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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 #include <linux/cgroup.h>
 30 #include <linux/cred.h>
 31 #include <linux/ctype.h>
 32 #include <linux/errno.h>
 33 #include <linux/init_task.h>
 34 #include <linux/kernel.h>
 35 #include <linux/list.h>
 36 #include <linux/magic.h>
 37 #include <linux/mm.h>
 38 #include <linux/mutex.h>
 39 #include <linux/mount.h>
 40 #include <linux/pagemap.h>
 41 #include <linux/proc_fs.h>
 42 #include <linux/rcupdate.h>
 43 #include <linux/sched.h>
 44 #include <linux/slab.h>
 45 #include <linux/spinlock.h>
 46 #include <linux/rwsem.h>
 47 #include <linux/string.h>
 48 #include <linux/sort.h>
 49 #include <linux/kmod.h>
 50 #include <linux/delayacct.h>
 51 #include <linux/cgroupstats.h>
 52 #include <linux/hashtable.h>
 53 #include <linux/pid_namespace.h>
 54 #include <linux/idr.h>
 55 #include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
 56 #include <linux/kthread.h>
 57 #include <linux/delay.h>
 58 
 59 #include <linux/atomic.h>
 60 
 61 /*
 62  * pidlists linger the following amount before being destroyed.  The goal
 63  * is avoiding frequent destruction in the middle of consecutive read calls
 64  * Expiring in the middle is a performance problem not a correctness one.
 65  * 1 sec should be enough.
 66  */
 67 #define CGROUP_PIDLIST_DESTROY_DELAY    HZ
 68 
 69 #define CGROUP_FILE_NAME_MAX            (MAX_CGROUP_TYPE_NAMELEN +      \
 70                                          MAX_CFTYPE_NAME + 2)
 71 
 72 /*
 73  * cgroup_tree_mutex nests above cgroup_mutex and protects cftypes, file
 74  * creation/removal and hierarchy changing operations including cgroup
 75  * creation, removal, css association and controller rebinding.  This outer
 76  * lock is needed mainly to resolve the circular dependency between kernfs
 77  * active ref and cgroup_mutex.  cgroup_tree_mutex nests above both.
 78  */
 79 static DEFINE_MUTEX(cgroup_tree_mutex);
 80 
 81 /*
 82  * cgroup_mutex is the master lock.  Any modification to cgroup or its
 83  * hierarchy must be performed while holding it.
 84  *
 85  * css_set_rwsem protects task->cgroups pointer, the list of css_set
 86  * objects, and the chain of tasks off each css_set.
 87  *
 88  * These locks are exported if CONFIG_PROVE_RCU so that accessors in
 89  * cgroup.h can use them for lockdep annotations.
 90  */
 91 #ifdef CONFIG_PROVE_RCU
 92 DEFINE_MUTEX(cgroup_mutex);
 93 DECLARE_RWSEM(css_set_rwsem);
 94 EXPORT_SYMBOL_GPL(cgroup_mutex);
 95 EXPORT_SYMBOL_GPL(css_set_rwsem);
 96 #else
 97 static DEFINE_MUTEX(cgroup_mutex);
 98 static DECLARE_RWSEM(css_set_rwsem);
 99 #endif
100 
101 /*
102  * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
103  * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
104  */
105 static DEFINE_SPINLOCK(release_agent_path_lock);
106 
107 #define cgroup_assert_mutexes_or_rcu_locked()                           \
108         rcu_lockdep_assert(rcu_read_lock_held() ||                      \
109                            lockdep_is_held(&cgroup_tree_mutex) ||       \
110                            lockdep_is_held(&cgroup_mutex),              \
111                            "cgroup_[tree_]mutex or RCU read lock required");
112 
113 /*
114  * cgroup destruction makes heavy use of work items and there can be a lot
115  * of concurrent destructions.  Use a separate workqueue so that cgroup
116  * destruction work items don't end up filling up max_active of system_wq
117  * which may lead to deadlock.
118  */
119 static struct workqueue_struct *cgroup_destroy_wq;
120 
121 /*
122  * pidlist destructions need to be flushed on cgroup destruction.  Use a
123  * separate workqueue as flush domain.
124  */
125 static struct workqueue_struct *cgroup_pidlist_destroy_wq;
126 
127 /* generate an array of cgroup subsystem pointers */
128 #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
129 static struct cgroup_subsys *cgroup_subsys[] = {
130 #include <linux/cgroup_subsys.h>
131 };
132 #undef SUBSYS
133 
134 /* array of cgroup subsystem names */
135 #define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
136 static const char *cgroup_subsys_name[] = {
137 #include <linux/cgroup_subsys.h>
138 };
139 #undef SUBSYS
140 
141 /*
142  * The default hierarchy, reserved for the subsystems that are otherwise
143  * unattached - it never has more than a single cgroup, and all tasks are
144  * part of that cgroup.
145  */
146 struct cgroup_root cgrp_dfl_root;
147 
148 /*
149  * The default hierarchy always exists but is hidden until mounted for the
150  * first time.  This is for backward compatibility.
151  */
152 static bool cgrp_dfl_root_visible;
153 
154 /* The list of hierarchy roots */
155 
156 static LIST_HEAD(cgroup_roots);
157 static int cgroup_root_count;
158 
159 /* hierarchy ID allocation and mapping, protected by cgroup_mutex */
160 static DEFINE_IDR(cgroup_hierarchy_idr);
161 
162 /*
163  * Assign a monotonically increasing serial number to cgroups.  It
164  * guarantees cgroups with bigger numbers are newer than those with smaller
165  * numbers.  Also, as cgroups are always appended to the parent's
166  * ->children list, it guarantees that sibling cgroups are always sorted in
167  * the ascending serial number order on the list.  Protected by
168  * cgroup_mutex.
169  */
170 static u64 cgroup_serial_nr_next = 1;
171 
172 /* This flag indicates whether tasks in the fork and exit paths should
173  * check for fork/exit handlers to call. This avoids us having to do
174  * extra work in the fork/exit path if none of the subsystems need to
175  * be called.
176  */
177 static int need_forkexit_callback __read_mostly;
178 
179 static struct cftype cgroup_base_files[];
180 
181 static void cgroup_put(struct cgroup *cgrp);
182 static int rebind_subsystems(struct cgroup_root *dst_root,
183                              unsigned long ss_mask);
184 static void cgroup_destroy_css_killed(struct cgroup *cgrp);
185 static int cgroup_destroy_locked(struct cgroup *cgrp);
186 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
187                               bool is_add);
188 static void cgroup_pidlist_destroy_all(struct cgroup *cgrp);
189 
190 /**
191  * cgroup_css - obtain a cgroup's css for the specified subsystem
192  * @cgrp: the cgroup of interest
193  * @ss: the subsystem of interest (%NULL returns the dummy_css)
194  *
195  * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
196  * function must be called either under cgroup_mutex or rcu_read_lock() and
197  * the caller is responsible for pinning the returned css if it wants to
198  * keep accessing it outside the said locks.  This function may return
199  * %NULL if @cgrp doesn't have @subsys_id enabled.
200  */
201 static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
202                                               struct cgroup_subsys *ss)
203 {
204         if (ss)
205                 return rcu_dereference_check(cgrp->subsys[ss->id],
206                                         lockdep_is_held(&cgroup_tree_mutex) ||
207                                         lockdep_is_held(&cgroup_mutex));
208         else
209                 return &cgrp->dummy_css;
210 }
211 
212 /* convenient tests for these bits */
213 static inline bool cgroup_is_dead(const struct cgroup *cgrp)
214 {
215         return test_bit(CGRP_DEAD, &cgrp->flags);
216 }
217 
218 struct cgroup_subsys_state *seq_css(struct seq_file *seq)
219 {
220         struct kernfs_open_file *of = seq->private;
221         struct cgroup *cgrp = of->kn->parent->priv;
222         struct cftype *cft = seq_cft(seq);
223 
224         /*
225          * This is open and unprotected implementation of cgroup_css().
226          * seq_css() is only called from a kernfs file operation which has
227          * an active reference on the file.  Because all the subsystem
228          * files are drained before a css is disassociated with a cgroup,
229          * the matching css from the cgroup's subsys table is guaranteed to
230          * be and stay valid until the enclosing operation is complete.
231          */
232         if (cft->ss)
233                 return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
234         else
235                 return &cgrp->dummy_css;
236 }
237 EXPORT_SYMBOL_GPL(seq_css);
238 
239 /**
240  * cgroup_is_descendant - test ancestry
241  * @cgrp: the cgroup to be tested
242  * @ancestor: possible ancestor of @cgrp
243  *
244  * Test whether @cgrp is a descendant of @ancestor.  It also returns %true
245  * if @cgrp == @ancestor.  This function is safe to call as long as @cgrp
246  * and @ancestor are accessible.
247  */
248 bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)
249 {
250         while (cgrp) {
251                 if (cgrp == ancestor)
252                         return true;
253                 cgrp = cgrp->parent;
254         }
255         return false;
256 }
257 
258 static int cgroup_is_releasable(const struct cgroup *cgrp)
259 {
260         const int bits =
261                 (1 << CGRP_RELEASABLE) |
262                 (1 << CGRP_NOTIFY_ON_RELEASE);
263         return (cgrp->flags & bits) == bits;
264 }
265 
266 static int notify_on_release(const struct cgroup *cgrp)
267 {
268         return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
269 }
270 
271 /**
272  * for_each_css - iterate all css's of a cgroup
273  * @css: the iteration cursor
274  * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
275  * @cgrp: the target cgroup to iterate css's of
276  *
277  * Should be called under cgroup_mutex.
278  */
279 #define for_each_css(css, ssid, cgrp)                                   \
280         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
281                 if (!((css) = rcu_dereference_check(                    \
282                                 (cgrp)->subsys[(ssid)],                 \
283                                 lockdep_is_held(&cgroup_tree_mutex) ||  \
284                                 lockdep_is_held(&cgroup_mutex)))) { }   \
285                 else
286 
287 /**
288  * for_each_subsys - iterate all enabled cgroup subsystems
289  * @ss: the iteration cursor
290  * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
291  */
292 #define for_each_subsys(ss, ssid)                                       \
293         for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&                \
294              (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
295 
296 /* iterate across the hierarchies */
297 #define for_each_root(root)                                             \
298         list_for_each_entry((root), &cgroup_roots, root_list)
299 
300 /**
301  * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
302  * @cgrp: the cgroup to be checked for liveness
303  *
304  * On success, returns true; the mutex should be later unlocked.  On
305  * failure returns false with no lock held.
306  */
307 static bool cgroup_lock_live_group(struct cgroup *cgrp)
308 {
309         mutex_lock(&cgroup_mutex);
310         if (cgroup_is_dead(cgrp)) {
311                 mutex_unlock(&cgroup_mutex);
312                 return false;
313         }
314         return true;
315 }
316 
317 /* the list of cgroups eligible for automatic release. Protected by
318  * release_list_lock */
319 static LIST_HEAD(release_list);
320 static DEFINE_RAW_SPINLOCK(release_list_lock);
321 static void cgroup_release_agent(struct work_struct *work);
322 static DECLARE_WORK(release_agent_work, cgroup_release_agent);
323 static void check_for_release(struct cgroup *cgrp);
324 
325 /*
326  * A cgroup can be associated with multiple css_sets as different tasks may
327  * belong to different cgroups on different hierarchies.  In the other
328  * direction, a css_set is naturally associated with multiple cgroups.
329  * This M:N relationship is represented by the following link structure
330  * which exists for each association and allows traversing the associations
331  * from both sides.
332  */
333 struct cgrp_cset_link {
334         /* the cgroup and css_set this link associates */
335         struct cgroup           *cgrp;
336         struct css_set          *cset;
337 
338         /* list of cgrp_cset_links anchored at cgrp->cset_links */
339         struct list_head        cset_link;
340 
341         /* list of cgrp_cset_links anchored at css_set->cgrp_links */
342         struct list_head        cgrp_link;
343 };
344 
345 /*
346  * The default css_set - used by init and its children prior to any
347  * hierarchies being mounted. It contains a pointer to the root state
348  * for each subsystem. Also used to anchor the list of css_sets. Not
349  * reference-counted, to improve performance when child cgroups
350  * haven't been created.
351  */
352 struct css_set init_css_set = {
353         .refcount               = ATOMIC_INIT(1),
354         .cgrp_links             = LIST_HEAD_INIT(init_css_set.cgrp_links),
355         .tasks                  = LIST_HEAD_INIT(init_css_set.tasks),
356         .mg_tasks               = LIST_HEAD_INIT(init_css_set.mg_tasks),
357         .mg_preload_node        = LIST_HEAD_INIT(init_css_set.mg_preload_node),
358         .mg_node                = LIST_HEAD_INIT(init_css_set.mg_node),
359 };
360 
361 static int css_set_count        = 1;    /* 1 for init_css_set */
362 
363 /*
364  * hash table for cgroup groups. This improves the performance to find
365  * an existing css_set. This hash doesn't (currently) take into
366  * account cgroups in empty hierarchies.
367  */
368 #define CSS_SET_HASH_BITS       7
369 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
370 
371 static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
372 {
373         unsigned long key = 0UL;
374         struct cgroup_subsys *ss;
375         int i;
376 
377         for_each_subsys(ss, i)
378                 key += (unsigned long)css[i];
379         key = (key >> 16) ^ key;
380 
381         return key;
382 }
383 
384 static void put_css_set_locked(struct css_set *cset, bool taskexit)
385 {
386         struct cgrp_cset_link *link, *tmp_link;
387 
388         lockdep_assert_held(&css_set_rwsem);
389 
390         if (!atomic_dec_and_test(&cset->refcount))
391                 return;
392 
393         /* This css_set is dead. unlink it and release cgroup refcounts */
394         hash_del(&cset->hlist);
395         css_set_count--;
396 
397         list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
398                 struct cgroup *cgrp = link->cgrp;
399 
400                 list_del(&link->cset_link);
401                 list_del(&link->cgrp_link);
402 
403                 /* @cgrp can't go away while we're holding css_set_rwsem */
404                 if (list_empty(&cgrp->cset_links) && notify_on_release(cgrp)) {
405                         if (taskexit)
406                                 set_bit(CGRP_RELEASABLE, &cgrp->flags);
407                         check_for_release(cgrp);
408                 }
409 
410                 kfree(link);
411         }
412 
413         kfree_rcu(cset, rcu_head);
414 }
415 
416 static void put_css_set(struct css_set *cset, bool taskexit)
417 {
418         /*
419          * Ensure that the refcount doesn't hit zero while any readers
420          * can see it. Similar to atomic_dec_and_lock(), but for an
421          * rwlock
422          */
423         if (atomic_add_unless(&cset->refcount, -1, 1))
424                 return;
425 
426         down_write(&css_set_rwsem);
427         put_css_set_locked(cset, taskexit);
428         up_write(&css_set_rwsem);
429 }
430 
431 /*
432  * refcounted get/put for css_set objects
433  */
434 static inline void get_css_set(struct css_set *cset)
435 {
436         atomic_inc(&cset->refcount);
437 }
438 
439 /**
440  * compare_css_sets - helper function for find_existing_css_set().
441  * @cset: candidate css_set being tested
442  * @old_cset: existing css_set for a task
443  * @new_cgrp: cgroup that's being entered by the task
444  * @template: desired set of css pointers in css_set (pre-calculated)
445  *
446  * Returns true if "cset" matches "old_cset" except for the hierarchy
447  * which "new_cgrp" belongs to, for which it should match "new_cgrp".
448  */
449 static bool compare_css_sets(struct css_set *cset,
450                              struct css_set *old_cset,
451                              struct cgroup *new_cgrp,
452                              struct cgroup_subsys_state *template[])
453 {
454         struct list_head *l1, *l2;
455 
456         if (memcmp(template, cset->subsys, sizeof(cset->subsys))) {
457                 /* Not all subsystems matched */
458                 return false;
459         }
460 
461         /*
462          * Compare cgroup pointers in order to distinguish between
463          * different cgroups in heirarchies with no subsystems. We
464          * could get by with just this check alone (and skip the
465          * memcmp above) but on most setups the memcmp check will
466          * avoid the need for this more expensive check on almost all
467          * candidates.
468          */
469 
470         l1 = &cset->cgrp_links;
471         l2 = &old_cset->cgrp_links;
472         while (1) {
473                 struct cgrp_cset_link *link1, *link2;
474                 struct cgroup *cgrp1, *cgrp2;
475 
476                 l1 = l1->next;
477                 l2 = l2->next;
478                 /* See if we reached the end - both lists are equal length. */
479                 if (l1 == &cset->cgrp_links) {
480                         BUG_ON(l2 != &old_cset->cgrp_links);
481                         break;
482                 } else {
483                         BUG_ON(l2 == &old_cset->cgrp_links);
484                 }
485                 /* Locate the cgroups associated with these links. */
486                 link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
487                 link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
488                 cgrp1 = link1->cgrp;
489                 cgrp2 = link2->cgrp;
490                 /* Hierarchies should be linked in the same order. */
491                 BUG_ON(cgrp1->root != cgrp2->root);
492 
493                 /*
494                  * If this hierarchy is the hierarchy of the cgroup
495                  * that's changing, then we need to check that this
496                  * css_set points to the new cgroup; if it's any other
497                  * hierarchy, then this css_set should point to the
498                  * same cgroup as the old css_set.
499                  */
500                 if (cgrp1->root == new_cgrp->root) {
501                         if (cgrp1 != new_cgrp)
502                                 return false;
503                 } else {
504                         if (cgrp1 != cgrp2)
505                                 return false;
506                 }
507         }
508         return true;
509 }
510 
511 /**
512  * find_existing_css_set - init css array and find the matching css_set
513  * @old_cset: the css_set that we're using before the cgroup transition
514  * @cgrp: the cgroup that we're moving into
515  * @template: out param for the new set of csses, should be clear on entry
516  */
517 static struct css_set *find_existing_css_set(struct css_set *old_cset,
518                                         struct cgroup *cgrp,
519                                         struct cgroup_subsys_state *template[])
520 {
521         struct cgroup_root *root = cgrp->root;
522         struct cgroup_subsys *ss;
523         struct css_set *cset;
524         unsigned long key;
525         int i;
526 
527         /*
528          * Build the set of subsystem state objects that we want to see in the
529          * new css_set. while subsystems can change globally, the entries here
530          * won't change, so no need for locking.
531          */
532         for_each_subsys(ss, i) {
533                 if (root->cgrp.subsys_mask & (1UL << i)) {
534                         /* Subsystem is in this hierarchy. So we want
535                          * the subsystem state from the new
536                          * cgroup */
537                         template[i] = cgroup_css(cgrp, ss);
538                 } else {
539                         /* Subsystem is not in this hierarchy, so we
540                          * don't want to change the subsystem state */
541                         template[i] = old_cset->subsys[i];
542                 }
543         }
544 
545         key = css_set_hash(template);
546         hash_for_each_possible(css_set_table, cset, hlist, key) {
547                 if (!compare_css_sets(cset, old_cset, cgrp, template))
548                         continue;
549 
550                 /* This css_set matches what we need */
551                 return cset;
552         }
553 
554         /* No existing cgroup group matched */
555         return NULL;
556 }
557 
558 static void free_cgrp_cset_links(struct list_head *links_to_free)
559 {
560         struct cgrp_cset_link *link, *tmp_link;
561 
562         list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
563                 list_del(&link->cset_link);
564                 kfree(link);
565         }
566 }
567 
568 /**
569  * allocate_cgrp_cset_links - allocate cgrp_cset_links
570  * @count: the number of links to allocate
571  * @tmp_links: list_head the allocated links are put on
572  *
573  * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
574  * through ->cset_link.  Returns 0 on success or -errno.
575  */
576 static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
577 {
578         struct cgrp_cset_link *link;
579         int i;
580 
581         INIT_LIST_HEAD(tmp_links);
582 
583         for (i = 0; i < count; i++) {
584                 link = kzalloc(sizeof(*link), GFP_KERNEL);
585                 if (!link) {
586                         free_cgrp_cset_links(tmp_links);
587                         return -ENOMEM;
588                 }
589                 list_add(&link->cset_link, tmp_links);
590         }
591         return 0;
592 }
593 
594 /**
595  * link_css_set - a helper function to link a css_set to a cgroup
596  * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
597  * @cset: the css_set to be linked
598  * @cgrp: the destination cgroup
599  */
600 static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
601                          struct cgroup *cgrp)
602 {
603         struct cgrp_cset_link *link;
604 
605         BUG_ON(list_empty(tmp_links));
606         link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
607         link->cset = cset;
608         link->cgrp = cgrp;
609         list_move(&link->cset_link, &cgrp->cset_links);
610         /*
611          * Always add links to the tail of the list so that the list
612          * is sorted by order of hierarchy creation
613          */
614         list_add_tail(&link->cgrp_link, &cset->cgrp_links);
615 }
616 
617 /**
618  * find_css_set - return a new css_set with one cgroup updated
619  * @old_cset: the baseline css_set
620  * @cgrp: the cgroup to be updated
621  *
622  * Return a new css_set that's equivalent to @old_cset, but with @cgrp
623  * substituted into the appropriate hierarchy.
