linux - kernel/cgroup.c

6022 lines · 162.0 KiB

1	/*
2	* Generic process-grouping system.
3	*
4	* Based originally on the cpuset system, extracted by Paul Menage
5	* Copyright (C) 2006 Google, Inc
6	*
7	* Notifications support
8	* Copyright (C) 2009 Nokia Corporation
9	* Author: Kirill A. Shutemov
10	*
11	* Copyright notices from the original cpuset code:
12	* --------------------------------------------------
13	* Copyright (C) 2003 BULL SA.
14	* Copyright (C) 2004-2006 Silicon Graphics, Inc.
15	*
16	* Portions derived from Patrick Mochel's sysfs code.
17	* sysfs is Copyright (c) 2001-3 Patrick Mochel
18	*
19	* 2003-10-10 Written by Simon Derr.
20	* 2003-10-22 Updates by Stephen Hemminger.
21	* 2004 May-July Rework by Paul Jackson.
22	* ---------------------------------------------------
23	*
24	* This file is subject to the terms and conditions of the GNU General Public
25	* License. See the file COPYING in the main directory of the Linux
26	* distribution for more details.
27	*/
28
29	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
30
31	#include <linux/cgroup.h>
32	#include <linux/cred.h>
33	#include <linux/ctype.h>
34	#include <linux/errno.h>
35	#include <linux/init_task.h>
36	#include <linux/kernel.h>
37	#include <linux/list.h>
38	#include <linux/magic.h>
39	#include <linux/mm.h>
40	#include <linux/mutex.h>
41	#include <linux/mount.h>
42	#include <linux/pagemap.h>
43	#include <linux/proc_fs.h>
44	#include <linux/rcupdate.h>
45	#include <linux/sched.h>
46	#include <linux/slab.h>
47	#include <linux/spinlock.h>
48	#include <linux/percpu-rwsem.h>
49	#include <linux/string.h>
50	#include <linux/sort.h>
51	#include <linux/kmod.h>
52	#include <linux/delayacct.h>
53	#include <linux/cgroupstats.h>
54	#include <linux/hashtable.h>
55	#include <linux/pid_namespace.h>
56	#include <linux/idr.h>
57	#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
58	#include <linux/kthread.h>
59	#include <linux/delay.h>
60	#include <linux/atomic.h>
61	#include <net/sock.h>
62
63	/*
64	* pidlists linger the following amount before being destroyed. The goal
65	* is avoiding frequent destruction in the middle of consecutive read calls
66	* Expiring in the middle is a performance problem not a correctness one.
67	* 1 sec should be enough.
68	*/
69	#define CGROUP_PIDLIST_DESTROY_DELAY HZ
70
71	#define CGROUP_FILE_NAME_MAX (MAX_CGROUP_TYPE_NAMELEN + \
72	MAX_CFTYPE_NAME + 2)
73
74	/*
75	* cgroup_mutex is the master lock. Any modification to cgroup or its
76	* hierarchy must be performed while holding it.
77	*
78	* css_set_lock protects task->cgroups pointer, the list of css_set
79	* objects, and the chain of tasks off each css_set.
80	*
81	* These locks are exported if CONFIG_PROVE_RCU so that accessors in
82	* cgroup.h can use them for lockdep annotations.
83	*/
84	#ifdef CONFIG_PROVE_RCU
85	DEFINE_MUTEX(cgroup_mutex);
86	DEFINE_SPINLOCK(css_set_lock);
87	EXPORT_SYMBOL_GPL(cgroup_mutex);
88	EXPORT_SYMBOL_GPL(css_set_lock);
89	#else
90	static DEFINE_MUTEX(cgroup_mutex);
91	static DEFINE_SPINLOCK(css_set_lock);
92	#endif
93
94	/*
95	* Protects cgroup_idr and css_idr so that IDs can be released without
96	* grabbing cgroup_mutex.
97	*/
98	static DEFINE_SPINLOCK(cgroup_idr_lock);
99
100	/*
101	* Protects cgroup_file->kn for !self csses. It synchronizes notifications
102	* against file removal/re-creation across css hiding.
103	*/
104	static DEFINE_SPINLOCK(cgroup_file_kn_lock);
105
106	/*
107	* Protects cgroup_subsys->release_agent_path. Modifying it also requires
108	* cgroup_mutex. Reading requires either cgroup_mutex or this spinlock.
109	*/
110	static DEFINE_SPINLOCK(release_agent_path_lock);
111
112	struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
113
114	#define cgroup_assert_mutex_or_rcu_locked() \
115	RCU_LOCKDEP_WARN(!rcu_read_lock_held() && \
116	!lockdep_is_held(&cgroup_mutex), \
117	"cgroup_mutex or RCU read lock required");
118
119	/*
120	* cgroup destruction makes heavy use of work items and there can be a lot
121	* of concurrent destructions. Use a separate workqueue so that cgroup
122	* destruction work items don't end up filling up max_active of system_wq
123	* which may lead to deadlock.
124	*/
125	static struct workqueue_struct *cgroup_destroy_wq;
126
127	/*
128	* pidlist destructions need to be flushed on cgroup destruction. Use a
129	* separate workqueue as flush domain.
130	*/
131	static struct workqueue_struct *cgroup_pidlist_destroy_wq;
132
133	/* generate an array of cgroup subsystem pointers */
134	#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
135	static struct cgroup_subsys *cgroup_subsys[] = {
136	#include <linux/cgroup_subsys.h>
137	};
138	#undef SUBSYS
139
140	/* array of cgroup subsystem names */
141	#define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
142	static const char *cgroup_subsys_name[] = {
143	#include <linux/cgroup_subsys.h>
144	};
145	#undef SUBSYS
146
147	/* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
148	#define SUBSYS(_x) \
149	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key); \
150	DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key); \
151	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key); \
152	EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
153	#include <linux/cgroup_subsys.h>
154	#undef SUBSYS
155
156	#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
157	static struct static_key_true *cgroup_subsys_enabled_key[] = {
158	#include <linux/cgroup_subsys.h>
159	};
160	#undef SUBSYS
161
162	#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
163	static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
164	#include <linux/cgroup_subsys.h>
165	};
166	#undef SUBSYS
167
168	/*
169	* The default hierarchy, reserved for the subsystems that are otherwise
170	* unattached - it never has more than a single cgroup, and all tasks are
171	* part of that cgroup.
172	*/
173	struct cgroup_root cgrp_dfl_root;
174	EXPORT_SYMBOL_GPL(cgrp_dfl_root);
175
176	/*
177	* The default hierarchy always exists but is hidden until mounted for the
178	* first time. This is for backward compatibility.
179	*/
180	static bool cgrp_dfl_root_visible;
181
182	/* some controllers are not supported in the default hierarchy */
183	static unsigned long cgrp_dfl_root_inhibit_ss_mask;
184
185	/* The list of hierarchy roots */
186
187	static LIST_HEAD(cgroup_roots);
188	static int cgroup_root_count;
189
190	/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
191	static DEFINE_IDR(cgroup_hierarchy_idr);
192
193	/*
194	* Assign a monotonically increasing serial number to csses. It guarantees
195	* cgroups with bigger numbers are newer than those with smaller numbers.
196	* Also, as csses are always appended to the parent's ->children list, it
197	* guarantees that sibling csses are always sorted in the ascending serial
198	* number order on the list. Protected by cgroup_mutex.
199	*/
200	static u64 css_serial_nr_next = 1;
201
202	/*
203	* These bitmask flags indicate whether tasks in the fork and exit paths have
204	* fork/exit handlers to call. This avoids us having to do extra work in the
205	* fork/exit path to check which subsystems have fork/exit callbacks.
206	*/
207	static unsigned long have_fork_callback __read_mostly;
208	static unsigned long have_exit_callback __read_mostly;
209	static unsigned long have_free_callback __read_mostly;
210
211	/* Ditto for the can_fork callback. */
212	static unsigned long have_canfork_callback __read_mostly;
213
214	static struct file_system_type cgroup2_fs_type;
215	static struct cftype cgroup_dfl_base_files[];
216	static struct cftype cgroup_legacy_base_files[];
217
218	static int rebind_subsystems(struct cgroup_root *dst_root,
219	unsigned long ss_mask);
220	static void css_task_iter_advance(struct css_task_iter *it);
221	static int cgroup_destroy_locked(struct cgroup *cgrp);
222	static int create_css(struct cgroup cgrp, struct cgroup_subsys ss,
223	bool visible);
224	static void css_release(struct percpu_ref *ref);
225	static void kill_css(struct cgroup_subsys_state *css);
226	static int cgroup_addrm_files(struct cgroup_subsys_state *css,
227	struct cgroup *cgrp, struct cftype cfts[],
228	bool is_add);
229
230	/**
231	* cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
232	* @ssid: subsys ID of interest
233	*
234	* cgroup_subsys_enabled() can only be used with literal subsys names which
235	* is fine for individual subsystems but unsuitable for cgroup core. This
236	* is slower static_key_enabled() based test indexed by @ssid.
237	*/
238	static bool cgroup_ssid_enabled(int ssid)
239	{
240	return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
241	}
242
243	/**
244	* cgroup_on_dfl - test whether a cgroup is on the default hierarchy
245	* @cgrp: the cgroup of interest
246	*
247	* The default hierarchy is the v2 interface of cgroup and this function
248	* can be used to test whether a cgroup is on the default hierarchy for
249	* cases where a subsystem should behave differnetly depending on the
250	* interface version.
251	*
252	* The set of behaviors which change on the default hierarchy are still
253	* being determined and the mount option is prefixed with __DEVEL__.
254	*
255	* List of changed behaviors:
256	*
257	* - Mount options "noprefix", "xattr", "clone_children", "release_agent"
258	* and "name" are disallowed.
259	*
260	* - When mounting an existing superblock, mount options should match.
261	*
262	* - Remount is disallowed.
263	*
264	* - rename(2) is disallowed.
265	*
266	* - "tasks" is removed. Everything should be at process granularity. Use
267	* "cgroup.procs" instead.
268	*
269	* - "cgroup.procs" is not sorted. pids will be unique unless they got
270	* recycled inbetween reads.
271	*
272	* - "release_agent" and "notify_on_release" are removed. Replacement
273	* notification mechanism will be implemented.
274	*
275	* - "cgroup.clone_children" is removed.
276	*
277	* - "cgroup.subtree_populated" is available. Its value is 0 if the cgroup
278	* and its descendants contain no task; otherwise, 1. The file also
279	* generates kernfs notification which can be monitored through poll and
280	* [di]notify when the value of the file changes.
281	*
282	* - cpuset: tasks will be kept in empty cpusets when hotplug happens and
283	* take masks of ancestors with non-empty cpus/mems, instead of being
284	* moved to an ancestor.
285	*
286	* - cpuset: a task can be moved into an empty cpuset, and again it takes
287	* masks of ancestors.
288	*
289	* - memcg: use_hierarchy is on by default and the cgroup file for the flag
290	* is not created.
291	*
292	* - blkcg: blk-throttle becomes properly hierarchical.
293	*
294	* - debug: disallowed on the default hierarchy.
295	*/
296	static bool cgroup_on_dfl(const struct cgroup *cgrp)
297	{
298	return cgrp->root == &cgrp_dfl_root;
299	}
300
301	/* IDR wrappers which synchronize using cgroup_idr_lock */
302	static int cgroup_idr_alloc(struct idr idr, void ptr, int start, int end,
303	gfp_t gfp_mask)
304	{
305	int ret;
306
307	idr_preload(gfp_mask);
308	spin_lock_bh(&cgroup_idr_lock);
309	ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
310	spin_unlock_bh(&cgroup_idr_lock);
311	idr_preload_end();
312	return ret;
313	}
314
315	static void cgroup_idr_replace(struct idr idr, void *ptr, int id)
316	{
317	void *ret;
318
319	spin_lock_bh(&cgroup_idr_lock);
320	ret = idr_replace(idr, ptr, id);
321	spin_unlock_bh(&cgroup_idr_lock);
322	return ret;
323	}
324
325	static void cgroup_idr_remove(struct idr *idr, int id)
326	{
327	spin_lock_bh(&cgroup_idr_lock);
328	idr_remove(idr, id);
329	spin_unlock_bh(&cgroup_idr_lock);
330	}
331
332	static struct cgroup cgroup_parent(struct cgroup cgrp)
333	{
334	struct cgroup_subsys_state *parent_css = cgrp->self.parent;
335
336	if (parent_css)
337	return container_of(parent_css, struct cgroup, self);
338	return NULL;
339	}
340
341	/**
342	* cgroup_css - obtain a cgroup's css for the specified subsystem
343	* @cgrp: the cgroup of interest
344	* @ss: the subsystem of interest (%NULL returns @cgrp->self)
345	*
346	* Return @cgrp's css (cgroup_subsys_state) associated with @ss. This
347	* function must be called either under cgroup_mutex or rcu_read_lock() and
348	* the caller is responsible for pinning the returned css if it wants to
349	* keep accessing it outside the said locks. This function may return
350	* %NULL if @cgrp doesn't have @subsys_id enabled.
351	*/
352	static struct cgroup_subsys_state cgroup_css(struct cgroup cgrp,
353	struct cgroup_subsys *ss)
354	{
355	if (ss)
356	return rcu_dereference_check(cgrp->subsys[ss->id],
357	lockdep_is_held(&cgroup_mutex));
358	else
359	return &cgrp->self;
360	}
361
362	/**
363	* cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
364	* @cgrp: the cgroup of interest
365	* @ss: the subsystem of interest (%NULL returns @cgrp->self)
366	*
367	* Similar to cgroup_css() but returns the effective css, which is defined
368	* as the matching css of the nearest ancestor including self which has @ss
369	* enabled. If @ss is associated with the hierarchy @cgrp is on, this
370	* function is guaranteed to return non-NULL css.
371	*/
372	static struct cgroup_subsys_state cgroup_e_css(struct cgroup cgrp,
373	struct cgroup_subsys *ss)
374	{
375	lockdep_assert_held(&cgroup_mutex);
376
377	if (!ss)
378	return &cgrp->self;
379
380	if (!(cgrp->root->subsys_mask & (1 << ss->id)))
381	return NULL;
382
383	/*
384	* This function is used while updating css associations and thus
385	* can't test the csses directly. Use ->child_subsys_mask.
386	*/
387	while (cgroup_parent(cgrp) &&
388	!(cgroup_parent(cgrp)->child_subsys_mask & (1 << ss->id)))
389	cgrp = cgroup_parent(cgrp);
390
391	return cgroup_css(cgrp, ss);
392	}
393
394	/**
395	* cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
396	* @cgrp: the cgroup of interest
397	* @ss: the subsystem of interest
398	*
399	* Find and get the effective css of @cgrp for @ss. The effective css is
400	* defined as the matching css of the nearest ancestor including self which
401	* has @ss enabled. If @ss is not mounted on the hierarchy @cgrp is on,
402	* the root css is returned, so this function always returns a valid css.
403	* The returned css must be put using css_put().
404	*/
405	struct cgroup_subsys_state cgroup_get_e_css(struct cgroup cgrp,
406	struct cgroup_subsys *ss)
407	{
408	struct cgroup_subsys_state *css;
409
410	rcu_read_lock();
411
412	do {
413	css = cgroup_css(cgrp, ss);
414
415	if (css && css_tryget_online(css))
416	goto out_unlock;
417	cgrp = cgroup_parent(cgrp);
418	} while (cgrp);
419
420	css = init_css_set.subsys[ss->id];
421	css_get(css);
422	out_unlock:
423	rcu_read_unlock();
424	return css;
425	}
426
427	/* convenient tests for these bits */
428	static inline bool cgroup_is_dead(const struct cgroup *cgrp)
429	{
430	return !(cgrp->self.flags & CSS_ONLINE);
431	}
432
433	static void cgroup_get(struct cgroup *cgrp)
434	{
435	WARN_ON_ONCE(cgroup_is_dead(cgrp));
436	css_get(&cgrp->self);
437	}
438
439	static bool cgroup_tryget(struct cgroup *cgrp)
440	{
441	return css_tryget(&cgrp->self);
442	}
443
444	struct cgroup_subsys_state of_css(struct kernfs_open_file of)
445	{
446	struct cgroup *cgrp = of->kn->parent->priv;
447	struct cftype *cft = of_cft(of);
448
449	/*
450	* This is open and unprotected implementation of cgroup_css().
451	* seq_css() is only called from a kernfs file operation which has
452	* an active reference on the file. Because all the subsystem
453	* files are drained before a css is disassociated with a cgroup,
454	* the matching css from the cgroup's subsys table is guaranteed to
455	* be and stay valid until the enclosing operation is complete.
456	*/
457	if (cft->ss)
458	return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
459	else
460	return &cgrp->self;
461	}
462	EXPORT_SYMBOL_GPL(of_css);
463
464	static int notify_on_release(const struct cgroup *cgrp)
465	{
466	return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
467	}
468
469	/**
470	* for_each_css - iterate all css's of a cgroup
471	* @css: the iteration cursor
472	* @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
473	* @cgrp: the target cgroup to iterate css's of
474	*
475	* Should be called under cgroup_[tree_]mutex.
476	*/
477	#define for_each_css(css, ssid, cgrp) \
478	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++) \
479	if (!((css) = rcu_dereference_check( \
480	(cgrp)->subsys[(ssid)], \
481	lockdep_is_held(&cgroup_mutex)))) { } \
482	else
483
484	/**
485	* for_each_e_css - iterate all effective css's of a cgroup
486	* @css: the iteration cursor
487	* @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
488	* @cgrp: the target cgroup to iterate css's of
489	*
490	* Should be called under cgroup_[tree_]mutex.
491	*/
492	#define for_each_e_css(css, ssid, cgrp) \
493	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++) \
494	if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
495	; \
496	else
497
498	/**
499	* for_each_subsys - iterate all enabled cgroup subsystems
500	* @ss: the iteration cursor
501	* @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
502	*/
503	#define for_each_subsys(ss, ssid) \
504	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT && \
505	(((ss) = cgroup_subsys[ssid]) \|\| true); (ssid)++)
506
507	/**
508	* for_each_subsys_which - filter for_each_subsys with a bitmask
509	* @ss: the iteration cursor
510	* @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
511	* @ss_maskp: a pointer to the bitmask
512	*
513	* The block will only run for cases where the ssid-th bit (1 << ssid) of
514	* mask is set to 1.
515	*/
516	#define for_each_subsys_which(ss, ssid, ss_maskp) \
517	if (!CGROUP_SUBSYS_COUNT) /* to avoid spurious gcc warning */ \
518	(ssid) = 0; \
519	else \
520	for_each_set_bit(ssid, ss_maskp, CGROUP_SUBSYS_COUNT) \
521	if (((ss) = cgroup_subsys[ssid]) && false) \
522	break; \
523	else
524
525	/* iterate across the hierarchies */
526	#define for_each_root(root) \
527	list_for_each_entry((root), &cgroup_roots, root_list)
528
529	/* iterate over child cgrps, lock should be held throughout iteration */
530	#define cgroup_for_each_live_child(child, cgrp) \
531	list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
532	if (({ lockdep_assert_held(&cgroup_mutex); \
533	cgroup_is_dead(child); })) \
534	; \
535	else
536
537	static void cgroup_release_agent(struct work_struct *work);
538	static void check_for_release(struct cgroup *cgrp);
539
540	/*
541	* A cgroup can be associated with multiple css_sets as different tasks may
542	* belong to different cgroups on different hierarchies. In the other
543	* direction, a css_set is naturally associated with multiple cgroups.
544	* This M:N relationship is represented by the following link structure
545	* which exists for each association and allows traversing the associations
546	* from both sides.
547	*/
548	struct cgrp_cset_link {
549	/* the cgroup and css_set this link associates */
550	struct cgroup *cgrp;
551	struct css_set *cset;
552
553	/* list of cgrp_cset_links anchored at cgrp->cset_links */
554	struct list_head cset_link;
555
556	/* list of cgrp_cset_links anchored at css_set->cgrp_links */
557	struct list_head cgrp_link;
558	};
559
560	/*
561	* The default css_set - used by init and its children prior to any
562	* hierarchies being mounted. It contains a pointer to the root state
563	* for each subsystem. Also used to anchor the list of css_sets. Not
564	* reference-counted, to improve performance when child cgroups
565	* haven't been created.
566	*/
567	struct css_set init_css_set = {
568	.refcount = ATOMIC_INIT(1),
569	.cgrp_links = LIST_HEAD_INIT(init_css_set.cgrp_links),
570	.tasks = LIST_HEAD_INIT(init_css_set.tasks),
571	.mg_tasks = LIST_HEAD_INIT(init_css_set.mg_tasks),
572	.mg_preload_node = LIST_HEAD_INIT(init_css_set.mg_preload_node),
573	.mg_node = LIST_HEAD_INIT(init_css_set.mg_node),
574	.task_iters = LIST_HEAD_INIT(init_css_set.task_iters),
575	};
576
577	static int css_set_count = 1; /* 1 for init_css_set */
578
579	/**
580	* css_set_populated - does a css_set contain any tasks?
581	* @cset: target css_set
582	*/
583	static bool css_set_populated(struct css_set *cset)
584	{
585	lockdep_assert_held(&css_set_lock);
586
587	return !list_empty(&cset->tasks) \|\| !list_empty(&cset->mg_tasks);
588	}
589
590	/**
591	* cgroup_update_populated - updated populated count of a cgroup
592	* @cgrp: the target cgroup
593	* @populated: inc or dec populated count
594	*
595	* One of the css_sets associated with @cgrp is either getting its first
596	* task or losing the last. Update @cgrp->populated_cnt accordingly. The
597	* count is propagated towards root so that a given cgroup's populated_cnt
598	* is zero iff the cgroup and all its descendants don't contain any tasks.
599	*
600	* @cgrp's interface file "cgroup.populated" is zero if
601	* @cgrp->populated_cnt is zero and 1 otherwise. When @cgrp->populated_cnt
602	* changes from or to zero, userland is notified that the content of the
603	* interface file has changed. This can be used to detect when @cgrp and
604	* its descendants become populated or empty.
605	*/
606	static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
607	{
608	lockdep_assert_held(&css_set_lock);
609
610	do {
611	bool trigger;
612
613	if (populated)
614	trigger = !cgrp->populated_cnt++;
615	else
616	trigger = !--cgrp->populated_cnt;
617
618	if (!trigger)
619	break;
620
621	check_for_release(cgrp);
622	cgroup_file_notify(&cgrp->events_file);
623
624	cgrp = cgroup_parent(cgrp);
625	} while (cgrp);
626	}
627
628	/**
629	* css_set_update_populated - update populated state of a css_set
630	* @cset: target css_set
631	* @populated: whether @cset is populated or depopulated
632	*
633	* @cset is either getting the first task or losing the last. Update the
634	* ->populated_cnt of all associated cgroups accordingly.
635	*/
636	static void css_set_update_populated(struct css_set *cset, bool populated)
637	{
638	struct cgrp_cset_link *link;
639
640	lockdep_assert_held(&css_set_lock);
641
642	list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
643	cgroup_update_populated(link->cgrp, populated);
644	}
645
646	/**
647	* css_set_move_task - move a task from one css_set to another
648	* @task: task being moved
649	* @from_cset: css_set @task currently belongs to (may be NULL)
650	* @to_cset: new css_set @task is being moved to (may be NULL)
651	* @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
652	*
653	* Move @task from @from_cset to @to_cset. If @task didn't belong to any
654	* css_set, @from_cset can be NULL. If @task is being disassociated
655	* instead of moved, @to_cset can be NULL.
656	*
657	* This function automatically handles populated_cnt updates and
658	* css_task_iter adjustments but the caller is responsible for managing
659	* @from_cset and @to_cset's reference counts.
660	*/
661	static void css_set_move_task(struct task_struct *task,
662	struct css_set from_cset, struct css_set to_cset,
663	bool use_mg_tasks)
664	{
665	lockdep_assert_held(&css_set_lock);
666
667	if (from_cset) {
668	struct css_task_iter it, pos;
669
670	WARN_ON_ONCE(list_empty(&task->cg_list));
671
672	/*
673	* @task is leaving, advance task iterators which are
674	* pointing to it so that they can resume at the next
675	* position. Advancing an iterator might remove it from
676	* the list, use safe walk. See css_task_iter_advance*()
677	* for details.
678	*/
679	list_for_each_entry_safe(it, pos, &from_cset->task_iters,
680	iters_node)
681	if (it->task_pos == &task->cg_list)
682	css_task_iter_advance(it);
683
684	list_del_init(&task->cg_list);
685	if (!css_set_populated(from_cset))
686	css_set_update_populated(from_cset, false);
687	} else {
688	WARN_ON_ONCE(!list_empty(&task->cg_list));
689	}
690
691	if (to_cset) {
692	/*
693	* We are synchronized through cgroup_threadgroup_rwsem
694	* against PF_EXITING setting such that we can't race
695	* against cgroup_exit() changing the css_set to
696	* init_css_set and dropping the old one.
697	*/
698	WARN_ON_ONCE(task->flags & PF_EXITING);
699
700	if (!css_set_populated(to_cset))
701	css_set_update_populated(to_cset, true);
702	rcu_assign_pointer(task->cgroups, to_cset);
703	list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
704	&to_cset->tasks);
705	}
706	}
707
708	/*
709	* hash table for cgroup groups. This improves the performance to find
710	* an existing css_set. This hash doesn't (currently) take into
711	* account cgroups in empty hierarchies.
