on_release(), then leave the task attached to the root cgroup in
5960  * each hierarchy for the remainder of its exit.  No need to bother with
5961  * init_css_set refcnting.  init_css_set never goes away and we can't race
5962  * with migration path - PF_EXITING is visible to migration path.
5963  */
5964 void cgroup_exit(struct task_struct *tsk)
5965 {
5966         struct cgroup_subsys *ss;
5967         struct css_set *cset;
5968         int i;
5969 
5970         /*
5971          * Unlink from @tsk from its css_set.  As migration path can't race
5972          * with us, we can check css_set and cg_list without synchronization.
5973          */
5974         cset = task_css_set(tsk);
5975 
5976         if (!list_empty(&tsk->cg_list)) {
5977                 spin_lock_bh(&css_set_lock);
5978                 css_set_move_task(tsk, cset, NULL, false);
5979                 spin_unlock_bh(&css_set_lock);
5980         } else {
5981                 get_css_set(cset);
5982         }
5983 
5984         /* see cgroup_post_fork() for details */
5985         do_each_subsys_mask(ss, i, have_exit_callback) {
5986                 ss->exit(tsk);
5987         } while_each_subsys_mask();
5988 }
5989 
5990 void cgroup_free(struct task_struct *task)
5991 {
5992         struct css_set *cset = task_css_set(task);
5993         struct cgroup_subsys *ss;
5994         int ssid;
5995 
5996         do_each_subsys_mask(ss, ssid, have_free_callback) {
5997                 ss->free(task);
5998         } while_each_subsys_mask();
5999 
6000         put_css_set(cset);
6001 }
6002 
6003 static void check_for_release(struct cgroup *cgrp)
6004 {
6005         if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) &&
6006             !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
6007                 schedule_work(&cgrp->release_agent_work);
6008 }
6009 
6010 /*
6011  * Notify userspace when a cgroup is released, by running the
6012  * configured release agent with the name of the cgroup (path
6013  * relative to the root of cgroup file system) as the argument.
6014  *
6015  * Most likely, this user command will try to rmdir this cgroup.
6016  *
6017  * This races with the possibility that some other task will be
6018  * attached to this cgroup before it is removed, or that some other
6019  * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
6020  * The presumed 'rmdir' will fail quietly if this cgroup is no longer
6021  * unused, and this cgroup will be reprieved from its death sentence,
6022  * to continue to serve a useful existence.  Next time it's released,
6023  * we will get notified again, if it still has 'notify_on_release' set.
6024  *
6025  * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
6026  * means only wait until the task is successfully execve()'d.  The
6027  * separate release agent task is forked by call_usermodehelper(),
6028  * then control in this thread returns here, without waiting for the
6029  * release agent task.  We don't bother to wait because the caller of
6030  * this routine has no use for the exit status of the release agent
6031  * task, so no sense holding our caller up for that.
