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

Linux/kernel/cgroup.c

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

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us