624  */
625 static struct css_set *find_css_set(struct css_set *old_cset,
626                                     struct cgroup *cgrp)
627 {
628         struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
629         struct css_set *cset;
630         struct list_head tmp_links;
631         struct cgrp_cset_link *link;
632         unsigned long key;
633 
634         lockdep_assert_held(&cgroup_mutex);
635 
636         /* First see if we already have a cgroup group that matches
637          * the desired set */
638         down_read(&css_set_rwsem);
639         cset = find_existing_css_set(old_cset, cgrp, template);
640         if (cset)
641                 get_css_set(cset);
642         up_read(&css_set_rwsem);
643 
644         if (cset)
645                 return cset;
646 
647         cset = kzalloc(sizeof(*cset), GFP_KERNEL);
648         if (!cset)
649                 return NULL;
650 
651         /* Allocate all the cgrp_cset_link objects that we'll need */
652         if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
653                 kfree(cset);
654                 return NULL;
655         }
656 
657         atomic_set(&cset->refcount, 1);
658         INIT_LIST_HEAD(&cset->cgrp_links);
659         INIT_LIST_HEAD(&cset->tasks);
660         INIT_LIST_HEAD(&cset->mg_tasks);
661         INIT_LIST_HEAD(&cset->mg_preload_node);
662         INIT_LIST_HEAD(&cset->mg_node);
663         INIT_HLIST_NODE(&cset->hlist);
664 
665         /* Copy the set of subsystem state objects generated in
666          * find_existing_css_set() */
667         memcpy(cset->subsys, template, sizeof(cset->subsys));
668 
669         down_write(&css_set_rwsem);
670         /* Add reference counts and links from the new css_set. */
671         list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
672                 struct cgroup *c = link->cgrp;
673 
674                 if (c->root == cgrp->root)
675                         c = cgrp;
676                 link_css_set(&tmp_links, cset, c);
677         }
678 
679         BUG_ON(!list_empty(&tmp_links));
680 
681         css_set_count++;
682 
683         /* Add this cgroup group to the hash table */
684         key = css_set_hash(cset->subsys);
685         hash_add(css_set_table, &cset->hlist, key);
686 
687         up_write(&css_set_rwsem);
688 
689         return cset;
690 }
691 
692 static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
693 {
694         struct cgroup *root_cgrp = kf_root->kn->priv;
695 
696         return root_cgrp->root;
697 }
698 
699 static int cgroup_init_root_id(struct cgroup_root *root)
700 {
701         int id;
702 
703         lockdep_assert_held(&cgroup_mutex);
704 
705         id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
706         if (id < 0)
707                 return id;
708 
709         root->hierarchy_id = id;
710         return 0;
711 }
712 
713 static void cgroup_exit_root_id(struct cgroup_root *root)
714 {
715         lockdep_assert_held(&cgroup_mutex);
716 
717         if (root->hierarchy_id) {
718                 idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
719                 root->hierarchy_id = 0;
720         }
721 }
722 
723 static void cgroup_free_root(struct cgroup_root *root)
724 {
725         if (root) {
726                 /* hierarhcy ID shoulid already have been released */
727                 WARN_ON_ONCE(root->hierarchy_id);
728 
729                 idr_destroy(&root->cgroup_idr);
730                 kfree(root);
731         }
732 }
733 
734 static void cgroup_destroy_root(struct cgroup_root *root)
735 {
736         struct cgroup *cgrp = &root->cgrp;
737         struct cgrp_cset_link *link, *tmp_link;
738 
739         mutex_lock(&cgroup_tree_mutex);
740         mutex_lock(&cgroup_mutex);
741 
742         BUG_ON(atomic_read(&root->nr_cgrps));
743         BUG_ON(!list_empty(&cgrp->children));
744 
745         /* Rebind all subsystems back to the default hierarchy */
746         rebind_subsystems(&cgrp_dfl_root, cgrp->subsys_mask);
747 
748         /*
749          * Release all the links from cset_links to this hierarchy's
750          * root cgroup
751          */
752         down_write(&css_set_rwsem);
753 
754         list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
755                 list_del(&link->cset_link);
756                 list_del(&link->cgrp_link);
757                 kfree(link);
758         }
759         up_write(&css_set_rwsem);
760 
761         if (!list_empty(&root->root_list)) {
762                 list_del(&root->root_list);
763                 cgroup_root_count--;
764         }
765 
766         cgroup_exit_root_id(root);
767 
768         mutex_unlock(&cgroup_mutex);
769         mutex_unlock(&cgroup_tree_mutex);
770 
771         kernfs_destroy_root(root->kf_root);
772         cgroup_free_root(root);
773 }
774 
775 /* look up cgroup associated with given css_set on the specified hierarchy */
776 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
777                                             struct cgroup_root *root)
778 {
779         struct cgroup *res = NULL;
780 
781         lockdep_assert_held(&cgroup_mutex);
782         lockdep_assert_held(&css_set_rwsem);
783 
784         if (cset == &init_css_set) {
785                 res = &root->cgrp;
786         } else {
787                 struct cgrp_cset_link *link;
788 
789                 list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
790                         struct cgroup *c = link->cgrp;
791 
792                         if (c->root == root) {
793                                 res = c;
794                                 break;
795                         }
796                 }
797         }
798 
799         BUG_ON(!res);
800         return res;
801 }
802 
803 /*
804  * Return the cgroup for "task" from the given hierarchy. Must be
805  * called with cgroup_mutex and css_set_rwsem held.
806  */
807 static struct cgroup *task_cgroup_from_root(struct task_struct *task,
808                                             struct cgroup_root *root)
809 {
810         /*
811          * No need to lock the task - since we hold cgroup_mutex the
812          * task can't change groups, so the only thing that can happen
813          * is that it exits and its css is set back to init_css_set.
814          */
815         return cset_cgroup_from_root(task_css_set(task), root);
816 }
817 
818 /*
819  * A task must hold cgroup_mutex to modify cgroups.
820  *
821  * Any task can increment and decrement the count field without lock.
822  * So in general, code holding cgroup_mutex can't rely on the count
823  * field not changing.  However, if the count goes to zero, then only
824  * cgroup_attach_task() can increment it again.  Because a count of zero
825  * means that no tasks are currently attached, therefore there is no
826  * way a task attached to that cgroup can fork (the other way to
827  * increment the count).  So code holding cgroup_mutex can safely
828  * assume that if the count is zero, it will stay zero. Similarly, if
829  * a task holds cgroup_mutex on a cgroup with zero count, it
830  * knows that the cgroup won't be removed, as cgroup_rmdir()
831  * needs that mutex.
832  *
833  * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
834  * (usually) take cgroup_mutex.  These are the two most performance
835  * critical pieces of code here.  The exception occurs on cgroup_exit(),
836  * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
837  * is taken, and if the cgroup count is zero, a usermode call made
838  * to the release agent with the name of the cgroup (path relative to
839  * the root of cgroup file system) as the argument.
840  *
841  * A cgroup can only be deleted if both its 'count' of using tasks
842  * is zero, and its list of 'children' cgroups is empty.  Since all
843  * tasks in the system use _some_ cgroup, and since there is always at
844  * least one task in the system (init, pid == 1), therefore, root cgroup
845  * always has either children cgroups and/or using tasks.  So we don't
846  * need a special hack to ensure that root cgroup cannot be deleted.
847  *
848  * P.S.  One more locking exception.  RCU is used to guard the
849  * update of a tasks cgroup pointer by cgroup_attach_task()
850  */
851 
852 static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask);
853 static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
854 static const struct file_operations proc_cgroupstats_operations;
855 
856 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
857                               char *buf)
858 {
859         if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
860             !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
861                 snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
862                          cft->ss->name, cft->name);
863         else
864                 strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
865         return buf;
866 }
867 
868 /**
869  * cgroup_file_mode - deduce file mode of a control file
870  * @cft: the control file in question
871  *
872  * returns cft->mode if ->mode is not 0
873  * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
874  * returns S_IRUGO if it has only a read handler
875  * returns S_IWUSR if it has only a write hander
876  */
877 static umode_t cgroup_file_mode(const struct cftype *cft)
878 {
879         umode_t mode = 0;
880 
881         if (cft->mode)
882                 return cft->mode;
883 
884         if (cft->read_u64 || cft->read_s64 || cft->seq_show)
885                 mode |= S_IRUGO;
886 
887         if (cft->write_u64 || cft->write_s64 || cft->write_string ||
888             cft->trigger)
889                 mode |= S_IWUSR;
890 
891         return mode;
892 }
893 
894 static void cgroup_free_fn(struct work_struct *work)
895 {
896         struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
897 
898         atomic_dec(&cgrp->root->nr_cgrps);
899         cgroup_pidlist_destroy_all(cgrp);
900 
901         if (cgrp->parent) {
902                 /*
903                  * We get a ref to the parent, and put the ref when this
904                  * cgroup is being freed, so it's guaranteed that the
905                  * parent won't be destroyed before its children.
906                  */
907                 cgroup_put(cgrp->parent);
908                 kernfs_put(cgrp->kn);
909                 kfree(cgrp);
910         } else {
911                 /*
912                  * This is root cgroup's refcnt reaching zero, which
913                  * indicates that the root should be released.
914                  */
915                 cgroup_destroy_root(cgrp->root);
916         }
917 }
918 
919 static void cgroup_free_rcu(struct rcu_head *head)
920 {
921         struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head);
922 
923         INIT_WORK(&cgrp->destroy_work, cgroup_free_fn);
924         queue_work(cgroup_destroy_wq, &cgrp->destroy_work);
925 }
926 
927 static void cgroup_get(struct cgroup *cgrp)
928 {
929         WARN_ON_ONCE(cgroup_is_dead(cgrp));
930         WARN_ON_ONCE(atomic_read(&cgrp->refcnt) <= 0);
931         atomic_inc(&cgrp->refcnt);
932 }
933 
934 static void cgroup_put(struct cgroup *cgrp)
935 {
936         if (!atomic_dec_and_test(&cgrp->refcnt))
937                 return;
938         if (WARN_ON_ONCE(cgrp->parent && !cgroup_is_dead(cgrp)))
939                 return;
940 
941         /*
942          * XXX: cgrp->id is only used to look up css's.  As cgroup and
943          * css's lifetimes will be decoupled, it should be made
944          * per-subsystem and moved to css->id so that lookups are
945          * successful until the target css is released.
946          */
947         mutex_lock(&cgroup_mutex);
948         idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
949         mutex_unlock(&cgroup_mutex);
950         cgrp->id = -1;
951 
952         call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
953 }
954 
955 static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
956 {
957         char name[CGROUP_FILE_NAME_MAX];
958 
959         lockdep_assert_held(&cgroup_tree_mutex);
960         kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
961 }
962 
963 /**
964  * cgroup_clear_dir - remove subsys files in a cgroup directory
965  * @cgrp: target cgroup
966  * @subsys_mask: mask of the subsystem ids whose files should be removed
967  */
968 static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask)
969 {
970         struct cgroup_subsys *ss;
971         int i;
972 
973         for_each_subsys(ss, i) {
974                 struct cftype *cfts;
975 
976                 if (!test_bit(i, &subsys_mask))
977                         continue;
978                 list_for_each_entry(cfts, &ss->cfts, node)
979                         cgroup_addrm_files(cgrp, cfts, false);
980         }
981 }
982 
983 static int rebind_subsystems(struct cgroup_root *dst_root,
984                              unsigned long ss_mask)
985 {
986         struct cgroup_subsys *ss;
987         int ssid, ret;
988 
989         lockdep_assert_held(&cgroup_tree_mutex);
990         lockdep_assert_held(&cgroup_mutex);
991 
992         for_each_subsys(ss, ssid) {
993                 if (!(ss_mask & (1 << ssid)))
994                         continue;
995 
996                 /* if @ss is on the dummy_root, we can always move it */
997                 if (ss->root == &cgrp_dfl_root)
998                         continue;
999 
1000                 /* if @ss has non-root cgroups attached to it, can't move */
1001                 if (!list_empty(&ss->root->cgrp.children))
1002                         return -EBUSY;
1003 
1004                 /* can't move between two non-dummy roots either */
1005                 if (dst_root != &cgrp_dfl_root)
1006                         return -EBUSY;
1007         }
1008 
1009         ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask);
1010         if (ret) {
1011                 if (dst_root != &cgrp_dfl_root)
1012                         return ret;
1013 
1014                 /*
1015                  * Rebinding back to the default root is not allowed to
1016                  * fail.  Using both default and non-default roots should
1017                  * be rare.  Moving subsystems back and forth even more so.
1018                  * Just warn about it and continue.
1019                  */
1020                 if (cgrp_dfl_root_visible) {
1021                         pr_warning("cgroup: failed to create files (%d) while rebinding 0x%lx to default root\n",
1022                                    ret, ss_mask);
1023                         pr_warning("cgroup: you may retry by moving them to a different hierarchy and unbinding\n");
1024                 }
1025         }
1026 
1027         /*
1028          * Nothing can fail from this point on.  Remove files for the
1029          * removed subsystems and rebind each subsystem.
1030          */
1031         mutex_unlock(&cgroup_mutex);
1032         for_each_subsys(ss, ssid)
1033                 if (ss_mask & (1 << ssid))
1034                         cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
1035         mutex_lock(&cgroup_mutex);
1036 
1037         for_each_subsys(ss, ssid) {
1038                 struct cgroup_root *src_root;
1039                 struct cgroup_subsys_state *css;
1040 
1041                 if (!(ss_mask & (1 << ssid)))
1042                         continue;
1043 
1044                 src_root = ss->root;
1045                 css = cgroup_css(&src_root->cgrp, ss);
1046 
1047                 WARN_ON(!css || cgroup_css(&dst_root->cgrp, ss));
1048 
1049                 RCU_INIT_POINTER(src_root->cgrp.subsys[ssid], NULL);
1050                 rcu_assign_pointer(dst_root->cgrp.subsys[ssid], css);
1051                 ss->root = dst_root;
1052                 css->cgroup = &dst_root->cgrp;
1053 
1054                 src_root->cgrp.subsys_mask &= ~(1 << ssid);
1055                 dst_root->cgrp.subsys_mask |= 1 << ssid;
1056 
1057                 if (ss->bind)
1058                         ss->bind(css);
1059         }
1060 
1061         kernfs_activate(dst_root->cgrp.kn);
1062         return 0;
1063 }
1064 
1065 static int cgroup_show_options(struct seq_file *seq,
1066                                struct kernfs_root *kf_root)
1067 {
1068         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1069         struct cgroup_subsys *ss;
1070         int ssid;
1071 
1072         for_each_subsys(ss, ssid)
1073                 if (root->cgrp.subsys_mask & (1 << ssid))
1074                         seq_printf(seq, ",%s", ss->name);
1075         if (root->flags & CGRP_ROOT_SANE_BEHAVIOR)
1076                 seq_puts(seq, ",sane_behavior");
1077         if (root->flags & CGRP_ROOT_NOPREFIX)
1078                 seq_puts(seq, ",noprefix");
1079         if (root->flags & CGRP_ROOT_XATTR)
1080                 seq_puts(seq, ",xattr");
1081 
1082         spin_lock(&release_agent_path_lock);
1083         if (strlen(root->release_agent_path))
1084                 seq_printf(seq, ",release_agent=%s", root->release_agent_path);
1085         spin_unlock(&release_agent_path_lock);
1086 
1087         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1088                 seq_puts(seq, ",clone_children");
1089         if (strlen(root->name))
1090                 seq_printf(seq, ",name=%s", root->name);
1091         return 0;
1092 }
1093 
1094 struct cgroup_sb_opts {
1095         unsigned long subsys_mask;
1096         unsigned long flags;
1097         char *release_agent;
1098         bool cpuset_clone_children;
1099         char *name;
1100         /* User explicitly requested empty subsystem */
1101         bool none;
1102 };
1103 
1104 /*
1105  * Convert a hierarchy specifier into a bitmask of subsystems and
1106  * flags. Call with cgroup_mutex held to protect the cgroup_subsys[]
1107  * array. This function takes refcounts on subsystems to be used, unless it
1108  * returns error, in which case no refcounts are taken.
1109  */
1110 static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1111 {
1112         char *token, *o = data;
1113         bool all_ss = false, one_ss = false;
1114         unsigned long mask = (unsigned long)-1;
1115         struct cgroup_subsys *ss;
1116         int i;
1117 
1118         BUG_ON(!mutex_is_locked(&cgroup_mutex));
1119 
1120 #ifdef CONFIG_CPUSETS
1121         mask = ~(1UL << cpuset_cgrp_id);
1122 #endif
1123 
1124         memset(opts, 0, sizeof(*opts));
1125 
1126         while ((token = strsep(&o, ",")) != NULL) {
1127                 if (!*token)
1128                         return -EINVAL;
1129                 if (!strcmp(token, "none")) {
1130                         /* Explicitly have no subsystems */
1131                         opts->none = true;
1132                         continue;
1133                 }
1134                 if (!strcmp(token, "all")) {
1135                         /* Mutually exclusive option 'all' + subsystem name */
1136                         if (one_ss)
1137                                 return -EINVAL;
1138                         all_ss = true;
1139                         continue;
1140                 }
1141                 if (!strcmp(token, "__DEVEL__sane_behavior")) {
1142                         opts->flags |= CGRP_ROOT_SANE_BEHAVIOR;
1143                         continue;
1144                 }
1145                 if (!strcmp(token, "noprefix")) {
1146                         opts->flags |= CGRP_ROOT_NOPREFIX;
1147                         continue;
1148                 }
1149                 if (!strcmp(token, "clone_children")) {
1150                         opts->cpuset_clone_children = true;
1151                         continue;
1152                 }
1153                 if (!strcmp(token, "xattr")) {
1154                         opts->flags |= CGRP_ROOT_XATTR;
1155                         continue;
1156                 }
1157                 if (!strncmp(token, "release_agent=", 14)) {
1158                         /* Specifying two release agents is forbidden */
1159                         if (opts->release_agent)
1160                                 return -EINVAL;
1161                         opts->release_agent =
1162                                 kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1163                         if (!opts->release_agent)
1164                                 return -ENOMEM;
1165                         continue;
1166                 }
1167                 if (!strncmp(token, "name=", 5)) {
1168                         const char *name = token + 5;
1169                         /* Can't specify an empty name */
1170                         if (!strlen(name))
1171                                 return -EINVAL;
1172                         /* Must match [\w.-]+ */
1173                         for (i = 0; i < strlen(name); i++) {
1174                                 char c = name[i];
1175                                 if (isalnum(c))
1176                                         continue;
1177                                 if ((c == '.') || (c == '-') || (c == '_'))
1178                                         continue;
1179                                 return -EINVAL;
1180                         }
1181                         /* Specifying two names is forbidden */
1182                         if (opts->name)
1183                                 return -EINVAL;
1184                         opts->name = kstrndup(name,
1185                                               MAX_CGROUP_ROOT_NAMELEN - 1,
1186                                               GFP_KERNEL);
1187                         if (!opts->name)
1188                                 return -ENOMEM;
1189 
1190                         continue;
1191                 }
1192 
1193                 for_each_subsys(ss, i) {
1194                         if (strcmp(token, ss->name))
1195                                 continue;
1196                         if (ss->disabled)
1197                                 continue;
1198 
1199                         /* Mutually exclusive option 'all' + subsystem name */
1200                         if (all_ss)
1201                                 return -EINVAL;
1202                         set_bit(i, &opts->subsys_mask);
1203                         one_ss = true;
1204 
1205                         break;
1206                 }
1207                 if (i == CGROUP_SUBSYS_COUNT)
1208                         return -ENOENT;
1209         }
1210 
1211         /* Consistency checks */
1212 
1213         if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) {
1214                 pr_warning("cgroup: sane_behavior: this is still under development and its behaviors will change, proceed at your own risk\n");
1215 
1216                 if ((opts->flags & (CGRP_ROOT_NOPREFIX | CGRP_ROOT_XATTR)) ||
1217                     opts->cpuset_clone_children || opts->release_agent ||
1218                     opts->name) {
1219                         pr_err("cgroup: sane_behavior: noprefix, xattr, clone_children, release_agent and name are not allowed\n");
1220                         return -EINVAL;
1221                 }
1222         } else {
1223                 /*
1224                  * If the 'all' option was specified select all the
1225                  * subsystems, otherwise if 'none', 'name=' and a subsystem
1226                  * name options were not specified, let's default to 'all'
1227                  */
1228                 if (all_ss || (!one_ss && !opts->none && !opts->name))
1229                         for_each_subsys(ss, i)
1230                                 if (!ss->disabled)
1231                                         set_bit(i, &opts->subsys_mask);
1232 
1233                 /*
1234                  * We either have to specify by name or by subsystems. (So
1235                  * all empty hierarchies must have a name).