6032  */
6033 static void cgroup_release_agent(struct work_struct *work)
6034 {
6035         struct cgroup *cgrp =
6036                 container_of(work, struct cgroup, release_agent_work);
6037         char *pathbuf = NULL, *agentbuf = NULL, *path;
6038         char *argv[3], *envp[3];
6039 
6040         mutex_lock(&cgroup_mutex);
6041 
6042         pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
6043         agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
6044         if (!pathbuf || !agentbuf)
6045                 goto out;
6046 
6047         spin_lock_bh(&css_set_lock);
6048         path = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);
6049         spin_unlock_bh(&css_set_lock);
6050         if (!path)
6051                 goto out;
6052 
6053         argv[0] = agentbuf;
6054         argv[1] = path;
6055         argv[2] = NULL;
6056 
6057         /* minimal command environment */
6058         envp[0] = "HOME=/";
6059         envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
6060         envp[2] = NULL;
6061 
6062         mutex_unlock(&cgroup_mutex);
6063         call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
6064         goto out_free;
6065 out:
6066         mutex_unlock(&cgroup_mutex);
6067 out_free:
6068         kfree(agentbuf);
6069         kfree(pathbuf);
6070 }
6071 
6072 static int __init cgroup_disable(char *str)
6073 {
6074         struct cgroup_subsys *ss;
6075         char *token;
6076         int i;
6077 
6078         while ((token = strsep(&str, ",")) != NULL) {
6079                 if (!*token)
6080                         continue;
6081 
6082                 for_each_subsys(ss, i) {
6083                         if (strcmp(token, ss->name) &&
6084                             strcmp(token, ss->legacy_name))
6085                                 continue;
6086                         cgroup_disable_mask |= 1 << i;
6087                 }
6088         }
6089         return 1;
6090 }
6091 __setup("cgroup_disable=", cgroup_disable);
6092 
6093 static int __init cgroup_no_v1(char *str)
6094 {
6095         struct cgroup_subsys *ss;
6096         char *token;
6097         int i;
6098 
6099         while ((token = strsep(&str, ",")) != NULL) {
6100                 if (!*token)
6101                         continue;
6102 
6103                 if (!strcmp(token, "all")) {
6104                         cgroup_no_v1_mask = U16_MAX;
6105                         break;
6106                 }
6107 
6108                 for_each_subsys(ss, i) {
6109                         if (strcmp(token, ss->name) &&
6110                             strcmp(token, ss->legacy_name))
6111                                 continue;
6112 
6113                         cgroup_no_v1_mask |= 1 << i;
6114                 }
6115         }
6116         return 1;
6117 }
6118 __setup("cgroup_no_v1=", cgroup_no_v1);
6119 
6120 /**
6121  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
6122  * @dentry: directory dentry of interest
6123  * @ss: subsystem of interest
6124  *
6125  * If @dentry is a directory for a cgroup which has @ss enabled on it, try
6126  * to get the corresponding css and return it.  If such css doesn't exist
6127  * or can't be pinned, an ERR_PTR value is returned.
6128  */
6129 struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
6130                                                        struct cgroup_subsys *ss)
6131 {
6132         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
6133         struct file_system_type *s_type = dentry->d_sb->s_type;
6134         struct cgroup_subsys_state *css = NULL;
6135         struct cgroup *cgrp;
6136 
6137         /* is @dentry a cgroup dir? */
6138         if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
6139             !kn || kernfs_type(kn) != KERNFS_DIR)
6140                 return ERR_PTR(-EBADF);
6141 
6142         rcu_read_lock();
6143 
6144         /*
6145          * This path doesn't originate from kernfs and @kn could already
6146          * have been or be removed at any point.  @kn->priv is RCU
6147          * protected for this access.  See css_release_work_fn() for details.
6148          */
6149         cgrp = rcu_dereference(kn->priv);
6150         if (cgrp)
6151                 css = cgroup_css(cgrp, ss);
6152 
6153         if (!css || !css_tryget_online(css))
6154                 css = ERR_PTR(-ENOENT);
6155 
6156         rcu_read_unlock();
6157         return css;
6158 }
6159 
6160 /**
6161  * css_from_id - lookup css by id
6162  * @id: the cgroup id
6163  * @ss: cgroup subsys to be looked into
6164  *
6165  * Returns the css if there's valid one with @id, otherwise returns NULL.
6166  * Should be called under rcu_read_lock().
6167  */
6168 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
6169 {
6170         WARN_ON_ONCE(!rcu_read_lock_held());
6171         return id > 0 ? idr_find(&ss->css_idr, id) : NULL;
6172 }
6173 
6174 /**
6175  * cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
6176  * @path: path on the default hierarchy
6177  *
6178  * Find the cgroup at @path on the default hierarchy, increment its
6179  * reference count and return it.  Returns pointer to the found cgroup on
6180  * success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
6181  * if @path points to a non-directory.