712	*/
713	#define CSS_SET_HASH_BITS 7
714	static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
715
716	static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
717	{
718	unsigned long key = 0UL;
719	struct cgroup_subsys *ss;
720	int i;
721
722	for_each_subsys(ss, i)
723	key += (unsigned long)css[i];
724	key = (key >> 16) ^ key;
725
726	return key;
727	}
728
729	static void put_css_set_locked(struct css_set *cset)
730	{
731	struct cgrp_cset_link link, tmp_link;
732	struct cgroup_subsys *ss;
733	int ssid;
734
735	lockdep_assert_held(&css_set_lock);
736
737	if (!atomic_dec_and_test(&cset->refcount))
738	return;
739
740	/* This css_set is dead. unlink it and release cgroup and css refs */
741	for_each_subsys(ss, ssid) {
742	list_del(&cset->e_cset_node[ssid]);
743	css_put(cset->subsys[ssid]);
744	}
745	hash_del(&cset->hlist);
746	css_set_count--;
747
748	list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
749	list_del(&link->cset_link);
750	list_del(&link->cgrp_link);
751	if (cgroup_parent(link->cgrp))
752	cgroup_put(link->cgrp);
753	kfree(link);
754	}
755
756	kfree_rcu(cset, rcu_head);
757	}
758
759	static void put_css_set(struct css_set *cset)
760	{
761	/*
762	* Ensure that the refcount doesn't hit zero while any readers
763	* can see it. Similar to atomic_dec_and_lock(), but for an
764	* rwlock
765	*/
766	if (atomic_add_unless(&cset->refcount, -1, 1))
767	return;
768
769	spin_lock_bh(&css_set_lock);
770	put_css_set_locked(cset);
771	spin_unlock_bh(&css_set_lock);
772	}
773
774	/*
775	* refcounted get/put for css_set objects
776	*/
777	static inline void get_css_set(struct css_set *cset)
778	{
779	atomic_inc(&cset->refcount);
780	}
781
782	/**
783	* compare_css_sets - helper function for find_existing_css_set().
784	* @cset: candidate css_set being tested
785	* @old_cset: existing css_set for a task
786	* @new_cgrp: cgroup that's being entered by the task
787	* @template: desired set of css pointers in css_set (pre-calculated)
788	*
789	* Returns true if "cset" matches "old_cset" except for the hierarchy
790	* which "new_cgrp" belongs to, for which it should match "new_cgrp".
791	*/
792	static bool compare_css_sets(struct css_set *cset,
793	struct css_set *old_cset,
794	struct cgroup *new_cgrp,
795	struct cgroup_subsys_state *template[])
796	{
797	struct list_head l1, l2;
798
799	/*
800	* On the default hierarchy, there can be csets which are
801	* associated with the same set of cgroups but different csses.
802	* Let's first ensure that csses match.
803	*/
804	if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
805	return false;
806
807	/*
808	* Compare cgroup pointers in order to distinguish between
809	* different cgroups in hierarchies. As different cgroups may
810	* share the same effective css, this comparison is always
811	* necessary.
812	*/
813	l1 = &cset->cgrp_links;
814	l2 = &old_cset->cgrp_links;
815	while (1) {
816	struct cgrp_cset_link link1, link2;
817	struct cgroup cgrp1, cgrp2;
818
819	l1 = l1->next;
820	l2 = l2->next;
821	/* See if we reached the end - both lists are equal length. */
822	if (l1 == &cset->cgrp_links) {
823	BUG_ON(l2 != &old_cset->cgrp_links);
824	break;
825	} else {
826	BUG_ON(l2 == &old_cset->cgrp_links);
827	}
828	/* Locate the cgroups associated with these links. */
829	link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
830	link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
831	cgrp1 = link1->cgrp;
832	cgrp2 = link2->cgrp;
833	/* Hierarchies should be linked in the same order. */
834	BUG_ON(cgrp1->root != cgrp2->root);
835
836	/*
837	* If this hierarchy is the hierarchy of the cgroup
838	* that's changing, then we need to check that this
839	* css_set points to the new cgroup; if it's any other
840	* hierarchy, then this css_set should point to the
841	* same cgroup as the old css_set.
842	*/
843	if (cgrp1->root == new_cgrp->root) {
844	if (cgrp1 != new_cgrp)
845	return false;
846	} else {
847	if (cgrp1 != cgrp2)
848	return false;
849	}
850	}
851	return true;
852	}
853
854	/**
855	* find_existing_css_set - init css array and find the matching css_set
856	* @old_cset: the css_set that we're using before the cgroup transition
857	* @cgrp: the cgroup that we're moving into
858	* @template: out param for the new set of csses, should be clear on entry
859	*/
860	static struct css_set find_existing_css_set(struct css_set old_cset,
861	struct cgroup *cgrp,
862	struct cgroup_subsys_state *template[])
863	{
864	struct cgroup_root *root = cgrp->root;
865	struct cgroup_subsys *ss;
866	struct css_set *cset;
867	unsigned long key;
868	int i;
869
870	/*
871	* Build the set of subsystem state objects that we want to see in the
872	* new css_set. while subsystems can change globally, the entries here
873	* won't change, so no need for locking.
874	*/
875	for_each_subsys(ss, i) {
876	if (root->subsys_mask & (1UL << i)) {
877	/*
878	* @ss is in this hierarchy, so we want the
879	* effective css from @cgrp.
880	*/
881	template[i] = cgroup_e_css(cgrp, ss);
882	} else {
883	/*
884	* @ss is not in this hierarchy, so we don't want
885	* to change the css.
886	*/
887	template[i] = old_cset->subsys[i];
888	}
889	}
890
891	key = css_set_hash(template);
892	hash_for_each_possible(css_set_table, cset, hlist, key) {
893	if (!compare_css_sets(cset, old_cset, cgrp, template))
894	continue;
895
896	/* This css_set matches what we need */
897	return cset;
898	}
899
900	/* No existing cgroup group matched */
901	return NULL;
902	}
903
904	static void free_cgrp_cset_links(struct list_head *links_to_free)
905	{
906	struct cgrp_cset_link link, tmp_link;
907
908	list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
909	list_del(&link->cset_link);
910	kfree(link);
911	}
912	}
913
914	/**
915	* allocate_cgrp_cset_links - allocate cgrp_cset_links
916	* @count: the number of links to allocate
917	* @tmp_links: list_head the allocated links are put on
918	*
919	* Allocate @count cgrp_cset_link structures and chain them on @tmp_links
920	* through ->cset_link. Returns 0 on success or -errno.
921	*/
922	static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
923	{
924	struct cgrp_cset_link *link;
925	int i;
926
927	INIT_LIST_HEAD(tmp_links);
928
929	for (i = 0; i < count; i++) {
930	link = kzalloc(sizeof(*link), GFP_KERNEL);
931	if (!link) {
932	free_cgrp_cset_links(tmp_links);
933	return -ENOMEM;
934	}
935	list_add(&link->cset_link, tmp_links);
936	}
937	return 0;
938	}
939
940	/**
941	* link_css_set - a helper function to link a css_set to a cgroup
942	* @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
943	* @cset: the css_set to be linked
944	* @cgrp: the destination cgroup
945	*/
946	static void link_css_set(struct list_head tmp_links, struct css_set cset,
947	struct cgroup *cgrp)
948	{
949	struct cgrp_cset_link *link;
950
951	BUG_ON(list_empty(tmp_links));
952
953	if (cgroup_on_dfl(cgrp))
954	cset->dfl_cgrp = cgrp;
955
956	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
957	link->cset = cset;
958	link->cgrp = cgrp;
959
960	/*
961	* Always add links to the tail of the lists so that the lists are
962	* in choronological order.
963	*/
964	list_move_tail(&link->cset_link, &cgrp->cset_links);
965	list_add_tail(&link->cgrp_link, &cset->cgrp_links);
966
967	if (cgroup_parent(cgrp))
968	cgroup_get(cgrp);
969	}
970
971	/**
972	* find_css_set - return a new css_set with one cgroup updated
973	* @old_cset: the baseline css_set
974	* @cgrp: the cgroup to be updated
975	*
976	* Return a new css_set that's equivalent to @old_cset, but with @cgrp
977	* substituted into the appropriate hierarchy.
978	*/
979	static struct css_set find_css_set(struct css_set old_cset,
980	struct cgroup *cgrp)
981	{
982	struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
983	struct css_set *cset;
984	struct list_head tmp_links;
985	struct cgrp_cset_link *link;
986	struct cgroup_subsys *ss;
987	unsigned long key;
988	int ssid;
989
990	lockdep_assert_held(&cgroup_mutex);
991
992	/* First see if we already have a cgroup group that matches
993	* the desired set */
994	spin_lock_bh(&css_set_lock);
995	cset = find_existing_css_set(old_cset, cgrp, template);
996	if (cset)
997	get_css_set(cset);
998	spin_unlock_bh(&css_set_lock);
999
1000	if (cset)
1001	return cset;
1002
1003	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1004	if (!cset)
1005	return NULL;
1006
1007	/* Allocate all the cgrp_cset_link objects that we'll need */
1008	if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1009	kfree(cset);
1010	return NULL;
1011	}
1012
1013	atomic_set(&cset->refcount, 1);
1014	INIT_LIST_HEAD(&cset->cgrp_links);
1015	INIT_LIST_HEAD(&cset->tasks);
1016	INIT_LIST_HEAD(&cset->mg_tasks);
1017	INIT_LIST_HEAD(&cset->mg_preload_node);
1018	INIT_LIST_HEAD(&cset->mg_node);
1019	INIT_LIST_HEAD(&cset->task_iters);
1020	INIT_HLIST_NODE(&cset->hlist);
1021
1022	/* Copy the set of subsystem state objects generated in
1023	* find_existing_css_set() */
1024	memcpy(cset->subsys, template, sizeof(cset->subsys));
1025
1026	spin_lock_bh(&css_set_lock);
1027	/* Add reference counts and links from the new css_set. */
1028	list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1029	struct cgroup *c = link->cgrp;
1030
1031	if (c->root == cgrp->root)
1032	c = cgrp;
1033	link_css_set(&tmp_links, cset, c);
1034	}
1035
1036	BUG_ON(!list_empty(&tmp_links));
1037
1038	css_set_count++;
1039
1040	/* Add @cset to the hash table */
1041	key = css_set_hash(cset->subsys);
1042	hash_add(css_set_table, &cset->hlist, key);
1043
1044	for_each_subsys(ss, ssid) {
1045	struct cgroup_subsys_state *css = cset->subsys[ssid];
1046
1047	list_add_tail(&cset->e_cset_node[ssid],
1048	&css->cgroup->e_csets[ssid]);
1049	css_get(css);
1050	}
1051
1052	spin_unlock_bh(&css_set_lock);
1053
1054	return cset;
1055	}
1056
1057	static struct cgroup_root cgroup_root_from_kf(struct kernfs_root kf_root)
1058	{
1059	struct cgroup *root_cgrp = kf_root->kn->priv;
1060
1061	return root_cgrp->root;
1062	}
1063
1064	static int cgroup_init_root_id(struct cgroup_root *root)
1065	{
1066	int id;
1067
1068	lockdep_assert_held(&cgroup_mutex);
1069
1070	id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1071	if (id < 0)
1072	return id;
1073
1074	root->hierarchy_id = id;
1075	return 0;
1076	}
1077
1078	static void cgroup_exit_root_id(struct cgroup_root *root)
1079	{
1080	lockdep_assert_held(&cgroup_mutex);
1081
1082	if (root->hierarchy_id) {
1083	idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1084	root->hierarchy_id = 0;
1085	}
1086	}
1087
1088	static void cgroup_free_root(struct cgroup_root *root)
1089	{
1090	if (root) {
1091	/* hierarchy ID should already have been released */
1092	WARN_ON_ONCE(root->hierarchy_id);
1093
1094	idr_destroy(&root->cgroup_idr);
1095	kfree(root);
1096	}
1097	}
1098
1099	static void cgroup_destroy_root(struct cgroup_root *root)
1100	{
1101	struct cgroup *cgrp = &root->cgrp;
1102	struct cgrp_cset_link link, tmp_link;
1103
1104	mutex_lock(&cgroup_mutex);
1105
1106	BUG_ON(atomic_read(&root->nr_cgrps));
1107	BUG_ON(!list_empty(&cgrp->self.children));
1108
1109	/* Rebind all subsystems back to the default hierarchy */
1110	rebind_subsystems(&cgrp_dfl_root, root->subsys_mask);
1111
1112	/*
1113	* Release all the links from cset_links to this hierarchy's
1114	* root cgroup
1115	*/
1116	spin_lock_bh(&css_set_lock);
1117
1118	list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1119	list_del(&link->cset_link);
1120	list_del(&link->cgrp_link);
1121	kfree(link);
1122	}
1123
1124	spin_unlock_bh(&css_set_lock);
1125
1126	if (!list_empty(&root->root_list)) {
1127	list_del(&root->root_list);
1128	cgroup_root_count--;
1129	}
1130
1131	cgroup_exit_root_id(root);
1132
1133	mutex_unlock(&cgroup_mutex);
1134
1135	kernfs_destroy_root(root->kf_root);
1136	cgroup_free_root(root);
1137	}
1138
1139	/* look up cgroup associated with given css_set on the specified hierarchy */
1140	static struct cgroup cset_cgroup_from_root(struct css_set cset,
1141	struct cgroup_root *root)
1142	{
1143	struct cgroup *res = NULL;
1144
1145	lockdep_assert_held(&cgroup_mutex);
1146	lockdep_assert_held(&css_set_lock);
1147
1148	if (cset == &init_css_set) {
1149	res = &root->cgrp;
1150	} else {
1151	struct cgrp_cset_link *link;
1152
1153	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1154	struct cgroup *c = link->cgrp;
1155
1156	if (c->root == root) {
1157	res = c;
1158	break;
1159	}
1160	}
1161	}
1162
1163	BUG_ON(!res);
1164	return res;
1165	}
1166
1167	/*
1168	* Return the cgroup for "task" from the given hierarchy. Must be
1169	* called with cgroup_mutex and css_set_lock held.
1170	*/
1171	static struct cgroup task_cgroup_from_root(struct task_struct task,
1172	struct cgroup_root *root)
1173	{
1174	/*
1175	* No need to lock the task - since we hold cgroup_mutex the
1176	* task can't change groups, so the only thing that can happen
1177	* is that it exits and its css is set back to init_css_set.
1178	*/
1179	return cset_cgroup_from_root(task_css_set(task), root);
1180	}
1181
1182	/*
1183	* A task must hold cgroup_mutex to modify cgroups.
1184	*
1185	* Any task can increment and decrement the count field without lock.
1186	* So in general, code holding cgroup_mutex can't rely on the count
1187	* field not changing. However, if the count goes to zero, then only
1188	* cgroup_attach_task() can increment it again. Because a count of zero
1189	* means that no tasks are currently attached, therefore there is no
1190	* way a task attached to that cgroup can fork (the other way to
1191	* increment the count). So code holding cgroup_mutex can safely
1192	* assume that if the count is zero, it will stay zero. Similarly, if
1193	* a task holds cgroup_mutex on a cgroup with zero count, it
1194	* knows that the cgroup won't be removed, as cgroup_rmdir()
1195	* needs that mutex.
1196	*
1197	* A cgroup can only be deleted if both its 'count' of using tasks
1198	* is zero, and its list of 'children' cgroups is empty. Since all
1199	* tasks in the system use _some_ cgroup, and since there is always at
1200	* least one task in the system (init, pid == 1), therefore, root cgroup
1201	* always has either children cgroups and/or using tasks. So we don't
1202	* need a special hack to ensure that root cgroup cannot be deleted.
1203	*
1204	* P.S. One more locking exception. RCU is used to guard the
1205	* update of a tasks cgroup pointer by cgroup_attach_task()
1206	*/
1207
1208	static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1209	static const struct file_operations proc_cgroupstats_operations;
1210
1211	static char cgroup_file_name(struct cgroup cgrp, const struct cftype *cft,
1212	char *buf)
1213	{
1214	struct cgroup_subsys *ss = cft->ss;
1215
1216	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1217	!(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
1218	snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
1219	cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1220	cft->name);
1221	else
1222	strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1223	return buf;
1224	}
1225
1226	/**
1227	* cgroup_file_mode - deduce file mode of a control file
1228	* @cft: the control file in question
1229	*
1230	* S_IRUGO for read, S_IWUSR for write.
1231	*/
1232	static umode_t cgroup_file_mode(const struct cftype *cft)
1233	{
1234	umode_t mode = 0;
1235
1236	if (cft->read_u64 \|\| cft->read_s64 \|\| cft->seq_show)
1237	mode \|= S_IRUGO;
1238
1239	if (cft->write_u64 \|\| cft->write_s64 \|\| cft->write) {
1240	if (cft->flags & CFTYPE_WORLD_WRITABLE)
1241	mode \|= S_IWUGO;
1242	else
1243	mode \|= S_IWUSR;
1244	}
1245
1246	return mode;
1247	}
1248
1249	/**
1250	* cgroup_calc_child_subsys_mask - calculate child_subsys_mask
1251	* @cgrp: the target cgroup
1252	* @subtree_control: the new subtree_control mask to consider
1253	*
1254	* On the default hierarchy, a subsystem may request other subsystems to be
1255	* enabled together through its ->depends_on mask. In such cases, more
1256	* subsystems than specified in "cgroup.subtree_control" may be enabled.
1257	*
1258	* This function calculates which subsystems need to be enabled if
1259	* @subtree_control is to be applied to @cgrp. The returned mask is always
1260	* a superset of @subtree_control and follows the usual hierarchy rules.
1261	*/
1262	static unsigned long cgroup_calc_child_subsys_mask(struct cgroup *cgrp,
1263	unsigned long subtree_control)
1264	{
1265	struct cgroup *parent = cgroup_parent(cgrp);
1266	unsigned long cur_ss_mask = subtree_control;
1267	struct cgroup_subsys *ss;
1268	int ssid;
1269
1270	lockdep_assert_held(&cgroup_mutex);
1271
1272	if (!cgroup_on_dfl(cgrp))
1273	return cur_ss_mask;
1274
1275	while (true) {
1276	unsigned long new_ss_mask = cur_ss_mask;
1277
1278	for_each_subsys_which(ss, ssid, &cur_ss_mask)
1279	new_ss_mask \|= ss->depends_on;
1280
1281	/*
1282	* Mask out subsystems which aren't available. This can
1283	* happen only if some depended-upon subsystems were bound
1284	* to non-default hierarchies.
1285	*/
1286	if (parent)
1287	new_ss_mask &= parent->child_subsys_mask;
1288	else
1289	new_ss_mask &= cgrp->root->subsys_mask;
1290
1291	if (new_ss_mask == cur_ss_mask)
1292	break;
1293	cur_ss_mask = new_ss_mask;
1294	}
1295
1296	return cur_ss_mask;
1297	}
1298
1299	/**
1300	* cgroup_refresh_child_subsys_mask - update child_subsys_mask
1301	* @cgrp: the target cgroup
1302	*
1303	* Update @cgrp->child_subsys_mask according to the current
1304	* @cgrp->subtree_control using cgroup_calc_child_subsys_mask().
1305	*/
1306	static void cgroup_refresh_child_subsys_mask(struct cgroup *cgrp)
1307	{
1308	cgrp->child_subsys_mask =
1309	cgroup_calc_child_subsys_mask(cgrp, cgrp->subtree_control);
1310	}
1311
1312	/**
1313	* cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1314	* @kn: the kernfs_node being serviced
1315	*
1316	* This helper undoes cgroup_kn_lock_live() and should be invoked before
1317	* the method finishes if locking succeeded. Note that once this function
1318	* returns the cgroup returned by cgroup_kn_lock_live() may become
1319	* inaccessible any time. If the caller intends to continue to access the
1320	* cgroup, it should pin it before invoking this function.
1321	*/
1322	static void cgroup_kn_unlock(struct kernfs_node *kn)
1323	{
1324	struct cgroup *cgrp;
1325
1326	if (kernfs_type(kn) == KERNFS_DIR)
1327	cgrp = kn->priv;
1328	else
1329	cgrp = kn->parent->priv;
1330
1331	mutex_unlock(&cgroup_mutex);
1332
1333	kernfs_unbreak_active_protection(kn);
1334	cgroup_put(cgrp);
1335	}
1336
1337	/**
1338	* cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1339	* @kn: the kernfs_node being serviced
1340	*
1341	* This helper is to be used by a cgroup kernfs method currently servicing
1342	* @kn. It breaks the active protection, performs cgroup locking and
1343	* verifies that the associated cgroup is alive. Returns the cgroup if
1344	* alive; otherwise, %NULL. A successful return should be undone by a
1345	* matching cgroup_kn_unlock() invocation.
1346	*
1347	* Any cgroup kernfs method implementation which requires locking the
1348	* associated cgroup should use this helper. It avoids nesting cgroup
1349	* locking under kernfs active protection and allows all kernfs operations
1350	* including self-removal.
1351	*/
1352	static struct cgroup cgroup_kn_lock_live(struct kernfs_node kn)
1353	{
1354	struct cgroup *cgrp;
1355
1356	if (kernfs_type(kn) == KERNFS_DIR)
1357	cgrp = kn->priv;
1358	else
1359	cgrp = kn->parent->priv;
1360
1361	/*
1362	* We're gonna grab cgroup_mutex which nests outside kernfs
1363	* active_ref. cgroup liveliness check alone provides enough
1364	* protection against removal. Ensure @cgrp stays accessible and
1365	* break the active_ref protection.
1366	*/
1367	if (!cgroup_tryget(cgrp))
1368	return NULL;
1369	kernfs_break_active_protection(kn);
1370
1371	mutex_lock(&cgroup_mutex);
1372
1373	if (!cgroup_is_dead(cgrp))
1374	return cgrp;
1375
1376	cgroup_kn_unlock(kn);
1377	return NULL;
1378	}
1379
1380	static void cgroup_rm_file(struct cgroup cgrp, const struct cftype cft)
1381	{
1382	char name[CGROUP_FILE_NAME_MAX];
1383
1384	lockdep_assert_held(&cgroup_mutex);
1385
1386	if (cft->file_offset) {
1387	struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1388	struct cgroup_file cfile = (void )css + cft->file_offset;
1389
1390	spin_lock_irq(&cgroup_file_kn_lock);
1391	cfile->kn = NULL;
1392	spin_unlock_irq(&cgroup_file_kn_lock);
1393	}
1394
1395	kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1396	}
1397
1398	/**
1399	* css_clear_dir - remove subsys files in a cgroup directory
1400	* @css: taget css
1401	* @cgrp_override: specify if target cgroup is different from css->cgroup
1402	*/
1403	static void css_clear_dir(struct cgroup_subsys_state *css,
1404	struct cgroup *cgrp_override)
1405	{
1406	struct cgroup *cgrp = cgrp_override ?: css->cgroup;
1407	struct cftype *cfts;
1408
1409	list_for_each_entry(cfts, &css->ss->cfts, node)
1410	cgroup_addrm_files(css, cgrp, cfts, false);
1411	}
1412
1413	/**
1414	* css_populate_dir - create subsys files in a cgroup directory
1415	* @css: target css
1416	* @cgrp_overried: specify if target cgroup is different from css->cgroup
1417	*
1418	* On failure, no file is added.
1419	*/
1420	static int css_populate_dir(struct cgroup_subsys_state *css,
1421	struct cgroup *cgrp_override)
1422	{
1423	struct cgroup *cgrp = cgrp_override ?: css->cgroup;
1424	struct cftype cfts, failed_cfts;
1425	int ret;
1426
1427	if (!css->ss) {
1428	if (cgroup_on_dfl(cgrp))
1429	cfts = cgroup_dfl_base_files;
1430	else
1431	cfts = cgroup_legacy_base_files;
1432
1433	return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1434	}
1435
1436	list_for_each_entry(cfts, &css->ss->cfts, node) {
1437	ret = cgroup_addrm_files(css, cgrp, cfts, true);
1438	if (ret < 0) {
1439	failed_cfts = cfts;
1440	goto err;
1441	}
1442	}
1443	return 0;
1444	err:
1445	list_for_each_entry(cfts, &css->ss->cfts, node) {
1446	if (cfts == failed_cfts)
1447	break;
1448	cgroup_addrm_files(css, cgrp, cfts, false);
1449	}
1450	return ret;
1451	}
1452
1453	static int rebind_subsystems(struct cgroup_root *dst_root,
1454	unsigned long ss_mask)
1455	{
1456	struct cgroup *dcgrp = &dst_root->cgrp;
1457	struct cgroup_subsys *ss;
1458	unsigned long tmp_ss_mask;
1459	int ssid, i, ret;
1460
1461	lockdep_assert_held(&cgroup_mutex);
1462
1463	for_each_subsys_which(ss, ssid, &ss_mask) {
1464	/* if @ss has non-root csses attached to it, can't move */
1465	if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)))
1466	return -EBUSY;
1467
1468	/* can't move between two non-dummy roots either */
1469	if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1470	return -EBUSY;
1471	}
1472
1473	/* skip creating root files on dfl_root for inhibited subsystems */
1474	tmp_ss_mask = ss_mask;
1475	if (dst_root == &cgrp_dfl_root)
1476	tmp_ss_mask &= ~cgrp_dfl_root_inhibit_ss_mask;
1477
1478	for_each_subsys_which(ss, ssid, &tmp_ss_mask) {
1479	struct cgroup *scgrp = &ss->root->cgrp;
1480	int tssid;
1481
1482	ret = css_populate_dir(cgroup_css(scgrp, ss), dcgrp);
1483	if (!ret)
1484	continue;
1485
1486	/*
1487	* Rebinding back to the default root is not allowed to
1488	* fail. Using both default and non-default roots should
1489	* be rare. Moving subsystems back and forth even more so.