1236                  */
1237                 if (!opts->subsys_mask && !opts->name)
1238                         return -EINVAL;
1239         }
1240 
1241         /*
1242          * Option noprefix was introduced just for backward compatibility
1243          * with the old cpuset, so we allow noprefix only if mounting just
1244          * the cpuset subsystem.
1245          */
1246         if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1247                 return -EINVAL;
1248 
1249 
1250         /* Can't specify "none" and some subsystems */
1251         if (opts->subsys_mask && opts->none)
1252                 return -EINVAL;
1253 
1254         return 0;
1255 }
1256 
1257 static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1258 {
1259         int ret = 0;
1260         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1261         struct cgroup_sb_opts opts;
1262         unsigned long added_mask, removed_mask;
1263 
1264         if (root->flags & CGRP_ROOT_SANE_BEHAVIOR) {
1265                 pr_err("cgroup: sane_behavior: remount is not allowed\n");
1266                 return -EINVAL;
1267         }
1268 
1269         mutex_lock(&cgroup_tree_mutex);
1270         mutex_lock(&cgroup_mutex);
1271 
1272         /* See what subsystems are wanted */
1273         ret = parse_cgroupfs_options(data, &opts);
1274         if (ret)
1275                 goto out_unlock;
1276 
1277         if (opts.subsys_mask != root->cgrp.subsys_mask || opts.release_agent)
1278                 pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
1279                            task_tgid_nr(current), current->comm);
1280 
1281         added_mask = opts.subsys_mask & ~root->cgrp.subsys_mask;
1282         removed_mask = root->cgrp.subsys_mask & ~opts.subsys_mask;
1283 
1284         /* Don't allow flags or name to change at remount */
1285         if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) ||
1286             (opts.name && strcmp(opts.name, root->name))) {
1287                 pr_err("cgroup: option or name mismatch, new: 0x%lx \"%s\", old: 0x%lx \"%s\"\n",
1288                        opts.flags & CGRP_ROOT_OPTION_MASK, opts.name ?: "",
1289                        root->flags & CGRP_ROOT_OPTION_MASK, root->name);
1290                 ret = -EINVAL;
1291                 goto out_unlock;
1292         }
1293 
1294         /* remounting is not allowed for populated hierarchies */
1295         if (!list_empty(&root->cgrp.children)) {
1296                 ret = -EBUSY;
1297                 goto out_unlock;
1298         }
1299 
1300         ret = rebind_subsystems(root, added_mask);
1301         if (ret)
1302                 goto out_unlock;
1303 
1304         rebind_subsystems(&cgrp_dfl_root, removed_mask);
1305 
1306         if (opts.release_agent) {
1307                 spin_lock(&release_agent_path_lock);
1308                 strcpy(root->release_agent_path, opts.release_agent);
1309                 spin_unlock(&release_agent_path_lock);
1310         }
1311  out_unlock:
1312         kfree(opts.release_agent);
1313         kfree(opts.name);
1314         mutex_unlock(&cgroup_mutex);
1315         mutex_unlock(&cgroup_tree_mutex);
1316         return ret;
1317 }
1318 
1319 /*
1320  * To reduce the fork() overhead for systems that are not actually using
1321  * their cgroups capability, we don't maintain the lists running through
1322  * each css_set to its tasks until we see the list actually used - in other
1323  * words after the first mount.
1324  */
1325 static bool use_task_css_set_links __read_mostly;
1326 
1327 static void cgroup_enable_task_cg_lists(void)
1328 {
1329         struct task_struct *p, *g;
1330 
1331         down_write(&css_set_rwsem);
1332 
1333         if (use_task_css_set_links)
1334                 goto out_unlock;
1335 
1336         use_task_css_set_links = true;
1337 
1338         /*
1339          * We need tasklist_lock because RCU is not safe against
1340          * while_each_thread(). Besides, a forking task that has passed
1341          * cgroup_post_fork() without seeing use_task_css_set_links = 1
1342          * is not guaranteed to have its child immediately visible in the
1343          * tasklist if we walk through it with RCU.
1344          */
1345         read_lock(&tasklist_lock);
1346         do_each_thread(g, p) {
1347                 WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1348                              task_css_set(p) != &init_css_set);
1349 
1350                 /*
1351                  * We should check if the process is exiting, otherwise
1352                  * it will race with cgroup_exit() in that the list
1353                  * entry won't be deleted though the process has exited.
1354                  * Do it while holding siglock so that we don't end up
1355                  * racing against cgroup_exit().
1356                  */
1357                 spin_lock_irq(&p->sighand->siglock);
1358                 if (!(p->flags & PF_EXITING)) {
1359                         struct css_set *cset = task_css_set(p);
1360 
1361                         list_add(&p->cg_list, &cset->tasks);
1362                         get_css_set(cset);
1363                 }
1364                 spin_unlock_irq(&p->sighand->siglock);
1365         } while_each_thread(g, p);
1366         read_unlock(&tasklist_lock);
1367 out_unlock:
1368         up_write(&css_set_rwsem);
1369 }
1370 
1371 static void init_cgroup_housekeeping(struct cgroup *cgrp)
1372 {
1373         atomic_set(&cgrp->refcnt, 1);
1374         INIT_LIST_HEAD(&cgrp->sibling);
1375         INIT_LIST_HEAD(&cgrp->children);
1376         INIT_LIST_HEAD(&cgrp->cset_links);
1377         INIT_LIST_HEAD(&cgrp->release_list);
1378         INIT_LIST_HEAD(&cgrp->pidlists);
1379         mutex_init(&cgrp->pidlist_mutex);
1380         cgrp->dummy_css.cgroup = cgrp;
1381 }
1382 
1383 static void init_cgroup_root(struct cgroup_root *root,
1384                              struct cgroup_sb_opts *opts)
1385 {
1386         struct cgroup *cgrp = &root->cgrp;
1387 
1388         INIT_LIST_HEAD(&root->root_list);
1389         atomic_set(&root->nr_cgrps, 1);
1390         cgrp->root = root;
1391         init_cgroup_housekeeping(cgrp);
1392         idr_init(&root->cgroup_idr);
1393 
1394         root->flags = opts->flags;
1395         if (opts->release_agent)
1396                 strcpy(root->release_agent_path, opts->release_agent);
1397         if (opts->name)
1398                 strcpy(root->name, opts->name);
1399         if (opts->cpuset_clone_children)
1400                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1401 }
1402 
1403 static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
1404 {
1405         LIST_HEAD(tmp_links);
1406         struct cgroup *root_cgrp = &root->cgrp;
1407         struct css_set *cset;
1408         int i, ret;
1409 
1410         lockdep_assert_held(&cgroup_tree_mutex);
1411         lockdep_assert_held(&cgroup_mutex);
1412 
1413         ret = idr_alloc(&root->cgroup_idr, root_cgrp, 0, 1, GFP_KERNEL);
1414         if (ret < 0)
1415                 goto out;
1416         root_cgrp->id = ret;
1417 
1418         /*
1419          * We're accessing css_set_count without locking css_set_rwsem here,
1420          * but that's OK - it can only be increased by someone holding
1421          * cgroup_lock, and that's us. The worst that can happen is that we
1422          * have some link structures left over
1423          */
1424         ret = allocate_cgrp_cset_links(css_set_count, &tmp_links);
1425         if (ret)
1426                 goto out;
1427 
1428         ret = cgroup_init_root_id(root);
1429         if (ret)
1430                 goto out;
1431 
1432         root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
1433                                            KERNFS_ROOT_CREATE_DEACTIVATED,
1434                                            root_cgrp);
1435         if (IS_ERR(root->kf_root)) {
1436                 ret = PTR_ERR(root->kf_root);
1437                 goto exit_root_id;
1438         }
1439         root_cgrp->kn = root->kf_root->kn;
1440 
1441         ret = cgroup_addrm_files(root_cgrp, cgroup_base_files, true);
1442         if (ret)
1443                 goto destroy_root;
1444 
1445         ret = rebind_subsystems(root, ss_mask);
1446         if (ret)
1447                 goto destroy_root;
1448 
1449         /*
1450          * There must be no failure case after here, since rebinding takes
1451          * care of subsystems' refcounts, which are explicitly dropped in
1452          * the failure exit path.
1453          */
1454         list_add(&root->root_list, &cgroup_roots);
1455         cgroup_root_count++;
1456 
1457         /*
1458          * Link the root cgroup in this hierarchy into all the css_set
1459          * objects.
1460          */
1461         down_write(&css_set_rwsem);
1462         hash_for_each(css_set_table, i, cset, hlist)
1463                 link_css_set(&tmp_links, cset, root_cgrp);
1464         up_write(&css_set_rwsem);
1465 
1466         BUG_ON(!list_empty(&root_cgrp->children));
1467         BUG_ON(atomic_read(&root->nr_cgrps) != 1);
1468 
1469         kernfs_activate(root_cgrp->kn);
1470         ret = 0;
1471         goto out;
1472 
1473 destroy_root:
1474         kernfs_destroy_root(root->kf_root);
1475         root->kf_root = NULL;
1476 exit_root_id:
1477         cgroup_exit_root_id(root);
1478 out:
1479         free_cgrp_cset_links(&tmp_links);
1480         return ret;
1481 }
1482 
1483 static struct dentry *cgroup_mount(struct file_system_type *fs_type,
1484                          int flags, const char *unused_dev_name,
1485                          void *data)
1486 {
1487         struct cgroup_root *root;
1488         struct cgroup_sb_opts opts;
1489         struct dentry *dentry;
1490         int ret;
1491         bool new_sb;
1492 
1493         /*
1494          * The first time anyone tries to mount a cgroup, enable the list
1495          * linking each css_set to its tasks and fix up all existing tasks.
1496          */
1497         if (!use_task_css_set_links)
1498                 cgroup_enable_task_cg_lists();
1499 
1500         mutex_lock(&cgroup_tree_mutex);
1501         mutex_lock(&cgroup_mutex);
1502 
1503         /* First find the desired set of subsystems */
1504         ret = parse_cgroupfs_options(data, &opts);
1505         if (ret)
1506                 goto out_unlock;
1507 retry:
1508         /* look for a matching existing root */
1509         if (!opts.subsys_mask && !opts.none && !opts.name) {
1510                 cgrp_dfl_root_visible = true;
1511                 root = &cgrp_dfl_root;
1512                 cgroup_get(&root->cgrp);
1513                 ret = 0;
1514                 goto out_unlock;
1515         }
1516 
1517         for_each_root(root) {
1518                 bool name_match = false;
1519 
1520                 if (root == &cgrp_dfl_root)
1521                         continue;
1522 
1523                 /*
1524                  * If we asked for a name then it must match.  Also, if
1525                  * name matches but sybsys_mask doesn't, we should fail.
1526                  * Remember whether name matched.
1527                  */
1528                 if (opts.name) {
1529                         if (strcmp(opts.name, root->name))
1530                                 continue;
1531                         name_match = true;
1532                 }
1533 
1534                 /*
1535                  * If we asked for subsystems (or explicitly for no
1536                  * subsystems) then they must match.
1537                  */
1538                 if ((opts.subsys_mask || opts.none) &&
1539                     (opts.subsys_mask != root->cgrp.subsys_mask)) {
1540                         if (!name_match)
1541                                 continue;
1542                         ret = -EBUSY;
1543                         goto out_unlock;
1544                 }
1545 
1546                 if ((root->flags ^ opts.flags) & CGRP_ROOT_OPTION_MASK) {
1547                         if ((root->flags | opts.flags) & CGRP_ROOT_SANE_BEHAVIOR) {
1548                                 pr_err("cgroup: sane_behavior: new mount options should match the existing superblock\n");
1549                                 ret = -EINVAL;
1550                                 goto out_unlock;
1551                         } else {
1552                                 pr_warning("cgroup: new mount options do not match the existing superblock, will be ignored\n");
1553                         }
1554                 }
1555 
1556                 /*
1557                  * A root's lifetime is governed by its root cgroup.  Zero
1558                  * ref indicate that the root is being destroyed.  Wait for
1559                  * destruction to complete so that the subsystems are free.
1560                  * We can use wait_queue for the wait but this path is
1561                  * super cold.  Let's just sleep for a bit and retry.
1562                  */
1563                 if (!atomic_inc_not_zero(&root->cgrp.refcnt)) {
1564                         mutex_unlock(&cgroup_mutex);
1565                         mutex_unlock(&cgroup_tree_mutex);
1566                         msleep(10);
1567                         mutex_lock(&cgroup_tree_mutex);
1568                         mutex_lock(&cgroup_mutex);
1569                         goto retry;
1570                 }
1571 
1572                 ret = 0;
1573                 goto out_unlock;
1574         }
1575 
1576         /*
1577          * No such thing, create a new one.  name= matching without subsys
1578          * specification is allowed for already existing hierarchies but we
1579          * can't create new one without subsys specification.
1580          */
1581         if (!opts.subsys_mask && !opts.none) {
1582                 ret = -EINVAL;
1583                 goto out_unlock;
1584         }
1585 
1586         root = kzalloc(sizeof(*root), GFP_KERNEL);
1587         if (!root) {
1588                 ret = -ENOMEM;
1589                 goto out_unlock;
1590         }
1591 
1592         init_cgroup_root(root, &opts);
1593 
1594         ret = cgroup_setup_root(root, opts.subsys_mask);
1595         if (ret)
1596                 cgroup_free_root(root);
1597 
1598 out_unlock:
1599         mutex_unlock(&cgroup_mutex);
1600         mutex_unlock(&cgroup_tree_mutex);
1601 
1602         kfree(opts.release_agent);
1603         kfree(opts.name);
1604 
1605         if (ret)
1606                 return ERR_PTR(ret);
1607 
1608         dentry = kernfs_mount(fs_type, flags, root->kf_root,
1609                                 CGROUP_SUPER_MAGIC, &new_sb);
1610         if (IS_ERR(dentry) || !new_sb)
1611                 cgroup_put(&root->cgrp);
1612         return dentry;
1613 }
1614 
1615 static void cgroup_kill_sb(struct super_block *sb)
1616 {
1617         struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
1618         struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1619 
1620         cgroup_put(&root->cgrp);
1621         kernfs_kill_sb(sb);
1622 }
1623 
1624 static struct file_system_type cgroup_fs_type = {
1625         .name = "cgroup",
1626         .mount = cgroup_mount,
1627         .kill_sb = cgroup_kill_sb,
1628 };
1629 
1630 static struct kobject *cgroup_kobj;
1631 
1632 /**
1633  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
1634  * @task: target task
1635  * @buf: the buffer to write the path into
1636  * @buflen: the length of the buffer
1637  *
1638  * Determine @task's cgroup on the first (the one with the lowest non-zero
1639  * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
1640  * function grabs cgroup_mutex and shouldn't be used inside locks used by
1641  * cgroup controller callbacks.
1642  *
1643  * Return value is the same as kernfs_path().
1644  */
1645 char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
1646 {
1647         struct cgroup_root *root;
1648         struct cgroup *cgrp;
1649         int hierarchy_id = 1;
1650         char *path = NULL;
1651 
1652         mutex_lock(&cgroup_mutex);
1653         down_read(&css_set_rwsem);
1654 
1655         root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
1656 
1657         if (root) {
1658                 cgrp = task_cgroup_from_root(task, root);
1659                 path = cgroup_path(cgrp, buf, buflen);
1660         } else {
1661                 /* if no hierarchy exists, everyone is in "/" */
1662                 if (strlcpy(buf, "/", buflen) < buflen)
1663                         path = buf;
1664         }
1665 
1666         up_read(&css_set_rwsem);
1667         mutex_unlock(&cgroup_mutex);
1668         return path;
1669 }
1670 EXPORT_SYMBOL_GPL(task_cgroup_path);
1671 
1672 /* used to track tasks and other necessary states during migration */
1673 struct cgroup_taskset {
1674         /* the src and dst cset list running through cset->mg_node */
1675         struct list_head        src_csets;
1676         struct list_head        dst_csets;
1677 
1678         /*
1679          * Fields for cgroup_taskset_*() iteration.
1680          *
1681          * Before migration is committed, the target migration tasks are on
1682          * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
1683          * the csets on ->dst_csets.  ->csets point to either ->src_csets
1684          * or ->dst_csets depending on whether migration is committed.
1685          *
1686          * ->cur_csets and ->cur_task point to the current task position
1687          * during iteration.
1688          */
1689         struct list_head        *csets;
1690         struct css_set          *cur_cset;
1691         struct task_struct      *cur_task;
1692 };
1693 
1694 /**
1695  * cgroup_taskset_first - reset taskset and return the first task
1696  * @tset: taskset of interest
1697  *
1698  * @tset iteration is initialized and the first task is returned.
1699  */
1700 struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset)
1701 {
1702         tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
1703         tset->cur_task = NULL;
1704 
1705         return cgroup_taskset_next(tset);
1706 }
1707 
1708 /**
1709  * cgroup_taskset_next - iterate to the next task in taskset
1710  * @tset: taskset of interest
1711  *
1712  * Return the next task in @tset.  Iteration must have been initialized
1713  * with cgroup_taskset_first().
1714  */
1715 struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
1716 {
1717         struct css_set *cset = tset->cur_cset;
1718         struct task_struct *task = tset->cur_task;
1719 
1720         while (&cset->mg_node != tset->csets) {
1721                 if (!task)
1722                         task = list_first_entry(&cset->mg_tasks,
1723                                                 struct task_struct, cg_list);
1724                 else
1725                         task = list_next_entry(task, cg_list);
1726 
1727                 if (&task->cg_list != &cset->mg_tasks) {
1728                         tset->cur_cset = cset;
1729                         tset->cur_task = task;
1730                         return task;
1731                 }
1732 
1733                 cset = list_next_entry(cset, mg_node);
1734                 task = NULL;
1735         }
1736 
1737         return NULL;
1738 }
1739 
1740 /**
1741  * cgroup_task_migrate - move a task from one cgroup to another.
1742  * @old_cgrp; the cgroup @tsk is being migrated from
1743  * @tsk: the task being migrated
1744  * @new_cset: the new css_set @tsk is being attached to
1745  *
1746  * Must be called with cgroup_mutex, threadgroup and css_set_rwsem locked.
1747  */
1748 static void cgroup_task_migrate(struct cgroup *old_cgrp,
1749                                 struct task_struct *tsk,
1750                                 struct css_set *new_cset)
1751 {
1752         struct css_set *old_cset;
1753 
1754         lockdep_assert_held(&cgroup_mutex);
1755         lockdep_assert_held(&css_set_rwsem);
1756 
1757         /*
1758          * We are synchronized through threadgroup_lock() against PF_EXITING
1759          * setting such that we can't race against cgroup_exit() changing the
1760          * css_set to init_css_set and dropping the old one.
1761          */
1762         WARN_ON_ONCE(tsk->flags & PF_EXITING);
1763         old_cset = task_css_set(tsk);
1764 
1765         get_css_set(new_cset);
1766         rcu_assign_pointer(tsk->cgroups, new_cset);
1767 
1768         /*
1769          * Use move_tail so that cgroup_taskset_first() still returns the
1770          * leader after migration.  This works because cgroup_migrate()
1771          * ensures that the dst_cset of the leader is the first on the
1772          * tset's dst_csets list.
1773          */
1774         list_move_tail(&tsk->cg_list, &new_cset->mg_tasks);
1775 
1776         /*
1777          * We just gained a reference on old_cset by taking it from the
1778          * task. As trading it for new_cset is protected by cgroup_mutex,
1779          * we're safe to drop it here; it will be freed under RCU.
1780          */
1781         set_bit(CGRP_RELEASABLE, &old_cgrp->flags);
1782         put_css_set_locked(old_cset, false);
1783 }
1784 
1785 /**
1786  * cgroup_migrate_finish - cleanup after attach
1787  * @preloaded_csets: list of preloaded css_sets
1788  *
1789  * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
1790  * those functions for details.
1791  */
1792 static void cgroup_migrate_finish(struct list_head *preloaded_csets)
1793 {
1794         struct css_set *cset, *tmp_cset;
1795 
1796         lockdep_assert_held(&cgroup_mutex);
1797 
1798         down_write(&css_set_rwsem);
1799         list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
1800                 cset->mg_src_cgrp = NULL;
1801                 cset->mg_dst_cset = NULL;
1802                 list_del_init(&cset->mg_preload_node);
1803                 put_css_set_locked(cset, false);
1804         }
1805         up_write(&css_set_rwsem);
1806 }
1807 
1808 /**
1809  * cgroup_migrate_add_src - add a migration source css_set
1810  * @src_cset: the source css_set to add
1811  * @dst_cgrp: the destination cgroup
1812  * @preloaded_csets: list of preloaded css_sets
1813  *
1814  * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
1815  * @src_cset and add it to @preloaded_csets, which should later be cleaned
1816  * up by cgroup_migrate_finish().
1817  *
1818  * This function may be called without holding threadgroup_lock even if the
1819  * target is a process.  Threads may be created and destroyed but as long
1820  * as cgroup_mutex is not dropped, no new css_set can be put into play and
1821  * the preloaded css_sets are guaranteed to cover all migrations.