6182  */
6183 struct cgroup *cgroup_get_from_path(const char *path)
6184 {
6185         struct kernfs_node *kn;
6186         struct cgroup *cgrp;
6187 
6188         mutex_lock(&cgroup_mutex);
6189 
6190         kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
6191         if (kn) {
6192                 if (kernfs_type(kn) == KERNFS_DIR) {
6193                         cgrp = kn->priv;
6194                         cgroup_get(cgrp);
6195                 } else {
6196                         cgrp = ERR_PTR(-ENOTDIR);
6197                 }
6198                 kernfs_put(kn);
6199         } else {
6200                 cgrp = ERR_PTR(-ENOENT);
6201         }
6202 
6203         mutex_unlock(&cgroup_mutex);
6204         return cgrp;
6205 }
6206 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
6207 
6208 /*
6209  * sock->sk_cgrp_data handling.  For more info, see sock_cgroup_data
6210  * definition in cgroup-defs.h.
6211  */
6212 #ifdef CONFIG_SOCK_CGROUP_DATA
6213 
6214 #if defined(CONFIG_CGROUP_NET_PRIO) || defined(CONFIG_CGROUP_NET_CLASSID)
6215 
6216 DEFINE_SPINLOCK(cgroup_sk_update_lock);
6217 static bool cgroup_sk_alloc_disabled __read_mostly;
6218 
6219 void cgroup_sk_alloc_disable(void)
6220 {
6221         if (cgroup_sk_alloc_disabled)
6222                 return;
6223         pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
6224         cgroup_sk_alloc_disabled = true;
6225 }
6226 
6227 #else
6228 
6229 #define cgroup_sk_alloc_disabled        false
6230 
6231 #endif
6232 
6233 void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
6234 {
6235         if (cgroup_sk_alloc_disabled)
6236                 return;
6237 
6238         rcu_read_lock();
6239 
6240         while (true) {
6241                 struct css_set *cset;
6242 
6243                 cset = task_css_set(current);
6244                 if (likely(cgroup_tryget(cset->dfl_cgrp))) {
6245                         skcd->val = (unsigned long)cset->dfl_cgrp;
6246                         break;
6247                 }
6248                 cpu_relax();
6249         }
6250 
6251         rcu_read_unlock();
6252 }
6253 
6254 void cgroup_sk_free(struct sock_cgroup_data *skcd)
6255 {
6256         cgroup_put(sock_cgroup_ptr(skcd));
6257 }
6258 
6259 #endif  /* CONFIG_SOCK_CGROUP_DATA */
6260 
6261 /* cgroup namespaces */
6262 
6263 static struct cgroup_namespace *alloc_cgroup_ns(void)
6264 {
6265         struct cgroup_namespace *new_ns;
6266         int ret;
6267 
6268         new_ns = kzalloc(sizeof(struct cgroup_namespace), GFP_KERNEL);
6269         if (!new_ns)
6270                 return ERR_PTR(-ENOMEM);
6271         ret = ns_alloc_inum(&new_ns->ns);
6272         if (ret) {
6273                 kfree(new_ns);
6274                 return ERR_PTR(ret);
6275         }
6276         atomic_set(&new_ns->count, 1);
6277         new_ns->ns.ops = &cgroupns_operations;
6278         return new_ns;
6279 }
6280 
6281 void free_cgroup_ns(struct cgroup_namespace *ns)
6282 {
6283         put_css_set(ns->root_cset);
6284         put_user_ns(ns->user_ns);
6285         ns_free_inum(&ns->ns);
6286         kfree(ns);
6287 }
6288 EXPORT_SYMBOL(free_cgroup_ns);
6289 
6290 struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
6291                                         struct user_namespace *user_ns,
6292                                         struct cgroup_namespace *old_ns)
6293 {
6294         struct cgroup_namespace *new_ns;
6295         struct css_set *cset;
6296 
6297         BUG_ON(!old_ns);
6298 
6299         if (!(flags & CLONE_NEWCGROUP)) {
6300                 get_cgroup_ns(old_ns);
6301                 return old_ns;
6302         }
6303 
6304         /* Allow only sysadmin to create cgroup namespace. */