1490	* Just warn about it and continue.
1491	*/
1492	if (dst_root == &cgrp_dfl_root) {
1493	if (cgrp_dfl_root_visible) {
1494	pr_warn("failed to create files (%d) while rebinding 0x%lx to default root\n",
1495	ret, ss_mask);
1496	pr_warn("you may retry by moving them to a different hierarchy and unbinding\n");
1497	}
1498	continue;
1499	}
1500
1501	for_each_subsys_which(ss, tssid, &tmp_ss_mask) {
1502	if (tssid == ssid)
1503	break;
1504	css_clear_dir(cgroup_css(scgrp, ss), dcgrp);
1505	}
1506	return ret;
1507	}
1508
1509	/*
1510	* Nothing can fail from this point on. Remove files for the
1511	* removed subsystems and rebind each subsystem.
1512	*/
1513	for_each_subsys_which(ss, ssid, &ss_mask) {
1514	struct cgroup_root *src_root = ss->root;
1515	struct cgroup *scgrp = &src_root->cgrp;
1516	struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1517	struct css_set *cset;
1518
1519	WARN_ON(!css \|\| cgroup_css(dcgrp, ss));
1520
1521	css_clear_dir(css, NULL);
1522
1523	RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1524	rcu_assign_pointer(dcgrp->subsys[ssid], css);
1525	ss->root = dst_root;
1526	css->cgroup = dcgrp;
1527
1528	spin_lock_bh(&css_set_lock);
1529	hash_for_each(css_set_table, i, cset, hlist)
1530	list_move_tail(&cset->e_cset_node[ss->id],
1531	&dcgrp->e_csets[ss->id]);
1532	spin_unlock_bh(&css_set_lock);
1533
1534	src_root->subsys_mask &= ~(1 << ssid);
1535	scgrp->subtree_control &= ~(1 << ssid);
1536	cgroup_refresh_child_subsys_mask(scgrp);
1537
1538	/* default hierarchy doesn't enable controllers by default */
1539	dst_root->subsys_mask \|= 1 << ssid;
1540	if (dst_root == &cgrp_dfl_root) {
1541	static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1542	} else {
1543	dcgrp->subtree_control \|= 1 << ssid;
1544	cgroup_refresh_child_subsys_mask(dcgrp);
1545	static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1546	}
1547
1548	if (ss->bind)
1549	ss->bind(css);
1550	}
1551
1552	kernfs_activate(dcgrp->kn);
1553	return 0;
1554	}
1555
1556	static int cgroup_show_options(struct seq_file *seq,
1557	struct kernfs_root *kf_root)
1558	{
1559	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1560	struct cgroup_subsys *ss;
1561	int ssid;
1562
1563	if (root != &cgrp_dfl_root)
1564	for_each_subsys(ss, ssid)
1565	if (root->subsys_mask & (1 << ssid))
1566	seq_show_option(seq, ss->legacy_name, NULL);
1567	if (root->flags & CGRP_ROOT_NOPREFIX)
1568	seq_puts(seq, ",noprefix");
1569	if (root->flags & CGRP_ROOT_XATTR)
1570	seq_puts(seq, ",xattr");
1571
1572	spin_lock(&release_agent_path_lock);
1573	if (strlen(root->release_agent_path))
1574	seq_show_option(seq, "release_agent",
1575	root->release_agent_path);
1576	spin_unlock(&release_agent_path_lock);
1577
1578	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1579	seq_puts(seq, ",clone_children");
1580	if (strlen(root->name))
1581	seq_show_option(seq, "name", root->name);
1582	return 0;
1583	}
1584
1585	struct cgroup_sb_opts {
1586	unsigned long subsys_mask;
1587	unsigned int flags;
1588	char *release_agent;
1589	bool cpuset_clone_children;
1590	char *name;
1591	/* User explicitly requested empty subsystem */
1592	bool none;
1593	};
1594
1595	static int parse_cgroupfs_options(char data, struct cgroup_sb_opts opts)
1596	{
1597	char token, o = data;
1598	bool all_ss = false, one_ss = false;
1599	unsigned long mask = -1UL;
1600	struct cgroup_subsys *ss;
1601	int nr_opts = 0;
1602	int i;
1603
1604	#ifdef CONFIG_CPUSETS
1605	mask = ~(1U << cpuset_cgrp_id);
1606	#endif
1607
1608	memset(opts, 0, sizeof(*opts));
1609
1610	while ((token = strsep(&o, ",")) != NULL) {
1611	nr_opts++;
1612
1613	if (!*token)
1614	return -EINVAL;
1615	if (!strcmp(token, "none")) {
1616	/* Explicitly have no subsystems */
1617	opts->none = true;
1618	continue;
1619	}
1620	if (!strcmp(token, "all")) {
1621	/* Mutually exclusive option 'all' + subsystem name */
1622	if (one_ss)
1623	return -EINVAL;
1624	all_ss = true;
1625	continue;
1626	}
1627	if (!strcmp(token, "noprefix")) {
1628	opts->flags \|= CGRP_ROOT_NOPREFIX;
1629	continue;
1630	}
1631	if (!strcmp(token, "clone_children")) {
1632	opts->cpuset_clone_children = true;
1633	continue;
1634	}
1635	if (!strcmp(token, "xattr")) {
1636	opts->flags \|= CGRP_ROOT_XATTR;
1637	continue;
1638	}
1639	if (!strncmp(token, "release_agent=", 14)) {
1640	/* Specifying two release agents is forbidden */
1641	if (opts->release_agent)
1642	return -EINVAL;
1643	opts->release_agent =
1644	kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1645	if (!opts->release_agent)
1646	return -ENOMEM;
1647	continue;
1648	}
1649	if (!strncmp(token, "name=", 5)) {
1650	const char *name = token + 5;
1651	/* Can't specify an empty name */
1652	if (!strlen(name))
1653	return -EINVAL;
1654	/* Must match [\w.-]+ */
1655	for (i = 0; i < strlen(name); i++) {
1656	char c = name[i];
1657	if (isalnum(c))
1658	continue;
1659	if ((c == '.') \|\| (c == '-') \|\| (c == '_'))
1660	continue;
1661	return -EINVAL;
1662	}
1663	/* Specifying two names is forbidden */
1664	if (opts->name)
1665	return -EINVAL;
1666	opts->name = kstrndup(name,
1667	MAX_CGROUP_ROOT_NAMELEN - 1,
1668	GFP_KERNEL);
1669	if (!opts->name)
1670	return -ENOMEM;
1671
1672	continue;
1673	}
1674
1675	for_each_subsys(ss, i) {
1676	if (strcmp(token, ss->legacy_name))
1677	continue;
1678	if (!cgroup_ssid_enabled(i))
1679	continue;
1680
1681	/* Mutually exclusive option 'all' + subsystem name */
1682	if (all_ss)
1683	return -EINVAL;
1684	opts->subsys_mask \|= (1 << i);
1685	one_ss = true;
1686
1687	break;
1688	}
1689	if (i == CGROUP_SUBSYS_COUNT)
1690	return -ENOENT;
1691	}
1692
1693	/*
1694	* If the 'all' option was specified select all the subsystems,
1695	* otherwise if 'none', 'name=' and a subsystem name options were
1696	* not specified, let's default to 'all'
1697	*/
1698	if (all_ss \|\| (!one_ss && !opts->none && !opts->name))
1699	for_each_subsys(ss, i)
1700	if (cgroup_ssid_enabled(i))
1701	opts->subsys_mask \|= (1 << i);
1702
1703	/*
1704	* We either have to specify by name or by subsystems. (So all
1705	* empty hierarchies must have a name).
1706	*/
1707	if (!opts->subsys_mask && !opts->name)
1708	return -EINVAL;
1709
1710	/*
1711	* Option noprefix was introduced just for backward compatibility
1712	* with the old cpuset, so we allow noprefix only if mounting just
1713	* the cpuset subsystem.
1714	*/
1715	if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1716	return -EINVAL;
1717
1718	/* Can't specify "none" and some subsystems */
1719	if (opts->subsys_mask && opts->none)
1720	return -EINVAL;
1721
1722	return 0;
1723	}
1724
1725	static int cgroup_remount(struct kernfs_root kf_root, int flags, char *data)
1726	{
1727	int ret = 0;
1728	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1729	struct cgroup_sb_opts opts;
1730	unsigned long added_mask, removed_mask;
1731
1732	if (root == &cgrp_dfl_root) {
1733	pr_err("remount is not allowed\n");
1734	return -EINVAL;
1735	}
1736
1737	mutex_lock(&cgroup_mutex);
1738
1739	/* See what subsystems are wanted */
1740	ret = parse_cgroupfs_options(data, &opts);
1741	if (ret)
1742	goto out_unlock;
1743
1744	if (opts.subsys_mask != root->subsys_mask \|\| opts.release_agent)
1745	pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
1746	task_tgid_nr(current), current->comm);
1747
1748	added_mask = opts.subsys_mask & ~root->subsys_mask;
1749	removed_mask = root->subsys_mask & ~opts.subsys_mask;
1750
1751	/* Don't allow flags or name to change at remount */
1752	if ((opts.flags ^ root->flags) \|\|
1753	(opts.name && strcmp(opts.name, root->name))) {
1754	pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
1755	opts.flags, opts.name ?: "", root->flags, root->name);
1756	ret = -EINVAL;
1757	goto out_unlock;
1758	}
1759
1760	/* remounting is not allowed for populated hierarchies */
1761	if (!list_empty(&root->cgrp.self.children)) {
1762	ret = -EBUSY;
1763	goto out_unlock;
1764	}
1765
1766	ret = rebind_subsystems(root, added_mask);
1767	if (ret)
1768	goto out_unlock;
1769
1770	rebind_subsystems(&cgrp_dfl_root, removed_mask);
1771
1772	if (opts.release_agent) {
1773	spin_lock(&release_agent_path_lock);
1774	strcpy(root->release_agent_path, opts.release_agent);
1775	spin_unlock(&release_agent_path_lock);
1776	}
1777	out_unlock:
1778	kfree(opts.release_agent);
1779	kfree(opts.name);
1780	mutex_unlock(&cgroup_mutex);
1781	return ret;
1782	}
1783
1784	/*
1785	* To reduce the fork() overhead for systems that are not actually using
1786	* their cgroups capability, we don't maintain the lists running through
1787	* each css_set to its tasks until we see the list actually used - in other
1788	* words after the first mount.
1789	*/
1790	static bool use_task_css_set_links __read_mostly;
1791
1792	static void cgroup_enable_task_cg_lists(void)
1793	{
1794	struct task_struct p, g;
1795
1796	spin_lock_bh(&css_set_lock);
1797
1798	if (use_task_css_set_links)
1799	goto out_unlock;
1800
1801	use_task_css_set_links = true;
1802
1803	/*
1804	* We need tasklist_lock because RCU is not safe against
1805	* while_each_thread(). Besides, a forking task that has passed
1806	* cgroup_post_fork() without seeing use_task_css_set_links = 1
1807	* is not guaranteed to have its child immediately visible in the
1808	* tasklist if we walk through it with RCU.
1809	*/
1810	read_lock(&tasklist_lock);
1811	do_each_thread(g, p) {
1812	WARN_ON_ONCE(!list_empty(&p->cg_list) \|\|
1813	task_css_set(p) != &init_css_set);
1814
1815	/*
1816	* We should check if the process is exiting, otherwise
1817	* it will race with cgroup_exit() in that the list
1818	* entry won't be deleted though the process has exited.
1819	* Do it while holding siglock so that we don't end up
1820	* racing against cgroup_exit().
1821	*/
1822	spin_lock_irq(&p->sighand->siglock);
1823	if (!(p->flags & PF_EXITING)) {
1824	struct css_set *cset = task_css_set(p);
1825
1826	if (!css_set_populated(cset))
1827	css_set_update_populated(cset, true);
1828	list_add_tail(&p->cg_list, &cset->tasks);
1829	get_css_set(cset);
1830	}
1831	spin_unlock_irq(&p->sighand->siglock);
1832	} while_each_thread(g, p);
1833	read_unlock(&tasklist_lock);
1834	out_unlock:
1835	spin_unlock_bh(&css_set_lock);
1836	}
1837
1838	static void init_cgroup_housekeeping(struct cgroup *cgrp)
1839	{
1840	struct cgroup_subsys *ss;
1841	int ssid;
1842
1843	INIT_LIST_HEAD(&cgrp->self.sibling);
1844	INIT_LIST_HEAD(&cgrp->self.children);
1845	INIT_LIST_HEAD(&cgrp->cset_links);
1846	INIT_LIST_HEAD(&cgrp->pidlists);
1847	mutex_init(&cgrp->pidlist_mutex);
1848	cgrp->self.cgroup = cgrp;
1849	cgrp->self.flags \|= CSS_ONLINE;
1850
1851	for_each_subsys(ss, ssid)
1852	INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1853
1854	init_waitqueue_head(&cgrp->offline_waitq);
1855	INIT_WORK(&cgrp->release_agent_work, cgroup_release_agent);
1856	}
1857
1858	static void init_cgroup_root(struct cgroup_root *root,
1859	struct cgroup_sb_opts *opts)
1860	{
1861	struct cgroup *cgrp = &root->cgrp;
1862
1863	INIT_LIST_HEAD(&root->root_list);
1864	atomic_set(&root->nr_cgrps, 1);
1865	cgrp->root = root;
1866	init_cgroup_housekeeping(cgrp);
1867	idr_init(&root->cgroup_idr);
1868
1869	root->flags = opts->flags;
1870	if (opts->release_agent)
1871	strcpy(root->release_agent_path, opts->release_agent);
1872	if (opts->name)
1873	strcpy(root->name, opts->name);
1874	if (opts->cpuset_clone_children)
1875	set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1876	}
1877
1878	static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
1879	{
1880	LIST_HEAD(tmp_links);
1881	struct cgroup *root_cgrp = &root->cgrp;
1882	struct css_set *cset;
1883	int i, ret;
1884
1885	lockdep_assert_held(&cgroup_mutex);
1886
1887	ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
1888	if (ret < 0)
1889	goto out;
1890	root_cgrp->id = ret;
1891	root_cgrp->ancestor_ids[0] = ret;
1892
1893	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
1894	GFP_KERNEL);
1895	if (ret)
1896	goto out;
1897
1898	/*
1899	* We're accessing css_set_count without locking css_set_lock here,
1900	* but that's OK - it can only be increased by someone holding
1901	* cgroup_lock, and that's us. The worst that can happen is that we
1902	* have some link structures left over
1903	*/
1904	ret = allocate_cgrp_cset_links(css_set_count, &tmp_links);
1905	if (ret)
1906	goto cancel_ref;
1907
1908	ret = cgroup_init_root_id(root);
1909	if (ret)
1910	goto cancel_ref;
1911
1912	root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
1913	KERNFS_ROOT_CREATE_DEACTIVATED,
1914	root_cgrp);
1915	if (IS_ERR(root->kf_root)) {
1916	ret = PTR_ERR(root->kf_root);
1917	goto exit_root_id;
1918	}
1919	root_cgrp->kn = root->kf_root->kn;
1920
1921	ret = css_populate_dir(&root_cgrp->self, NULL);
1922	if (ret)
1923	goto destroy_root;
1924
1925	ret = rebind_subsystems(root, ss_mask);
1926	if (ret)
1927	goto destroy_root;
1928
1929	/*
1930	* There must be no failure case after here, since rebinding takes
1931	* care of subsystems' refcounts, which are explicitly dropped in
1932	* the failure exit path.
1933	*/
1934	list_add(&root->root_list, &cgroup_roots);
1935	cgroup_root_count++;
1936
1937	/*
1938	* Link the root cgroup in this hierarchy into all the css_set
1939	* objects.
1940	*/
1941	spin_lock_bh(&css_set_lock);
1942	hash_for_each(css_set_table, i, cset, hlist) {
1943	link_css_set(&tmp_links, cset, root_cgrp);
1944	if (css_set_populated(cset))
1945	cgroup_update_populated(root_cgrp, true);
1946	}
1947	spin_unlock_bh(&css_set_lock);
1948
1949	BUG_ON(!list_empty(&root_cgrp->self.children));
1950	BUG_ON(atomic_read(&root->nr_cgrps) != 1);
1951
1952	kernfs_activate(root_cgrp->kn);
1953	ret = 0;
1954	goto out;
1955
1956	destroy_root:
1957	kernfs_destroy_root(root->kf_root);
1958	root->kf_root = NULL;
1959	exit_root_id:
1960	cgroup_exit_root_id(root);
1961	cancel_ref:
1962	percpu_ref_exit(&root_cgrp->self.refcnt);
1963	out:
1964	free_cgrp_cset_links(&tmp_links);
1965	return ret;
1966	}
1967
1968	static struct dentry cgroup_mount(struct file_system_type fs_type,
1969	int flags, const char *unused_dev_name,
1970	void *data)
1971	{
1972	bool is_v2 = fs_type == &cgroup2_fs_type;
1973	struct super_block *pinned_sb = NULL;
1974	struct cgroup_subsys *ss;
1975	struct cgroup_root *root;
1976	struct cgroup_sb_opts opts;
1977	struct dentry *dentry;
1978	int ret;
1979	int i;
1980	bool new_sb;
1981
1982	/*
1983	* The first time anyone tries to mount a cgroup, enable the list
1984	* linking each css_set to its tasks and fix up all existing tasks.
1985	*/
1986	if (!use_task_css_set_links)
1987	cgroup_enable_task_cg_lists();
1988
1989	if (is_v2) {
1990	if (data) {
1991	pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
1992	return ERR_PTR(-EINVAL);
1993	}
1994	cgrp_dfl_root_visible = true;
1995	root = &cgrp_dfl_root;
1996	cgroup_get(&root->cgrp);
1997	goto out_mount;
1998	}
1999
2000	mutex_lock(&cgroup_mutex);
2001
2002	/* First find the desired set of subsystems */
2003	ret = parse_cgroupfs_options(data, &opts);
2004	if (ret)
2005	goto out_unlock;
2006
2007	/*
2008	* Destruction of cgroup root is asynchronous, so subsystems may
2009	* still be dying after the previous unmount. Let's drain the
2010	* dying subsystems. We just need to ensure that the ones
2011	* unmounted previously finish dying and don't care about new ones
2012	* starting. Testing ref liveliness is good enough.
2013	*/
2014	for_each_subsys(ss, i) {
2015	if (!(opts.subsys_mask & (1 << i)) \|\|
2016	ss->root == &cgrp_dfl_root)
2017	continue;
2018
2019	if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
2020	mutex_unlock(&cgroup_mutex);
2021	msleep(10);
2022	ret = restart_syscall();
2023	goto out_free;
2024	}
2025	cgroup_put(&ss->root->cgrp);
2026	}
2027
2028	for_each_root(root) {
2029	bool name_match = false;
2030
2031	if (root == &cgrp_dfl_root)
2032	continue;
2033
2034	/*
2035	* If we asked for a name then it must match. Also, if
2036	* name matches but sybsys_mask doesn't, we should fail.
2037	* Remember whether name matched.
2038	*/
2039	if (opts.name) {
2040	if (strcmp(opts.name, root->name))
2041	continue;
2042	name_match = true;
2043	}
2044
2045	/*
2046	* If we asked for subsystems (or explicitly for no
2047	* subsystems) then they must match.
2048	*/
2049	if ((opts.subsys_mask \|\| opts.none) &&
2050	(opts.subsys_mask != root->subsys_mask)) {
2051	if (!name_match)
2052	continue;
2053	ret = -EBUSY;
2054	goto out_unlock;
2055	}
2056
2057	if (root->flags ^ opts.flags)
2058	pr_warn("new mount options do not match the existing superblock, will be ignored\n");
2059
2060	/*
2061	* We want to reuse @root whose lifetime is governed by its
2062	* ->cgrp. Let's check whether @root is alive and keep it
2063	* that way. As cgroup_kill_sb() can happen anytime, we
2064	* want to block it by pinning the sb so that @root doesn't
2065	* get killed before mount is complete.
2066	*
2067	* With the sb pinned, tryget_live can reliably indicate
2068	* whether @root can be reused. If it's being killed,
2069	* drain it. We can use wait_queue for the wait but this
2070	* path is super cold. Let's just sleep a bit and retry.
2071	*/
2072	pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
2073	if (IS_ERR(pinned_sb) \|\|
2074	!percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
2075	mutex_unlock(&cgroup_mutex);
2076	if (!IS_ERR_OR_NULL(pinned_sb))
2077	deactivate_super(pinned_sb);
2078	msleep(10);
2079	ret = restart_syscall();
2080	goto out_free;
2081	}
2082
2083	ret = 0;
2084	goto out_unlock;
2085	}
2086
2087	/*
2088	* No such thing, create a new one. name= matching without subsys
2089	* specification is allowed for already existing hierarchies but we
2090	* can't create new one without subsys specification.
2091	*/
2092	if (!opts.subsys_mask && !opts.none) {
2093	ret = -EINVAL;
2094	goto out_unlock;
2095	}
2096
2097	root = kzalloc(sizeof(*root), GFP_KERNEL);
2098	if (!root) {
2099	ret = -ENOMEM;
2100	goto out_unlock;
2101	}
2102
2103	init_cgroup_root(root, &opts);
2104
2105	ret = cgroup_setup_root(root, opts.subsys_mask);
2106	if (ret)
2107	cgroup_free_root(root);
2108
2109	out_unlock:
2110	mutex_unlock(&cgroup_mutex);
2111	out_free:
2112	kfree(opts.release_agent);
2113	kfree(opts.name);
2114
2115	if (ret)
2116	return ERR_PTR(ret);
2117	out_mount:
2118	dentry = kernfs_mount(fs_type, flags, root->kf_root,
2119	is_v2 ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC,
2120	&new_sb);
2121	if (IS_ERR(dentry) \|\| !new_sb)
2122	cgroup_put(&root->cgrp);
2123
2124	/*
2125	* If @pinned_sb, we're reusing an existing root and holding an
2126	* extra ref on its sb. Mount is complete. Put the extra ref.
2127	*/
2128	if (pinned_sb) {
2129	WARN_ON(new_sb);
2130	deactivate_super(pinned_sb);
2131	}
2132
2133	return dentry;
2134	}
2135
2136	static void cgroup_kill_sb(struct super_block *sb)
2137	{
2138	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2139	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2140
2141	/*
2142	* If @root doesn't have any mounts or children, start killing it.
2143	* This prevents new mounts by disabling percpu_ref_tryget_live().
2144	* cgroup_mount() may wait for @root's release.
2145	*
2146	* And don't kill the default root.
2147	*/
2148	if (!list_empty(&root->cgrp.self.children) \|\|
2149	root == &cgrp_dfl_root)
2150	cgroup_put(&root->cgrp);
2151	else
2152	percpu_ref_kill(&root->cgrp.self.refcnt);
2153
2154	kernfs_kill_sb(sb);
2155	}
2156
2157	static struct file_system_type cgroup_fs_type = {
2158	.name = "cgroup",
2159	.mount = cgroup_mount,
2160	.kill_sb = cgroup_kill_sb,
2161	};
2162
2163	static struct file_system_type cgroup2_fs_type = {
2164	.name = "cgroup2",
2165	.mount = cgroup_mount,
2166	.kill_sb = cgroup_kill_sb,
2167	};
2168
2169	/**
2170	* task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2171	* @task: target task
2172	* @buf: the buffer to write the path into
2173	* @buflen: the length of the buffer
2174	*
2175	* Determine @task's cgroup on the first (the one with the lowest non-zero
2176	* hierarchy_id) cgroup hierarchy and copy its path into @buf. This
2177	* function grabs cgroup_mutex and shouldn't be used inside locks used by
2178	* cgroup controller callbacks.
2179	*
2180	* Return value is the same as kernfs_path().
2181	*/
2182	char task_cgroup_path(struct task_struct task, char *buf, size_t buflen)
2183	{
2184	struct cgroup_root *root;
2185	struct cgroup *cgrp;
2186	int hierarchy_id = 1;
2187	char *path = NULL;
2188
2189	mutex_lock(&cgroup_mutex);
2190	spin_lock_bh(&css_set_lock);
2191
2192	root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2193
2194	if (root) {
2195	cgrp = task_cgroup_from_root(task, root);
2196	path = cgroup_path(cgrp, buf, buflen);
2197	} else {
2198	/* if no hierarchy exists, everyone is in "/" */
2199	if (strlcpy(buf, "/", buflen) < buflen)
2200	path = buf;
2201	}
2202
2203	spin_unlock_bh(&css_set_lock);
2204	mutex_unlock(&cgroup_mutex);
2205	return path;
2206	}
2207	EXPORT_SYMBOL_GPL(task_cgroup_path);
2208
2209	/* used to track tasks and other necessary states during migration */
2210	struct cgroup_taskset {
2211	/* the src and dst cset list running through cset->mg_node */
2212	struct list_head src_csets;
2213	struct list_head dst_csets;
2214
2215	/* the subsys currently being processed */
2216	int ssid;
2217
2218	/*
2219	* Fields for cgroup_taskset_*() iteration.