1822  */
1823 static void cgroup_migrate_add_src(struct css_set *src_cset,
1824                                    struct cgroup *dst_cgrp,
1825                                    struct list_head *preloaded_csets)
1826 {
1827         struct cgroup *src_cgrp;
1828 
1829         lockdep_assert_held(&cgroup_mutex);
1830         lockdep_assert_held(&css_set_rwsem);
1831 
1832         src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
1833 
1834         /* nothing to do if this cset already belongs to the cgroup */
1835         if (src_cgrp == dst_cgrp)
1836                 return;
1837 
1838         if (!list_empty(&src_cset->mg_preload_node))
1839                 return;
1840 
1841         WARN_ON(src_cset->mg_src_cgrp);
1842         WARN_ON(!list_empty(&src_cset->mg_tasks));
1843         WARN_ON(!list_empty(&src_cset->mg_node));
1844 
1845         src_cset->mg_src_cgrp = src_cgrp;
1846         get_css_set(src_cset);
1847         list_add(&src_cset->mg_preload_node, preloaded_csets);
1848 }
1849 
1850 /**
1851  * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
1852  * @dst_cgrp: the destination cgroup
1853  * @preloaded_csets: list of preloaded source css_sets
1854  *
1855  * Tasks are about to be moved to @dst_cgrp and all the source css_sets
1856  * have been preloaded to @preloaded_csets.  This function looks up and
1857  * pins all destination css_sets, links each to its source, and put them on
1858  * @preloaded_csets.
1859  *
1860  * This function must be called after cgroup_migrate_add_src() has been
1861  * called on each migration source css_set.  After migration is performed
1862  * using cgroup_migrate(), cgroup_migrate_finish() must be called on
1863  * @preloaded_csets.
1864  */
1865 static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
1866                                       struct list_head *preloaded_csets)
1867 {
1868         LIST_HEAD(csets);
1869         struct css_set *src_cset;
1870 
1871         lockdep_assert_held(&cgroup_mutex);
1872 
1873         /* look up the dst cset for each src cset and link it to src */
1874         list_for_each_entry(src_cset, preloaded_csets, mg_preload_node) {
1875                 struct css_set *dst_cset;
1876 
1877                 dst_cset = find_css_set(src_cset, dst_cgrp);
1878                 if (!dst_cset)
1879                         goto err;
1880 
1881                 WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
1882                 src_cset->mg_dst_cset = dst_cset;
1883 
1884                 if (list_empty(&dst_cset->mg_preload_node))
1885                         list_add(&dst_cset->mg_preload_node, &csets);
1886                 else
1887                         put_css_set(dst_cset, false);
1888         }
1889 
1890         list_splice(&csets, preloaded_csets);
1891         return 0;
1892 err:
1893         cgroup_migrate_finish(&csets);
1894         return -ENOMEM;
1895 }
1896 
1897 /**
1898  * cgroup_migrate - migrate a process or task to a cgroup
1899  * @cgrp: the destination cgroup
1900  * @leader: the leader of the process or the task to migrate
1901  * @threadgroup: whether @leader points to the whole process or a single task
1902  *
1903  * Migrate a process or task denoted by @leader to @cgrp.  If migrating a
1904  * process, the caller must be holding threadgroup_lock of @leader.  The
1905  * caller is also responsible for invoking cgroup_migrate_add_src() and
1906  * cgroup_migrate_prepare_dst() on the targets before invoking this
1907  * function and following up with cgroup_migrate_finish().
1908  *
1909  * As long as a controller's ->can_attach() doesn't fail, this function is
1910  * guaranteed to succeed.  This means that, excluding ->can_attach()
1911  * failure, when migrating multiple targets, the success or failure can be
1912  * decided for all targets by invoking group_migrate_prepare_dst() before
1913  * actually starting migrating.
1914  */
1915 static int cgroup_migrate(struct cgroup *cgrp, struct task_struct *leader,
1916                           bool threadgroup)
1917 {
1918         struct cgroup_taskset tset = {
1919                 .src_csets      = LIST_HEAD_INIT(tset.src_csets),
1920                 .dst_csets      = LIST_HEAD_INIT(tset.dst_csets),
1921                 .csets          = &tset.src_csets,
1922         };
1923         struct cgroup_subsys_state *css, *failed_css = NULL;
1924         struct css_set *cset, *tmp_cset;
1925         struct task_struct *task, *tmp_task;
1926         int i, ret;
1927 
1928         /*
1929          * Prevent freeing of tasks while we take a snapshot. Tasks that are
1930          * already PF_EXITING could be freed from underneath us unless we
1931          * take an rcu_read_lock.
1932          */
1933         down_write(&css_set_rwsem);
1934         rcu_read_lock();
1935         task = leader;
1936         do {
1937                 /* @task either already exited or can't exit until the end */
1938                 if (task->flags & PF_EXITING)
1939                         goto next;
1940 
1941                 /* leave @task alone if post_fork() hasn't linked it yet */
1942                 if (list_empty(&task->cg_list))
1943                         goto next;
1944 
1945                 cset = task_css_set(task);
1946                 if (!cset->mg_src_cgrp)
1947                         goto next;
1948 
1949                 /*
1950                  * cgroup_taskset_first() must always return the leader.
1951                  * Take care to avoid disturbing the ordering.
1952                  */
1953                 list_move_tail(&task->cg_list, &cset->mg_tasks);
1954                 if (list_empty(&cset->mg_node))
1955                         list_add_tail(&cset->mg_node, &tset.src_csets);
1956                 if (list_empty(&cset->mg_dst_cset->mg_node))
1957                         list_move_tail(&cset->mg_dst_cset->mg_node,
1958                                        &tset.dst_csets);
1959         next:
1960                 if (!threadgroup)
1961                         break;
1962         } while_each_thread(leader, task);
1963         rcu_read_unlock();
1964         up_write(&css_set_rwsem);
1965 
1966         /* methods shouldn't be called if no task is actually migrating */
1967         if (list_empty(&tset.src_csets))
1968                 return 0;
1969 
1970         /* check that we can legitimately attach to the cgroup */
1971         for_each_css(css, i, cgrp) {
1972                 if (css->ss->can_attach) {
1973                         ret = css->ss->can_attach(css, &tset);
1974                         if (ret) {
1975                                 failed_css = css;
1976                                 goto out_cancel_attach;
1977                         }
1978                 }
1979         }
1980 
1981         /*
1982          * Now that we're guaranteed success, proceed to move all tasks to
1983          * the new cgroup.  There are no failure cases after here, so this
1984          * is the commit point.
1985          */
1986         down_write(&css_set_rwsem);
1987         list_for_each_entry(cset, &tset.src_csets, mg_node) {
1988                 list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list)
1989                         cgroup_task_migrate(cset->mg_src_cgrp, task,
1990                                             cset->mg_dst_cset);
1991         }
1992         up_write(&css_set_rwsem);
1993 
1994         /*
1995          * Migration is committed, all target tasks are now on dst_csets.
1996          * Nothing is sensitive to fork() after this point.  Notify
1997          * controllers that migration is complete.
1998          */
1999         tset.csets = &tset.dst_csets;
2000 
2001         for_each_css(css, i, cgrp)
2002                 if (css->ss->attach)
2003                         css->ss->attach(css, &tset);
2004 
2005         ret = 0;
2006         goto out_release_tset;
2007 
2008 out_cancel_attach:
2009         for_each_css(css, i, cgrp) {
2010                 if (css == failed_css)
2011                         break;
2012                 if (css->ss->cancel_attach)
2013                         css->ss->cancel_attach(css, &tset);
2014         }
2015 out_release_tset:
2016         down_write(&css_set_rwsem);
2017         list_splice_init(&tset.dst_csets, &tset.src_csets);
2018         list_for_each_entry_safe(cset, tmp_cset, &tset.src_csets, mg_node) {
2019                 list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2020                 list_del_init(&cset->mg_node);
2021         }
2022         up_write(&css_set_rwsem);
2023         return ret;
2024 }
2025 
2026 /**
2027  * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2028  * @dst_cgrp: the cgroup to attach to
2029  * @leader: the task or the leader of the threadgroup to be attached
2030  * @threadgroup: attach the whole threadgroup?
2031  *
2032  * Call holding cgroup_mutex and threadgroup_lock of @leader.
2033  */
2034 static int cgroup_attach_task(struct cgroup *dst_cgrp,
2035                               struct task_struct *leader, bool threadgroup)
2036 {
2037         LIST_HEAD(preloaded_csets);
2038         struct task_struct *task;
2039         int ret;
2040 
2041         /* look up all src csets */
2042         down_read(&css_set_rwsem);
2043         rcu_read_lock();
2044         task = leader;
2045         do {
2046                 cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
2047                                        &preloaded_csets);
2048                 if (!threadgroup)
2049                         break;
2050         } while_each_thread(leader, task);
2051         rcu_read_unlock();
2052         up_read(&css_set_rwsem);
2053 
2054         /* prepare dst csets and commit */
2055         ret = cgroup_migrate_prepare_dst(dst_cgrp, &preloaded_csets);
2056         if (!ret)
2057                 ret = cgroup_migrate(dst_cgrp, leader, threadgroup);
2058 
2059         cgroup_migrate_finish(&preloaded_csets);
2060         return ret;
2061 }
2062 
2063 /*
2064  * Find the task_struct of the task to attach by vpid and pass it along to the
2065  * function to attach either it or all tasks in its threadgroup. Will lock
2066  * cgroup_mutex and threadgroup.
2067  */
2068 static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
2069 {
2070         struct task_struct *tsk;
2071         const struct cred *cred = current_cred(), *tcred;
2072         int ret;
2073 
2074         if (!cgroup_lock_live_group(cgrp))
2075                 return -ENODEV;
2076 
2077 retry_find_task:
2078         rcu_read_lock();
2079         if (pid) {
2080                 tsk = find_task_by_vpid(pid);
2081                 if (!tsk) {
2082                         rcu_read_unlock();
2083                         ret = -ESRCH;
2084                         goto out_unlock_cgroup;
2085                 }
2086                 /*
2087                  * even if we're attaching all tasks in the thread group, we
2088                  * only need to check permissions on one of them.
2089                  */
2090                 tcred = __task_cred(tsk);
2091                 if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2092                     !uid_eq(cred->euid, tcred->uid) &&
2093                     !uid_eq(cred->euid, tcred->suid)) {
2094                         rcu_read_unlock();
2095                         ret = -EACCES;
2096                         goto out_unlock_cgroup;
2097                 }
2098         } else
2099                 tsk = current;
2100 
2101         if (threadgroup)
2102                 tsk = tsk->group_leader;
2103 
2104         /*
2105          * Workqueue threads may acquire PF_NO_SETAFFINITY and become
2106          * trapped in a cpuset, or RT worker may be born in a cgroup
2107          * with no rt_runtime allocated.  Just say no.
2108          */
2109         if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
2110                 ret = -EINVAL;
2111                 rcu_read_unlock();
2112                 goto out_unlock_cgroup;
2113         }
2114 
2115         get_task_struct(tsk);
2116         rcu_read_unlock();
2117 
2118         threadgroup_lock(tsk);
2119         if (threadgroup) {
2120                 if (!thread_group_leader(tsk)) {
2121                         /*
2122                          * a race with de_thread from another thread's exec()
2123                          * may strip us of our leadership, if this happens,
2124                          * there is no choice but to throw this task away and
2125                          * try again; this is
2126                          * "double-double-toil-and-trouble-check locking".
2127                          */
2128                         threadgroup_unlock(tsk);
2129                         put_task_struct(tsk);
2130                         goto retry_find_task;
2131                 }
2132         }
2133 
2134         ret = cgroup_attach_task(cgrp, tsk, threadgroup);
2135 
2136         threadgroup_unlock(tsk);
2137 
2138         put_task_struct(tsk);
2139 out_unlock_cgroup:
2140         mutex_unlock(&cgroup_mutex);
2141         return ret;
2142 }
2143 
2144 /**
2145  * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2146  * @from: attach to all cgroups of a given task
2147  * @tsk: the task to be attached
2148  */
2149 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2150 {
2151         struct cgroup_root *root;
2152         int retval = 0;
2153 
2154         mutex_lock(&cgroup_mutex);
2155         for_each_root(root) {
2156                 struct cgroup *from_cgrp;
2157 
2158                 if (root == &cgrp_dfl_root)
2159                         continue;
2160 
2161                 down_read(&css_set_rwsem);
2162                 from_cgrp = task_cgroup_from_root(from, root);
2163                 up_read(&css_set_rwsem);
2164 
2165                 retval = cgroup_attach_task(from_cgrp, tsk, false);
2166                 if (retval)
2167                         break;
2168         }
2169         mutex_unlock(&cgroup_mutex);
2170 
2171         return retval;
2172 }
2173 EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2174 
2175 static int cgroup_tasks_write(struct cgroup_subsys_state *css,
2176                               struct cftype *cft, u64 pid)
2177 {
2178         return attach_task_by_pid(css->cgroup, pid, false);
2179 }
2180 
2181 static int cgroup_procs_write(struct cgroup_subsys_state *css,
2182                               struct cftype *cft, u64 tgid)
2183 {
2184         return attach_task_by_pid(css->cgroup, tgid, true);
2185 }
2186 
2187 static int cgroup_release_agent_write(struct cgroup_subsys_state *css,
2188                                       struct cftype *cft, char *buffer)
2189 {
2190         struct cgroup_root *root = css->cgroup->root;
2191 
2192         BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX);
2193         if (!cgroup_lock_live_group(css->cgroup))
2194                 return -ENODEV;
2195         spin_lock(&release_agent_path_lock);
2196         strlcpy(root->release_agent_path, buffer,
2197                 sizeof(root->release_agent_path));
2198         spin_unlock(&release_agent_path_lock);
2199         mutex_unlock(&cgroup_mutex);
2200         return 0;
2201 }
2202 
2203 static int cgroup_release_agent_show(struct seq_file *seq, void *v)
2204 {
2205         struct cgroup *cgrp = seq_css(seq)->cgroup;
2206 
2207         if (!cgroup_lock_live_group(cgrp))
2208                 return -ENODEV;
2209         seq_puts(seq, cgrp->root->release_agent_path);
2210         seq_putc(seq, '\n');
2211         mutex_unlock(&cgroup_mutex);
2212         return 0;
2213 }
2214 
2215 static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
2216 {
2217         struct cgroup *cgrp = seq_css(seq)->cgroup;
2218 
2219         seq_printf(seq, "%d\n", cgroup_sane_behavior(cgrp));
2220         return 0;
2221 }
2222 
2223 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
2224                                  size_t nbytes, loff_t off)
2225 {
2226         struct cgroup *cgrp = of->kn->parent->priv;
2227         struct cftype *cft = of->kn->priv;
2228         struct cgroup_subsys_state *css;
2229         int ret;
2230 
2231         /*
2232          * kernfs guarantees that a file isn't deleted with operations in
2233          * flight, which means that the matching css is and stays alive and
2234          * doesn't need to be pinned.  The RCU locking is not necessary
2235          * either.  It's just for the convenience of using cgroup_css().
2236          */
2237         rcu_read_lock();
2238         css = cgroup_css(cgrp, cft->ss);
2239         rcu_read_unlock();
2240 
2241         if (cft->write_string) {
2242                 ret = cft->write_string(css, cft, strstrip(buf));
2243         } else if (cft->write_u64) {
2244                 unsigned long long v;
2245                 ret = kstrtoull(buf, 0, &v);
2246                 if (!ret)
2247                         ret = cft->write_u64(css, cft, v);
2248         } else if (cft->write_s64) {
2249                 long long v;
2250                 ret = kstrtoll(buf, 0, &v);
2251                 if (!ret)
2252                         ret = cft->write_s64(css, cft, v);
2253         } else if (cft->trigger) {
2254                 ret = cft->trigger(css, (unsigned int)cft->private);
2255         } else {
2256                 ret = -EINVAL;
2257         }
2258 
2259         return ret ?: nbytes;
2260 }
2261 
2262 static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
2263 {
2264         return seq_cft(seq)->seq_start(seq, ppos);
2265 }
2266 
2267 static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
2268 {
2269         return seq_cft(seq)->seq_next(seq, v, ppos);
2270 }
2271 
2272 static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
2273 {
2274         seq_cft(seq)->seq_stop(seq, v);
2275 }
2276 
2277 static int cgroup_seqfile_show(struct seq_file *m, void *arg)
2278 {
2279         struct cftype *cft = seq_cft(m);
2280         struct cgroup_subsys_state *css = seq_css(m);
2281 
2282         if (cft->seq_show)
2283                 return cft->seq_show(m, arg);
2284 
2285         if (cft->read_u64)
2286                 seq_printf(m, "%llu\n", cft->read_u64(css, cft));
2287         else if (cft->read_s64)
2288                 seq_printf(m, "%lld\n", cft->read_s64(css, cft));
2289         else
2290                 return -EINVAL;
2291         return 0;
2292 }
2293 
2294 static struct kernfs_ops cgroup_kf_single_ops = {
2295         .atomic_write_len       = PAGE_SIZE,
2296         .write                  = cgroup_file_write,
2297         .seq_show               = cgroup_seqfile_show,
2298 };
2299 
2300 static struct kernfs_ops cgroup_kf_ops = {
2301         .atomic_write_len       = PAGE_SIZE,
2302         .write                  = cgroup_file_write,
2303         .seq_start              = cgroup_seqfile_start,
2304         .seq_next               = cgroup_seqfile_next,
2305         .seq_stop               = cgroup_seqfile_stop,
2306         .seq_show               = cgroup_seqfile_show,
2307 };
2308 
2309 /*
2310  * cgroup_rename - Only allow simple rename of directories in place.
2311  */
2312 static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
2313                          const char *new_name_str)
2314 {
2315         struct cgroup *cgrp = kn->priv;
2316         int ret;
2317 
2318         if (kernfs_type(kn) != KERNFS_DIR)
2319                 return -ENOTDIR;
2320         if (kn->parent != new_parent)
2321                 return -EIO;
2322 
2323         /*
2324          * This isn't a proper migration and its usefulness is very
2325          * limited.  Disallow if sane_behavior.
2326          */
2327         if (cgroup_sane_behavior(cgrp))
2328                 return -EPERM;
2329 
2330         /*
2331          * We're gonna grab cgroup_tree_mutex which nests outside kernfs
2332          * active_ref.  kernfs_rename() doesn't require active_ref
2333          * protection.  Break them before grabbing cgroup_tree_mutex.
2334          */
2335         kernfs_break_active_protection(new_parent);
2336         kernfs_break_active_protection(kn);
2337 
2338         mutex_lock(&cgroup_tree_mutex);
2339         mutex_lock(&cgroup_mutex);
2340 
2341         ret = kernfs_rename(kn, new_parent, new_name_str);
2342 
2343         mutex_unlock(&cgroup_mutex);
2344         mutex_unlock(&cgroup_tree_mutex);
2345 
2346         kernfs_unbreak_active_protection(kn);
2347         kernfs_unbreak_active_protection(new_parent);
2348         return ret;
2349 }
2350 
2351 /* set uid and gid of cgroup dirs and files to that of the creator */
2352 static int cgroup_kn_set_ugid(struct kernfs_node *kn)
2353 {
2354         struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
2355                                .ia_uid = current_fsuid(),
2356                                .ia_gid = current_fsgid(), };
2357 
2358         if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
2359             gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
2360                 return 0;
2361 
2362         return kernfs_setattr(kn, &iattr);
2363 }
2364 
2365 static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
2366 {
2367         char name[CGROUP_FILE_NAME_MAX];
2368         struct kernfs_node *kn;
2369         struct lock_class_key *key = NULL;
2370         int ret;
2371 
2372 #ifdef CONFIG_DEBUG_LOCK_ALLOC
2373         key = &cft->lockdep_key;
2374 #endif
2375         kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
2376                                   cgroup_file_mode(cft), 0, cft->kf_ops, cft,
2377                                   NULL, false, key);
2378         if (IS_ERR(kn))
2379                 return PTR_ERR(kn);
2380 
2381         ret = cgroup_kn_set_ugid(kn);
2382         if (ret)
2383                 kernfs_remove(kn);
2384         return ret;
2385 }
2386 
2387 /**
2388  * cgroup_addrm_files - add or remove files to a cgroup directory
2389  * @cgrp: the target cgroup
2390  * @cfts: array of cftypes to be added
2391  * @is_add: whether to add or remove
2392  *
2393  * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
2394  * For removals, this function never fails.  If addition fails, this
2395  * function doesn't remove files already added.  The caller is responsible
2396  * for cleaning up.
