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

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