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

Linux/kernel/cgroup.c

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

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