2397  */
2398 static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
2399                               bool is_add)
2400 {
2401         struct cftype *cft;
2402         int ret;
2403 
2404         lockdep_assert_held(&cgroup_tree_mutex);
2405 
2406         for (cft = cfts; cft->name[0] != '\0'; cft++) {
2407                 /* does cft->flags tell us to skip this file on @cgrp? */
2408                 if ((cft->flags & CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
2409                         continue;
2410                 if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp))
2411                         continue;
2412                 if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
2413                         continue;
2414                 if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgrp->parent)
2415                         continue;
2416 
2417                 if (is_add) {
2418                         ret = cgroup_add_file(cgrp, cft);
2419                         if (ret) {
2420                                 pr_warn("cgroup_addrm_files: failed to add %s, err=%d\n",
2421                                         cft->name, ret);
2422                                 return ret;
2423                         }
2424                 } else {
2425                         cgroup_rm_file(cgrp, cft);
2426                 }
2427         }
2428         return 0;
2429 }
2430 
2431 static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
2432 {
2433         LIST_HEAD(pending);
2434         struct cgroup_subsys *ss = cfts[0].ss;
2435         struct cgroup *root = &ss->root->cgrp;
2436         struct cgroup_subsys_state *css;
2437         int ret = 0;
2438 
2439         lockdep_assert_held(&cgroup_tree_mutex);
2440 
2441         /* don't bother if @ss isn't attached */
2442         if (ss->root == &cgrp_dfl_root)
2443                 return 0;
2444 
2445         /* add/rm files for all cgroups created before */
2446         css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
2447                 struct cgroup *cgrp = css->cgroup;
2448 
2449                 if (cgroup_is_dead(cgrp))
2450                         continue;
2451 
2452                 ret = cgroup_addrm_files(cgrp, cfts, is_add);
2453                 if (ret)
2454                         break;
2455         }
2456 
2457         if (is_add && !ret)
2458                 kernfs_activate(root->kn);
2459         return ret;
2460 }
2461 
2462 static void cgroup_exit_cftypes(struct cftype *cfts)
2463 {
2464         struct cftype *cft;
2465 
2466         for (cft = cfts; cft->name[0] != '\0'; cft++) {
2467                 /* free copy for custom atomic_write_len, see init_cftypes() */
2468                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
2469                         kfree(cft->kf_ops);
2470                 cft->kf_ops = NULL;
2471                 cft->ss = NULL;
2472         }
2473 }
2474 
2475 static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
2476 {
2477         struct cftype *cft;
2478 
2479         for (cft = cfts; cft->name[0] != '\0'; cft++) {
2480                 struct kernfs_ops *kf_ops;
2481 
2482                 WARN_ON(cft->ss || cft->kf_ops);
2483 
2484                 if (cft->seq_start)
2485                         kf_ops = &cgroup_kf_ops;
2486                 else
2487                         kf_ops = &cgroup_kf_single_ops;
2488 
2489                 /*
2490                  * Ugh... if @cft wants a custom max_write_len, we need to
2491                  * make a copy of kf_ops to set its atomic_write_len.
2492                  */
2493                 if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
2494                         kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
2495                         if (!kf_ops) {
2496                                 cgroup_exit_cftypes(cfts);
2497                                 return -ENOMEM;
2498                         }
2499                         kf_ops->atomic_write_len = cft->max_write_len;
2500                 }
2501 
2502                 cft->kf_ops = kf_ops;
2503                 cft->ss = ss;
2504         }
2505 
2506         return 0;
2507 }
2508 
2509 static int cgroup_rm_cftypes_locked(struct cftype *cfts)
2510 {
2511         lockdep_assert_held(&cgroup_tree_mutex);
2512 
2513         if (!cfts || !cfts[0].ss)
2514                 return -ENOENT;
2515 
2516         list_del(&cfts->node);
2517         cgroup_apply_cftypes(cfts, false);
2518         cgroup_exit_cftypes(cfts);
2519         return 0;
2520 }
2521 
2522 /**
2523  * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
2524  * @cfts: zero-length name terminated array of cftypes
2525  *
2526  * Unregister @cfts.  Files described by @cfts are removed from all
2527  * existing cgroups and all future cgroups won't have them either.  This
2528  * function can be called anytime whether @cfts' subsys is attached or not.
2529  *
2530  * Returns 0 on successful unregistration, -ENOENT if @cfts is not
2531  * registered.
2532  */
2533 int cgroup_rm_cftypes(struct cftype *cfts)
2534 {
2535         int ret;
2536 
2537         mutex_lock(&cgroup_tree_mutex);
2538         ret = cgroup_rm_cftypes_locked(cfts);
2539         mutex_unlock(&cgroup_tree_mutex);
2540         return ret;
2541 }
2542 
2543 /**
2544  * cgroup_add_cftypes - add an array of cftypes to a subsystem
2545  * @ss: target cgroup subsystem
2546  * @cfts: zero-length name terminated array of cftypes
2547  *
2548  * Register @cfts to @ss.  Files described by @cfts are created for all
2549  * existing cgroups to which @ss is attached and all future cgroups will
2550  * have them too.  This function can be called anytime whether @ss is
2551  * attached or not.
2552  *
2553  * Returns 0 on successful registration, -errno on failure.  Note that this
2554  * function currently returns 0 as long as @cfts registration is successful
2555  * even if some file creation attempts on existing cgroups fail.
2556  */
2557 int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
2558 {
2559         int ret;
2560 
2561         if (!cfts || cfts[0].name[0] == '\0')
2562                 return 0;
2563 
2564         ret = cgroup_init_cftypes(ss, cfts);
2565         if (ret)
2566                 return ret;
2567 
2568         mutex_lock(&cgroup_tree_mutex);
2569 
2570         list_add_tail(&cfts->node, &ss->cfts);
2571         ret = cgroup_apply_cftypes(cfts, true);
2572         if (ret)
2573                 cgroup_rm_cftypes_locked(cfts);
2574 
2575         mutex_unlock(&cgroup_tree_mutex);
2576         return ret;
2577 }
2578 
2579 /**
2580  * cgroup_task_count - count the number of tasks in a cgroup.
2581  * @cgrp: the cgroup in question
2582  *
2583  * Return the number of tasks in the cgroup.
2584  */
2585 static int cgroup_task_count(const struct cgroup *cgrp)
2586 {
2587         int count = 0;
2588         struct cgrp_cset_link *link;
2589 
2590         down_read(&css_set_rwsem);
2591         list_for_each_entry(link, &cgrp->cset_links, cset_link)
2592                 count += atomic_read(&link->cset->refcount);
2593         up_read(&css_set_rwsem);
2594         return count;
2595 }
2596 
2597 /**
2598  * css_next_child - find the next child of a given css
2599  * @pos_css: the current position (%NULL to initiate traversal)
2600  * @parent_css: css whose children to walk
2601  *
2602  * This function returns the next child of @parent_css and should be called
2603  * under either cgroup_mutex or RCU read lock.  The only requirement is
2604  * that @parent_css and @pos_css are accessible.  The next sibling is
2605  * guaranteed to be returned regardless of their states.
2606  */
2607 struct cgroup_subsys_state *
2608 css_next_child(struct cgroup_subsys_state *pos_css,
2609                struct cgroup_subsys_state *parent_css)
2610 {
2611         struct cgroup *pos = pos_css ? pos_css->cgroup : NULL;
2612         struct cgroup *cgrp = parent_css->cgroup;
2613         struct cgroup *next;
2614 
2615         cgroup_assert_mutexes_or_rcu_locked();
2616 
2617         /*
2618          * @pos could already have been removed.  Once a cgroup is removed,
2619          * its ->sibling.next is no longer updated when its next sibling
2620          * changes.  As CGRP_DEAD assertion is serialized and happens
2621          * before the cgroup is taken off the ->sibling list, if we see it
2622          * unasserted, it's guaranteed that the next sibling hasn't
2623          * finished its grace period even if it's already removed, and thus
2624          * safe to dereference from this RCU critical section.  If
2625          * ->sibling.next is inaccessible, cgroup_is_dead() is guaranteed
2626          * to be visible as %true here.
2627          *
2628          * If @pos is dead, its next pointer can't be dereferenced;
2629          * however, as each cgroup is given a monotonically increasing
2630          * unique serial number and always appended to the sibling list,
2631          * the next one can be found by walking the parent's children until
2632          * we see a cgroup with higher serial number than @pos's.  While
2633          * this path can be slower, it's taken only when either the current
2634          * cgroup is removed or iteration and removal race.
2635          */
2636         if (!pos) {
2637                 next = list_entry_rcu(cgrp->children.next, struct cgroup, sibling);
2638         } else if (likely(!cgroup_is_dead(pos))) {
2639                 next = list_entry_rcu(pos->sibling.next, struct cgroup, sibling);
2640         } else {
2641                 list_for_each_entry_rcu(next, &cgrp->children, sibling)
2642                         if (next->serial_nr > pos->serial_nr)
2643                                 break;
2644         }
2645 
2646         if (&next->sibling == &cgrp->children)
2647                 return NULL;
2648 
2649         return cgroup_css(next, parent_css->ss);
2650 }
2651 
2652 /**
2653  * css_next_descendant_pre - find the next descendant for pre-order walk
2654  * @pos: the current position (%NULL to initiate traversal)
2655  * @root: css whose descendants to walk
2656  *
2657  * To be used by css_for_each_descendant_pre().  Find the next descendant
2658  * to visit for pre-order traversal of @root's descendants.  @root is
2659  * included in the iteration and the first node to be visited.
2660  *
2661  * While this function requires cgroup_mutex or RCU read locking, it
2662  * doesn't require the whole traversal to be contained in a single critical
2663  * section.  This function will return the correct next descendant as long
2664  * as both @pos and @root are accessible and @pos is a descendant of @root.
2665  */
2666 struct cgroup_subsys_state *
2667 css_next_descendant_pre(struct cgroup_subsys_state *pos,
2668                         struct cgroup_subsys_state *root)
2669 {
2670         struct cgroup_subsys_state *next;
2671 
2672         cgroup_assert_mutexes_or_rcu_locked();
2673 
2674         /* if first iteration, visit @root */
2675         if (!pos)
2676                 return root;
2677 
2678         /* visit the first child if exists */
2679         next = css_next_child(NULL, pos);
2680         if (next)
2681                 return next;
2682 
2683         /* no child, visit my or the closest ancestor's next sibling */
2684         while (pos != root) {
2685                 next = css_next_child(pos, css_parent(pos));
2686                 if (next)
2687                         return next;
2688                 pos = css_parent(pos);
2689         }
2690 
2691         return NULL;
2692 }
2693 
2694 /**
2695  * css_rightmost_descendant - return the rightmost descendant of a css
2696  * @pos: css of interest
2697  *
2698  * Return the rightmost descendant of @pos.  If there's no descendant, @pos
2699  * is returned.  This can be used during pre-order traversal to skip
2700  * subtree of @pos.
2701  *
2702  * While this function requires cgroup_mutex or RCU read locking, it
2703  * doesn't require the whole traversal to be contained in a single critical
2704  * section.  This function will return the correct rightmost descendant as
2705  * long as @pos is accessible.
2706  */
2707 struct cgroup_subsys_state *
2708 css_rightmost_descendant(struct cgroup_subsys_state *pos)
2709 {
2710         struct cgroup_subsys_state *last, *tmp;
2711 
2712         cgroup_assert_mutexes_or_rcu_locked();
2713 
2714         do {
2715                 last = pos;
2716                 /* ->prev isn't RCU safe, walk ->next till the end */
2717                 pos = NULL;
2718                 css_for_each_child(tmp, last)
2719                         pos = tmp;
2720         } while (pos);
2721 
2722         return last;
2723 }
2724 
2725 static struct cgroup_subsys_state *
2726 css_leftmost_descendant(struct cgroup_subsys_state *pos)
2727 {
2728         struct cgroup_subsys_state *last;
2729 
2730         do {
2731                 last = pos;
2732                 pos = css_next_child(NULL, pos);
2733         } while (pos);
2734 
2735         return last;
2736 }
2737 
2738 /**
2739  * css_next_descendant_post - find the next descendant for post-order walk
2740  * @pos: the current position (%NULL to initiate traversal)
2741  * @root: css whose descendants to walk
2742  *
2743  * To be used by css_for_each_descendant_post().  Find the next descendant
2744  * to visit for post-order traversal of @root's descendants.  @root is
2745  * included in the iteration and the last node to be visited.
2746  *
2747  * While this function requires cgroup_mutex or RCU read locking, it
2748  * doesn't require the whole traversal to be contained in a single critical
2749  * section.  This function will return the correct next descendant as long
2750  * as both @pos and @cgroup are accessible and @pos is a descendant of
2751  * @cgroup.
2752  */
2753 struct cgroup_subsys_state *
2754 css_next_descendant_post(struct cgroup_subsys_state *pos,
2755                          struct cgroup_subsys_state *root)
2756 {
2757         struct cgroup_subsys_state *next;
2758 
2759         cgroup_assert_mutexes_or_rcu_locked();
2760 
2761         /* if first iteration, visit leftmost descendant which may be @root */
2762         if (!pos)
2763                 return css_leftmost_descendant(root);
2764 
2765         /* if we visited @root, we're done */
2766         if (pos == root)
2767                 return NULL;
2768 
2769         /* if there's an unvisited sibling, visit its leftmost descendant */
2770         next = css_next_child(pos, css_parent(pos));
2771         if (next)
2772                 return css_leftmost_descendant(next);
2773 
2774         /* no sibling left, visit parent */
2775         return css_parent(pos);
2776 }
2777 
2778 /**
2779  * css_advance_task_iter - advance a task itererator to the next css_set
2780  * @it: the iterator to advance
2781  *
2782  * Advance @it to the next css_set to walk.
2783  */
2784 static void css_advance_task_iter(struct css_task_iter *it)
2785 {
2786         struct list_head *l = it->cset_link;
2787         struct cgrp_cset_link *link;
2788         struct css_set *cset;
2789 
2790         /* Advance to the next non-empty css_set */
2791         do {
2792                 l = l->next;
2793                 if (l == &it->origin_css->cgroup->cset_links) {
2794                         it->cset_link = NULL;
2795                         return;
2796                 }
2797                 link = list_entry(l, struct cgrp_cset_link, cset_link);
2798                 cset = link->cset;
2799         } while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks));
2800 
2801         it->cset_link = l;
2802 
2803         if (!list_empty(&cset->tasks))
2804                 it->task = cset->tasks.next;
2805         else
2806                 it->task = cset->mg_tasks.next;
2807 }
2808 
2809 /**
2810  * css_task_iter_start - initiate task iteration
2811  * @css: the css to walk tasks of
2812  * @it: the task iterator to use
2813  *
2814  * Initiate iteration through the tasks of @css.  The caller can call
2815  * css_task_iter_next() to walk through the tasks until the function
2816  * returns NULL.  On completion of iteration, css_task_iter_end() must be
2817  * called.
2818  *
2819  * Note that this function acquires a lock which is released when the
2820  * iteration finishes.  The caller can't sleep while iteration is in
2821  * progress.
2822  */
2823 void css_task_iter_start(struct cgroup_subsys_state *css,
2824                          struct css_task_iter *it)
2825         __acquires(css_set_rwsem)
2826 {
2827         /* no one should try to iterate before mounting cgroups */
2828         WARN_ON_ONCE(!use_task_css_set_links);
2829 
2830         down_read(&css_set_rwsem);
2831 
2832         it->origin_css = css;
2833         it->cset_link = &css->cgroup->cset_links;
2834 
2835         css_advance_task_iter(it);
2836 }
2837 
2838 /**
2839  * css_task_iter_next - return the next task for the iterator
2840  * @it: the task iterator being iterated
2841  *
2842  * The "next" function for task iteration.  @it should have been
2843  * initialized via css_task_iter_start().  Returns NULL when the iteration
2844  * reaches the end.
2845  */
2846 struct task_struct *css_task_iter_next(struct css_task_iter *it)
2847 {
2848         struct task_struct *res;
2849         struct list_head *l = it->task;
2850         struct cgrp_cset_link *link = list_entry(it->cset_link,
2851                                         struct cgrp_cset_link, cset_link);
2852 
2853         /* If the iterator cg is NULL, we have no tasks */
2854         if (!it->cset_link)
2855                 return NULL;
2856         res = list_entry(l, struct task_struct, cg_list);
2857 
2858         /*
2859          * Advance iterator to find next entry.  cset->tasks is consumed
2860          * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
2861          * next cset.
2862          */
2863         l = l->next;
2864 
2865         if (l == &link->cset->tasks)
2866                 l = link->cset->mg_tasks.next;
2867 
2868         if (l == &link->cset->mg_tasks)
2869                 css_advance_task_iter(it);
2870         else
2871                 it->task = l;
2872 
2873         return res;
2874 }
2875 
2876 /**
2877  * css_task_iter_end - finish task iteration
2878  * @it: the task iterator to finish
2879  *
2880  * Finish task iteration started by css_task_iter_start().
2881  */
2882 void css_task_iter_end(struct css_task_iter *it)
2883         __releases(css_set_rwsem)
2884 {
2885         up_read(&css_set_rwsem);
2886 }
2887 
2888 /**
2889  * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
2890  * @to: cgroup to which the tasks will be moved
2891  * @from: cgroup in which the tasks currently reside
2892  *
2893  * Locking rules between cgroup_post_fork() and the migration path
2894  * guarantee that, if a task is forking while being migrated, the new child
2895  * is guaranteed to be either visible in the source cgroup after the
2896  * parent's migration is complete or put into the target cgroup.  No task
2897  * can slip out of migration through forking.
2898  */
2899 int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
2900 {
2901         LIST_HEAD(preloaded_csets);
2902         struct cgrp_cset_link *link;
2903         struct css_task_iter it;
2904         struct task_struct *task;
2905         int ret;
2906 
2907         mutex_lock(&cgroup_mutex);
2908 
2909         /* all tasks in @from are being moved, all csets are source */
2910         down_read(&css_set_rwsem);
2911         list_for_each_entry(link, &from->cset_links, cset_link)
2912                 cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
2913         up_read(&css_set_rwsem);
2914 
2915         ret = cgroup_migrate_prepare_dst(to, &preloaded_csets);
2916         if (ret)
2917                 goto out_err;
2918 
2919         /*
2920          * Migrate tasks one-by-one until @form is empty.  This fails iff
2921          * ->can_attach() fails.
2922          */
2923         do {
2924                 css_task_iter_start(&from->dummy_css, &it);
2925                 task = css_task_iter_next(&it);
2926                 if (task)
2927                         get_task_struct(task);
2928                 css_task_iter_end(&it);
2929 
2930                 if (task) {
2931                         ret = cgroup_migrate(to, task, false);
2932                         put_task_struct(task);
2933                 }
2934         } while (task && !ret);
2935 out_err:
2936         cgroup_migrate_finish(&preloaded_csets);
2937         mutex_unlock(&cgroup_mutex);
2938         return ret;
2939 }
2940 
2941 /*
2942  * Stuff for reading the 'tasks'/'procs' files.
2943  *
2944  * Reading this file can return large amounts of data if a cgroup has
2945  * *lots* of attached tasks. So it may need several calls to read(),
2946  * but we cannot guarantee that the information we produce is correct
2947  * unless we produce it entirely atomically.
2948  *
2949  */
2950 
2951 /* which pidlist file are we talking about? */
2952 enum cgroup_filetype {
2953         CGROUP_FILE_PROCS,
2954         CGROUP_FILE_TASKS,
2955 };
2956 
2957 /*
2958  * A pidlist is a list of pids that virtually represents the contents of one
2959  * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
2960  * a pair (one each for procs, tasks) for each pid namespace that's relevant
2961  * to the cgroup.
2962  */
2963 struct cgroup_pidlist {
2964         /*
2965          * used to find which pidlist is wanted. doesn't change as long as
2966          * this particular list stays in the list.
2967         */
2968         struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
2969         /* array of xids */
2970         pid_t *list;
2971         /* how many elements the above list has */
2972         int length;
2973         /* each of these stored in a list by its cgroup */
2974         struct list_head links;
2975         /* pointer to the cgroup we belong to, for list removal purposes */
2976         struct cgroup *owner;
2977         /* for delayed destruction */
2978         struct delayed_work destroy_dwork;
2979 };
2980 
2981 /*
2982  * The following two functions "fix" the issue where there are more pids
2983  * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
2984  * TODO: replace with a kernel-wide solution to this problem
2985  */
2986 #define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
2987 static void *pidlist_allocate(int count)
2988 {
2989         if (PIDLIST_TOO_LARGE(count))
2990                 return vmalloc(count * sizeof(pid_t));
2991         else
2992                 return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
2993 }
2994 
2995 static void pidlist_free(void *p)
2996 {
2997         if (is_vmalloc_addr(p))
2998                 vfree(p);
2999         else
3000                 kfree(p);
3001 }
3002 
3003 /*
3004  * Used to destroy all pidlists lingering waiting for destroy timer.  None
3005  * should be left afterwards.