6305         if (!ns_capable(user_ns, CAP_SYS_ADMIN))
6306                 return ERR_PTR(-EPERM);
6307 
6308         mutex_lock(&cgroup_mutex);
6309         spin_lock_bh(&css_set_lock);
6310 
6311         cset = task_css_set(current);
6312         get_css_set(cset);
6313 
6314         spin_unlock_bh(&css_set_lock);
6315         mutex_unlock(&cgroup_mutex);
6316 
6317         new_ns = alloc_cgroup_ns();
6318         if (IS_ERR(new_ns)) {
6319                 put_css_set(cset);
6320                 return new_ns;
6321         }
6322 
6323         new_ns->user_ns = get_user_ns(user_ns);
6324         new_ns->root_cset = cset;
6325 
6326         return new_ns;
6327 }
6328 
6329 static inline struct cgroup_namespace *to_cg_ns(struct ns_common *ns)
6330 {
6331         return container_of(ns, struct cgroup_namespace, ns);
6332 }
6333 
6334 static int cgroupns_install(struct nsproxy *nsproxy, struct ns_common *ns)
6335 {
6336         struct cgroup_namespace *cgroup_ns = to_cg_ns(ns);
6337 
6338         if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN) ||
6339             !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
6340                 return -EPERM;
6341 
6342         /* Don't need to do anything if we are attaching to our own cgroupns. */
6343         if (cgroup_ns == nsproxy->cgroup_ns)
6344                 return 0;
6345 
6346         get_cgroup_ns(cgroup_ns);
6347         put_cgroup_ns(nsproxy->cgroup_ns);
6348         nsproxy->cgroup_ns = cgroup_ns;
6349 
6350         return 0;
6351 }
6352 
6353 static struct ns_common *cgroupns_get(struct task_struct *task)
6354 {
6355         struct cgroup_namespace *ns = NULL;
6356         struct nsproxy *nsproxy;
6357 
6358         task_lock(task);
6359         nsproxy = task->nsproxy;
6360         if (nsproxy) {
6361                 ns = nsproxy->cgroup_ns;
6362                 get_cgroup_ns(ns);
6363         }
6364         task_unlock(task);
6365 
6366         return ns ? &ns->ns : NULL;
6367 }
6368 
6369 static void cgroupns_put(struct ns_common *ns)
6370 {
6371         put_cgroup_ns(to_cg_ns(ns));
6372 }
6373 
6374 const struct proc_ns_operations cgroupns_operations = {
6375         .name           = "cgroup",
6376         .type           = CLONE_NEWCGROUP,
6377         .get            = cgroupns_get,
6378         .put            = cgroupns_put,
6379         .install        = cgroupns_install,
6380 };
6381 
6382 static __init int cgroup_namespaces_init(void)
6383 {
6384         return 0;
6385 }
6386 subsys_initcall(cgroup_namespaces_init);
6387 
6388 #ifdef CONFIG_CGROUP_DEBUG
6389 static struct cgroup_subsys_state *
6390 debug_css_alloc(struct cgroup_subsys_state *parent_css)
6391 {
6392         struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
6393 
6394         if (!css)
6395                 return ERR_PTR(-ENOMEM);
6396 
6397         return css;
6398 }
6399 
6400 static void debug_css_free(struct cgroup_subsys_state *css)
6401 {
6402         kfree(css);
6403 }
6404 
6405 static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
6406                                 struct cftype *cft)
6407 {
6408         return cgroup_task_count(css->cgroup);
6409 }
6410 
6411 static u64 current_css_set_read(struct cgroup_subsys_state *css,
6412                                 struct cftype *cft)
6413 {
6414         return (u64)(unsigned long)current->cgroups;
6415 }
6416 
6417 static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
6418                                          struct cftype *cft)
6419 {
6420         u64 count;
6421 
6422         rcu_read_lock();
6423         count = atomic_read(&task_css_set(current)->refcount);
6424         rcu_read_unlock();
6425         return count;
6426 }