2220	*
2221	* Before migration is committed, the target migration tasks are on
2222	* ->mg_tasks of the csets on ->src_csets. After, on ->mg_tasks of
2223	* the csets on ->dst_csets. ->csets point to either ->src_csets
2224	* or ->dst_csets depending on whether migration is committed.
2225	*
2226	* ->cur_csets and ->cur_task point to the current task position
2227	* during iteration.
2228	*/
2229	struct list_head *csets;
2230	struct css_set *cur_cset;
2231	struct task_struct *cur_task;
2232	};
2233
2234	#define CGROUP_TASKSET_INIT(tset) (struct cgroup_taskset){ \
2235	.src_csets = LIST_HEAD_INIT(tset.src_csets), \
2236	.dst_csets = LIST_HEAD_INIT(tset.dst_csets), \
2237	.csets = &tset.src_csets, \
2238	}
2239
2240	/**
2241	* cgroup_taskset_add - try to add a migration target task to a taskset
2242	* @task: target task
2243	* @tset: target taskset
2244	*
2245	* Add @task, which is a migration target, to @tset. This function becomes
2246	* noop if @task doesn't need to be migrated. @task's css_set should have
2247	* been added as a migration source and @task->cg_list will be moved from
2248	* the css_set's tasks list to mg_tasks one.
2249	*/
2250	static void cgroup_taskset_add(struct task_struct *task,
2251	struct cgroup_taskset *tset)
2252	{
2253	struct css_set *cset;
2254
2255	lockdep_assert_held(&css_set_lock);
2256
2257	/* @task either already exited or can't exit until the end */
2258	if (task->flags & PF_EXITING)
2259	return;
2260
2261	/* leave @task alone if post_fork() hasn't linked it yet */
2262	if (list_empty(&task->cg_list))
2263	return;
2264
2265	cset = task_css_set(task);
2266	if (!cset->mg_src_cgrp)
2267	return;
2268
2269	list_move_tail(&task->cg_list, &cset->mg_tasks);
2270	if (list_empty(&cset->mg_node))
2271	list_add_tail(&cset->mg_node, &tset->src_csets);
2272	if (list_empty(&cset->mg_dst_cset->mg_node))
2273	list_move_tail(&cset->mg_dst_cset->mg_node,
2274	&tset->dst_csets);
2275	}
2276
2277	/**
2278	* cgroup_taskset_first - reset taskset and return the first task
2279	* @tset: taskset of interest
2280	* @dst_cssp: output variable for the destination css
2281	*
2282	* @tset iteration is initialized and the first task is returned.
2283	*/
2284	struct task_struct cgroup_taskset_first(struct cgroup_taskset tset,
2285	struct cgroup_subsys_state **dst_cssp)
2286	{
2287	tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2288	tset->cur_task = NULL;
2289
2290	return cgroup_taskset_next(tset, dst_cssp);
2291	}
2292
2293	/**
2294	* cgroup_taskset_next - iterate to the next task in taskset
2295	* @tset: taskset of interest
2296	* @dst_cssp: output variable for the destination css
2297	*
2298	* Return the next task in @tset. Iteration must have been initialized
2299	* with cgroup_taskset_first().
2300	*/
2301	struct task_struct cgroup_taskset_next(struct cgroup_taskset tset,
2302	struct cgroup_subsys_state **dst_cssp)
2303	{
2304	struct css_set *cset = tset->cur_cset;
2305	struct task_struct *task = tset->cur_task;
2306
2307	while (&cset->mg_node != tset->csets) {
2308	if (!task)
2309	task = list_first_entry(&cset->mg_tasks,
2310	struct task_struct, cg_list);
2311	else
2312	task = list_next_entry(task, cg_list);
2313
2314	if (&task->cg_list != &cset->mg_tasks) {
2315	tset->cur_cset = cset;
2316	tset->cur_task = task;
2317
2318	/*
2319	* This function may be called both before and
2320	* after cgroup_taskset_migrate(). The two cases
2321	* can be distinguished by looking at whether @cset
2322	* has its ->mg_dst_cset set.
2323	*/
2324	if (cset->mg_dst_cset)
2325	*dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2326	else
2327	*dst_cssp = cset->subsys[tset->ssid];
2328
2329	return task;
2330	}
2331
2332	cset = list_next_entry(cset, mg_node);
2333	task = NULL;
2334	}
2335
2336	return NULL;
2337	}
2338
2339	/**
2340	* cgroup_taskset_migrate - migrate a taskset to a cgroup
2341	* @tset: taget taskset
2342	* @dst_cgrp: destination cgroup
2343	*
2344	* Migrate tasks in @tset to @dst_cgrp. This function fails iff one of the
2345	* ->can_attach callbacks fails and guarantees that either all or none of
2346	* the tasks in @tset are migrated. @tset is consumed regardless of
2347	* success.
2348	*/
2349	static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
2350	struct cgroup *dst_cgrp)
2351	{
2352	struct cgroup_subsys_state css, failed_css = NULL;
2353	struct task_struct task, tmp_task;
2354	struct css_set cset, tmp_cset;
2355	int i, ret;
2356
2357	/* methods shouldn't be called if no task is actually migrating */
2358	if (list_empty(&tset->src_csets))
2359	return 0;
2360
2361	/* check that we can legitimately attach to the cgroup */
2362	for_each_e_css(css, i, dst_cgrp) {
2363	if (css->ss->can_attach) {
2364	tset->ssid = i;
2365	ret = css->ss->can_attach(tset);
2366	if (ret) {
2367	failed_css = css;
2368	goto out_cancel_attach;
2369	}
2370	}
2371	}
2372
2373	/*
2374	* Now that we're guaranteed success, proceed to move all tasks to
2375	* the new cgroup. There are no failure cases after here, so this
2376	* is the commit point.
2377	*/
2378	spin_lock_bh(&css_set_lock);
2379	list_for_each_entry(cset, &tset->src_csets, mg_node) {
2380	list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2381	struct css_set *from_cset = task_css_set(task);
2382	struct css_set *to_cset = cset->mg_dst_cset;
2383
2384	get_css_set(to_cset);
2385	css_set_move_task(task, from_cset, to_cset, true);
2386	put_css_set_locked(from_cset);
2387	}
2388	}
2389	spin_unlock_bh(&css_set_lock);
2390
2391	/*
2392	* Migration is committed, all target tasks are now on dst_csets.
2393	* Nothing is sensitive to fork() after this point. Notify
2394	* controllers that migration is complete.
2395	*/
2396	tset->csets = &tset->dst_csets;
2397
2398	for_each_e_css(css, i, dst_cgrp) {
2399	if (css->ss->attach) {
2400	tset->ssid = i;
2401	css->ss->attach(tset);
2402	}
2403	}
2404
2405	ret = 0;
2406	goto out_release_tset;
2407
2408	out_cancel_attach:
2409	for_each_e_css(css, i, dst_cgrp) {
2410	if (css == failed_css)
2411	break;
2412	if (css->ss->cancel_attach) {
2413	tset->ssid = i;
2414	css->ss->cancel_attach(tset);
2415	}
2416	}
2417	out_release_tset:
2418	spin_lock_bh(&css_set_lock);
2419	list_splice_init(&tset->dst_csets, &tset->src_csets);
2420	list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2421	list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2422	list_del_init(&cset->mg_node);
2423	}
2424	spin_unlock_bh(&css_set_lock);
2425	return ret;
2426	}
2427
2428	/**
2429	* cgroup_migrate_finish - cleanup after attach
2430	* @preloaded_csets: list of preloaded css_sets
2431	*
2432	* Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst(). See
2433	* those functions for details.
2434	*/
2435	static void cgroup_migrate_finish(struct list_head *preloaded_csets)
2436	{
2437	struct css_set cset, tmp_cset;
2438
2439	lockdep_assert_held(&cgroup_mutex);
2440
2441	spin_lock_bh(&css_set_lock);
2442	list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
2443	cset->mg_src_cgrp = NULL;
2444	cset->mg_dst_cset = NULL;
2445	list_del_init(&cset->mg_preload_node);
2446	put_css_set_locked(cset);
2447	}
2448	spin_unlock_bh(&css_set_lock);
2449	}
2450
2451	/**
2452	* cgroup_migrate_add_src - add a migration source css_set
2453	* @src_cset: the source css_set to add
2454	* @dst_cgrp: the destination cgroup
2455	* @preloaded_csets: list of preloaded css_sets
2456	*
2457	* Tasks belonging to @src_cset are about to be migrated to @dst_cgrp. Pin
2458	* @src_cset and add it to @preloaded_csets, which should later be cleaned
2459	* up by cgroup_migrate_finish().
2460	*
2461	* This function may be called without holding cgroup_threadgroup_rwsem
2462	* even if the target is a process. Threads may be created and destroyed
2463	* but as long as cgroup_mutex is not dropped, no new css_set can be put
2464	* into play and the preloaded css_sets are guaranteed to cover all
2465	* migrations.
2466	*/
2467	static void cgroup_migrate_add_src(struct css_set *src_cset,
2468	struct cgroup *dst_cgrp,
2469	struct list_head *preloaded_csets)
2470	{
2471	struct cgroup *src_cgrp;
2472
2473	lockdep_assert_held(&cgroup_mutex);
2474	lockdep_assert_held(&css_set_lock);
2475
2476	src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2477
2478	if (!list_empty(&src_cset->mg_preload_node))
2479	return;
2480
2481	WARN_ON(src_cset->mg_src_cgrp);
2482	WARN_ON(!list_empty(&src_cset->mg_tasks));
2483	WARN_ON(!list_empty(&src_cset->mg_node));
2484
2485	src_cset->mg_src_cgrp = src_cgrp;
2486	get_css_set(src_cset);
2487	list_add(&src_cset->mg_preload_node, preloaded_csets);
2488	}
2489
2490	/**
2491	* cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2492	* @dst_cgrp: the destination cgroup (may be %NULL)
2493	* @preloaded_csets: list of preloaded source css_sets
2494	*
2495	* Tasks are about to be moved to @dst_cgrp and all the source css_sets
2496	* have been preloaded to @preloaded_csets. This function looks up and
2497	* pins all destination css_sets, links each to its source, and append them
2498	* to @preloaded_csets. If @dst_cgrp is %NULL, the destination of each
2499	* source css_set is assumed to be its cgroup on the default hierarchy.
2500	*
2501	* This function must be called after cgroup_migrate_add_src() has been
2502	* called on each migration source css_set. After migration is performed
2503	* using cgroup_migrate(), cgroup_migrate_finish() must be called on
2504	* @preloaded_csets.
2505	*/
2506	static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
2507	struct list_head *preloaded_csets)
2508	{
2509	LIST_HEAD(csets);
2510	struct css_set src_cset, tmp_cset;
2511
2512	lockdep_assert_held(&cgroup_mutex);
2513
2514	/*
2515	* Except for the root, child_subsys_mask must be zero for a cgroup
2516	* with tasks so that child cgroups don't compete against tasks.
2517	*/
2518	if (dst_cgrp && cgroup_on_dfl(dst_cgrp) && cgroup_parent(dst_cgrp) &&
2519	dst_cgrp->child_subsys_mask)
2520	return -EBUSY;
2521
2522	/* look up the dst cset for each src cset and link it to src */
2523	list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
2524	struct css_set *dst_cset;
2525
2526	dst_cset = find_css_set(src_cset,
2527	dst_cgrp ?: src_cset->dfl_cgrp);
2528	if (!dst_cset)
2529	goto err;
2530
2531	WARN_ON_ONCE(src_cset->mg_dst_cset \|\| dst_cset->mg_dst_cset);
2532
2533	/*
2534	* If src cset equals dst, it's noop. Drop the src.
2535	* cgroup_migrate() will skip the cset too. Note that we
2536	* can't handle src == dst as some nodes are used by both.
2537	*/
2538	if (src_cset == dst_cset) {
2539	src_cset->mg_src_cgrp = NULL;
2540	list_del_init(&src_cset->mg_preload_node);
2541	put_css_set(src_cset);
2542	put_css_set(dst_cset);
2543	continue;
2544	}
2545
2546	src_cset->mg_dst_cset = dst_cset;
2547
2548	if (list_empty(&dst_cset->mg_preload_node))
2549	list_add(&dst_cset->mg_preload_node, &csets);
2550	else
2551	put_css_set(dst_cset);
2552	}
2553
2554	list_splice_tail(&csets, preloaded_csets);
2555	return 0;
2556	err:
2557	cgroup_migrate_finish(&csets);
2558	return -ENOMEM;
2559	}
2560
2561	/**
2562	* cgroup_migrate - migrate a process or task to a cgroup
2563	* @leader: the leader of the process or the task to migrate
2564	* @threadgroup: whether @leader points to the whole process or a single task
2565	* @cgrp: the destination cgroup
2566	*
2567	* Migrate a process or task denoted by @leader to @cgrp. If migrating a
2568	* process, the caller must be holding cgroup_threadgroup_rwsem. The
2569	* caller is also responsible for invoking cgroup_migrate_add_src() and
2570	* cgroup_migrate_prepare_dst() on the targets before invoking this
2571	* function and following up with cgroup_migrate_finish().
2572	*
2573	* As long as a controller's ->can_attach() doesn't fail, this function is
2574	* guaranteed to succeed. This means that, excluding ->can_attach()
2575	* failure, when migrating multiple targets, the success or failure can be
2576	* decided for all targets by invoking group_migrate_prepare_dst() before
2577	* actually starting migrating.
2578	*/
2579	static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2580	struct cgroup *cgrp)
2581	{
2582	struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
2583	struct task_struct *task;
2584
2585	/*
2586	* Prevent freeing of tasks while we take a snapshot. Tasks that are
2587	* already PF_EXITING could be freed from underneath us unless we
2588	* take an rcu_read_lock.
2589	*/
2590	spin_lock_bh(&css_set_lock);
2591	rcu_read_lock();
2592	task = leader;
2593	do {
2594	cgroup_taskset_add(task, &tset);
2595	if (!threadgroup)
2596	break;
2597	} while_each_thread(leader, task);
2598	rcu_read_unlock();
2599	spin_unlock_bh(&css_set_lock);
2600
2601	return cgroup_taskset_migrate(&tset, cgrp);
2602	}
2603
2604	/**
2605	* cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2606	* @dst_cgrp: the cgroup to attach to
2607	* @leader: the task or the leader of the threadgroup to be attached
2608	* @threadgroup: attach the whole threadgroup?
2609	*
2610	* Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2611	*/
2612	static int cgroup_attach_task(struct cgroup *dst_cgrp,
2613	struct task_struct *leader, bool threadgroup)
2614	{
2615	LIST_HEAD(preloaded_csets);
2616	struct task_struct *task;
2617	int ret;
2618
2619	/* look up all src csets */
2620	spin_lock_bh(&css_set_lock);
2621	rcu_read_lock();
2622	task = leader;
2623	do {
2624	cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
2625	&preloaded_csets);
2626	if (!threadgroup)
2627	break;
2628	} while_each_thread(leader, task);
2629	rcu_read_unlock();
2630	spin_unlock_bh(&css_set_lock);
2631
2632	/* prepare dst csets and commit */
2633	ret = cgroup_migrate_prepare_dst(dst_cgrp, &preloaded_csets);
2634	if (!ret)
2635	ret = cgroup_migrate(leader, threadgroup, dst_cgrp);
2636
2637	cgroup_migrate_finish(&preloaded_csets);
2638	return ret;
2639	}
2640
2641	static int cgroup_procs_write_permission(struct task_struct *task,
2642	struct cgroup *dst_cgrp,
2643	struct kernfs_open_file *of)
2644	{
2645	const struct cred *cred = current_cred();
2646	const struct cred *tcred = get_task_cred(task);
2647	int ret = 0;
2648
2649	/*
2650	* even if we're attaching all tasks in the thread group, we only
2651	* need to check permissions on one of them.
2652	*/
2653	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2654	!uid_eq(cred->euid, tcred->uid) &&
2655	!uid_eq(cred->euid, tcred->suid))
2656	ret = -EACCES;
2657
2658	if (!ret && cgroup_on_dfl(dst_cgrp)) {
2659	struct super_block *sb = of->file->f_path.dentry->d_sb;
2660	struct cgroup *cgrp;
2661	struct inode *inode;
2662
2663	spin_lock_bh(&css_set_lock);
2664	cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
2665	spin_unlock_bh(&css_set_lock);
2666
2667	while (!cgroup_is_descendant(dst_cgrp, cgrp))
2668	cgrp = cgroup_parent(cgrp);
2669
2670	ret = -ENOMEM;
2671	inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
2672	if (inode) {
2673	ret = inode_permission(inode, MAY_WRITE);
2674	iput(inode);
2675	}
2676	}
2677
2678	put_cred(tcred);
2679	return ret;
2680	}
2681
2682	/*
2683	* Find the task_struct of the task to attach by vpid and pass it along to the
2684	* function to attach either it or all tasks in its threadgroup. Will lock
2685	* cgroup_mutex and threadgroup.
2686	*/
2687	static ssize_t __cgroup_procs_write(struct kernfs_open_file of, char buf,
2688	size_t nbytes, loff_t off, bool threadgroup)
2689	{
2690	struct task_struct *tsk;
2691	struct cgroup *cgrp;
2692	pid_t pid;
2693	int ret;
2694
2695	if (kstrtoint(strstrip(buf), 0, &pid) \|\| pid < 0)
2696	return -EINVAL;
2697
2698	cgrp = cgroup_kn_lock_live(of->kn);
2699	if (!cgrp)
2700	return -ENODEV;
2701
2702	percpu_down_write(&cgroup_threadgroup_rwsem);
2703	rcu_read_lock();
2704	if (pid) {
2705	tsk = find_task_by_vpid(pid);
2706	if (!tsk) {
2707	ret = -ESRCH;
2708	goto out_unlock_rcu;
2709	}
2710	} else {
2711	tsk = current;
2712	}
2713
2714	if (threadgroup)
2715	tsk = tsk->group_leader;
2716
2717	/*
2718	* Workqueue threads may acquire PF_NO_SETAFFINITY and become
2719	* trapped in a cpuset, or RT worker may be born in a cgroup
2720	* with no rt_runtime allocated. Just say no.
2721	*/
2722	if (tsk == kthreadd_task \|\| (tsk->flags & PF_NO_SETAFFINITY)) {
2723	ret = -EINVAL;
2724	goto out_unlock_rcu;
2725	}
2726
2727	get_task_struct(tsk);
2728	rcu_read_unlock();
2729
2730	ret = cgroup_procs_write_permission(tsk, cgrp, of);
2731	if (!ret)
2732	ret = cgroup_attach_task(cgrp, tsk, threadgroup);
2733
2734	put_task_struct(tsk);
2735	goto out_unlock_threadgroup;
2736
2737	out_unlock_rcu:
2738	rcu_read_unlock();
2739	out_unlock_threadgroup:
2740	percpu_up_write(&cgroup_threadgroup_rwsem);
2741	cgroup_kn_unlock(of->kn);
2742	return ret ?: nbytes;
2743	}
2744
2745	/**
2746	* cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2747	* @from: attach to all cgroups of a given task
2748	* @tsk: the task to be attached
2749	*/
2750	int cgroup_attach_task_all(struct task_struct from, struct task_struct tsk)
2751	{
2752	struct cgroup_root *root;
2753	int retval = 0;
2754
2755	mutex_lock(&cgroup_mutex);
2756	for_each_root(root) {
2757	struct cgroup *from_cgrp;
2758
2759	if (root == &cgrp_dfl_root)
2760	continue;
2761
2762	spin_lock_bh(&css_set_lock);
2763	from_cgrp = task_cgroup_from_root(from, root);
2764	spin_unlock_bh(&css_set_lock);
2765
2766	retval = cgroup_attach_task(from_cgrp, tsk, false);
2767	if (retval)
2768	break;
2769	}
2770	mutex_unlock(&cgroup_mutex);
2771
2772	return retval;
2773	}
2774	EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2775
2776	static ssize_t cgroup_tasks_write(struct kernfs_open_file *of,
2777	char *buf, size_t nbytes, loff_t off)
2778	{
2779	return __cgroup_procs_write(of, buf, nbytes, off, false);
2780	}
2781
2782	static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
2783	char *buf, size_t nbytes, loff_t off)
2784	{
2785	return __cgroup_procs_write(of, buf, nbytes, off, true);
2786	}
2787
2788	static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
2789	char *buf, size_t nbytes, loff_t off)
2790	{
2791	struct cgroup *cgrp;
2792
2793	BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
2794
2795	cgrp = cgroup_kn_lock_live(of->kn);
2796	if (!cgrp)
2797	return -ENODEV;
2798	spin_lock(&release_agent_path_lock);
2799	strlcpy(cgrp->root->release_agent_path, strstrip(buf),
2800	sizeof(cgrp->root->release_agent_path));
2801	spin_unlock(&release_agent_path_lock);
2802	cgroup_kn_unlock(of->kn);
2803	return nbytes;
2804	}
2805
2806	static int cgroup_release_agent_show(struct seq_file seq, void v)
2807	{
2808	struct cgroup *cgrp = seq_css(seq)->cgroup;
2809
2810	spin_lock(&release_agent_path_lock);
2811	seq_puts(seq, cgrp->root->release_agent_path);
2812	spin_unlock(&release_agent_path_lock);
2813	seq_putc(seq, '\n');
2814	return 0;
2815	}
2816
2817	static int cgroup_sane_behavior_show(struct seq_file seq, void v)
2818	{
2819	seq_puts(seq, "0\n");
2820	return 0;
2821	}
2822
2823	static void cgroup_print_ss_mask(struct seq_file *seq, unsigned long ss_mask)
2824	{
2825	struct cgroup_subsys *ss;
2826	bool printed = false;
2827	int ssid;
2828
2829	for_each_subsys_which(ss, ssid, &ss_mask) {
2830	if (printed)
2831	seq_putc(seq, ' ');
2832	seq_printf(seq, "%s", ss->name);
2833	printed = true;
2834	}
2835	if (printed)
2836	seq_putc(seq, '\n');
2837	}
2838
2839	/* show controllers which are currently attached to the default hierarchy */
2840	static int cgroup_root_controllers_show(struct seq_file seq, void v)
2841	{
2842	struct cgroup *cgrp = seq_css(seq)->cgroup;
2843
2844	cgroup_print_ss_mask(seq, cgrp->root->subsys_mask &
2845	~cgrp_dfl_root_inhibit_ss_mask);
2846	return 0;
2847	}
2848
2849	/* show controllers which are enabled from the parent */
2850	static int cgroup_controllers_show(struct seq_file seq, void v)
2851	{
2852	struct cgroup *cgrp = seq_css(seq)->cgroup;
2853
2854	cgroup_print_ss_mask(seq, cgroup_parent(cgrp)->subtree_control);
2855	return 0;
2856	}
2857
2858	/* show controllers which are enabled for a given cgroup's children */
2859	static int cgroup_subtree_control_show(struct seq_file seq, void v)
2860	{
2861	struct cgroup *cgrp = seq_css(seq)->cgroup;
2862
2863	cgroup_print_ss_mask(seq, cgrp->subtree_control);
2864	return 0;
2865	}
2866
2867	/**
2868	* cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
2869	* @cgrp: root of the subtree to update csses for
2870	*
2871	* @cgrp's child_subsys_mask has changed and its subtree's (self excluded)
2872	* css associations need to be updated accordingly. This function looks up
2873	* all css_sets which are attached to the subtree, creates the matching
2874	* updated css_sets and migrates the tasks to the new ones.
2875	*/
2876	static int cgroup_update_dfl_csses(struct cgroup *cgrp)
2877	{
2878	LIST_HEAD(preloaded_csets);
2879	struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
2880	struct cgroup_subsys_state *css;
2881	struct css_set *src_cset;
2882	int ret;
2883
2884	lockdep_assert_held(&cgroup_mutex);
2885
2886	percpu_down_write(&cgroup_threadgroup_rwsem);
2887
2888	/* look up all csses currently attached to @cgrp's subtree */
2889	spin_lock_bh(&css_set_lock);
2890	css_for_each_descendant_pre(css, cgroup_css(cgrp, NULL)) {
2891	struct cgrp_cset_link *link;
2892
2893	/* self is not affected by child_subsys_mask change */
2894	if (css->cgroup == cgrp)
2895	continue;
2896
2897	list_for_each_entry(link, &css->cgroup->cset_links, cset_link)
2898	cgroup_migrate_add_src(link->cset, cgrp,
2899	&preloaded_csets);
2900	}
2901	spin_unlock_bh(&css_set_lock);
2902
2903	/* NULL dst indicates self on default hierarchy */
2904	ret = cgroup_migrate_prepare_dst(NULL, &preloaded_csets);
2905	if (ret)
2906	goto out_finish;
2907
2908	spin_lock_bh(&css_set_lock);
2909	list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
2910	struct task_struct task, ntask;
2911
2912	/* src_csets precede dst_csets, break on the first dst_cset */
2913	if (!src_cset->mg_src_cgrp)
2914	break;
2915
2916	/* all tasks in src_csets need to be migrated */
2917	list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
2918	cgroup_taskset_add(task, &tset);
2919	}
2920	spin_unlock_bh(&css_set_lock);
2921
2922	ret = cgroup_taskset_migrate(&tset, cgrp);
2923	out_finish:
2924	cgroup_migrate_finish(&preloaded_csets);
2925	percpu_up_write(&cgroup_threadgroup_rwsem);
2926	return ret;
2927	}
2928
2929	/* change the enabled child controllers for a cgroup in the default hierarchy */
2930	static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
2931	char *buf, size_t nbytes,
2932	loff_t off)
2933	{
2934	unsigned long enable = 0, disable = 0;
2935	unsigned long css_enable, css_disable, old_sc, new_sc, old_ss, new_ss;
2936	struct cgroup cgrp, child;
2937	struct cgroup_subsys *ss;
2938	char *tok;
2939	int ssid, ret;
2940
2941	/*
2942	* Parse input - space separated list of subsystem names prefixed
2943	* with either + or -.