3006  */
3007 static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
3008 {
3009         struct cgroup_pidlist *l, *tmp_l;
3010 
3011         mutex_lock(&cgrp->pidlist_mutex);
3012         list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
3013                 mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
3014         mutex_unlock(&cgrp->pidlist_mutex);
3015 
3016         flush_workqueue(cgroup_pidlist_destroy_wq);
3017         BUG_ON(!list_empty(&cgrp->pidlists));
3018 }
3019 
3020 static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
3021 {
3022         struct delayed_work *dwork = to_delayed_work(work);
3023         struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
3024                                                 destroy_dwork);
3025         struct cgroup_pidlist *tofree = NULL;
3026 
3027         mutex_lock(&l->owner->pidlist_mutex);
3028 
3029         /*
3030          * Destroy iff we didn't get queued again.  The state won't change
3031          * as destroy_dwork can only be queued while locked.
3032          */
3033         if (!delayed_work_pending(dwork)) {
3034                 list_del(&l->links);
3035                 pidlist_free(l->list);
3036                 put_pid_ns(l->key.ns);
3037                 tofree = l;
3038         }
3039 
3040         mutex_unlock(&l->owner->pidlist_mutex);
3041         kfree(tofree);
3042 }
3043 
3044 /*
3045  * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
3046  * Returns the number of unique elements.
3047  */
3048 static int pidlist_uniq(pid_t *list, int length)
3049 {
3050         int src, dest = 1;
3051 
3052         /*
3053          * we presume the 0th element is unique, so i starts at 1. trivial
3054          * edge cases first; no work needs to be done for either
3055          */
3056         if (length == 0 || length == 1)
3057                 return length;
3058         /* src and dest walk down the list; dest counts unique elements */
3059         for (src = 1; src < length; src++) {
3060                 /* find next unique element */
3061                 while (list[src] == list[src-1]) {
3062                         src++;
3063                         if (src == length)
3064                                 goto after;
3065                 }
3066                 /* dest always points to where the next unique element goes */
3067                 list[dest] = list[src];
3068                 dest++;
3069         }
3070 after:
3071         return dest;
3072 }
3073 
3074 /*
3075  * The two pid files - task and cgroup.procs - guaranteed that the result
3076  * is sorted, which forced this whole pidlist fiasco.  As pid order is
3077  * different per namespace, each namespace needs differently sorted list,
3078  * making it impossible to use, for example, single rbtree of member tasks
3079  * sorted by task pointer.  As pidlists can be fairly large, allocating one
3080  * per open file is dangerous, so cgroup had to implement shared pool of
3081  * pidlists keyed by cgroup and namespace.
3082  *
3083  * All this extra complexity was caused by the original implementation
3084  * committing to an entirely unnecessary property.  In the long term, we
3085  * want to do away with it.  Explicitly scramble sort order if
3086  * sane_behavior so that no such expectation exists in the new interface.
3087  *
3088  * Scrambling is done by swapping every two consecutive bits, which is
3089  * non-identity one-to-one mapping which disturbs sort order sufficiently.
3090  */
3091 static pid_t pid_fry(pid_t pid)
3092 {
3093         unsigned a = pid & 0x55555555;
3094         unsigned b = pid & 0xAAAAAAAA;
3095 
3096         return (a << 1) | (b >> 1);
3097 }
3098 
3099 static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
3100 {
3101         if (cgroup_sane_behavior(cgrp))
3102                 return pid_fry(pid);
3103         else
3104                 return pid;
3105 }
3106 
3107 static int cmppid(const void *a, const void *b)
3108 {
3109         return *(pid_t *)a - *(pid_t *)b;
3110 }
3111 
3112 static int fried_cmppid(const void *a, const void *b)
3113 {
3114         return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b);
3115 }
3116 
3117 static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
3118                                                   enum cgroup_filetype type)
3119 {
3120         struct cgroup_pidlist *l;
3121         /* don't need task_nsproxy() if we're looking at ourself */
3122         struct pid_namespace *ns = task_active_pid_ns(current);
3123 
3124         lockdep_assert_held(&cgrp->pidlist_mutex);
3125 
3126         list_for_each_entry(l, &cgrp->pidlists, links)
3127                 if (l->key.type == type && l->key.ns == ns)
3128                         return l;
3129         return NULL;
3130 }
3131 
3132 /*
3133  * find the appropriate pidlist for our purpose (given procs vs tasks)
3134  * returns with the lock on that pidlist already held, and takes care
3135  * of the use count, or returns NULL with no locks held if we're out of
3136  * memory.
3137  */
3138 static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
3139                                                 enum cgroup_filetype type)
3140 {
3141         struct cgroup_pidlist *l;
3142 
3143         lockdep_assert_held(&cgrp->pidlist_mutex);
3144 
3145         l = cgroup_pidlist_find(cgrp, type);
3146         if (l)
3147                 return l;
3148 
3149         /* entry not found; create a new one */
3150         l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
3151         if (!l)
3152                 return l;
3153 
3154         INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
3155         l->key.type = type;
3156         /* don't need task_nsproxy() if we're looking at ourself */
3157         l->key.ns = get_pid_ns(task_active_pid_ns(current));
3158         l->owner = cgrp;
3159         list_add(&l->links, &cgrp->pidlists);
3160         return l;
3161 }
3162 
3163 /*
3164  * Load a cgroup's pidarray with either procs' tgids or tasks' pids
3165  */
3166 static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
3167                               struct cgroup_pidlist **lp)
3168 {
3169         pid_t *array;
3170         int length;
3171         int pid, n = 0; /* used for populating the array */
3172         struct css_task_iter it;
3173         struct task_struct *tsk;
3174         struct cgroup_pidlist *l;
3175 
3176         lockdep_assert_held(&cgrp->pidlist_mutex);
3177 
3178         /*
3179          * If cgroup gets more users after we read count, we won't have
3180          * enough space - tough.  This race is indistinguishable to the
3181          * caller from the case that the additional cgroup users didn't
3182          * show up until sometime later on.
3183          */
3184         length = cgroup_task_count(cgrp);
3185         array = pidlist_allocate(length);
3186         if (!array)
3187                 return -ENOMEM;
3188         /* now, populate the array */
3189         css_task_iter_start(&cgrp->dummy_css, &it);
3190         while ((tsk = css_task_iter_next(&it))) {
3191                 if (unlikely(n == length))
3192                         break;
3193                 /* get tgid or pid for procs or tasks file respectively */
3194                 if (type == CGROUP_FILE_PROCS)
3195                         pid = task_tgid_vnr(tsk);
3196                 else
3197                         pid = task_pid_vnr(tsk);
3198                 if (pid > 0) /* make sure to only use valid results */
3199                         array[n++] = pid;
3200         }
3201         css_task_iter_end(&it);
3202         length = n;
3203         /* now sort & (if procs) strip out duplicates */
3204         if (cgroup_sane_behavior(cgrp))
3205                 sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
3206         else
3207                 sort(array, length, sizeof(pid_t), cmppid, NULL);
3208         if (type == CGROUP_FILE_PROCS)
3209                 length = pidlist_uniq(array, length);
3210 
3211         l = cgroup_pidlist_find_create(cgrp, type);
3212         if (!l) {
3213                 mutex_unlock(&cgrp->pidlist_mutex);
3214                 pidlist_free(array);
3215                 return -ENOMEM;
3216         }
3217 
3218         /* store array, freeing old if necessary */
3219         pidlist_free(l->list);
3220         l->list = array;
3221         l->length = length;
3222         *lp = l;
3223         return 0;
3224 }
3225 
3226 /**
3227  * cgroupstats_build - build and fill cgroupstats
3228  * @stats: cgroupstats to fill information into
3229  * @dentry: A dentry entry belonging to the cgroup for which stats have
3230  * been requested.
3231  *
3232  * Build and fill cgroupstats so that taskstats can export it to user
3233  * space.
3234  */
3235 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
3236 {
3237         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
3238         struct cgroup *cgrp;
3239         struct css_task_iter it;
3240         struct task_struct *tsk;
3241 
3242         /* it should be kernfs_node belonging to cgroupfs and is a directory */
3243         if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
3244             kernfs_type(kn) != KERNFS_DIR)
3245                 return -EINVAL;
3246 
3247         mutex_lock(&cgroup_mutex);
3248 
3249         /*
3250          * We aren't being called from kernfs and there's no guarantee on
3251          * @kn->priv's validity.  For this and css_tryget_from_dir(),
3252          * @kn->priv is RCU safe.  Let's do the RCU dancing.
3253          */
3254         rcu_read_lock();
3255         cgrp = rcu_dereference(kn->priv);
3256         if (!cgrp || cgroup_is_dead(cgrp)) {
3257                 rcu_read_unlock();
3258                 mutex_unlock(&cgroup_mutex);
3259                 return -ENOENT;
3260         }
3261         rcu_read_unlock();
3262 
3263         css_task_iter_start(&cgrp->dummy_css, &it);
3264         while ((tsk = css_task_iter_next(&it))) {
3265                 switch (tsk->state) {
3266                 case TASK_RUNNING:
3267                         stats->nr_running++;
3268                         break;
3269                 case TASK_INTERRUPTIBLE:
3270                         stats->nr_sleeping++;
3271                         break;
3272                 case TASK_UNINTERRUPTIBLE:
3273                         stats->nr_uninterruptible++;
3274                         break;
3275                 case TASK_STOPPED:
3276                         stats->nr_stopped++;
3277                         break;
3278                 default:
3279                         if (delayacct_is_task_waiting_on_io(tsk))
3280                                 stats->nr_io_wait++;
3281                         break;
3282                 }
3283         }
3284         css_task_iter_end(&it);
3285 
3286         mutex_unlock(&cgroup_mutex);
3287         return 0;
3288 }
3289 
3290 
3291 /*
3292  * seq_file methods for the tasks/procs files. The seq_file position is the
3293  * next pid to display; the seq_file iterator is a pointer to the pid
3294  * in the cgroup->l->list array.
3295  */
3296 
3297 static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
3298 {
3299         /*
3300          * Initially we receive a position value that corresponds to
3301          * one more than the last pid shown (or 0 on the first call or
3302          * after a seek to the start). Use a binary-search to find the
3303          * next pid to display, if any
3304          */
3305         struct kernfs_open_file *of = s->private;
3306         struct cgroup *cgrp = seq_css(s)->cgroup;
3307         struct cgroup_pidlist *l;
3308         enum cgroup_filetype type = seq_cft(s)->private;
3309         int index = 0, pid = *pos;
3310         int *iter, ret;
3311 
3312         mutex_lock(&cgrp->pidlist_mutex);
3313 
3314         /*
3315          * !NULL @of->priv indicates that this isn't the first start()
3316          * after open.  If the matching pidlist is around, we can use that.
3317          * Look for it.  Note that @of->priv can't be used directly.  It
3318          * could already have been destroyed.
3319          */
3320         if (of->priv)
3321                 of->priv = cgroup_pidlist_find(cgrp, type);
3322 
3323         /*
3324          * Either this is the first start() after open or the matching
3325          * pidlist has been destroyed inbetween.  Create a new one.
3326          */
3327         if (!of->priv) {
3328                 ret = pidlist_array_load(cgrp, type,
3329                                          (struct cgroup_pidlist **)&of->priv);
3330                 if (ret)
3331                         return ERR_PTR(ret);
3332         }
3333         l = of->priv;
3334 
3335         if (pid) {
3336                 int end = l->length;
3337 
3338                 while (index < end) {
3339                         int mid = (index + end) / 2;
3340                         if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
3341                                 index = mid;
3342                                 break;
3343                         } else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
3344                                 index = mid + 1;
3345                         else
3346                                 end = mid;
3347                 }
3348         }
3349         /* If we're off the end of the array, we're done */
3350         if (index >= l->length)
3351                 return NULL;
3352         /* Update the abstract position to be the actual pid that we found */
3353         iter = l->list + index;
3354         *pos = cgroup_pid_fry(cgrp, *iter);
3355         return iter;
3356 }
3357 
3358 static void cgroup_pidlist_stop(struct seq_file *s, void *v)
3359 {
3360         struct kernfs_open_file *of = s->private;
3361         struct cgroup_pidlist *l = of->priv;
3362 
3363         if (l)
3364                 mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
3365                                  CGROUP_PIDLIST_DESTROY_DELAY);
3366         mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
3367 }
3368 
3369 static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
3370 {
3371         struct kernfs_open_file *of = s->private;
3372         struct cgroup_pidlist *l = of->priv;
3373         pid_t *p = v;
3374         pid_t *end = l->list + l->length;
3375         /*
3376          * Advance to the next pid in the array. If this goes off the
3377          * end, we're done
3378          */
3379         p++;
3380         if (p >= end) {
3381                 return NULL;
3382         } else {
3383                 *pos = cgroup_pid_fry(seq_css(s)->cgroup, *p);
3384                 return p;
3385         }
3386 }
3387 
3388 static int cgroup_pidlist_show(struct seq_file *s, void *v)
3389 {
3390         return seq_printf(s, "%d\n", *(int *)v);
3391 }
3392 
3393 /*
3394  * seq_operations functions for iterating on pidlists through seq_file -
3395  * independent of whether it's tasks or procs
3396  */
3397 static const struct seq_operations cgroup_pidlist_seq_operations = {
3398         .start = cgroup_pidlist_start,
3399         .stop = cgroup_pidlist_stop,
3400         .next = cgroup_pidlist_next,
3401         .show = cgroup_pidlist_show,
3402 };
3403 
3404 static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
3405                                          struct cftype *cft)
3406 {
3407         return notify_on_release(css->cgroup);
3408 }
3409 
3410 static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
3411                                           struct cftype *cft, u64 val)
3412 {
3413         clear_bit(CGRP_RELEASABLE, &css->cgroup->flags);
3414         if (val)
3415                 set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
3416         else
3417                 clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
3418         return 0;
3419 }
3420 
3421 static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
3422                                       struct cftype *cft)
3423 {
3424         return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3425 }
3426 
3427 static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
3428                                        struct cftype *cft, u64 val)
3429 {
3430         if (val)
3431                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3432         else
3433                 clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3434         return 0;
3435 }
3436 
3437 static struct cftype cgroup_base_files[] = {
3438         {
3439                 .name = "cgroup.procs",
3440                 .seq_start = cgroup_pidlist_start,
3441                 .seq_next = cgroup_pidlist_next,
3442                 .seq_stop = cgroup_pidlist_stop,
3443                 .seq_show = cgroup_pidlist_show,
3444                 .private = CGROUP_FILE_PROCS,
3445                 .write_u64 = cgroup_procs_write,
3446                 .mode = S_IRUGO | S_IWUSR,
3447         },
3448         {
3449                 .name = "cgroup.clone_children",
3450                 .flags = CFTYPE_INSANE,
3451                 .read_u64 = cgroup_clone_children_read,
3452                 .write_u64 = cgroup_clone_children_write,
3453         },
3454         {
3455                 .name = "cgroup.sane_behavior",
3456                 .flags = CFTYPE_ONLY_ON_ROOT,
3457                 .seq_show = cgroup_sane_behavior_show,
3458         },
3459 
3460         /*
3461          * Historical crazy stuff.  These don't have "cgroup."  prefix and
3462          * don't exist if sane_behavior.  If you're depending on these, be
3463          * prepared to be burned.
3464          */
3465         {
3466                 .name = "tasks",
3467                 .flags = CFTYPE_INSANE,         /* use "procs" instead */
3468                 .seq_start = cgroup_pidlist_start,
3469                 .seq_next = cgroup_pidlist_next,
3470                 .seq_stop = cgroup_pidlist_stop,
3471                 .seq_show = cgroup_pidlist_show,
3472                 .private = CGROUP_FILE_TASKS,
3473                 .write_u64 = cgroup_tasks_write,
3474                 .mode = S_IRUGO | S_IWUSR,
3475         },
3476         {
3477                 .name = "notify_on_release",
3478                 .flags = CFTYPE_INSANE,
3479                 .read_u64 = cgroup_read_notify_on_release,
3480                 .write_u64 = cgroup_write_notify_on_release,
3481         },
3482         {
3483                 .name = "release_agent",
3484                 .flags = CFTYPE_INSANE | CFTYPE_ONLY_ON_ROOT,
3485                 .seq_show = cgroup_release_agent_show,
3486                 .write_string = cgroup_release_agent_write,
3487                 .max_write_len = PATH_MAX - 1,
3488         },
3489         { }     /* terminate */
3490 };
3491 
3492 /**
3493  * cgroup_populate_dir - create subsys files in a cgroup directory
3494  * @cgrp: target cgroup
3495  * @subsys_mask: mask of the subsystem ids whose files should be added
3496  *
3497  * On failure, no file is added.
3498  */
3499 static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
3500 {
3501         struct cgroup_subsys *ss;
3502         int i, ret = 0;
3503 
3504         /* process cftsets of each subsystem */
3505         for_each_subsys(ss, i) {
3506                 struct cftype *cfts;
3507 
3508                 if (!test_bit(i, &subsys_mask))
3509                         continue;
3510 
3511                 list_for_each_entry(cfts, &ss->cfts, node) {
3512                         ret = cgroup_addrm_files(cgrp, cfts, true);
3513                         if (ret < 0)
3514                                 goto err;
3515                 }
3516         }
3517         return 0;
3518 err:
3519         cgroup_clear_dir(cgrp, subsys_mask);
3520         return ret;
3521 }
3522 
3523 /*
3524  * css destruction is four-stage process.
3525  *
3526  * 1. Destruction starts.  Killing of the percpu_ref is initiated.
3527  *    Implemented in kill_css().
3528  *
3529  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
3530  *    and thus css_tryget() is guaranteed to fail, the css can be offlined
3531  *    by invoking offline_css().  After offlining, the base ref is put.
3532  *    Implemented in css_killed_work_fn().
3533  *
3534  * 3. When the percpu_ref reaches zero, the only possible remaining
3535  *    accessors are inside RCU read sections.  css_release() schedules the
3536  *    RCU callback.
3537  *
3538  * 4. After the grace period, the css can be freed.  Implemented in
3539  *    css_free_work_fn().
3540  *
3541  * It is actually hairier because both step 2 and 4 require process context
3542  * and thus involve punting to css->destroy_work adding two additional
3543  * steps to the already complex sequence.
3544  */
3545 static void css_free_work_fn(struct work_struct *work)
3546 {
3547         struct cgroup_subsys_state *css =
3548                 container_of(work, struct cgroup_subsys_state, destroy_work);
3549         struct cgroup *cgrp = css->cgroup;
3550 
3551         if (css->parent)
3552                 css_put(css->parent);
3553 
3554         css->ss->css_free(css);
3555         cgroup_put(cgrp);
3556 }
3557 
3558 static void css_free_rcu_fn(struct rcu_head *rcu_head)
3559 {
3560         struct cgroup_subsys_state *css =
3561                 container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
3562 
3563         INIT_WORK(&css->destroy_work, css_free_work_fn);
3564         queue_work(cgroup_destroy_wq, &css->destroy_work);
3565 }
3566 
3567 static void css_release(struct percpu_ref *ref)
3568 {
3569         struct cgroup_subsys_state *css =
3570                 container_of(ref, struct cgroup_subsys_state, refcnt);
3571 
3572         RCU_INIT_POINTER(css->cgroup->subsys[css->ss->id], NULL);
3573         call_rcu(&css->rcu_head, css_free_rcu_fn);
3574 }
3575 
3576 static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss,
3577                      struct cgroup *cgrp)
3578 {
3579         css->cgroup = cgrp;
3580         css->ss = ss;
3581         css->flags = 0;
3582 
3583         if (cgrp->parent)
3584                 css->parent = cgroup_css(cgrp->parent, ss);
3585         else
3586                 css->flags |= CSS_ROOT;
3587 
3588         BUG_ON(cgroup_css(cgrp, ss));
3589 }
3590 
3591 /* invoke ->css_online() on a new CSS and mark it online if successful */
3592 static int online_css(struct cgroup_subsys_state *css)
3593 {
3594         struct cgroup_subsys *ss = css->ss;
3595         int ret = 0;
3596 
3597         lockdep_assert_held(&cgroup_tree_mutex);
3598         lockdep_assert_held(&cgroup_mutex);
3599 
3600         if (ss->css_online)
3601                 ret = ss->css_online(css);
3602         if (!ret) {
3603                 css->flags |= CSS_ONLINE;
3604                 css->cgroup->nr_css++;
3605                 rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
3606         }
3607         return ret;
3608 }
3609 
3610 /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
3611 static void offline_css(struct cgroup_subsys_state *css)
3612 {
3613         struct cgroup_subsys *ss = css->ss;
3614 
3615         lockdep_assert_held(&cgroup_tree_mutex);
3616         lockdep_assert_held(&cgroup_mutex);
3617 
3618         if (!(css->flags & CSS_ONLINE))
3619                 return;
3620 
3621         if (ss->css_offline)
3622                 ss->css_offline(css);
3623 
3624         css->flags &= ~CSS_ONLINE;
3625         css->cgroup->nr_css--;
3626         RCU_INIT_POINTER(css->cgroup->subsys[ss->id], css);
3627 }
3628 
3629 /**
3630  * create_css - create a cgroup_subsys_state
3631  * @cgrp: the cgroup new css will be associated with
3632  * @ss: the subsys of new css
3633  *
3634  * Create a new css associated with @cgrp - @ss pair.  On success, the new
3635  * css is online and installed in @cgrp with all interface files created.