6427 
6428 static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
6429 {
6430         struct cgrp_cset_link *link;
6431         struct css_set *cset;
6432         char *name_buf;
6433 
6434         name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
6435         if (!name_buf)
6436                 return -ENOMEM;
6437 
6438         spin_lock_bh(&css_set_lock);
6439         rcu_read_lock();
6440         cset = rcu_dereference(current->cgroups);
6441         list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
6442                 struct cgroup *c = link->cgrp;
6443 
6444                 cgroup_name(c, name_buf, NAME_MAX + 1);
6445                 seq_printf(seq, "Root %d group %s\n",
6446                            c->root->hierarchy_id, name_buf);
6447         }
6448         rcu_read_unlock();
6449         spin_unlock_bh(&css_set_lock);
6450         kfree(name_buf);
6451         return 0;
6452 }
6453 
6454 #define MAX_TASKS_SHOWN_PER_CSS 25
6455 static int cgroup_css_links_read(struct seq_file *seq, void *v)
6456 {
6457         struct cgroup_subsys_state *css = seq_css(seq);
6458         struct cgrp_cset_link *link;
6459 
6460         spin_lock_bh(&css_set_lock);
6461         list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
6462                 struct css_set *cset = link->cset;
6463                 struct task_struct *task;
6464                 int count = 0;
6465 
6466                 seq_printf(seq, "css_set %p\n", cset);
6467 
6468                 list_for_each_entry(task, &cset->tasks, cg_list) {
6469                         if (count++ > MAX_TASKS_SHOWN_PER_CSS)
6470                                 goto overflow;
6471                         seq_printf(seq, "  task %d\n", task_pid_vnr(task));
6472                 }
6473 
6474                 list_for_each_entry(task, &cset->mg_tasks, cg_list) {
6475                         if (count++ > MAX_TASKS_SHOWN_PER_CSS)
6476                                 goto overflow;
6477                         seq_printf(seq, "  task %d\n", task_pid_vnr(task));
6478                 }
6479                 continue;
6480         overflow:
6481                 seq_puts(seq, "  ...\n");
6482         }
6483         spin_unlock_bh(&css_set_lock);
6484         return 0;
6485 }
6486 
6487 static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
6488 {
6489         return (!cgroup_is_populated(css->cgroup) &&
6490                 !css_has_online_children(&css->cgroup->self));
6491 }
6492 
6493 static struct cftype debug_files[] =  {
6494         {
6495                 .name = "taskcount",
6496                 .read_u64 = debug_taskcount_read,
6497         },
6498 
6499         {
6500                 .name = "current_css_set",
6501                 .read_u64 = current_css_set_read,
6502         },
6503 
6504         {
6505                 .name = "current_css_set_refcount",
6506                 .read_u64 = current_css_set_refcount_read,
6507         },
6508 
6509         {
6510                 .name = "current_css_set_cg_links",
6511                 .seq_show = current_css_set_cg_links_read,
6512         },
6513 
6514         {
6515                 .name = "cgroup_css_links",
6516                 .seq_show = cgroup_css_links_read,
6517         },
6518 
6519         {
6520                 .name = "releasable",
6521                 .read_u64 = releasable_read,
6522         },
6523 
6524         { }     /* terminate */
6525 };
6526 
6527 struct cgroup_subsys debug_cgrp_subsys = {
6528         .css_alloc = debug_css_alloc,
6529         .css_free = debug_css_free,
6530         .legacy_cftypes = debug_files,
6531 };
6532 #endif /* CONFIG_CGROUP_DEBUG */
6533 

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