2944	*/
2945	buf = strstrip(buf);
2946	while ((tok = strsep(&buf, " "))) {
2947	unsigned long tmp_ss_mask = ~cgrp_dfl_root_inhibit_ss_mask;
2948
2949	if (tok[0] == '\0')
2950	continue;
2951	for_each_subsys_which(ss, ssid, &tmp_ss_mask) {
2952	if (!cgroup_ssid_enabled(ssid) \|\|
2953	strcmp(tok + 1, ss->name))
2954	continue;
2955
2956	if (*tok == '+') {
2957	enable \|= 1 << ssid;
2958	disable &= ~(1 << ssid);
2959	} else if (*tok == '-') {
2960	disable \|= 1 << ssid;
2961	enable &= ~(1 << ssid);
2962	} else {
2963	return -EINVAL;
2964	}
2965	break;
2966	}
2967	if (ssid == CGROUP_SUBSYS_COUNT)
2968	return -EINVAL;
2969	}
2970
2971	cgrp = cgroup_kn_lock_live(of->kn);
2972	if (!cgrp)
2973	return -ENODEV;
2974
2975	for_each_subsys(ss, ssid) {
2976	if (enable & (1 << ssid)) {
2977	if (cgrp->subtree_control & (1 << ssid)) {
2978	enable &= ~(1 << ssid);
2979	continue;
2980	}
2981
2982	/* unavailable or not enabled on the parent? */
2983	if (!(cgrp_dfl_root.subsys_mask & (1 << ssid)) \|\|
2984	(cgroup_parent(cgrp) &&
2985	!(cgroup_parent(cgrp)->subtree_control & (1 << ssid)))) {
2986	ret = -ENOENT;
2987	goto out_unlock;
2988	}
2989	} else if (disable & (1 << ssid)) {
2990	if (!(cgrp->subtree_control & (1 << ssid))) {
2991	disable &= ~(1 << ssid);
2992	continue;
2993	}
2994
2995	/* a child has it enabled? */
2996	cgroup_for_each_live_child(child, cgrp) {
2997	if (child->subtree_control & (1 << ssid)) {
2998	ret = -EBUSY;
2999	goto out_unlock;
3000	}
3001	}
3002	}
3003	}
3004
3005	if (!enable && !disable) {
3006	ret = 0;
3007	goto out_unlock;
3008	}
3009
3010	/*
3011	* Except for the root, subtree_control must be zero for a cgroup
3012	* with tasks so that child cgroups don't compete against tasks.
3013	*/
3014	if (enable && cgroup_parent(cgrp) && !list_empty(&cgrp->cset_links)) {
3015	ret = -EBUSY;
3016	goto out_unlock;
3017	}
3018
3019	/*
3020	* Update subsys masks and calculate what needs to be done. More
3021	* subsystems than specified may need to be enabled or disabled
3022	* depending on subsystem dependencies.
3023	*/
3024	old_sc = cgrp->subtree_control;
3025	old_ss = cgrp->child_subsys_mask;
3026	new_sc = (old_sc \| enable) & ~disable;
3027	new_ss = cgroup_calc_child_subsys_mask(cgrp, new_sc);
3028
3029	css_enable = ~old_ss & new_ss;
3030	css_disable = old_ss & ~new_ss;
3031	enable \|= css_enable;
3032	disable \|= css_disable;
3033
3034	/*
3035	* Because css offlining is asynchronous, userland might try to
3036	* re-enable the same controller while the previous instance is
3037	* still around. In such cases, wait till it's gone using
3038	* offline_waitq.
3039	*/
3040	for_each_subsys_which(ss, ssid, &css_enable) {
3041	cgroup_for_each_live_child(child, cgrp) {
3042	DEFINE_WAIT(wait);
3043
3044	if (!cgroup_css(child, ss))
3045	continue;
3046
3047	cgroup_get(child);
3048	prepare_to_wait(&child->offline_waitq, &wait,
3049	TASK_UNINTERRUPTIBLE);
3050	cgroup_kn_unlock(of->kn);
3051	schedule();
3052	finish_wait(&child->offline_waitq, &wait);
3053	cgroup_put(child);
3054
3055	return restart_syscall();
3056	}
3057	}
3058
3059	cgrp->subtree_control = new_sc;
3060	cgrp->child_subsys_mask = new_ss;
3061
3062	/*
3063	* Create new csses or make the existing ones visible. A css is
3064	* created invisible if it's being implicitly enabled through
3065	* dependency. An invisible css is made visible when the userland
3066	* explicitly enables it.
3067	*/
3068	for_each_subsys(ss, ssid) {
3069	if (!(enable & (1 << ssid)))
3070	continue;
3071
3072	cgroup_for_each_live_child(child, cgrp) {
3073	if (css_enable & (1 << ssid))
3074	ret = create_css(child, ss,
3075	cgrp->subtree_control & (1 << ssid));
3076	else
3077	ret = css_populate_dir(cgroup_css(child, ss),
3078	NULL);
3079	if (ret)
3080	goto err_undo_css;
3081	}
3082	}
3083
3084	/*
3085	* At this point, cgroup_e_css() results reflect the new csses
3086	* making the following cgroup_update_dfl_csses() properly update
3087	* css associations of all tasks in the subtree.
3088	*/
3089	ret = cgroup_update_dfl_csses(cgrp);
3090	if (ret)
3091	goto err_undo_css;
3092
3093	/*
3094	* All tasks are migrated out of disabled csses. Kill or hide
3095	* them. A css is hidden when the userland requests it to be
3096	* disabled while other subsystems are still depending on it. The
3097	* css must not actively control resources and be in the vanilla
3098	* state if it's made visible again later. Controllers which may
3099	* be depended upon should provide ->css_reset() for this purpose.
3100	*/
3101	for_each_subsys(ss, ssid) {
3102	if (!(disable & (1 << ssid)))
3103	continue;
3104
3105	cgroup_for_each_live_child(child, cgrp) {
3106	struct cgroup_subsys_state *css = cgroup_css(child, ss);
3107
3108	if (css_disable & (1 << ssid)) {
3109	kill_css(css);
3110	} else {
3111	css_clear_dir(css, NULL);
3112	if (ss->css_reset)
3113	ss->css_reset(css);
3114	}
3115	}
3116	}
3117
3118	/*
3119	* The effective csses of all the descendants (excluding @cgrp) may
3120	* have changed. Subsystems can optionally subscribe to this event
3121	* by implementing ->css_e_css_changed() which is invoked if any of
3122	* the effective csses seen from the css's cgroup may have changed.
3123	*/
3124	for_each_subsys(ss, ssid) {
3125	struct cgroup_subsys_state *this_css = cgroup_css(cgrp, ss);
3126	struct cgroup_subsys_state *css;
3127
3128	if (!ss->css_e_css_changed \|\| !this_css)
3129	continue;
3130
3131	css_for_each_descendant_pre(css, this_css)
3132	if (css != this_css)
3133	ss->css_e_css_changed(css);
3134	}
3135
3136	kernfs_activate(cgrp->kn);
3137	ret = 0;
3138	out_unlock:
3139	cgroup_kn_unlock(of->kn);
3140	return ret ?: nbytes;
3141
3142	err_undo_css:
3143	cgrp->subtree_control = old_sc;
3144	cgrp->child_subsys_mask = old_ss;
3145
3146	for_each_subsys(ss, ssid) {
3147	if (!(enable & (1 << ssid)))
3148	continue;
3149
3150	cgroup_for_each_live_child(child, cgrp) {
3151	struct cgroup_subsys_state *css = cgroup_css(child, ss);
3152
3153	if (!css)
3154	continue;
3155
3156	if (css_enable & (1 << ssid))
3157	kill_css(css);
3158	else
3159	css_clear_dir(css, NULL);
3160	}
3161	}
3162	goto out_unlock;
3163	}
3164
3165	static int cgroup_events_show(struct seq_file seq, void v)
3166	{
3167	seq_printf(seq, "populated %d\n",
3168	cgroup_is_populated(seq_css(seq)->cgroup));
3169	return 0;
3170	}
3171
3172	static ssize_t cgroup_file_write(struct kernfs_open_file of, char buf,
3173	size_t nbytes, loff_t off)
3174	{
3175	struct cgroup *cgrp = of->kn->parent->priv;
3176	struct cftype *cft = of->kn->priv;
3177	struct cgroup_subsys_state *css;
3178	int ret;
3179
3180	if (cft->write)
3181	return cft->write(of, buf, nbytes, off);
3182
3183	/*
3184	* kernfs guarantees that a file isn't deleted with operations in
3185	* flight, which means that the matching css is and stays alive and
3186	* doesn't need to be pinned. The RCU locking is not necessary
3187	* either. It's just for the convenience of using cgroup_css().
3188	*/
3189	rcu_read_lock();
3190	css = cgroup_css(cgrp, cft->ss);
3191	rcu_read_unlock();
3192
3193	if (cft->write_u64) {
3194	unsigned long long v;
3195	ret = kstrtoull(buf, 0, &v);
3196	if (!ret)
3197	ret = cft->write_u64(css, cft, v);
3198	} else if (cft->write_s64) {
3199	long long v;
3200	ret = kstrtoll(buf, 0, &v);
3201	if (!ret)
3202	ret = cft->write_s64(css, cft, v);
3203	} else {
3204	ret = -EINVAL;
3205	}
3206
3207	return ret ?: nbytes;
3208	}
3209
3210	static void cgroup_seqfile_start(struct seq_file seq, loff_t *ppos)
3211	{
3212	return seq_cft(seq)->seq_start(seq, ppos);
3213	}
3214
3215	static void cgroup_seqfile_next(struct seq_file seq, void v, loff_t ppos)
3216	{
3217	return seq_cft(seq)->seq_next(seq, v, ppos);
3218	}
3219
3220	static void cgroup_seqfile_stop(struct seq_file seq, void v)
3221	{
3222	seq_cft(seq)->seq_stop(seq, v);
3223	}
3224
3225	static int cgroup_seqfile_show(struct seq_file m, void arg)
3226	{
3227	struct cftype *cft = seq_cft(m);
3228	struct cgroup_subsys_state *css = seq_css(m);
3229
3230	if (cft->seq_show)
3231	return cft->seq_show(m, arg);
3232
3233	if (cft->read_u64)
3234	seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3235	else if (cft->read_s64)
3236	seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3237	else
3238	return -EINVAL;
3239	return 0;
3240	}
3241
3242	static struct kernfs_ops cgroup_kf_single_ops = {
3243	.atomic_write_len = PAGE_SIZE,
3244	.write = cgroup_file_write,
3245	.seq_show = cgroup_seqfile_show,
3246	};
3247
3248	static struct kernfs_ops cgroup_kf_ops = {
3249	.atomic_write_len = PAGE_SIZE,
3250	.write = cgroup_file_write,
3251	.seq_start = cgroup_seqfile_start,
3252	.seq_next = cgroup_seqfile_next,
3253	.seq_stop = cgroup_seqfile_stop,
3254	.seq_show = cgroup_seqfile_show,
3255	};
3256
3257	/*
3258	* cgroup_rename - Only allow simple rename of directories in place.
3259	*/
3260	static int cgroup_rename(struct kernfs_node kn, struct kernfs_node new_parent,
3261	const char *new_name_str)
3262	{
3263	struct cgroup *cgrp = kn->priv;
3264	int ret;
3265
3266	if (kernfs_type(kn) != KERNFS_DIR)
3267	return -ENOTDIR;
3268	if (kn->parent != new_parent)
3269	return -EIO;
3270
3271	/*
3272	* This isn't a proper migration and its usefulness is very
3273	* limited. Disallow on the default hierarchy.
3274	*/
3275	if (cgroup_on_dfl(cgrp))
3276	return -EPERM;
3277
3278	/*
3279	* We're gonna grab cgroup_mutex which nests outside kernfs
3280	* active_ref. kernfs_rename() doesn't require active_ref
3281	* protection. Break them before grabbing cgroup_mutex.
3282	*/
3283	kernfs_break_active_protection(new_parent);
3284	kernfs_break_active_protection(kn);
3285
3286	mutex_lock(&cgroup_mutex);
3287
3288	ret = kernfs_rename(kn, new_parent, new_name_str);
3289
3290	mutex_unlock(&cgroup_mutex);
3291
3292	kernfs_unbreak_active_protection(kn);
3293	kernfs_unbreak_active_protection(new_parent);
3294	return ret;
3295	}
3296
3297	/* set uid and gid of cgroup dirs and files to that of the creator */
3298	static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3299	{
3300	struct iattr iattr = { .ia_valid = ATTR_UID \| ATTR_GID,
3301	.ia_uid = current_fsuid(),
3302	.ia_gid = current_fsgid(), };
3303
3304	if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3305	gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3306	return 0;
3307
3308	return kernfs_setattr(kn, &iattr);
3309	}
3310
3311	static int cgroup_add_file(struct cgroup_subsys_state css, struct cgroup cgrp,
3312	struct cftype *cft)
3313	{
3314	char name[CGROUP_FILE_NAME_MAX];
3315	struct kernfs_node *kn;
3316	struct lock_class_key *key = NULL;
3317	int ret;
3318
3319	#ifdef CONFIG_DEBUG_LOCK_ALLOC
3320	key = &cft->lockdep_key;
3321	#endif
3322	kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3323	cgroup_file_mode(cft), 0, cft->kf_ops, cft,
3324	NULL, key);
3325	if (IS_ERR(kn))
3326	return PTR_ERR(kn);
3327
3328	ret = cgroup_kn_set_ugid(kn);
3329	if (ret) {
3330	kernfs_remove(kn);
3331	return ret;
3332	}
3333
3334	if (cft->file_offset) {
3335	struct cgroup_file cfile = (void )css + cft->file_offset;
3336
3337	spin_lock_irq(&cgroup_file_kn_lock);
3338	cfile->kn = kn;
3339	spin_unlock_irq(&cgroup_file_kn_lock);
3340	}
3341
3342	return 0;
3343	}
3344
3345	/**
3346	* cgroup_addrm_files - add or remove files to a cgroup directory
3347	* @css: the target css
3348	* @cgrp: the target cgroup (usually css->cgroup)
3349	* @cfts: array of cftypes to be added
3350	* @is_add: whether to add or remove
3351	*
3352	* Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3353	* For removals, this function never fails.
3354	*/
3355	static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3356	struct cgroup *cgrp, struct cftype cfts[],
3357	bool is_add)
3358	{
3359	struct cftype cft, cft_end = NULL;
3360	int ret;
3361
3362	lockdep_assert_held(&cgroup_mutex);
3363
3364	restart:
3365	for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3366	/* does cft->flags tell us to skip this file on @cgrp? */
3367	if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3368	continue;
3369	if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3370	continue;
3371	if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3372	continue;
3373	if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3374	continue;
3375
3376	if (is_add) {
3377	ret = cgroup_add_file(css, cgrp, cft);
3378	if (ret) {
3379	pr_warn("%s: failed to add %s, err=%d\n",
3380	__func__, cft->name, ret);
3381	cft_end = cft;
3382	is_add = false;
3383	goto restart;
3384	}
3385	} else {
3386	cgroup_rm_file(cgrp, cft);
3387	}
3388	}
3389	return 0;
3390	}
3391
3392	static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3393	{
3394	LIST_HEAD(pending);
3395	struct cgroup_subsys *ss = cfts[0].ss;
3396	struct cgroup *root = &ss->root->cgrp;
3397	struct cgroup_subsys_state *css;
3398	int ret = 0;
3399
3400	lockdep_assert_held(&cgroup_mutex);
3401
3402	/* add/rm files for all cgroups created before */
3403	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3404	struct cgroup *cgrp = css->cgroup;
3405
3406	if (cgroup_is_dead(cgrp))
3407	continue;
3408
3409	ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3410	if (ret)
3411	break;
3412	}
3413
3414	if (is_add && !ret)
3415	kernfs_activate(root->kn);
3416	return ret;
3417	}
3418
3419	static void cgroup_exit_cftypes(struct cftype *cfts)
3420	{
3421	struct cftype *cft;
3422
3423	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3424	/* free copy for custom atomic_write_len, see init_cftypes() */
3425	if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3426	kfree(cft->kf_ops);
3427	cft->kf_ops = NULL;
3428	cft->ss = NULL;
3429
3430	/* revert flags set by cgroup core while adding @cfts */
3431	cft->flags &= ~(__CFTYPE_ONLY_ON_DFL \| __CFTYPE_NOT_ON_DFL);
3432	}
3433	}
3434
3435	static int cgroup_init_cftypes(struct cgroup_subsys ss, struct cftype cfts)
3436	{
3437	struct cftype *cft;
3438
3439	for (cft = cfts; cft->name[0] != '\0'; cft++) {
3440	struct kernfs_ops *kf_ops;
3441
3442	WARN_ON(cft->ss \|\| cft->kf_ops);
3443
3444	if (cft->seq_start)
3445	kf_ops = &cgroup_kf_ops;
3446	else
3447	kf_ops = &cgroup_kf_single_ops;
3448
3449	/*
3450	* Ugh... if @cft wants a custom max_write_len, we need to
3451	* make a copy of kf_ops to set its atomic_write_len.
3452	*/
3453	if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3454	kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3455	if (!kf_ops) {
3456	cgroup_exit_cftypes(cfts);
3457	return -ENOMEM;
3458	}
3459	kf_ops->atomic_write_len = cft->max_write_len;
3460	}
3461
3462	cft->kf_ops = kf_ops;
3463	cft->ss = ss;
3464	}
3465
3466	return 0;
3467	}
3468
3469	static int cgroup_rm_cftypes_locked(struct cftype *cfts)
3470	{
3471	lockdep_assert_held(&cgroup_mutex);
3472
3473	if (!cfts \|\| !cfts[0].ss)
3474	return -ENOENT;
3475
3476	list_del(&cfts->node);
3477	cgroup_apply_cftypes(cfts, false);
3478	cgroup_exit_cftypes(cfts);
3479	return 0;
3480	}
3481
3482	/**
3483	* cgroup_rm_cftypes - remove an array of cftypes from a subsystem
3484	* @cfts: zero-length name terminated array of cftypes
3485	*
3486	* Unregister @cfts. Files described by @cfts are removed from all
3487	* existing cgroups and all future cgroups won't have them either. This
3488	* function can be called anytime whether @cfts' subsys is attached or not.
3489	*
3490	* Returns 0 on successful unregistration, -ENOENT if @cfts is not
3491	* registered.
3492	*/
3493	int cgroup_rm_cftypes(struct cftype *cfts)
3494	{
3495	int ret;
3496
3497	mutex_lock(&cgroup_mutex);
3498	ret = cgroup_rm_cftypes_locked(cfts);
3499	mutex_unlock(&cgroup_mutex);
3500	return ret;
3501	}
3502
3503	/**
3504	* cgroup_add_cftypes - add an array of cftypes to a subsystem
3505	* @ss: target cgroup subsystem
3506	* @cfts: zero-length name terminated array of cftypes
3507	*
3508	* Register @cfts to @ss. Files described by @cfts are created for all
3509	* existing cgroups to which @ss is attached and all future cgroups will
3510	* have them too. This function can be called anytime whether @ss is
3511	* attached or not.
3512	*
3513	* Returns 0 on successful registration, -errno on failure. Note that this
3514	* function currently returns 0 as long as @cfts registration is successful
3515	* even if some file creation attempts on existing cgroups fail.
3516	*/
3517	static int cgroup_add_cftypes(struct cgroup_subsys ss, struct cftype cfts)
3518	{
3519	int ret;
3520
3521	if (!cgroup_ssid_enabled(ss->id))
3522	return 0;
3523
3524	if (!cfts \|\| cfts[0].name[0] == '\0')
3525	return 0;
3526
3527	ret = cgroup_init_cftypes(ss, cfts);
3528	if (ret)
3529	return ret;
3530
3531	mutex_lock(&cgroup_mutex);
3532
3533	list_add_tail(&cfts->node, &ss->cfts);
3534	ret = cgroup_apply_cftypes(cfts, true);
3535	if (ret)
3536	cgroup_rm_cftypes_locked(cfts);
3537
3538	mutex_unlock(&cgroup_mutex);
3539	return ret;
3540	}
3541
3542	/**
3543	* cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
3544	* @ss: target cgroup subsystem
3545	* @cfts: zero-length name terminated array of cftypes
3546	*
3547	* Similar to cgroup_add_cftypes() but the added files are only used for
3548	* the default hierarchy.
3549	*/
3550	int cgroup_add_dfl_cftypes(struct cgroup_subsys ss, struct cftype cfts)
3551	{
3552	struct cftype *cft;
3553
3554	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3555	cft->flags \|= __CFTYPE_ONLY_ON_DFL;
3556	return cgroup_add_cftypes(ss, cfts);
3557	}
3558
3559	/**
3560	* cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
3561	* @ss: target cgroup subsystem
3562	* @cfts: zero-length name terminated array of cftypes
3563	*
3564	* Similar to cgroup_add_cftypes() but the added files are only used for
3565	* the legacy hierarchies.
3566	*/
3567	int cgroup_add_legacy_cftypes(struct cgroup_subsys ss, struct cftype cfts)
3568	{
3569	struct cftype *cft;
3570
3571	for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3572	cft->flags \|= __CFTYPE_NOT_ON_DFL;
3573	return cgroup_add_cftypes(ss, cfts);
3574	}
3575
3576	/**
3577	* cgroup_file_notify - generate a file modified event for a cgroup_file
3578	* @cfile: target cgroup_file
3579	*
3580	* @cfile must have been obtained by setting cftype->file_offset.
3581	*/
3582	void cgroup_file_notify(struct cgroup_file *cfile)
3583	{
3584	unsigned long flags;
3585
3586	spin_lock_irqsave(&cgroup_file_kn_lock, flags);
3587	if (cfile->kn)
3588	kernfs_notify(cfile->kn);
3589	spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
3590	}
3591
3592	/**
3593	* cgroup_task_count - count the number of tasks in a cgroup.
3594	* @cgrp: the cgroup in question
3595	*
3596	* Return the number of tasks in the cgroup.
3597	*/
3598	static int cgroup_task_count(const struct cgroup *cgrp)
3599	{
3600	int count = 0;
3601	struct cgrp_cset_link *link;
3602
3603	spin_lock_bh(&css_set_lock);
3604	list_for_each_entry(link, &cgrp->cset_links, cset_link)
3605	count += atomic_read(&link->cset->refcount);
3606	spin_unlock_bh(&css_set_lock);
3607	return count;
3608	}
3609
3610	/**
3611	* css_next_child - find the next child of a given css
3612	* @pos: the current position (%NULL to initiate traversal)
3613	* @parent: css whose children to walk
3614	*
3615	* This function returns the next child of @parent and should be called
3616	* under either cgroup_mutex or RCU read lock. The only requirement is
3617	* that @parent and @pos are accessible. The next sibling is guaranteed to
3618	* be returned regardless of their states.
3619	*
3620	* If a subsystem synchronizes ->css_online() and the start of iteration, a
3621	* css which finished ->css_online() is guaranteed to be visible in the
3622	* future iterations and will stay visible until the last reference is put.
3623	* A css which hasn't finished ->css_online() or already finished
3624	* ->css_offline() may show up during traversal. It's each subsystem's
3625	* responsibility to synchronize against on/offlining.
3626	*/
3627	struct cgroup_subsys_state css_next_child(struct cgroup_subsys_state pos,
3628	struct cgroup_subsys_state *parent)
3629	{
3630	struct cgroup_subsys_state *next;
3631
3632	cgroup_assert_mutex_or_rcu_locked();
3633
3634	/*
3635	* @pos could already have been unlinked from the sibling list.
3636	* Once a cgroup is removed, its ->sibling.next is no longer
3637	* updated when its next sibling changes. CSS_RELEASED is set when
3638	* @pos is taken off list, at which time its next pointer is valid,
3639	* and, as releases are serialized, the one pointed to by the next
3640	* pointer is guaranteed to not have started release yet. This
3641	* implies that if we observe !CSS_RELEASED on @pos in this RCU
3642	* critical section, the one pointed to by its next pointer is
3643	* guaranteed to not have finished its RCU grace period even if we
3644	* have dropped rcu_read_lock() inbetween iterations.
3645	*
3646	* If @pos has CSS_RELEASED set, its next pointer can't be
3647	* dereferenced; however, as each css is given a monotonically
3648	* increasing unique serial number and always appended to the
3649	* sibling list, the next one can be found by walking the parent's
3650	* children until the first css with higher serial number than
3651	* @pos's. While this path can be slower, it happens iff iteration
3652	* races against release and the race window is very small.
3653	*/
3654	if (!pos) {
3655	next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
3656	} else if (likely(!(pos->flags & CSS_RELEASED))) {
3657	next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
3658	} else {
3659	list_for_each_entry_rcu(next, &parent->children, sibling)
3660	if (next->serial_nr > pos->serial_nr)
3661	break;
3662	}
3663
3664	/*
3665	* @next, if not pointing to the head, can be dereferenced and is
3666	* the next sibling.