3636  * Returns 0 on success, -errno on failure.
3637  */
3638 static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
3639 {
3640         struct cgroup *parent = cgrp->parent;
3641         struct cgroup_subsys_state *css;
3642         int err;
3643 
3644         lockdep_assert_held(&cgroup_mutex);
3645 
3646         css = ss->css_alloc(cgroup_css(parent, ss));
3647         if (IS_ERR(css))
3648                 return PTR_ERR(css);
3649 
3650         err = percpu_ref_init(&css->refcnt, css_release);
3651         if (err)
3652                 goto err_free_css;
3653 
3654         init_css(css, ss, cgrp);
3655 
3656         err = cgroup_populate_dir(cgrp, 1 << ss->id);
3657         if (err)
3658                 goto err_free_percpu_ref;
3659 
3660         err = online_css(css);
3661         if (err)
3662                 goto err_clear_dir;
3663 
3664         cgroup_get(cgrp);
3665         css_get(css->parent);
3666 
3667         cgrp->subsys_mask |= 1 << ss->id;
3668 
3669         if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
3670             parent->parent) {
3671                 pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
3672                            current->comm, current->pid, ss->name);
3673                 if (!strcmp(ss->name, "memory"))
3674                         pr_warning("cgroup: \"memory\" requires setting use_hierarchy to 1 on the root.\n");
3675                 ss->warned_broken_hierarchy = true;
3676         }
3677 
3678         return 0;
3679 
3680 err_clear_dir:
3681         cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
3682 err_free_percpu_ref:
3683         percpu_ref_cancel_init(&css->refcnt);
3684 err_free_css:
3685         ss->css_free(css);
3686         return err;
3687 }
3688 
3689 /**
3690  * cgroup_create - create a cgroup
3691  * @parent: cgroup that will be parent of the new cgroup
3692  * @name: name of the new cgroup
3693  * @mode: mode to set on new cgroup
3694  */
3695 static long cgroup_create(struct cgroup *parent, const char *name,
3696                           umode_t mode)
3697 {
3698         struct cgroup *cgrp;
3699         struct cgroup_root *root = parent->root;
3700         int ssid, err;
3701         struct cgroup_subsys *ss;
3702         struct kernfs_node *kn;
3703 
3704         /*
3705          * XXX: The default hierarchy isn't fully implemented yet.  Block
3706          * !root cgroup creation on it for now.
3707          */
3708         if (root == &cgrp_dfl_root)
3709                 return -EINVAL;
3710 
3711         /* allocate the cgroup and its ID, 0 is reserved for the root */
3712         cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
3713         if (!cgrp)
3714                 return -ENOMEM;
3715 
3716         mutex_lock(&cgroup_tree_mutex);
3717 
3718         /*
3719          * Only live parents can have children.  Note that the liveliness
3720          * check isn't strictly necessary because cgroup_mkdir() and
3721          * cgroup_rmdir() are fully synchronized by i_mutex; however, do it
3722          * anyway so that locking is contained inside cgroup proper and we
3723          * don't get nasty surprises if we ever grow another caller.
3724          */
3725         if (!cgroup_lock_live_group(parent)) {
3726                 err = -ENODEV;
3727                 goto err_unlock_tree;
3728         }
3729 
3730         /*
3731          * Temporarily set the pointer to NULL, so idr_find() won't return
3732          * a half-baked cgroup.
3733          */
3734         cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 1, 0, GFP_KERNEL);
3735         if (cgrp->id < 0) {
3736                 err = -ENOMEM;
3737                 goto err_unlock;
3738         }
3739 
3740         init_cgroup_housekeeping(cgrp);
3741 
3742         cgrp->parent = parent;
3743         cgrp->dummy_css.parent = &parent->dummy_css;
3744         cgrp->root = parent->root;
3745 
3746         if (notify_on_release(parent))
3747                 set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3748 
3749         if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
3750                 set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
3751 
3752         /* create the directory */
3753         kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
3754         if (IS_ERR(kn)) {
3755                 err = PTR_ERR(kn);
3756                 goto err_free_id;
3757         }
3758         cgrp->kn = kn;
3759 
3760         /*
3761          * This extra ref will be put in cgroup_free_fn() and guarantees
3762          * that @cgrp->kn is always accessible.
3763          */
3764         kernfs_get(kn);
3765 
3766         cgrp->serial_nr = cgroup_serial_nr_next++;
3767 
3768         /* allocation complete, commit to creation */
3769         list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
3770         atomic_inc(&root->nr_cgrps);
3771         cgroup_get(parent);
3772 
3773         /*
3774          * @cgrp is now fully operational.  If something fails after this
3775          * point, it'll be released via the normal destruction path.
3776          */
3777         idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
3778 
3779         err = cgroup_kn_set_ugid(kn);
3780         if (err)
3781                 goto err_destroy;
3782 
3783         err = cgroup_addrm_files(cgrp, cgroup_base_files, true);
3784         if (err)
3785                 goto err_destroy;
3786 
3787         /* let's create and online css's */
3788         for_each_subsys(ss, ssid) {
3789                 if (root->cgrp.subsys_mask & (1 << ssid)) {
3790                         err = create_css(cgrp, ss);
3791                         if (err)
3792                                 goto err_destroy;
3793                 }
3794         }
3795 
3796         kernfs_activate(kn);
3797 
3798         mutex_unlock(&cgroup_mutex);
3799         mutex_unlock(&cgroup_tree_mutex);
3800 
3801         return 0;
3802 
3803 err_free_id:
3804         idr_remove(&root->cgroup_idr, cgrp->id);
3805 err_unlock:
3806         mutex_unlock(&cgroup_mutex);
3807 err_unlock_tree:
3808         mutex_unlock(&cgroup_tree_mutex);
3809         kfree(cgrp);
3810         return err;
3811 
3812 err_destroy:
3813         cgroup_destroy_locked(cgrp);
3814         mutex_unlock(&cgroup_mutex);
3815         mutex_unlock(&cgroup_tree_mutex);
3816         return err;
3817 }
3818 
3819 static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
3820                         umode_t mode)
3821 {
3822         struct cgroup *parent = parent_kn->priv;
3823         int ret;
3824 
3825         /*
3826          * cgroup_create() grabs cgroup_tree_mutex which nests outside
3827          * kernfs active_ref and cgroup_create() already synchronizes
3828          * properly against removal through cgroup_lock_live_group().
3829          * Break it before calling cgroup_create().
3830          */
3831         cgroup_get(parent);
3832         kernfs_break_active_protection(parent_kn);
3833 
3834         ret = cgroup_create(parent, name, mode);
3835 
3836         kernfs_unbreak_active_protection(parent_kn);
3837         cgroup_put(parent);
3838         return ret;
3839 }
3840 
3841 /*
3842  * This is called when the refcnt of a css is confirmed to be killed.
3843  * css_tryget() is now guaranteed to fail.
3844  */
3845 static void css_killed_work_fn(struct work_struct *work)
3846 {
3847         struct cgroup_subsys_state *css =
3848                 container_of(work, struct cgroup_subsys_state, destroy_work);
3849         struct cgroup *cgrp = css->cgroup;
3850 
3851         mutex_lock(&cgroup_tree_mutex);
3852         mutex_lock(&cgroup_mutex);
3853 
3854         /*
3855          * css_tryget() is guaranteed to fail now.  Tell subsystems to
3856          * initate destruction.
3857          */
3858         offline_css(css);
3859 
3860         /*
3861          * If @cgrp is marked dead, it's waiting for refs of all css's to
3862          * be disabled before proceeding to the second phase of cgroup
3863          * destruction.  If we are the last one, kick it off.
3864          */
3865         if (!cgrp->nr_css && cgroup_is_dead(cgrp))
3866                 cgroup_destroy_css_killed(cgrp);
3867 
3868         mutex_unlock(&cgroup_mutex);
3869         mutex_unlock(&cgroup_tree_mutex);
3870 
3871         /*
3872          * Put the css refs from kill_css().  Each css holds an extra
3873          * reference to the cgroup's dentry and cgroup removal proceeds
3874          * regardless of css refs.  On the last put of each css, whenever
3875          * that may be, the extra dentry ref is put so that dentry
3876          * destruction happens only after all css's are released.
3877          */
3878         css_put(css);
3879 }
3880 
3881 /* css kill confirmation processing requires process context, bounce */
3882 static void css_killed_ref_fn(struct percpu_ref *ref)
3883 {
3884         struct cgroup_subsys_state *css =
3885                 container_of(ref, struct cgroup_subsys_state, refcnt);
3886 
3887         INIT_WORK(&css->destroy_work, css_killed_work_fn);
3888         queue_work(cgroup_destroy_wq, &css->destroy_work);
3889 }
3890 
3891 static void __kill_css(struct cgroup_subsys_state *css)
3892 {
3893         lockdep_assert_held(&cgroup_tree_mutex);
3894 
3895         /*
3896          * This must happen before css is disassociated with its cgroup.
3897          * See seq_css() for details.
3898          */
3899         cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
3900 
3901         /*
3902          * Killing would put the base ref, but we need to keep it alive
3903          * until after ->css_offline().
3904          */
3905         css_get(css);
3906 
3907         /*
3908          * cgroup core guarantees that, by the time ->css_offline() is
3909          * invoked, no new css reference will be given out via
3910          * css_tryget().  We can't simply call percpu_ref_kill() and
3911          * proceed to offlining css's because percpu_ref_kill() doesn't
3912          * guarantee that the ref is seen as killed on all CPUs on return.
3913          *
3914          * Use percpu_ref_kill_and_confirm() to get notifications as each
3915          * css is confirmed to be seen as killed on all CPUs.
3916          */
3917         percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
3918 }
3919 
3920 /**
3921  * kill_css - destroy a css
3922  * @css: css to destroy
3923  *
3924  * This function initiates destruction of @css by removing cgroup interface
3925  * files and putting its base reference.  ->css_offline() will be invoked
3926  * asynchronously once css_tryget() is guaranteed to fail and when the
3927  * reference count reaches zero, @css will be released.
3928  */
3929 static void kill_css(struct cgroup_subsys_state *css)
3930 {
3931         struct cgroup *cgrp = css->cgroup;
3932 
3933         lockdep_assert_held(&cgroup_tree_mutex);
3934 
3935         /* if already killed, noop */
3936         if (cgrp->subsys_mask & (1 << css->ss->id)) {
3937                 cgrp->subsys_mask &= ~(1 << css->ss->id);
3938                 __kill_css(css);
3939         }
3940 }
3941 
3942 /**
3943  * cgroup_destroy_locked - the first stage of cgroup destruction
3944  * @cgrp: cgroup to be destroyed
3945  *
3946  * css's make use of percpu refcnts whose killing latency shouldn't be
3947  * exposed to userland and are RCU protected.  Also, cgroup core needs to
3948  * guarantee that css_tryget() won't succeed by the time ->css_offline() is
3949  * invoked.  To satisfy all the requirements, destruction is implemented in
3950  * the following two steps.
3951  *
3952  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
3953  *     userland visible parts and start killing the percpu refcnts of
3954  *     css's.  Set up so that the next stage will be kicked off once all
3955  *     the percpu refcnts are confirmed to be killed.
3956  *
3957  * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
3958  *     rest of destruction.  Once all cgroup references are gone, the
3959  *     cgroup is RCU-freed.
3960  *
3961  * This function implements s1.  After this step, @cgrp is gone as far as
3962  * the userland is concerned and a new cgroup with the same name may be
3963  * created.  As cgroup doesn't care about the names internally, this
3964  * doesn't cause any problem.
3965  */
3966 static int cgroup_destroy_locked(struct cgroup *cgrp)
3967         __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
3968 {
3969         struct cgroup *child;
3970         struct cgroup_subsys_state *css;
3971         bool empty;
3972         int ssid;
3973 
3974         lockdep_assert_held(&cgroup_tree_mutex);
3975         lockdep_assert_held(&cgroup_mutex);
3976 
3977         /*
3978          * css_set_rwsem synchronizes access to ->cset_links and prevents
3979          * @cgrp from being removed while put_css_set() is in progress.
3980          */
3981         down_read(&css_set_rwsem);
3982         empty = list_empty(&cgrp->cset_links);
3983         up_read(&css_set_rwsem);
3984         if (!empty)
3985                 return -EBUSY;
3986 
3987         /*
3988          * Make sure there's no live children.  We can't test ->children
3989          * emptiness as dead children linger on it while being destroyed;
3990          * otherwise, "rmdir parent/child parent" may fail with -EBUSY.
3991          */
3992         empty = true;
3993         rcu_read_lock();
3994         list_for_each_entry_rcu(child, &cgrp->children, sibling) {
3995                 empty = cgroup_is_dead(child);
3996                 if (!empty)
3997                         break;
3998         }
3999         rcu_read_unlock();
4000         if (!empty)
4001                 return -EBUSY;
4002 
4003         /*
4004          * Mark @cgrp dead.  This prevents further task migration and child
4005          * creation by disabling cgroup_lock_live_group().  Note that
4006          * CGRP_DEAD assertion is depended upon by css_next_child() to
4007          * resume iteration after dropping RCU read lock.  See
4008          * css_next_child() for details.
4009          */
4010         set_bit(CGRP_DEAD, &cgrp->flags);
4011 
4012         /*
4013          * Initiate massacre of all css's.  cgroup_destroy_css_killed()
4014          * will be invoked to perform the rest of destruction once the
4015          * percpu refs of all css's are confirmed to be killed.  This
4016          * involves removing the subsystem's files, drop cgroup_mutex.
4017          */
4018         mutex_unlock(&cgroup_mutex);
4019         for_each_css(css, ssid, cgrp)
4020                 kill_css(css);
4021         mutex_lock(&cgroup_mutex);
4022 
4023         /* CGRP_DEAD is set, remove from ->release_list for the last time */
4024         raw_spin_lock(&release_list_lock);
4025         if (!list_empty(&cgrp->release_list))
4026                 list_del_init(&cgrp->release_list);
4027         raw_spin_unlock(&release_list_lock);
4028 
4029         /*
4030          * If @cgrp has css's attached, the second stage of cgroup
4031          * destruction is kicked off from css_killed_work_fn() after the
4032          * refs of all attached css's are killed.  If @cgrp doesn't have
4033          * any css, we kick it off here.
4034          */
4035         if (!cgrp->nr_css)
4036                 cgroup_destroy_css_killed(cgrp);
4037 
4038         /* remove @cgrp directory along with the base files */
4039         mutex_unlock(&cgroup_mutex);
4040 
4041         /*
4042          * There are two control paths which try to determine cgroup from
4043          * dentry without going through kernfs - cgroupstats_build() and
4044          * css_tryget_from_dir().  Those are supported by RCU protecting
4045          * clearing of cgrp->kn->priv backpointer, which should happen
4046          * after all files under it have been removed.
4047          */
4048         kernfs_remove(cgrp->kn);        /* @cgrp has an extra ref on its kn */
4049         RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);
4050 
4051         mutex_lock(&cgroup_mutex);
4052 
4053         return 0;
4054 };
4055 
4056 /**
4057  * cgroup_destroy_css_killed - the second step of cgroup destruction
4058  * @work: cgroup->destroy_free_work
4059  *
4060  * This function is invoked from a work item for a cgroup which is being
4061  * destroyed after all css's are offlined and performs the rest of
4062  * destruction.  This is the second step of destruction described in the
4063  * comment above cgroup_destroy_locked().
4064  */
4065 static void cgroup_destroy_css_killed(struct cgroup *cgrp)
4066 {
4067         struct cgroup *parent = cgrp->parent;
4068 
4069         lockdep_assert_held(&cgroup_tree_mutex);
4070         lockdep_assert_held(&cgroup_mutex);
4071 
4072         /* delete this cgroup from parent->children */
4073         list_del_rcu(&cgrp->sibling);
4074 
4075         cgroup_put(cgrp);
4076 
4077         set_bit(CGRP_RELEASABLE, &parent->flags);
4078         check_for_release(parent);
4079 }
4080 
4081 static int cgroup_rmdir(struct kernfs_node *kn)
4082 {
4083         struct cgroup *cgrp = kn->priv;
4084         int ret = 0;
4085 
4086         /*
4087          * This is self-destruction but @kn can't be removed while this
4088          * callback is in progress.  Let's break active protection.  Once
4089          * the protection is broken, @cgrp can be destroyed at any point.
4090          * Pin it so that it stays accessible.
4091          */
4092         cgroup_get(cgrp);
4093         kernfs_break_active_protection(kn);
4094 
4095         mutex_lock(&cgroup_tree_mutex);
4096         mutex_lock(&cgroup_mutex);
4097 
4098         /*
4099          * @cgrp might already have been destroyed while we're trying to
4100          * grab the mutexes.
4101          */
4102         if (!cgroup_is_dead(cgrp))
4103                 ret = cgroup_destroy_locked(cgrp);
4104 
4105         mutex_unlock(&cgroup_mutex);
4106         mutex_unlock(&cgroup_tree_mutex);
4107 
4108         kernfs_unbreak_active_protection(kn);
4109         cgroup_put(cgrp);
4110         return ret;
4111 }
4112 
4113 static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
4114         .remount_fs             = cgroup_remount,
4115         .show_options           = cgroup_show_options,
4116         .mkdir                  = cgroup_mkdir,
4117         .rmdir                  = cgroup_rmdir,
4118         .rename                 = cgroup_rename,
4119 };
4120 
4121 static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
4122 {
4123         struct cgroup_subsys_state *css;
4124 
4125         printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
4126 
4127         mutex_lock(&cgroup_tree_mutex);
4128         mutex_lock(&cgroup_mutex);
4129 
4130         INIT_LIST_HEAD(&ss->cfts);
4131 
4132         /* Create the root cgroup state for this subsystem */
4133         ss->root = &cgrp_dfl_root;
4134         css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
4135         /* We don't handle early failures gracefully */
4136         BUG_ON(IS_ERR(css));
4137         init_css(css, ss, &cgrp_dfl_root.cgrp);
4138 
4139         /* Update the init_css_set to contain a subsys
4140          * pointer to this state - since the subsystem is
4141          * newly registered, all tasks and hence the
4142          * init_css_set is in the subsystem's root cgroup. */
4143         init_css_set.subsys[ss->id] = css;
4144 
4145         need_forkexit_callback |= ss->fork || ss->exit;
4146 
4147         /* At system boot, before all subsystems have been
4148          * registered, no tasks have been forked, so we don't
4149          * need to invoke fork callbacks here. */
4150         BUG_ON(!list_empty(&init_task.tasks));
4151 
4152         BUG_ON(online_css(css));
4153 
4154         cgrp_dfl_root.cgrp.subsys_mask |= 1 << ss->id;
4155 
4156         mutex_unlock(&cgroup_mutex);
4157         mutex_unlock(&cgroup_tree_mutex);
4158 }
4159 
4160 /**
4161  * cgroup_init_early - cgroup initialization at system boot
4162  *
4163  * Initialize cgroups at system boot, and initialize any
4164  * subsystems that request early init.
4165  */
4166 int __init cgroup_init_early(void)
4167 {
4168         static struct cgroup_sb_opts __initdata opts =
4169                 { .flags = CGRP_ROOT_SANE_BEHAVIOR };
4170         struct cgroup_subsys *ss;
4171         int i;
4172 
4173         init_cgroup_root(&cgrp_dfl_root, &opts);
4174         RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
4175 
4176         for_each_subsys(ss, i) {
4177                 WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
4178                      "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p name:id=%d:%s\n",
4179                      i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
4180                      ss->id, ss->name);
4181                 WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
4182                      "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
4183 
4184                 ss->id = i;
4185                 ss->name = cgroup_subsys_name[i];
4186 
4187                 if (ss->early_init)
4188                         cgroup_init_subsys(ss);
4189         }
4190         return 0;
4191 }
4192 
4193 /**
4194  * cgroup_init - cgroup initialization
4195  *
4196  * Register cgroup filesystem and /proc file, and initialize
4197  * any subsystems that didn't request early init.
4198  */
4199 int __init cgroup_init(void)
4200 {
4201         struct cgroup_subsys *ss;
4202         unsigned long key;
4203         int ssid, err;
4204 
4205         BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
4206 
4207         mutex_lock(&cgroup_tree_mutex);
4208         mutex_lock(&cgroup_mutex);
4209 
4210         /* Add init_css_set to the hash table */
4211         key = css_set_hash(init_css_set.subsys);
4212         hash_add(css_set_table, &init_css_set.hlist, key);
4213 
4214         BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
4215 
4216         mutex_unlock(&cgroup_mutex);
4217         mutex_unlock(&cgroup_tree_mutex);
4218 
4219         for_each_subsys(ss, ssid) {
4220                 if (!ss->early_init)
4221                         cgroup_init_subsys(ss);
4222 
4223                 /*
4224                  * cftype registration needs kmalloc and can't be done
4225                  * during early_init.  Register base cftypes separately.
4226                  */
4227                 if (ss->base_cftypes)
4228                         WARN_ON(cgroup_add_cftypes(ss, ss->base_cftypes));
4229         }
4230 
4231         cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
4232         if (!cgroup_kobj)
4233                 return -ENOMEM;
4234 
4235         err = register_filesystem(&cgroup_fs_type);
4236         if (err < 0) {
4237                 kobject_put(cgroup_kobj);
4238                 return err;
4239         }
4240 
4241         proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
4242         return 0;
4243 }
4244 
4245 static int __init cgroup_wq_init(void)
4246 {
4247         /*
4248          * There isn't much point in executing destruction path in
4249          * parallel.  Good chunk is serialized with cgroup_mutex anyway.
4250          * Use 1 for @max_active.
4251          *
4252          * We would prefer to do this in cgroup_init() above, but that
4253          * is called before init_workqueues(): so leave this until after.
4254          */
4255         cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
4256         BUG_ON(!cgroup_destroy_wq);
4257 
4258         /*
4259          * Used to destroy pidlists and separate to serve as flush domain.
4260          * Cap @max_active to 1 too.
4261          */
4262         cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
4263                                                     0, 1);
4264         BUG_ON(!cgroup_pidlist_destroy_wq);
4265 
4266         return 0;
4267 }
4268 core_initcall(cgroup_wq_init);
4269 
4270 /*
4271  * proc_cgroup_show()
4272  *  - Print task's cgroup paths into seq_file, one line for each hierarchy
4273  *  - Used for /proc/<pid>/cgroup.
4274  */
4275 
4276 /* TODO: Use a proper seq_file iterator */
4277 int proc_cgroup_show(struct seq_file *m, void *v)
4278 {
4279         struct pid *pid;
4280         struct task_struct *tsk;
4281         char *buf, *path;
4282         int retval;
4283         struct cgroup_root *root;
4284 
4285         retval = -ENOMEM;
4286         buf = kmalloc(PATH_MAX, GFP_KERNEL);
4287         if (!buf)
4288                 goto out;
4289 
4290         retval = -ESRCH;
4291         pid = m->private;
4292         tsk = get_pid_task(pid, PIDTYPE_PID);
4293         if (!tsk)
4294                 goto out_free;
4295 
4296         retval = 0;
4297 
4298         mutex_lock(&cgroup_mutex);
4299         down_read(&css_set_rwsem);
4300 
4301         for_each_root(root) {
4302                 struct cgroup_subsys *ss;
4303                 struct cgroup *cgrp;
4304                 int ssid, count = 0;
4305 
4306                 if (root == &cgrp_dfl_root && !cgrp_dfl_root_visible)
4307                         continue;
4308 
4309                 seq_printf(m, "%d:", root->hierarchy_id);
4310                 for_each_subsys(ss, ssid)
4311                         if (root->cgrp.subsys_mask & (1 << ssid))
4312                                 seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
4313                 if (strlen(root->name))
4314                         seq_printf(m, "%sname=%s", count ? "," : "",
4315                                    root->name);
4316                 seq_putc(m, ':');
4317                 cgrp = task_cgroup_from_root(tsk, root);
4318                 path = cgroup_path(cgrp, buf, PATH_MAX);
4319                 if (!path) {
4320                         retval = -ENAMETOOLONG;
4321                         goto out_unlock;
4322                 }
4323                 seq_puts(m, path);
4324                 seq_putc(m, '\n');
4325         }
4326 
4327 out_unlock:
4328         up_read(&css_set_rwsem);
4329         mutex_unlock(&cgroup_mutex);
4330         put_task_struct(tsk);
4331 out_free:
4332         kfree(buf);
4333 out:
4334         return retval;
4335 }
4336 
4337 /* Display information about each subsystem and each hierarchy */
4338 static int proc_cgroupstats_show(struct seq_file *m, void *v)
4339 {
4340         struct cgroup_subsys *ss;
4341         int i;
4342 
4343         seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
4344         /*
4345          * ideally we don't want subsystems moving around while we do this.
4346          * cgroup_mutex is also necessary to guarantee an atomic snapshot of
4347          * subsys/hierarchy state.
4348          */
4349         mutex_lock(&cgroup_mutex);
4350 
4351         for_each_subsys(ss, i)
4352                 seq_printf(m, "%s\t%d\t%d\t%d\n",
4353                            ss->name, ss->root->hierarchy_id,
4354                            atomic_read(&ss->root->nr_cgrps), !ss->disabled);
4355 
4356         mutex_unlock(&cgroup_mutex);
4357         return 0;
4358 }
4359 
4360 static int cgroupstats_open(struct inode *inode, struct file *file)
4361 {
4362         return single_open(file, proc_cgroupstats_show, NULL);
4363 }
4364 
4365 static const struct file_operations proc_cgroupstats_operations = {
4366         .open = cgroupstats_open,
4367         .read = seq_read,
4368         .llseek = seq_lseek,
4369         .release = single_release,
4370 };
4371 
4372 /**
4373  * cgroup_fork - initialize cgroup related fields during copy_process()
4374  * @child: pointer to task_struct of forking parent process.
4375  *
4376  * A task is associated with the init_css_set until cgroup_post_fork()
4377  * attaches it to the parent's css_set.  Empty cg_list indicates that
4378  * @child isn't holding reference to its css_set.
4379  */
4380 void cgroup_fork(struct task_struct *child)
4381 {
4382         RCU_INIT_POINTER(child->cgroups, &init_css_set);
4383         INIT_LIST_HEAD(&child->cg_list);
4384 }
4385 
4386 /**
4387  * cgroup_post_fork - called on a new task after adding it to the task list
4388  * @child: the task in question
4389  *
4390  * Adds the task to the list running through its css_set if necessary and
4391  * call the subsystem fork() callbacks.  Has to be after the task is
4392  * visible on the task list in case we race with the first call to
4393  * cgroup_task_iter_start() - to guarantee that the new task ends up on its
4394  * list.
4395  */
4396 void cgroup_post_fork(struct task_struct *child)
4397 {
4398         struct cgroup_subsys *ss;
4399         int i;
4400 
4401         /*
4402          * This may race against cgroup_enable_task_cg_links().  As that
4403          * function sets use_task_css_set_links before grabbing
4404          * tasklist_lock and we just went through tasklist_lock to add
4405          * @child, it's guaranteed that either we see the set
4406          * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
4407          * @child during its iteration.
4408          *
4409          * If we won the race, @child is associated with %current's
4410          * css_set.  Grabbing css_set_rwsem guarantees both that the
4411          * association is stable, and, on completion of the parent's
4412          * migration, @child is visible in the source of migration or
4413          * already in the destination cgroup.  This guarantee is necessary
4414          * when implementing operations which need to migrate all tasks of
4415          * a cgroup to another.
4416          *
4417          * Note that if we lose to cgroup_enable_task_cg_links(), @child
4418          * will remain in init_css_set.  This is safe because all tasks are
4419          * in the init_css_set before cg_links is enabled and there's no
4420          * operation which transfers all tasks out of init_css_set.
4421          */
4422         if (use_task_css_set_links) {
4423                 struct css_set *cset;
4424 
4425                 down_write(&css_set_rwsem);
4426                 cset = task_css_set(current);
4427                 if (list_empty(&child->cg_list)) {
4428                         rcu_assign_pointer(child->cgroups, cset);
4429                         list_add(&child->cg_list, &cset->tasks);
4430                         get_css_set(cset);
4431                 }
4432                 up_write(&css_set_rwsem);
4433         }
4434 
4435         /*
4436          * Call ss->fork().  This must happen after @child is linked on
4437          * css_set; otherwise, @child might change state between ->fork()
4438          * and addition to css_set.
4439          */
4440         if (need_forkexit_callback) {
4441                 for_each_subsys(ss, i)
4442                         if (ss->fork)
4443                                 ss->fork(child);
4444         }
4445 }
4446 
4447 /**
4448  * cgroup_exit - detach cgroup from exiting task
4449  * @tsk: pointer to task_struct of exiting process
4450  *
4451  * Description: Detach cgroup from @tsk and release it.
4452  *
4453  * Note that cgroups marked notify_on_release force every task in
4454  * them to take the global cgroup_mutex mutex when exiting.
4455  * This could impact scaling on very large systems.  Be reluctant to
4456  * use notify_on_release cgroups where very high task exit scaling
4457  * is required on large systems.
4458  *
4459  * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
4460  * call cgroup_exit() while the task is still competent to handle
4461  * notify_on_release(), then leave the task attached to the root cgroup in
4462  * each hierarchy for the remainder of its exit.  No need to bother with
4463  * init_css_set refcnting.  init_css_set never goes away and we can't race
4464  * with migration path - PF_EXITING is visible to migration path.
4465  */
4466 void cgroup_exit(struct task_struct *tsk)
4467 {
4468         struct cgroup_subsys *ss;
4469         struct css_set *cset;
4470         bool put_cset = false;
4471         int i;
4472 
4473         /*
4474          * Unlink from @tsk from its css_set.  As migration path can't race
4475          * with us, we can check cg_list without grabbing css_set_rwsem.
4476          */
4477         if (!list_empty(&tsk->cg_list)) {
4478                 down_write(&css_set_rwsem);
4479                 list_del_init(&tsk->cg_list);
4480                 up_write(&css_set_rwsem);
4481                 put_cset = true;
4482         }
4483 
4484         /* Reassign the task to the init_css_set. */
4485         cset = task_css_set(tsk);
4486         RCU_INIT_POINTER(tsk->cgroups, &init_css_set);
4487 
4488         if (need_forkexit_callback) {
4489                 /* see cgroup_post_fork() for details */
4490                 for_each_subsys(ss, i) {
4491                         if (ss->exit) {
4492                                 struct cgroup_subsys_state *old_css = cset->subsys[i];
4493                                 struct cgroup_subsys_state *css = task_css(tsk, i);
4494 
4495                                 ss->exit(css, old_css, tsk);
4496                         }
4497                 }
4498         }
4499 
4500         if (put_cset)
4501                 put_css_set(cset, true);
4502 }
4503 
4504 static void check_for_release(struct cgroup *cgrp)
4505 {
4506         if (cgroup_is_releasable(cgrp) &&
4507             list_empty(&cgrp->cset_links) && list_empty(&cgrp->children)) {
4508                 /*
4509                  * Control Group is currently removeable. If it's not
4510                  * already queued for a userspace notification, queue
4511                  * it now
4512                  */
4513                 int need_schedule_work = 0;
4514 
4515                 raw_spin_lock(&release_list_lock);
4516                 if (!cgroup_is_dead(cgrp) &&
4517                     list_empty(&cgrp->release_list)) {
4518                         list_add(&cgrp->release_list, &release_list);
4519                         need_schedule_work = 1;
4520                 }
4521                 raw_spin_unlock(&release_list_lock);
4522                 if (need_schedule_work)
4523                         schedule_work(&release_agent_work);
4524         }
4525 }
4526 
4527 /*
4528  * Notify userspace when a cgroup is released, by running the
4529  * configured release agent with the name of the cgroup (path
4530  * relative to the root of cgroup file system) as the argument.
4531  *
4532  * Most likely, this user command will try to rmdir this cgroup.
4533  *
4534  * This races with the possibility that some other task will be
4535  * attached to this cgroup before it is removed, or that some other
4536  * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
4537  * The presumed 'rmdir' will fail quietly if this cgroup is no longer
4538  * unused, and this cgroup will be reprieved from its death sentence,
4539  * to continue to serve a useful existence.  Next time it's released,
4540  * we will get notified again, if it still has 'notify_on_release' set.
4541  *
4542  * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
4543  * means only wait until the task is successfully execve()'d.  The
4544  * separate release agent task is forked by call_usermodehelper(),
4545  * then control in this thread returns here, without waiting for the
4546  * release agent task.  We don't bother to wait because the caller of
4547  * this routine has no use for the exit status of the release agent
4548  * task, so no sense holding our caller up for that.
4549  */
4550 static void cgroup_release_agent(struct work_struct *work)
4551 {
4552         BUG_ON(work != &release_agent_work);
4553         mutex_lock(&cgroup_mutex);
4554         raw_spin_lock(&release_list_lock);
4555         while (!list_empty(&release_list)) {
4556                 char *argv[3], *envp[3];
4557                 int i;
4558                 char *pathbuf = NULL, *agentbuf = NULL, *path;
4559                 struct cgroup *cgrp = list_entry(release_list.next,
4560                                                     struct cgroup,
4561                                                     release_list);
4562                 list_del_init(&cgrp->release_list);
4563                 raw_spin_unlock(&release_list_lock);
4564                 pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
4565                 if (!pathbuf)
4566                         goto continue_free;
4567                 path = cgroup_path(cgrp, pathbuf, PATH_MAX);
4568                 if (!path)
4569                         goto continue_free;
4570                 agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
4571                 if (!agentbuf)
4572                         goto continue_free;
4573 
4574                 i = 0;
4575                 argv[i++] = agentbuf;
4576                 argv[i++] = path;
4577                 argv[i] = NULL;
4578 
4579                 i = 0;
4580                 /* minimal command environment */
4581                 envp[i++] = "HOME=/";
4582                 envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
4583                 envp[i] = NULL;
4584 
4585                 /* Drop the lock while we invoke the usermode helper,
4586                  * since the exec could involve hitting disk and hence
4587                  * be a slow process */
4588                 mutex_unlock(&cgroup_mutex);
4589                 call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
4590                 mutex_lock(&cgroup_mutex);
4591  continue_free:
4592                 kfree(pathbuf);
4593                 kfree(agentbuf);
4594                 raw_spin_lock(&release_list_lock);
4595         }
4596         raw_spin_unlock(&release_list_lock);
4597         mutex_unlock(&cgroup_mutex);
4598 }
4599 
4600 static int __init cgroup_disable(char *str)
4601 {
4602         struct cgroup_subsys *ss;
4603         char *token;
4604         int i;
4605 
4606         while ((token = strsep(&str, ",")) != NULL) {
4607                 if (!*token)
4608                         continue;
4609 
4610                 for_each_subsys(ss, i) {
4611                         if (!strcmp(token, ss->name)) {
4612                                 ss->disabled = 1;
4613                                 printk(KERN_INFO "Disabling %s control group"
4614                                         " subsystem\n", ss->name);
4615                                 break;
4616                         }
4617                 }
4618         }
4619         return 1;
4620 }
4621 __setup("cgroup_disable=", cgroup_disable);
4622 
4623 /**
4624  * css_tryget_from_dir - get corresponding css from the dentry of a cgroup dir
4625  * @dentry: directory dentry of interest
4626  * @ss: subsystem of interest
4627  *
4628  * If @dentry is a directory for a cgroup which has @ss enabled on it, try
4629  * to get the corresponding css and return it.  If such css doesn't exist
4630  * or can't be pinned, an ERR_PTR value is returned.
4631  */
4632 struct cgroup_subsys_state *css_tryget_from_dir(struct dentry *dentry,
4633                                                 struct cgroup_subsys *ss)
4634 {
4635         struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
4636         struct cgroup_subsys_state *css = NULL;
4637         struct cgroup *cgrp;
4638 
4639         /* is @dentry a cgroup dir? */
4640         if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
4641             kernfs_type(kn) != KERNFS_DIR)
4642                 return ERR_PTR(-EBADF);
4643 
4644         rcu_read_lock();
4645 
4646         /*
4647          * This path doesn't originate from kernfs and @kn could already
4648          * have been or be removed at any point.  @kn->priv is RCU
4649          * protected for this access.  See destroy_locked() for details.
4650          */
4651         cgrp = rcu_dereference(kn->priv);
4652         if (cgrp)
4653                 css = cgroup_css(cgrp, ss);
4654 
4655         if (!css || !css_tryget(css))
4656                 css = ERR_PTR(-ENOENT);
4657 
4658         rcu_read_unlock();
4659         return css;
4660 }
4661 
4662 /**
4663  * css_from_id - lookup css by id
4664  * @id: the cgroup id
4665  * @ss: cgroup subsys to be looked into
4666  *
4667  * Returns the css if there's valid one with @id, otherwise returns NULL.
4668  * Should be called under rcu_read_lock().
4669  */
4670 struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
4671 {
4672         struct cgroup *cgrp;
4673 
4674         cgroup_assert_mutexes_or_rcu_locked();
4675 
4676         cgrp = idr_find(&ss->root->cgroup_idr, id);
4677         if (cgrp)
4678                 return cgroup_css(cgrp, ss);
4679         return NULL;
4680 }
4681 
4682 #ifdef CONFIG_CGROUP_DEBUG
4683 static struct cgroup_subsys_state *
4684 debug_css_alloc(struct cgroup_subsys_state *parent_css)
4685 {
4686         struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
4687 
4688         if (!css)
4689                 return ERR_PTR(-ENOMEM);
4690 
4691         return css;
4692 }
4693 
4694 static void debug_css_free(struct cgroup_subsys_state *css)
4695 {
4696         kfree(css);
4697 }
4698 
4699 static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
4700                                 struct cftype *cft)
4701 {
4702         return cgroup_task_count(css->cgroup);
4703 }
4704 
4705 static u64 current_css_set_read(struct cgroup_subsys_state *css,
4706                                 struct cftype *cft)
4707 {
4708         return (u64)(unsigned long)current->cgroups;
4709 }
4710 
4711 static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
4712                                          struct cftype *cft)
4713 {
4714         u64 count;
4715 
4716         rcu_read_lock();
4717         count = atomic_read(&task_css_set(current)->refcount);
4718         rcu_read_unlock();
4719         return count;
4720 }
4721 
4722 static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
4723 {
4724         struct cgrp_cset_link *link;
4725         struct css_set *cset;
4726         char *name_buf;
4727 
4728         name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
4729         if (!name_buf)
4730                 return -ENOMEM;
4731 
4732         down_read(&css_set_rwsem);
4733         rcu_read_lock();
4734         cset = rcu_dereference(current->cgroups);
4735         list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
4736                 struct cgroup *c = link->cgrp;
4737 
4738                 cgroup_name(c, name_buf, NAME_MAX + 1);
4739                 seq_printf(seq, "Root %d group %s\n",
4740                            c->root->hierarchy_id, name_buf);
4741         }
4742         rcu_read_unlock();
4743         up_read(&css_set_rwsem);
4744         kfree(name_buf);
4745         return 0;
4746 }
4747 
4748 #define MAX_TASKS_SHOWN_PER_CSS 25
4749 static int cgroup_css_links_read(struct seq_file *seq, void *v)
4750 {
4751         struct cgroup_subsys_state *css = seq_css(seq);
4752         struct cgrp_cset_link *link;
4753 
4754         down_read(&css_set_rwsem);
4755         list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
4756                 struct css_set *cset = link->cset;
4757                 struct task_struct *task;
4758                 int count = 0;
4759 
4760                 seq_printf(seq, "css_set %p\n", cset);
4761 
4762                 list_for_each_entry(task, &cset->tasks, cg_list) {
4763                         if (count++ > MAX_TASKS_SHOWN_PER_CSS)
4764                                 goto overflow;
4765                         seq_printf(seq, "  task %d\n", task_pid_vnr(task));
4766                 }
4767 
4768                 list_for_each_entry(task, &cset->mg_tasks, cg_list) {
4769                         if (count++ > MAX_TASKS_SHOWN_PER_CSS)
4770                                 goto overflow;
4771                         seq_printf(seq, "  task %d\n", task_pid_vnr(task));
4772                 }
4773                 continue;
4774         overflow:
4775                 seq_puts(seq, "  ...\n");
4776         }
4777         up_read(&css_set_rwsem);
4778         return 0;
4779 }
4780 
4781 static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
4782 {
4783         return test_bit(CGRP_RELEASABLE, &css->cgroup->flags);
4784 }
4785 
4786 static struct cftype debug_files[] =  {
4787         {
4788                 .name = "taskcount",
4789                 .read_u64 = debug_taskcount_read,
4790         },
4791 
4792         {
4793                 .name = "current_css_set",
4794                 .read_u64 = current_css_set_read,
4795         },
4796 
4797         {
4798                 .name = "current_css_set_refcount",
4799                 .read_u64 = current_css_set_refcount_read,
4800         },
4801 
4802         {
4803                 .name = "current_css_set_cg_links",
4804                 .seq_show = current_css_set_cg_links_read,
4805         },
4806 
4807         {
4808                 .name = "cgroup_css_links",
4809                 .seq_show = cgroup_css_links_read,
4810         },
4811 
4812         {
4813                 .name = "releasable",
4814                 .read_u64 = releasable_read,
4815         },
4816 
4817         { }     /* terminate */
4818 };
4819 
4820 struct cgroup_subsys debug_cgrp_subsys = {
4821         .css_alloc = debug_css_alloc,
4822         .css_free = debug_css_free,
4823         .base_cftypes = debug_files,
4824 };
4825 #endif /* CONFIG_CGROUP_DEBUG */
4826 

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