3667	*/
3668	if (&next->sibling != &parent->children)
3669	return next;
3670	return NULL;
3671	}
3672
3673	/**
3674	* css_next_descendant_pre - find the next descendant for pre-order walk
3675	* @pos: the current position (%NULL to initiate traversal)
3676	* @root: css whose descendants to walk
3677	*
3678	* To be used by css_for_each_descendant_pre(). Find the next descendant
3679	* to visit for pre-order traversal of @root's descendants. @root is
3680	* included in the iteration and the first node to be visited.
3681	*
3682	* While this function requires cgroup_mutex or RCU read locking, it
3683	* doesn't require the whole traversal to be contained in a single critical
3684	* section. This function will return the correct next descendant as long
3685	* as both @pos and @root are accessible and @pos is a descendant of @root.
3686	*
3687	* If a subsystem synchronizes ->css_online() and the start of iteration, a
3688	* css which finished ->css_online() is guaranteed to be visible in the
3689	* future iterations and will stay visible until the last reference is put.
3690	* A css which hasn't finished ->css_online() or already finished
3691	* ->css_offline() may show up during traversal. It's each subsystem's
3692	* responsibility to synchronize against on/offlining.
3693	*/
3694	struct cgroup_subsys_state *
3695	css_next_descendant_pre(struct cgroup_subsys_state *pos,
3696	struct cgroup_subsys_state *root)
3697	{
3698	struct cgroup_subsys_state *next;
3699
3700	cgroup_assert_mutex_or_rcu_locked();
3701
3702	/* if first iteration, visit @root */
3703	if (!pos)
3704	return root;
3705
3706	/* visit the first child if exists */
3707	next = css_next_child(NULL, pos);
3708	if (next)
3709	return next;
3710
3711	/* no child, visit my or the closest ancestor's next sibling */
3712	while (pos != root) {
3713	next = css_next_child(pos, pos->parent);
3714	if (next)
3715	return next;
3716	pos = pos->parent;
3717	}
3718
3719	return NULL;
3720	}
3721
3722	/**
3723	* css_rightmost_descendant - return the rightmost descendant of a css
3724	* @pos: css of interest
3725	*
3726	* Return the rightmost descendant of @pos. If there's no descendant, @pos
3727	* is returned. This can be used during pre-order traversal to skip
3728	* subtree of @pos.
3729	*
3730	* While this function requires cgroup_mutex or RCU read locking, it
3731	* doesn't require the whole traversal to be contained in a single critical
3732	* section. This function will return the correct rightmost descendant as
3733	* long as @pos is accessible.
3734	*/
3735	struct cgroup_subsys_state *
3736	css_rightmost_descendant(struct cgroup_subsys_state *pos)
3737	{
3738	struct cgroup_subsys_state last, tmp;
3739
3740	cgroup_assert_mutex_or_rcu_locked();
3741
3742	do {
3743	last = pos;
3744	/* ->prev isn't RCU safe, walk ->next till the end */
3745	pos = NULL;
3746	css_for_each_child(tmp, last)
3747	pos = tmp;
3748	} while (pos);
3749
3750	return last;
3751	}
3752
3753	static struct cgroup_subsys_state *
3754	css_leftmost_descendant(struct cgroup_subsys_state *pos)
3755	{
3756	struct cgroup_subsys_state *last;
3757
3758	do {
3759	last = pos;
3760	pos = css_next_child(NULL, pos);
3761	} while (pos);
3762
3763	return last;
3764	}
3765
3766	/**
3767	* css_next_descendant_post - find the next descendant for post-order walk
3768	* @pos: the current position (%NULL to initiate traversal)
3769	* @root: css whose descendants to walk
3770	*
3771	* To be used by css_for_each_descendant_post(). Find the next descendant
3772	* to visit for post-order traversal of @root's descendants. @root is
3773	* included in the iteration and the last node to be visited.
3774	*
3775	* While this function requires cgroup_mutex or RCU read locking, it
3776	* doesn't require the whole traversal to be contained in a single critical
3777	* section. This function will return the correct next descendant as long
3778	* as both @pos and @cgroup are accessible and @pos is a descendant of
3779	* @cgroup.
3780	*
3781	* If a subsystem synchronizes ->css_online() and the start of iteration, a
3782	* css which finished ->css_online() is guaranteed to be visible in the
3783	* future iterations and will stay visible until the last reference is put.
3784	* A css which hasn't finished ->css_online() or already finished
3785	* ->css_offline() may show up during traversal. It's each subsystem's
3786	* responsibility to synchronize against on/offlining.
3787	*/
3788	struct cgroup_subsys_state *
3789	css_next_descendant_post(struct cgroup_subsys_state *pos,
3790	struct cgroup_subsys_state *root)
3791	{
3792	struct cgroup_subsys_state *next;
3793
3794	cgroup_assert_mutex_or_rcu_locked();
3795
3796	/* if first iteration, visit leftmost descendant which may be @root */
3797	if (!pos)
3798	return css_leftmost_descendant(root);
3799
3800	/* if we visited @root, we're done */
3801	if (pos == root)
3802	return NULL;
3803
3804	/* if there's an unvisited sibling, visit its leftmost descendant */
3805	next = css_next_child(pos, pos->parent);
3806	if (next)
3807	return css_leftmost_descendant(next);
3808
3809	/* no sibling left, visit parent */
3810	return pos->parent;
3811	}
3812
3813	/**
3814	* css_has_online_children - does a css have online children
3815	* @css: the target css
3816	*
3817	* Returns %true if @css has any online children; otherwise, %false. This
3818	* function can be called from any context but the caller is responsible
3819	* for synchronizing against on/offlining as necessary.
3820	*/
3821	bool css_has_online_children(struct cgroup_subsys_state *css)
3822	{
3823	struct cgroup_subsys_state *child;
3824	bool ret = false;
3825
3826	rcu_read_lock();
3827	css_for_each_child(child, css) {
3828	if (child->flags & CSS_ONLINE) {
3829	ret = true;
3830	break;
3831	}
3832	}
3833	rcu_read_unlock();
3834	return ret;
3835	}
3836
3837	/**
3838	* css_task_iter_advance_css_set - advance a task itererator to the next css_set
3839	* @it: the iterator to advance
3840	*
3841	* Advance @it to the next css_set to walk.
3842	*/
3843	static void css_task_iter_advance_css_set(struct css_task_iter *it)
3844	{
3845	struct list_head *l = it->cset_pos;
3846	struct cgrp_cset_link *link;
3847	struct css_set *cset;
3848
3849	lockdep_assert_held(&css_set_lock);
3850
3851	/* Advance to the next non-empty css_set */
3852	do {
3853	l = l->next;
3854	if (l == it->cset_head) {
3855	it->cset_pos = NULL;
3856	it->task_pos = NULL;
3857	return;
3858	}
3859
3860	if (it->ss) {
3861	cset = container_of(l, struct css_set,
3862	e_cset_node[it->ss->id]);
3863	} else {
3864	link = list_entry(l, struct cgrp_cset_link, cset_link);
3865	cset = link->cset;
3866	}
3867	} while (!css_set_populated(cset));
3868
3869	it->cset_pos = l;
3870
3871	if (!list_empty(&cset->tasks))
3872	it->task_pos = cset->tasks.next;
3873	else
3874	it->task_pos = cset->mg_tasks.next;
3875
3876	it->tasks_head = &cset->tasks;
3877	it->mg_tasks_head = &cset->mg_tasks;
3878
3879	/*
3880	* We don't keep css_sets locked across iteration steps and thus
3881	* need to take steps to ensure that iteration can be resumed after
3882	* the lock is re-acquired. Iteration is performed at two levels -
3883	* css_sets and tasks in them.
3884	*
3885	* Once created, a css_set never leaves its cgroup lists, so a
3886	* pinned css_set is guaranteed to stay put and we can resume
3887	* iteration afterwards.
3888	*
3889	* Tasks may leave @cset across iteration steps. This is resolved
3890	* by registering each iterator with the css_set currently being
3891	* walked and making css_set_move_task() advance iterators whose
3892	* next task is leaving.
3893	*/
3894	if (it->cur_cset) {
3895	list_del(&it->iters_node);
3896	put_css_set_locked(it->cur_cset);
3897	}
3898	get_css_set(cset);
3899	it->cur_cset = cset;
3900	list_add(&it->iters_node, &cset->task_iters);
3901	}
3902
3903	static void css_task_iter_advance(struct css_task_iter *it)
3904	{
3905	struct list_head *l = it->task_pos;
3906
3907	lockdep_assert_held(&css_set_lock);
3908	WARN_ON_ONCE(!l);
3909
3910	/*
3911	* Advance iterator to find next entry. cset->tasks is consumed
3912	* first and then ->mg_tasks. After ->mg_tasks, we move onto the
3913	* next cset.
3914	*/
3915	l = l->next;
3916
3917	if (l == it->tasks_head)
3918	l = it->mg_tasks_head->next;
3919
3920	if (l == it->mg_tasks_head)
3921	css_task_iter_advance_css_set(it);
3922	else
3923	it->task_pos = l;
3924	}
3925
3926	/**
3927	* css_task_iter_start - initiate task iteration
3928	* @css: the css to walk tasks of
3929	* @it: the task iterator to use
3930	*
3931	* Initiate iteration through the tasks of @css. The caller can call
3932	* css_task_iter_next() to walk through the tasks until the function
3933	* returns NULL. On completion of iteration, css_task_iter_end() must be
3934	* called.
3935	*/
3936	void css_task_iter_start(struct cgroup_subsys_state *css,
3937	struct css_task_iter *it)
3938	{
3939	/* no one should try to iterate before mounting cgroups */
3940	WARN_ON_ONCE(!use_task_css_set_links);
3941
3942	memset(it, 0, sizeof(*it));
3943
3944	spin_lock_bh(&css_set_lock);
3945
3946	it->ss = css->ss;
3947
3948	if (it->ss)
3949	it->cset_pos = &css->cgroup->e_csets[css->ss->id];
3950	else
3951	it->cset_pos = &css->cgroup->cset_links;
3952
3953	it->cset_head = it->cset_pos;
3954
3955	css_task_iter_advance_css_set(it);
3956
3957	spin_unlock_bh(&css_set_lock);
3958	}
3959
3960	/**
3961	* css_task_iter_next - return the next task for the iterator
3962	* @it: the task iterator being iterated
3963	*
3964	* The "next" function for task iteration. @it should have been
3965	* initialized via css_task_iter_start(). Returns NULL when the iteration
3966	* reaches the end.
3967	*/
3968	struct task_struct css_task_iter_next(struct css_task_iter it)
3969	{
3970	if (it->cur_task) {
3971	put_task_struct(it->cur_task);
3972	it->cur_task = NULL;
3973	}
3974
3975	spin_lock_bh(&css_set_lock);
3976
3977	if (it->task_pos) {
3978	it->cur_task = list_entry(it->task_pos, struct task_struct,
3979	cg_list);
3980	get_task_struct(it->cur_task);
3981	css_task_iter_advance(it);
3982	}
3983
3984	spin_unlock_bh(&css_set_lock);
3985
3986	return it->cur_task;
3987	}
3988
3989	/**
3990	* css_task_iter_end - finish task iteration
3991	* @it: the task iterator to finish
3992	*
3993	* Finish task iteration started by css_task_iter_start().
3994	*/
3995	void css_task_iter_end(struct css_task_iter *it)
3996	{
3997	if (it->cur_cset) {
3998	spin_lock_bh(&css_set_lock);
3999	list_del(&it->iters_node);
4000	put_css_set_locked(it->cur_cset);
4001	spin_unlock_bh(&css_set_lock);
4002	}
4003
4004	if (it->cur_task)
4005	put_task_struct(it->cur_task);
4006	}
4007
4008	/**
4009	* cgroup_trasnsfer_tasks - move tasks from one cgroup to another
4010	* @to: cgroup to which the tasks will be moved
4011	* @from: cgroup in which the tasks currently reside
4012	*
4013	* Locking rules between cgroup_post_fork() and the migration path
4014	* guarantee that, if a task is forking while being migrated, the new child
4015	* is guaranteed to be either visible in the source cgroup after the
4016	* parent's migration is complete or put into the target cgroup. No task
4017	* can slip out of migration through forking.
4018	*/
4019	int cgroup_transfer_tasks(struct cgroup to, struct cgroup from)
4020	{
4021	LIST_HEAD(preloaded_csets);
4022	struct cgrp_cset_link *link;
4023	struct css_task_iter it;
4024	struct task_struct *task;
4025	int ret;
4026
4027	mutex_lock(&cgroup_mutex);
4028
4029	/* all tasks in @from are being moved, all csets are source */
4030	spin_lock_bh(&css_set_lock);
4031	list_for_each_entry(link, &from->cset_links, cset_link)
4032	cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
4033	spin_unlock_bh(&css_set_lock);
4034
4035	ret = cgroup_migrate_prepare_dst(to, &preloaded_csets);
4036	if (ret)
4037	goto out_err;
4038
4039	/*
4040	* Migrate tasks one-by-one until @from is empty. This fails iff
4041	* ->can_attach() fails.
4042	*/
4043	do {
4044	css_task_iter_start(&from->self, &it);
4045	task = css_task_iter_next(&it);
4046	if (task)
4047	get_task_struct(task);
4048	css_task_iter_end(&it);
4049
4050	if (task) {
4051	ret = cgroup_migrate(task, false, to);
4052	put_task_struct(task);
4053	}
4054	} while (task && !ret);
4055	out_err:
4056	cgroup_migrate_finish(&preloaded_csets);
4057	mutex_unlock(&cgroup_mutex);
4058	return ret;
4059	}
4060
4061	/*
4062	* Stuff for reading the 'tasks'/'procs' files.
4063	*
4064	* Reading this file can return large amounts of data if a cgroup has
4065	* lots of attached tasks. So it may need several calls to read(),
4066	* but we cannot guarantee that the information we produce is correct
4067	* unless we produce it entirely atomically.
4068	*
4069	*/
4070
4071	/* which pidlist file are we talking about? */
4072	enum cgroup_filetype {
4073	CGROUP_FILE_PROCS,
4074	CGROUP_FILE_TASKS,
4075	};
4076
4077	/*
4078	* A pidlist is a list of pids that virtually represents the contents of one
4079	* of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
4080	* a pair (one each for procs, tasks) for each pid namespace that's relevant
4081	* to the cgroup.
4082	*/
4083	struct cgroup_pidlist {
4084	/*
4085	* used to find which pidlist is wanted. doesn't change as long as
4086	* this particular list stays in the list.
4087	*/
4088	struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
4089	/* array of xids */
4090	pid_t *list;
4091	/* how many elements the above list has */
4092	int length;
4093	/* each of these stored in a list by its cgroup */
4094	struct list_head links;
4095	/* pointer to the cgroup we belong to, for list removal purposes */
4096	struct cgroup *owner;
4097	/* for delayed destruction */
4098	struct delayed_work destroy_dwork;
4099	};
4100
4101	/*
4102	* The following two functions "fix" the issue where there are more pids
4103	* than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
4104	* TODO: replace with a kernel-wide solution to this problem
4105	*/
4106	#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
4107	static void *pidlist_allocate(int count)
4108	{
4109	if (PIDLIST_TOO_LARGE(count))
4110	return vmalloc(count * sizeof(pid_t));
4111	else
4112	return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
4113	}
4114
4115	static void pidlist_free(void *p)
4116	{
4117	kvfree(p);
4118	}
4119
4120	/*
4121	* Used to destroy all pidlists lingering waiting for destroy timer. None
4122	* should be left afterwards.
4123	*/
4124	static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
4125	{
4126	struct cgroup_pidlist l, tmp_l;
4127
4128	mutex_lock(&cgrp->pidlist_mutex);
4129	list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
4130	mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
4131	mutex_unlock(&cgrp->pidlist_mutex);
4132
4133	flush_workqueue(cgroup_pidlist_destroy_wq);
4134	BUG_ON(!list_empty(&cgrp->pidlists));
4135	}
4136
4137	static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
4138	{
4139	struct delayed_work *dwork = to_delayed_work(work);
4140	struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
4141	destroy_dwork);
4142	struct cgroup_pidlist *tofree = NULL;
4143
4144	mutex_lock(&l->owner->pidlist_mutex);
4145
4146	/*
4147	* Destroy iff we didn't get queued again. The state won't change
4148	* as destroy_dwork can only be queued while locked.
4149	*/
4150	if (!delayed_work_pending(dwork)) {
4151	list_del(&l->links);
4152	pidlist_free(l->list);
4153	put_pid_ns(l->key.ns);
4154	tofree = l;
4155	}
4156
4157	mutex_unlock(&l->owner->pidlist_mutex);
4158	kfree(tofree);
4159	}
4160
4161	/*
4162	* pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
4163	* Returns the number of unique elements.
4164	*/
4165	static int pidlist_uniq(pid_t *list, int length)
4166	{
4167	int src, dest = 1;
4168
4169	/*
4170	* we presume the 0th element is unique, so i starts at 1. trivial
4171	* edge cases first; no work needs to be done for either
4172	*/
4173	if (length == 0 \|\| length == 1)
4174	return length;
4175	/* src and dest walk down the list; dest counts unique elements */
4176	for (src = 1; src < length; src++) {
4177	/* find next unique element */
4178	while (list[src] == list[src-1]) {
4179	src++;
4180	if (src == length)
4181	goto after;
4182	}
4183	/* dest always points to where the next unique element goes */
4184	list[dest] = list[src];
4185	dest++;
4186	}
4187	after:
4188	return dest;
4189	}
4190
4191	/*
4192	* The two pid files - task and cgroup.procs - guaranteed that the result
4193	* is sorted, which forced this whole pidlist fiasco. As pid order is
4194	* different per namespace, each namespace needs differently sorted list,
4195	* making it impossible to use, for example, single rbtree of member tasks
4196	* sorted by task pointer. As pidlists can be fairly large, allocating one
4197	* per open file is dangerous, so cgroup had to implement shared pool of
4198	* pidlists keyed by cgroup and namespace.
4199	*
4200	* All this extra complexity was caused by the original implementation
4201	* committing to an entirely unnecessary property. In the long term, we
4202	* want to do away with it. Explicitly scramble sort order if on the
4203	* default hierarchy so that no such expectation exists in the new
4204	* interface.
4205	*
4206	* Scrambling is done by swapping every two consecutive bits, which is
4207	* non-identity one-to-one mapping which disturbs sort order sufficiently.
4208	*/
4209	static pid_t pid_fry(pid_t pid)
4210	{
4211	unsigned a = pid & 0x55555555;
4212	unsigned b = pid & 0xAAAAAAAA;
4213
4214	return (a << 1) \| (b >> 1);
4215	}
4216
4217	static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
4218	{
4219	if (cgroup_on_dfl(cgrp))
4220	return pid_fry(pid);
4221	else
4222	return pid;
4223	}
4224
4225	static int cmppid(const void a, const void b)
4226	{
4227	return (pid_t )a - (pid_t )b;
4228	}
4229
4230	static int fried_cmppid(const void a, const void b)
4231	{
4232	return pid_fry((pid_t )a) - pid_fry((pid_t )b);
4233	}
4234
4235	static struct cgroup_pidlist cgroup_pidlist_find(struct cgroup cgrp,
4236	enum cgroup_filetype type)
4237	{
4238	struct cgroup_pidlist *l;
4239	/* don't need task_nsproxy() if we're looking at ourself */
4240	struct pid_namespace *ns = task_active_pid_ns(current);
4241
4242	lockdep_assert_held(&cgrp->pidlist_mutex);
4243
4244	list_for_each_entry(l, &cgrp->pidlists, links)
4245	if (l->key.type == type && l->key.ns == ns)
4246	return l;
4247	return NULL;
4248	}
4249
4250	/*
4251	* find the appropriate pidlist for our purpose (given procs vs tasks)
4252	* returns with the lock on that pidlist already held, and takes care
4253	* of the use count, or returns NULL with no locks held if we're out of
4254	* memory.
4255	*/
4256	static struct cgroup_pidlist cgroup_pidlist_find_create(struct cgroup cgrp,
4257	enum cgroup_filetype type)
4258	{
4259	struct cgroup_pidlist *l;
4260
4261	lockdep_assert_held(&cgrp->pidlist_mutex);
4262
4263	l = cgroup_pidlist_find(cgrp, type);
4264	if (l)
4265	return l;
4266
4267	/* entry not found; create a new one */
4268	l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
4269	if (!l)
4270	return l;
4271
4272	INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
4273	l->key.type = type;
4274	/* don't need task_nsproxy() if we're looking at ourself */
4275	l->key.ns = get_pid_ns(task_active_pid_ns(current));
4276	l->owner = cgrp;
4277	list_add(&l->links, &cgrp->pidlists);
4278	return l;
4279	}
4280
4281	/*
4282	* Load a cgroup's pidarray with either procs' tgids or tasks' pids
4283	*/
4284	static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
4285	struct cgroup_pidlist **lp)
4286	{
4287	pid_t *array;
4288	int length;
4289	int pid, n = 0; /* used for populating the array */
4290	struct css_task_iter it;
4291	struct task_struct *tsk;
4292	struct cgroup_pidlist *l;
4293
4294	lockdep_assert_held(&cgrp->pidlist_mutex);
4295
4296	/*
4297	* If cgroup gets more users after we read count, we won't have
4298	* enough space - tough. This race is indistinguishable to the
4299	* caller from the case that the additional cgroup users didn't
4300	* show up until sometime later on.
4301	*/
4302	length = cgroup_task_count(cgrp);
4303	array = pidlist_allocate(length);
4304	if (!array)
4305	return -ENOMEM;
4306	/* now, populate the array */
4307	css_task_iter_start(&cgrp->self, &it);
4308	while ((tsk = css_task_iter_next(&it))) {
4309	if (unlikely(n == length))
4310	break;
4311	/* get tgid or pid for procs or tasks file respectively */
4312	if (type == CGROUP_FILE_PROCS)
4313	pid = task_tgid_vnr(tsk);
4314	else
4315	pid = task_pid_vnr(tsk);
4316	if (pid > 0) /* make sure to only use valid results */
4317	array[n++] = pid;
4318	}
4319	css_task_iter_end(&it);
4320	length = n;
4321	/* now sort & (if procs) strip out duplicates */
4322	if (cgroup_on_dfl(cgrp))
4323	sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
4324	else
4325	sort(array, length, sizeof(pid_t), cmppid, NULL);
4326	if (type == CGROUP_FILE_PROCS)
4327	length = pidlist_uniq(array, length);
4328
4329	l = cgroup_pidlist_find_create(cgrp, type);
4330	if (!l) {
4331	pidlist_free(array);
4332	return -ENOMEM;
4333	}
4334
4335	/* store array, freeing old if necessary */
4336	pidlist_free(l->list);
4337	l->list = array;
4338	l->length = length;
4339	*lp = l;
4340	return 0;
4341	}
4342
4343	/**
4344	* cgroupstats_build - build and fill cgroupstats
4345	* @stats: cgroupstats to fill information into
4346	* @dentry: A dentry entry belonging to the cgroup for which stats have
4347	* been requested.
4348	*
4349	* Build and fill cgroupstats so that taskstats can export it to user
4350	* space.
4351	*/
4352	int cgroupstats_build(struct cgroupstats stats, struct dentry dentry)
4353	{
4354	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
4355	struct cgroup *cgrp;
4356	struct css_task_iter it;
4357	struct task_struct *tsk;
4358
4359	/* it should be kernfs_node belonging to cgroupfs and is a directory */
4360	if (dentry->d_sb->s_type != &cgroup_fs_type \|\| !kn \|\|
4361	kernfs_type(kn) != KERNFS_DIR)
4362	return -EINVAL;
4363
4364	mutex_lock(&cgroup_mutex);
4365
4366	/*
4367	* We aren't being called from kernfs and there's no guarantee on
4368	* @kn->priv's validity. For this and css_tryget_online_from_dir(),
4369	* @kn->priv is RCU safe. Let's do the RCU dancing.
4370	*/
4371	rcu_read_lock();
4372	cgrp = rcu_dereference(kn->priv);
4373	if (!cgrp \|\| cgroup_is_dead(cgrp)) {
4374	rcu_read_unlock();
4375	mutex_unlock(&cgroup_mutex);
4376	return -ENOENT;
4377	}
4378	rcu_read_unlock();
4379
4380	css_task_iter_start(&cgrp->self, &it);
4381	while ((tsk = css_task_iter_next(&it))) {
4382	switch (tsk->state) {
4383	case TASK_RUNNING:
4384	stats->nr_running++;
4385	break;
4386	case TASK_INTERRUPTIBLE:
4387	stats->nr_sleeping++;
4388	break;
4389	case TASK_UNINTERRUPTIBLE:
4390	stats->nr_uninterruptible++;
4391	break;
4392	case TASK_STOPPED:
4393	stats->nr_stopped++;
4394	break;
4395	default:
4396	if (delayacct_is_task_waiting_on_io(tsk))
4397	stats->nr_io_wait++;
4398	break;
4399	}
4400	}
4401	css_task_iter_end(&it);
4402
4403	mutex_unlock(&cgroup_mutex);
4404	return 0;
4405	}
4406
4407
4408	/*
4409	* seq_file methods for the tasks/procs files. The seq_file position is the
4410	* next pid to display; the seq_file iterator is a pointer to the pid
4411	* in the cgroup->l->list array.
4412	*/
4413
4414	static void cgroup_pidlist_start(struct seq_file s, loff_t *pos)
4415	{
4416	/*
4417	* Initially we receive a position value that corresponds to
4418	* one more than the last pid shown (or 0 on the first call or
4419	* after a seek to the start). Use a binary-search to find the
4420	* next pid to display, if any
4421	*/
4422	struct kernfs_open_file *of = s->private;
4423	struct cgroup *cgrp = seq_css(s)->cgroup;
4424	struct cgroup_pidlist *l;
4425	enum cgroup_filetype type = seq_cft(s)->private;
4426	int index = 0, pid = *pos;
4427	int *iter, ret;
4428
4429	mutex_lock(&cgrp->pidlist_mutex);
4430
4431	/*
4432	* !NULL @of->priv indicates that this isn't the first start()
4433	* after open. If the matching pidlist is around, we can use that.
4434	* Look for it. Note that @of->priv can't be used directly. It
4435	* could already have been destroyed.
4436	*/
4437	if (of->priv)
4438	of->priv = cgroup_pidlist_find(cgrp, type);
4439
4440	/*
4441	* Either this is the first start() after open or the matching
4442	* pidlist has been destroyed inbetween. Create a new one.
4443	*/
4444	if (!of->priv) {
4445	ret = pidlist_array_load(cgrp, type,
4446	(struct cgroup_pidlist **)&of->priv);
4447	if (ret)
4448	return ERR_PTR(ret);
4449	}
4450	l = of->priv;
4451
4452	if (pid) {
4453	int end = l->length;
4454
4455	while (index < end) {
4456	int mid = (index + end) / 2;
4457	if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
4458	index = mid;
4459	break;
4460	} else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
4461	index = mid + 1;
4462	else
4463	end = mid;
4464	}
4465	}
4466	/* If we're off the end of the array, we're done */
4467	if (index >= l->length)
4468	return NULL;
4469	/* Update the abstract position to be the actual pid that we found */
4470	iter = l->list + index;
4471	pos = cgroup_pid_fry(cgrp, iter);
4472	return iter;
4473	}
4474
4475	static void cgroup_pidlist_stop(struct seq_file s, void v)
4476	{
4477	struct kernfs_open_file *of = s->private;
4478	struct cgroup_pidlist *l = of->priv;
4479
4480	if (l)
4481	mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
4482	CGROUP_PIDLIST_DESTROY_DELAY);
4483	mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
4484	}
4485
4486	static void cgroup_pidlist_next(struct seq_file s, void v, loff_t pos)
4487	{
4488	struct kernfs_open_file *of = s->private;
4489	struct cgroup_pidlist *l = of->priv;
4490	pid_t *p = v;
4491	pid_t *end = l->list + l->length;
4492	/*
4493	* Advance to the next pid in the array. If this goes off the
4494	* end, we're done
4495	*/
4496	p++;
4497	if (p >= end) {
4498	return NULL;
4499	} else {
4500	pos = cgroup_pid_fry(seq_css(s)->cgroup, p);
4501	return p;
4502	}
4503	}
4504
4505	static int cgroup_pidlist_show(struct seq_file s, void v)
4506	{
4507	seq_printf(s, "%d\n", (int )v);
4508
4509	return 0;
4510	}
4511
4512	static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
4513	struct cftype *cft)
4514	{
4515	return notify_on_release(css->cgroup);
4516	}
4517
4518	static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
4519	struct cftype *cft, u64 val)
4520	{
4521	if (val)
4522	set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4523	else
4524	clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4525	return 0;
4526	}
4527
4528	static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
4529	struct cftype *cft)
4530	{
4531	return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4532	}
4533
4534	static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
4535	struct cftype *cft, u64 val)
4536	{
4537	if (val)
4538	set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4539	else
4540	clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4541	return 0;
4542	}
4543
4544	/* cgroup core interface files for the default hierarchy */
4545	static struct cftype cgroup_dfl_base_files[] = {
4546	{
4547	.name = "cgroup.procs",
4548	.file_offset = offsetof(struct cgroup, procs_file),
4549	.seq_start = cgroup_pidlist_start,
4550	.seq_next = cgroup_pidlist_next,
4551	.seq_stop = cgroup_pidlist_stop,
4552	.seq_show = cgroup_pidlist_show,
4553	.private = CGROUP_FILE_PROCS,
4554	.write = cgroup_procs_write,
4555	},
4556	{
4557	.name = "cgroup.controllers",
4558	.flags = CFTYPE_ONLY_ON_ROOT,
4559	.seq_show = cgroup_root_controllers_show,
4560	},
4561	{
4562	.name = "cgroup.controllers",
4563	.flags = CFTYPE_NOT_ON_ROOT,
4564	.seq_show = cgroup_controllers_show,
4565	},
4566	{
4567	.name = "cgroup.subtree_control",
4568	.seq_show = cgroup_subtree_control_show,
4569	.write = cgroup_subtree_control_write,
4570	},
4571	{
4572	.name = "cgroup.events",
4573	.flags = CFTYPE_NOT_ON_ROOT,
4574	.file_offset = offsetof(struct cgroup, events_file),
4575	.seq_show = cgroup_events_show,
4576	},
4577	{ } /* terminate */
4578	};
4579
4580	/* cgroup core interface files for the legacy hierarchies */
4581	static struct cftype cgroup_legacy_base_files[] = {
4582	{
4583	.name = "cgroup.procs",
4584	.seq_start = cgroup_pidlist_start,
4585	.seq_next = cgroup_pidlist_next,
4586	.seq_stop = cgroup_pidlist_stop,
4587	.seq_show = cgroup_pidlist_show,
4588	.private = CGROUP_FILE_PROCS,
4589	.write = cgroup_procs_write,
4590	},
4591	{
4592	.name = "cgroup.clone_children",
4593	.read_u64 = cgroup_clone_children_read,
4594	.write_u64 = cgroup_clone_children_write,
4595	},
4596	{
4597	.name = "cgroup.sane_behavior",
4598	.flags = CFTYPE_ONLY_ON_ROOT,
4599	.seq_show = cgroup_sane_behavior_show,
4600	},
4601	{
4602	.name = "tasks",
4603	.seq_start = cgroup_pidlist_start,
4604	.seq_next = cgroup_pidlist_next,
4605	.seq_stop = cgroup_pidlist_stop,
4606	.seq_show = cgroup_pidlist_show,
4607	.private = CGROUP_FILE_TASKS,
4608	.write = cgroup_tasks_write,
4609	},
4610	{
4611	.name = "notify_on_release",
4612	.read_u64 = cgroup_read_notify_on_release,
4613	.write_u64 = cgroup_write_notify_on_release,
4614	},
4615	{
4616	.name = "release_agent",
4617	.flags = CFTYPE_ONLY_ON_ROOT,
4618	.seq_show = cgroup_release_agent_show,
4619	.write = cgroup_release_agent_write,
4620	.max_write_len = PATH_MAX - 1,
4621	},
4622	{ } /* terminate */
4623	};
4624
4625	/*
4626	* css destruction is four-stage process.
4627	*
4628	* 1. Destruction starts. Killing of the percpu_ref is initiated.
4629	* Implemented in kill_css().
4630	*
4631	* 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4632	* and thus css_tryget_online() is guaranteed to fail, the css can be
4633	* offlined by invoking offline_css(). After offlining, the base ref is
4634	* put. Implemented in css_killed_work_fn().
4635	*
4636	* 3. When the percpu_ref reaches zero, the only possible remaining
4637	* accessors are inside RCU read sections. css_release() schedules the
4638	* RCU callback.
4639	*
4640	* 4. After the grace period, the css can be freed. Implemented in
4641	* css_free_work_fn().
4642	*
4643	* It is actually hairier because both step 2 and 4 require process context
4644	* and thus involve punting to css->destroy_work adding two additional
4645	* steps to the already complex sequence.
4646	*/
4647	static void css_free_work_fn(struct work_struct *work)
4648	{
4649	struct cgroup_subsys_state *css =
4650	container_of(work, struct cgroup_subsys_state, destroy_work);
4651	struct cgroup_subsys *ss = css->ss;
4652	struct cgroup *cgrp = css->cgroup;
4653
4654	percpu_ref_exit(&css->refcnt);
4655
4656	if (ss) {
4657	/* css free path */
4658	int id = css->id;
4659
4660	if (css->parent)
4661	css_put(css->parent);
4662
4663	ss->css_free(css);
4664	cgroup_idr_remove(&ss->css_idr, id);
4665	cgroup_put(cgrp);
4666	} else {
4667	/* cgroup free path */
4668	atomic_dec(&cgrp->root->nr_cgrps);
4669	cgroup_pidlist_destroy_all(cgrp);
4670	cancel_work_sync(&cgrp->release_agent_work);
4671
4672	if (cgroup_parent(cgrp)) {
4673	/*
4674	* We get a ref to the parent, and put the ref when
4675	* this cgroup is being freed, so it's guaranteed
4676	* that the parent won't be destroyed before its
4677	* children.
4678	*/
4679	cgroup_put(cgroup_parent(cgrp));
4680	kernfs_put(cgrp->kn);
4681	kfree(cgrp);
4682	} else {
4683	/*
4684	* This is root cgroup's refcnt reaching zero,
4685	* which indicates that the root should be
4686	* released.
4687	*/
4688	cgroup_destroy_root(cgrp->root);
4689	}
4690	}
4691	}
4692
4693	static void css_free_rcu_fn(struct rcu_head *rcu_head)
4694	{
4695	struct cgroup_subsys_state *css =
4696	container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
4697
4698	INIT_WORK(&css->destroy_work, css_free_work_fn);
4699	queue_work(cgroup_destroy_wq, &css->destroy_work);
4700	}
4701
4702	static void css_release_work_fn(struct work_struct *work)
4703	{
4704	struct cgroup_subsys_state *css =
4705	container_of(work, struct cgroup_subsys_state, destroy_work);
4706	struct cgroup_subsys *ss = css->ss;
4707	struct cgroup *cgrp = css->cgroup;
4708
4709	mutex_lock(&cgroup_mutex);
4710
4711	css->flags \|= CSS_RELEASED;
4712	list_del_rcu(&css->sibling);
4713
4714	if (ss) {
4715	/* css release path */
4716	cgroup_idr_replace(&ss->css_idr, NULL, css->id);
4717	if (ss->css_released)
4718	ss->css_released(css);
4719	} else {
4720	/* cgroup release path */
4721	cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
4722	cgrp->id = -1;
4723
4724	/*
4725	* There are two control paths which try to determine
4726	* cgroup from dentry without going through kernfs -
4727	* cgroupstats_build() and css_tryget_online_from_dir().
4728	* Those are supported by RCU protecting clearing of
4729	* cgrp->kn->priv backpointer.
4730	*/
4731	RCU_INIT_POINTER((void __rcu __force *)&cgrp->kn->priv, NULL);
4732	}
4733
4734	mutex_unlock(&cgroup_mutex);
4735
4736	call_rcu(&css->rcu_head, css_free_rcu_fn);
4737	}
4738
4739	static void css_release(struct percpu_ref *ref)
4740	{
4741	struct cgroup_subsys_state *css =
4742	container_of(ref, struct cgroup_subsys_state, refcnt);
4743
4744	INIT_WORK(&css->destroy_work, css_release_work_fn);
4745	queue_work(cgroup_destroy_wq, &css->destroy_work);
4746	}
4747
4748	static void init_and_link_css(struct cgroup_subsys_state *css,
4749	struct cgroup_subsys ss, struct cgroup cgrp)
4750	{
4751	lockdep_assert_held(&cgroup_mutex);
4752
4753	cgroup_get(cgrp);
4754
4755	memset(css, 0, sizeof(*css));
4756	css->cgroup = cgrp;
4757	css->ss = ss;
4758	INIT_LIST_HEAD(&css->sibling);
4759	INIT_LIST_HEAD(&css->children);
4760	css->serial_nr = css_serial_nr_next++;
4761
4762	if (cgroup_parent(cgrp)) {
4763	css->parent = cgroup_css(cgroup_parent(cgrp), ss);
4764	css_get(css->parent);
4765	}
4766
4767	BUG_ON(cgroup_css(cgrp, ss));
4768	}
4769
4770	/* invoke ->css_online() on a new CSS and mark it online if successful */
4771	static int online_css(struct cgroup_subsys_state *css)
4772	{
4773	struct cgroup_subsys *ss = css->ss;
4774	int ret = 0;
4775
4776	lockdep_assert_held(&cgroup_mutex);
4777
4778	if (ss->css_online)
4779	ret = ss->css_online(css);
4780	if (!ret) {
4781	css->flags \|= CSS_ONLINE;
4782	rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
4783	}
4784	return ret;
4785	}
4786
4787	/* if the CSS is online, invoke ->css_offline() on it and mark it offline */
4788	static void offline_css(struct cgroup_subsys_state *css)
4789	{
4790	struct cgroup_subsys *ss = css->ss;
4791
4792	lockdep_assert_held(&cgroup_mutex);
4793
4794	if (!(css->flags & CSS_ONLINE))
4795	return;
4796
4797	if (ss->css_offline)
4798	ss->css_offline(css);
4799
4800	css->flags &= ~CSS_ONLINE;
4801	RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
4802
4803	wake_up_all(&css->cgroup->offline_waitq);
4804	}
4805
4806	/**
4807	* create_css - create a cgroup_subsys_state
4808	* @cgrp: the cgroup new css will be associated with
4809	* @ss: the subsys of new css
4810	* @visible: whether to create control knobs for the new css or not
4811	*
4812	* Create a new css associated with @cgrp - @ss pair. On success, the new
4813	* css is online and installed in @cgrp with all interface files created if
4814	* @visible. Returns 0 on success, -errno on failure.
4815	*/
4816	static int create_css(struct cgroup cgrp, struct cgroup_subsys ss,
4817	bool visible)
4818	{
4819	struct cgroup *parent = cgroup_parent(cgrp);
4820	struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
4821	struct cgroup_subsys_state *css;
4822	int err;
4823
4824	lockdep_assert_held(&cgroup_mutex);
4825
4826	css = ss->css_alloc(parent_css);
4827	if (IS_ERR(css))
4828	return PTR_ERR(css);
4829
4830	init_and_link_css(css, ss, cgrp);
4831
4832	err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
4833	if (err)
4834	goto err_free_css;
4835
4836	err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
4837	if (err < 0)
4838	goto err_free_percpu_ref;
4839	css->id = err;
4840
4841	if (visible) {
4842	err = css_populate_dir(css, NULL);
4843	if (err)
4844	goto err_free_id;
4845	}
4846
4847	/* @css is ready to be brought online now, make it visible */
4848	list_add_tail_rcu(&css->sibling, &parent_css->children);
4849	cgroup_idr_replace(&ss->css_idr, css, css->id);
4850
4851	err = online_css(css);
4852	if (err)
4853	goto err_list_del;
4854
4855	if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
4856	cgroup_parent(parent)) {
4857	pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
4858	current->comm, current->pid, ss->name);
4859	if (!strcmp(ss->name, "memory"))
4860	pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
4861	ss->warned_broken_hierarchy = true;
4862	}
4863
4864	return 0;
4865
4866	err_list_del:
4867	list_del_rcu(&css->sibling);
4868	css_clear_dir(css, NULL);
4869	err_free_id:
4870	cgroup_idr_remove(&ss->css_idr, css->id);
4871	err_free_percpu_ref:
4872	percpu_ref_exit(&css->refcnt);
4873	err_free_css:
4874	call_rcu(&css->rcu_head, css_free_rcu_fn);
4875	return err;
4876	}
4877
4878	static int cgroup_mkdir(struct kernfs_node parent_kn, const char name,
4879	umode_t mode)
4880	{
4881	struct cgroup parent, cgrp, *tcgrp;
4882	struct cgroup_root *root;
4883	struct cgroup_subsys *ss;
4884	struct kernfs_node *kn;
4885	int level, ssid, ret;
4886
4887	/* Do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable.
4888	*/
4889	if (strchr(name, '\n'))
4890	return -EINVAL;
4891
4892	parent = cgroup_kn_lock_live(parent_kn);
4893	if (!parent)
4894	return -ENODEV;
4895	root = parent->root;
4896	level = parent->level + 1;
4897
4898	/* allocate the cgroup and its ID, 0 is reserved for the root */
4899	cgrp = kzalloc(sizeof(*cgrp) +
4900	sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
4901	if (!cgrp) {
4902	ret = -ENOMEM;
4903	goto out_unlock;
4904	}
4905
4906	ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
4907	if (ret)
4908	goto out_free_cgrp;
4909
4910	/*
4911	* Temporarily set the pointer to NULL, so idr_find() won't return
4912	* a half-baked cgroup.
4913	*/
4914	cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
4915	if (cgrp->id < 0) {
4916	ret = -ENOMEM;
4917	goto out_cancel_ref;
4918	}
4919
4920	init_cgroup_housekeeping(cgrp);
4921
4922	cgrp->self.parent = &parent->self;
4923	cgrp->root = root;
4924	cgrp->level = level;
4925
4926	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp))
4927	cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
4928
4929	if (notify_on_release(parent))
4930	set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
4931
4932	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
4933	set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
4934
4935	/* create the directory */
4936	kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
4937	if (IS_ERR(kn)) {
4938	ret = PTR_ERR(kn);
4939	goto out_free_id;
4940	}
4941	cgrp->kn = kn;
4942
4943	/*
4944	* This extra ref will be put in cgroup_free_fn() and guarantees
4945	* that @cgrp->kn is always accessible.
4946	*/
4947	kernfs_get(kn);
4948
4949	cgrp->self.serial_nr = css_serial_nr_next++;
4950
4951	/* allocation complete, commit to creation */
4952	list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
4953	atomic_inc(&root->nr_cgrps);
4954	cgroup_get(parent);
4955
4956	/*
4957	* @cgrp is now fully operational. If something fails after this
4958	* point, it'll be released via the normal destruction path.
4959	*/
4960	cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
4961
4962	ret = cgroup_kn_set_ugid(kn);
4963	if (ret)
4964	goto out_destroy;
4965
4966	ret = css_populate_dir(&cgrp->self, NULL);
4967	if (ret)
4968	goto out_destroy;
4969
4970	/* let's create and online css's */
4971	for_each_subsys(ss, ssid) {
4972	if (parent->child_subsys_mask & (1 << ssid)) {
4973	ret = create_css(cgrp, ss,
4974	parent->subtree_control & (1 << ssid));
4975	if (ret)
4976	goto out_destroy;
4977	}
4978	}
4979
4980	/*
4981	* On the default hierarchy, a child doesn't automatically inherit
4982	* subtree_control from the parent. Each is configured manually.
4983	*/
4984	if (!cgroup_on_dfl(cgrp)) {
4985	cgrp->subtree_control = parent->subtree_control;
4986	cgroup_refresh_child_subsys_mask(cgrp);
4987	}
4988
4989	kernfs_activate(kn);
4990
4991	ret = 0;
4992	goto out_unlock;
4993
4994	out_free_id:
4995	cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
4996	out_cancel_ref:
4997	percpu_ref_exit(&cgrp->self.refcnt);
4998	out_free_cgrp:
4999	kfree(cgrp);
5000	out_unlock:
5001	cgroup_kn_unlock(parent_kn);
5002	return ret;
5003
5004	out_destroy:
5005	cgroup_destroy_locked(cgrp);
5006	goto out_unlock;
5007	}
5008
5009	/*
5010	* This is called when the refcnt of a css is confirmed to be killed.
5011	* css_tryget_online() is now guaranteed to fail. Tell the subsystem to
5012	* initate destruction and put the css ref from kill_css().
5013	*/
5014	static void css_killed_work_fn(struct work_struct *work)
5015	{
5016	struct cgroup_subsys_state *css =
5017	container_of(work, struct cgroup_subsys_state, destroy_work);
5018
5019	mutex_lock(&cgroup_mutex);
5020	offline_css(css);
5021	mutex_unlock(&cgroup_mutex);
5022
5023	css_put(css);
5024	}
5025
5026	/* css kill confirmation processing requires process context, bounce */
5027	static void css_killed_ref_fn(struct percpu_ref *ref)
5028	{
5029	struct cgroup_subsys_state *css =
5030	container_of(ref, struct cgroup_subsys_state, refcnt);
5031
5032	INIT_WORK(&css->destroy_work, css_killed_work_fn);
5033	queue_work(cgroup_destroy_wq, &css->destroy_work);
5034	}
5035
5036	/**
5037	* kill_css - destroy a css
5038	* @css: css to destroy
5039	*
5040	* This function initiates destruction of @css by removing cgroup interface
5041	* files and putting its base reference. ->css_offline() will be invoked
5042	* asynchronously once css_tryget_online() is guaranteed to fail and when
5043	* the reference count reaches zero, @css will be released.
5044	*/
5045	static void kill_css(struct cgroup_subsys_state *css)
5046	{
5047	lockdep_assert_held(&cgroup_mutex);
5048
5049	/*
5050	* This must happen before css is disassociated with its cgroup.
5051	* See seq_css() for details.
5052	*/
5053	css_clear_dir(css, NULL);
5054
5055	/*
5056	* Killing would put the base ref, but we need to keep it alive
5057	* until after ->css_offline().
5058	*/
5059	css_get(css);
5060
5061	/*
5062	* cgroup core guarantees that, by the time ->css_offline() is
5063	* invoked, no new css reference will be given out via
5064	* css_tryget_online(). We can't simply call percpu_ref_kill() and
5065	* proceed to offlining css's because percpu_ref_kill() doesn't
5066	* guarantee that the ref is seen as killed on all CPUs on return.
5067	*
5068	* Use percpu_ref_kill_and_confirm() to get notifications as each
5069	* css is confirmed to be seen as killed on all CPUs.
5070	*/
5071	percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5072	}
5073
5074	/**
5075	* cgroup_destroy_locked - the first stage of cgroup destruction
5076	* @cgrp: cgroup to be destroyed
5077	*
5078	* css's make use of percpu refcnts whose killing latency shouldn't be
5079	* exposed to userland and are RCU protected. Also, cgroup core needs to
5080	* guarantee that css_tryget_online() won't succeed by the time
5081	* ->css_offline() is invoked. To satisfy all the requirements,
5082	* destruction is implemented in the following two steps.
5083	*
5084	* s1. Verify @cgrp can be destroyed and mark it dying. Remove all
5085	* userland visible parts and start killing the percpu refcnts of
5086	* css's. Set up so that the next stage will be kicked off once all
5087	* the percpu refcnts are confirmed to be killed.
5088	*
5089	* s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5090	* rest of destruction. Once all cgroup references are gone, the
5091	* cgroup is RCU-freed.
5092	*
5093	* This function implements s1. After this step, @cgrp is gone as far as
5094	* the userland is concerned and a new cgroup with the same name may be
5095	* created. As cgroup doesn't care about the names internally, this
5096	* doesn't cause any problem.
5097	*/
5098	static int cgroup_destroy_locked(struct cgroup *cgrp)
5099	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5100	{
5101	struct cgroup_subsys_state *css;
5102	int ssid;
5103
5104	lockdep_assert_held(&cgroup_mutex);
5105
5106	/*
5107	* Only migration can raise populated from zero and we're already
5108	* holding cgroup_mutex.
5109	*/
5110	if (cgroup_is_populated(cgrp))
5111	return -EBUSY;
5112
5113	/*
5114	* Make sure there's no live children. We can't test emptiness of
5115	* ->self.children as dead children linger on it while being
5116	* drained; otherwise, "rmdir parent/child parent" may fail.
5117	*/
5118	if (css_has_online_children(&cgrp->self))
5119	return -EBUSY;
5120
5121	/*
5122	* Mark @cgrp dead. This prevents further task migration and child
5123	* creation by disabling cgroup_lock_live_group().
5124	*/
5125	cgrp->self.flags &= ~CSS_ONLINE;
5126
5127	/* initiate massacre of all css's */
5128	for_each_css(css, ssid, cgrp)
5129	kill_css(css);
5130
5131	/*
5132	* Remove @cgrp directory along with the base files. @cgrp has an
5133	* extra ref on its kn.
5134	*/
5135	kernfs_remove(cgrp->kn);
5136
5137	check_for_release(cgroup_parent(cgrp));
5138
5139	/* put the base reference */
5140	percpu_ref_kill(&cgrp->self.refcnt);
5141
5142	return 0;
5143	};
5144
5145	static int cgroup_rmdir(struct kernfs_node *kn)
5146	{
5147	struct cgroup *cgrp;
5148	int ret = 0;
5149
5150	cgrp = cgroup_kn_lock_live(kn);
5151	if (!cgrp)
5152	return 0;
5153
5154	ret = cgroup_destroy_locked(cgrp);
5155
5156	cgroup_kn_unlock(kn);
5157	return ret;
5158	}
5159
5160	static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5161	.remount_fs = cgroup_remount,
5162	.show_options = cgroup_show_options,
5163	.mkdir = cgroup_mkdir,
5164	.rmdir = cgroup_rmdir,
5165	.rename = cgroup_rename,
5166	};
5167
5168	static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5169	{
5170	struct cgroup_subsys_state *css;
5171
5172	pr_debug("Initializing cgroup subsys %s\n", ss->name);
5173
5174	mutex_lock(&cgroup_mutex);
5175
5176	idr_init(&ss->css_idr);
5177	INIT_LIST_HEAD(&ss->cfts);
5178
5179	/* Create the root cgroup state for this subsystem */
5180	ss->root = &cgrp_dfl_root;
5181	css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5182	/* We don't handle early failures gracefully */
5183	BUG_ON(IS_ERR(css));
5184	init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5185
5186	/*
5187	* Root csses are never destroyed and we can't initialize
5188	* percpu_ref during early init. Disable refcnting.
5189	*/
5190	css->flags \|= CSS_NO_REF;
5191
5192	if (early) {
5193	/* allocation can't be done safely during early init */
5194	css->id = 1;
5195	} else {
5196	css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5197	BUG_ON(css->id < 0);
5198	}
5199
5200	/* Update the init_css_set to contain a subsys
5201	* pointer to this state - since the subsystem is
5202	* newly registered, all tasks and hence the
5203	* init_css_set is in the subsystem's root cgroup. */
5204	init_css_set.subsys[ss->id] = css;
5205
5206	have_fork_callback \|= (bool)ss->fork << ss->id;
5207	have_exit_callback \|= (bool)ss->exit << ss->id;
5208	have_free_callback \|= (bool)ss->free << ss->id;
5209	have_canfork_callback \|= (bool)ss->can_fork << ss->id;
5210
5211	/* At system boot, before all subsystems have been
5212	* registered, no tasks have been forked, so we don't
5213	* need to invoke fork callbacks here. */
5214	BUG_ON(!list_empty(&init_task.tasks));
5215
5216	BUG_ON(online_css(css));
5217
5218	mutex_unlock(&cgroup_mutex);
5219	}
5220
5221	/**
5222	* cgroup_init_early - cgroup initialization at system boot
5223	*
5224	* Initialize cgroups at system boot, and initialize any
5225	* subsystems that request early init.
5226	*/
5227	int __init cgroup_init_early(void)
5228	{
5229	static struct cgroup_sb_opts __initdata opts;
5230	struct cgroup_subsys *ss;
5231	int i;
5232
5233	init_cgroup_root(&cgrp_dfl_root, &opts);
5234	cgrp_dfl_root.cgrp.self.flags \|= CSS_NO_REF;
5235
5236	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5237
5238	for_each_subsys(ss, i) {
5239	WARN(!ss->css_alloc \|\| !ss->css_free \|\| ss->name \|\| ss->id,
5240	"invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p name:id=%d:%s\n",
5241	i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5242	ss->id, ss->name);
5243	WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5244	"cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5245
5246	ss->id = i;
5247	ss->name = cgroup_subsys_name[i];
5248	if (!ss->legacy_name)
5249	ss->legacy_name = cgroup_subsys_name[i];
5250
5251	if (ss->early_init)
5252	cgroup_init_subsys(ss, true);
5253	}
5254	return 0;
5255	}
5256
5257	static unsigned long cgroup_disable_mask __initdata;
5258
5259	/**
5260	* cgroup_init - cgroup initialization
5261	*
5262	* Register cgroup filesystem and /proc file, and initialize
5263	* any subsystems that didn't request early init.
5264	*/
5265	int __init cgroup_init(void)
5266	{
5267	struct cgroup_subsys *ss;
5268	unsigned long key;
5269	int ssid;
5270
5271	BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
5272	BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
5273	BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
5274
5275	mutex_lock(&cgroup_mutex);
5276
5277	/* Add init_css_set to the hash table */
5278	key = css_set_hash(init_css_set.subsys);
5279	hash_add(css_set_table, &init_css_set.hlist, key);
5280
5281	BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5282
5283	mutex_unlock(&cgroup_mutex);
5284
5285	for_each_subsys(ss, ssid) {
5286	if (ss->early_init) {
5287	struct cgroup_subsys_state *css =
5288	init_css_set.subsys[ss->id];
5289
5290	css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5291	GFP_KERNEL);
5292	BUG_ON(css->id < 0);
5293	} else {
5294	cgroup_init_subsys(ss, false);
5295	}
5296
5297	list_add_tail(&init_css_set.e_cset_node[ssid],
5298	&cgrp_dfl_root.cgrp.e_csets[ssid]);
5299
5300	/*
5301	* Setting dfl_root subsys_mask needs to consider the
5302	* disabled flag and cftype registration needs kmalloc,
5303	* both of which aren't available during early_init.
5304	*/
5305	if (cgroup_disable_mask & (1 << ssid)) {
5306	static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5307	printk(KERN_INFO "Disabling %s control group subsystem\n",
5308	ss->name);
5309	continue;
5310	}
5311
5312	cgrp_dfl_root.subsys_mask \|= 1 << ss->id;
5313
5314	if (!ss->dfl_cftypes)
5315	cgrp_dfl_root_inhibit_ss_mask \|= 1 << ss->id;
5316
5317	if (ss->dfl_cftypes == ss->legacy_cftypes) {
5318	WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5319	} else {
5320	WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5321	WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5322	}
5323
5324	if (ss->bind)
5325	ss->bind(init_css_set.subsys[ssid]);
5326	}
5327
5328	WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5329	WARN_ON(register_filesystem(&cgroup_fs_type));
5330	WARN_ON(register_filesystem(&cgroup2_fs_type));
5331	WARN_ON(!proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations));
5332
5333	return 0;
5334	}
5335
5336	static int __init cgroup_wq_init(void)
5337	{
5338	/*
5339	* There isn't much point in executing destruction path in
5340	* parallel. Good chunk is serialized with cgroup_mutex anyway.
5341	* Use 1 for @max_active.
5342	*
5343	* We would prefer to do this in cgroup_init() above, but that
5344	* is called before init_workqueues(): so leave this until after.
5345	*/
5346	cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5347	BUG_ON(!cgroup_destroy_wq);
5348
5349	/*
5350	* Used to destroy pidlists and separate to serve as flush domain.
5351	* Cap @max_active to 1 too.
5352	*/
5353	cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
5354	0, 1);
5355	BUG_ON(!cgroup_pidlist_destroy_wq);
5356
5357	return 0;
5358	}
5359	core_initcall(cgroup_wq_init);
5360
5361	/*
5362	* proc_cgroup_show()
5363	* - Print task's cgroup paths into seq_file, one line for each hierarchy
5364	* - Used for /proc/<pid>/cgroup.
5365	*/
5366	int proc_cgroup_show(struct seq_file m, struct pid_namespace ns,
5367	struct pid pid, struct task_struct tsk)
5368	{
5369	char buf, path;
5370	int retval;
5371	struct cgroup_root *root;
5372
5373	retval = -ENOMEM;
5374	buf = kmalloc(PATH_MAX, GFP_KERNEL);
5375	if (!buf)
5376	goto out;
5377
5378	mutex_lock(&cgroup_mutex);
5379	spin_lock_bh(&css_set_lock);
5380
5381	for_each_root(root) {
5382	struct cgroup_subsys *ss;
5383	struct cgroup *cgrp;
5384	int ssid, count = 0;
5385
5386	if (root == &cgrp_dfl_root && !cgrp_dfl_root_visible)
5387	continue;
5388
5389	seq_printf(m, "%d:", root->hierarchy_id);
5390	if (root != &cgrp_dfl_root)
5391	for_each_subsys(ss, ssid)
5392	if (root->subsys_mask & (1 << ssid))
5393	seq_printf(m, "%s%s", count++ ? "," : "",
5394	ss->legacy_name);
5395	if (strlen(root->name))
5396	seq_printf(m, "%sname=%s", count ? "," : "",
5397	root->name);
5398	seq_putc(m, ':');
5399
5400	cgrp = task_cgroup_from_root(tsk, root);
5401
5402	/*
5403	* On traditional hierarchies, all zombie tasks show up as
5404	* belonging to the root cgroup. On the default hierarchy,
5405	* while a zombie doesn't show up in "cgroup.procs" and
5406	* thus can't be migrated, its /proc/PID/cgroup keeps
5407	* reporting the cgroup it belonged to before exiting. If
5408	* the cgroup is removed before the zombie is reaped,
5409	* " (deleted)" is appended to the cgroup path.
5410	*/
5411	if (cgroup_on_dfl(cgrp) \|\| !(tsk->flags & PF_EXITING)) {
5412	path = cgroup_path(cgrp, buf, PATH_MAX);
5413	if (!path) {
5414	retval = -ENAMETOOLONG;
5415	goto out_unlock;
5416	}
5417	} else {
5418	path = "/";
5419	}
5420
5421	seq_puts(m, path);
5422
5423	if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5424	seq_puts(m, " (deleted)\n");
5425	else
5426	seq_putc(m, '\n');
5427	}
5428
5429	retval = 0;
5430	out_unlock:
5431	spin_unlock_bh(&css_set_lock);
5432	mutex_unlock(&cgroup_mutex);
5433	kfree(buf);
5434	out:
5435	return retval;
5436	}
5437
5438	/* Display information about each subsystem and each hierarchy */
5439	static int proc_cgroupstats_show(struct seq_file m, void v)
5440	{
5441	struct cgroup_subsys *ss;
5442	int i;
5443
5444	seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
5445	/*
5446	* ideally we don't want subsystems moving around while we do this.
5447	* cgroup_mutex is also necessary to guarantee an atomic snapshot of
5448	* subsys/hierarchy state.
5449	*/
5450	mutex_lock(&cgroup_mutex);
5451
5452	for_each_subsys(ss, i)
5453	seq_printf(m, "%s\t%d\t%d\t%d\n",
5454	ss->legacy_name, ss->root->hierarchy_id,
5455	atomic_read(&ss->root->nr_cgrps),
5456	cgroup_ssid_enabled(i));
5457
5458	mutex_unlock(&cgroup_mutex);
5459	return 0;
5460	}
5461
5462	static int cgroupstats_open(struct inode inode, struct file file)
5463	{
5464	return single_open(file, proc_cgroupstats_show, NULL);
5465	}
5466
5467	static const struct file_operations proc_cgroupstats_operations = {
5468	.open = cgroupstats_open,
5469	.read = seq_read,
5470	.llseek = seq_lseek,
5471	.release = single_release,
5472	};
5473
5474	/**
5475	* cgroup_fork - initialize cgroup related fields during copy_process()
5476	* @child: pointer to task_struct of forking parent process.
5477	*
5478	* A task is associated with the init_css_set until cgroup_post_fork()
5479	* attaches it to the parent's css_set. Empty cg_list indicates that
5480	* @child isn't holding reference to its css_set.
5481	*/
5482	void cgroup_fork(struct task_struct *child)
5483	{
5484	RCU_INIT_POINTER(child->cgroups, &init_css_set);
5485	INIT_LIST_HEAD(&child->cg_list);
5486	}
5487
5488	/**
5489	* cgroup_can_fork - called on a new task before the process is exposed
5490	* @child: the task in question.
5491	*
5492	* This calls the subsystem can_fork() callbacks. If the can_fork() callback
5493	* returns an error, the fork aborts with that error code. This allows for
5494	* a cgroup subsystem to conditionally allow or deny new forks.
5495	*/
5496	int cgroup_can_fork(struct task_struct *child)
5497	{
5498	struct cgroup_subsys *ss;
5499	int i, j, ret;
5500
5501	for_each_subsys_which(ss, i, &have_canfork_callback) {
5502	ret = ss->can_fork(child);
5503	if (ret)
5504	goto out_revert;
5505	}
5506
5507	return 0;
5508
5509	out_revert:
5510	for_each_subsys(ss, j) {
5511	if (j >= i)
5512	break;
5513	if (ss->cancel_fork)
5514	ss->cancel_fork(child);
5515	}
5516
5517	return ret;
5518	}
5519
5520	/**
5521	* cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5522	* @child: the task in question
5523	*
5524	* This calls the cancel_fork() callbacks if a fork failed after
5525	* cgroup_can_fork() succeded.
5526	*/
5527	void cgroup_cancel_fork(struct task_struct *child)
5528	{
5529	struct cgroup_subsys *ss;
5530	int i;
5531
5532	for_each_subsys(ss, i)
5533	if (ss->cancel_fork)
5534	ss->cancel_fork(child);
5535	}
5536
5537	/**
5538	* cgroup_post_fork - called on a new task after adding it to the task list
5539	* @child: the task in question
5540	*
5541	* Adds the task to the list running through its css_set if necessary and
5542	* call the subsystem fork() callbacks. Has to be after the task is
5543	* visible on the task list in case we race with the first call to
5544	* cgroup_task_iter_start() - to guarantee that the new task ends up on its
5545	* list.
5546	*/
5547	void cgroup_post_fork(struct task_struct *child)
5548	{
5549	struct cgroup_subsys *ss;
5550	int i;
5551
5552	/*
5553	* This may race against cgroup_enable_task_cg_lists(). As that
5554	* function sets use_task_css_set_links before grabbing
5555	* tasklist_lock and we just went through tasklist_lock to add
5556	* @child, it's guaranteed that either we see the set
5557	* use_task_css_set_links or cgroup_enable_task_cg_lists() sees
5558	* @child during its iteration.
5559	*
5560	* If we won the race, @child is associated with %current's
5561	* css_set. Grabbing css_set_lock guarantees both that the
5562	* association is stable, and, on completion of the parent's
5563	* migration, @child is visible in the source of migration or
5564	* already in the destination cgroup. This guarantee is necessary
5565	* when implementing operations which need to migrate all tasks of
5566	* a cgroup to another.
5567	*
5568	* Note that if we lose to cgroup_enable_task_cg_lists(), @child
5569	* will remain in init_css_set. This is safe because all tasks are
5570	* in the init_css_set before cg_links is enabled and there's no
5571	* operation which transfers all tasks out of init_css_set.
5572	*/
5573	if (use_task_css_set_links) {
5574	struct css_set *cset;
5575
5576	spin_lock_bh(&css_set_lock);
5577	cset = task_css_set(current);
5578	if (list_empty(&child->cg_list)) {
5579	get_css_set(cset);
5580	css_set_move_task(child, NULL, cset, false);
5581	}
5582	spin_unlock_bh(&css_set_lock);
5583	}
5584
5585	/*
5586	* Call ss->fork(). This must happen after @child is linked on
5587	* css_set; otherwise, @child might change state between ->fork()
5588	* and addition to css_set.
5589	*/
5590	for_each_subsys_which(ss, i, &have_fork_callback)
5591	ss->fork(child);
5592	}
5593
5594	/**
5595	* cgroup_exit - detach cgroup from exiting task
5596	* @tsk: pointer to task_struct of exiting process
5597	*
5598	* Description: Detach cgroup from @tsk and release it.
5599	*
5600	* Note that cgroups marked notify_on_release force every task in
5601	* them to take the global cgroup_mutex mutex when exiting.
5602	* This could impact scaling on very large systems. Be reluctant to
5603	* use notify_on_release cgroups where very high task exit scaling
5604	* is required on large systems.
5605	*
5606	* We set the exiting tasks cgroup to the root cgroup (top_cgroup). We
5607	* call cgroup_exit() while the task is still competent to handle
5608	* notify_on_release(), then leave the task attached to the root cgroup in
5609	* each hierarchy for the remainder of its exit. No need to bother with
5610	* init_css_set refcnting. init_css_set never goes away and we can't race
5611	* with migration path - PF_EXITING is visible to migration path.
5612	*/
5613	void cgroup_exit(struct task_struct *tsk)
5614	{
5615	struct cgroup_subsys *ss;
5616	struct css_set *cset;
5617	int i;
5618
5619	/*
5620	* Unlink from @tsk from its css_set. As migration path can't race
5621	* with us, we can check css_set and cg_list without synchronization.
5622	*/
5623	cset = task_css_set(tsk);
5624
5625	if (!list_empty(&tsk->cg_list)) {
5626	spin_lock_bh(&css_set_lock);
5627	css_set_move_task(tsk, cset, NULL, false);
5628	spin_unlock_bh(&css_set_lock);
5629	} else {
5630	get_css_set(cset);
5631	}
5632
5633	/* see cgroup_post_fork() for details */
5634	for_each_subsys_which(ss, i, &have_exit_callback)
5635	ss->exit(tsk);
5636	}
5637
5638	void cgroup_free(struct task_struct *task)
5639	{
5640	struct css_set *cset = task_css_set(task);
5641	struct cgroup_subsys *ss;
5642	int ssid;
5643
5644	for_each_subsys_which(ss, ssid, &have_free_callback)
5645	ss->free(task);
5646
5647	put_css_set(cset);
5648	}
5649
5650	static void check_for_release(struct cgroup *cgrp)
5651	{
5652	if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) &&
5653	!css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
5654	schedule_work(&cgrp->release_agent_work);
5655	}
5656
5657	/*
5658	* Notify userspace when a cgroup is released, by running the
5659	* configured release agent with the name of the cgroup (path
5660	* relative to the root of cgroup file system) as the argument.
5661	*
5662	* Most likely, this user command will try to rmdir this cgroup.
5663	*
5664	* This races with the possibility that some other task will be
5665	* attached to this cgroup before it is removed, or that some other
5666	* user task will 'mkdir' a child cgroup of this cgroup. That's ok.
5667	* The presumed 'rmdir' will fail quietly if this cgroup is no longer
5668	* unused, and this cgroup will be reprieved from its death sentence,
5669	* to continue to serve a useful existence. Next time it's released,
5670	* we will get notified again, if it still has 'notify_on_release' set.
5671	*
5672	* The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
5673	* means only wait until the task is successfully execve()'d. The
5674	* separate release agent task is forked by call_usermodehelper(),
5675	* then control in this thread returns here, without waiting for the
5676	* release agent task. We don't bother to wait because the caller of
5677	* this routine has no use for the exit status of the release agent
5678	* task, so no sense holding our caller up for that.
5679	*/
5680	static void cgroup_release_agent(struct work_struct *work)
5681	{
5682	struct cgroup *cgrp =
5683	container_of(work, struct cgroup, release_agent_work);
5684	char pathbuf = NULL, agentbuf = NULL, *path;
5685	char argv[3], envp[3];
5686
5687	mutex_lock(&cgroup_mutex);
5688
5689	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
5690	agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
5691	if (!pathbuf \|\| !agentbuf)
5692	goto out;
5693
5694	path = cgroup_path(cgrp, pathbuf, PATH_MAX);
5695	if (!path)
5696	goto out;
5697
5698	argv[0] = agentbuf;
5699	argv[1] = path;
5700	argv[2] = NULL;
5701
5702	/* minimal command environment */
5703	envp[0] = "HOME=/";
5704	envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
5705	envp[2] = NULL;
5706
5707	mutex_unlock(&cgroup_mutex);
5708	call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
5709	goto out_free;
5710	out:
5711	mutex_unlock(&cgroup_mutex);
5712	out_free:
5713	kfree(agentbuf);
5714	kfree(pathbuf);
5715	}
5716
5717	static int __init cgroup_disable(char *str)
5718	{
5719	struct cgroup_subsys *ss;
5720	char *token;
5721	int i;
5722
5723	while ((token = strsep(&str, ",")) != NULL) {
5724	if (!*token)
5725	continue;
5726
5727	for_each_subsys(ss, i) {
5728	if (strcmp(token, ss->name) &&
5729	strcmp(token, ss->legacy_name))
5730	continue;
5731	cgroup_disable_mask \|= 1 << i;
5732	}
5733	}
5734	return 1;
5735	}
5736	__setup("cgroup_disable=", cgroup_disable);
5737
5738	/**
5739	* css_tryget_online_from_dir - get corresponding css from a cgroup dentry
5740	* @dentry: directory dentry of interest
5741	* @ss: subsystem of interest
5742	*
5743	* If @dentry is a directory for a cgroup which has @ss enabled on it, try
5744	* to get the corresponding css and return it. If such css doesn't exist
5745	* or can't be pinned, an ERR_PTR value is returned.
5746	*/
5747	struct cgroup_subsys_state css_tryget_online_from_dir(struct dentry dentry,
5748	struct cgroup_subsys *ss)
5749	{
5750	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
5751	struct cgroup_subsys_state *css = NULL;
5752	struct cgroup *cgrp;
5753
5754	/* is @dentry a cgroup dir? */
5755	if (dentry->d_sb->s_type != &cgroup_fs_type \|\| !kn \|\|
5756	kernfs_type(kn) != KERNFS_DIR)
5757	return ERR_PTR(-EBADF);
5758
5759	rcu_read_lock();
5760
5761	/*
5762	* This path doesn't originate from kernfs and @kn could already
5763	* have been or be removed at any point. @kn->priv is RCU
5764	* protected for this access. See css_release_work_fn() for details.
5765	*/
5766	cgrp = rcu_dereference(kn->priv);
5767	if (cgrp)
5768	css = cgroup_css(cgrp, ss);
5769
5770	if (!css \|\| !css_tryget_online(css))
5771	css = ERR_PTR(-ENOENT);
5772
5773	rcu_read_unlock();
5774	return css;
5775	}
5776
5777	/**
5778	* css_from_id - lookup css by id
5779	* @id: the cgroup id
5780	* @ss: cgroup subsys to be looked into
5781	*
5782	* Returns the css if there's valid one with @id, otherwise returns NULL.
5783	* Should be called under rcu_read_lock().
5784	*/
5785	struct cgroup_subsys_state css_from_id(int id, struct cgroup_subsys ss)
5786	{
5787	WARN_ON_ONCE(!rcu_read_lock_held());
5788	return id > 0 ? idr_find(&ss->css_idr, id) : NULL;
5789	}
5790
5791	/**
5792	* cgroup_get_from_path - lookup and get a cgroup from its default hierarchy path
5793	* @path: path on the default hierarchy
5794	*
5795	* Find the cgroup at @path on the default hierarchy, increment its
5796	* reference count and return it. Returns pointer to the found cgroup on
5797	* success, ERR_PTR(-ENOENT) if @path doens't exist and ERR_PTR(-ENOTDIR)
5798	* if @path points to a non-directory.
5799	*/
5800	struct cgroup cgroup_get_from_path(const char path)
5801	{
5802	struct kernfs_node *kn;
5803	struct cgroup *cgrp;
5804
5805	mutex_lock(&cgroup_mutex);
5806
5807	kn = kernfs_walk_and_get(cgrp_dfl_root.cgrp.kn, path);
5808	if (kn) {
5809	if (kernfs_type(kn) == KERNFS_DIR) {
5810	cgrp = kn->priv;
5811	cgroup_get(cgrp);
5812	} else {
5813	cgrp = ERR_PTR(-ENOTDIR);
5814	}
5815	kernfs_put(kn);
5816	} else {
5817	cgrp = ERR_PTR(-ENOENT);
5818	}
5819
5820	mutex_unlock(&cgroup_mutex);
5821	return cgrp;
5822	}
5823	EXPORT_SYMBOL_GPL(cgroup_get_from_path);
5824
5825	/*
5826	* sock->sk_cgrp_data handling. For more info, see sock_cgroup_data
5827	* definition in cgroup-defs.h.
5828	*/
5829	#ifdef CONFIG_SOCK_CGROUP_DATA
5830
5831	#if defined(CONFIG_CGROUP_NET_PRIO) \|\| defined(CONFIG_CGROUP_NET_CLASSID)
5832
5833	DEFINE_SPINLOCK(cgroup_sk_update_lock);
5834	static bool cgroup_sk_alloc_disabled __read_mostly;
5835
5836	void cgroup_sk_alloc_disable(void)
5837	{
5838	if (cgroup_sk_alloc_disabled)
5839	return;
5840	pr_info("cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation\n");
5841	cgroup_sk_alloc_disabled = true;
5842	}
5843
5844	#else
5845
5846	#define cgroup_sk_alloc_disabled false
5847
5848	#endif
5849
5850	void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
5851	{
5852	if (cgroup_sk_alloc_disabled)
5853	return;
5854
5855	rcu_read_lock();
5856
5857	while (true) {
5858	struct css_set *cset;
5859
5860	cset = task_css_set(current);
5861	if (likely(cgroup_tryget(cset->dfl_cgrp))) {
5862	skcd->val = (unsigned long)cset->dfl_cgrp;
5863	break;
5864	}
5865	cpu_relax();
5866	}
5867
5868	rcu_read_unlock();
5869	}
5870
5871	void cgroup_sk_free(struct sock_cgroup_data *skcd)
5872	{
5873	cgroup_put(sock_cgroup_ptr(skcd));
5874	}
5875
5876	#endif /* CONFIG_SOCK_CGROUP_DATA */
5877
5878	#ifdef CONFIG_CGROUP_DEBUG
5879	static struct cgroup_subsys_state *
5880	debug_css_alloc(struct cgroup_subsys_state *parent_css)
5881	{
5882	struct cgroup_subsys_state css = kzalloc(sizeof(css), GFP_KERNEL);
5883
5884	if (!css)
5885	return ERR_PTR(-ENOMEM);
5886
5887	return css;
5888	}
5889
5890	static void debug_css_free(struct cgroup_subsys_state *css)
5891	{
5892	kfree(css);
5893	}
5894
5895	static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
5896	struct cftype *cft)
5897	{
5898	return cgroup_task_count(css->cgroup);
5899	}
5900
5901	static u64 current_css_set_read(struct cgroup_subsys_state *css,
5902	struct cftype *cft)
5903	{
5904	return (u64)(unsigned long)current->cgroups;
5905	}
5906
5907	static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
5908	struct cftype *cft)
5909	{
5910	u64 count;
5911
5912	rcu_read_lock();
5913	count = atomic_read(&task_css_set(current)->refcount);
5914	rcu_read_unlock();
5915	return count;
5916	}
5917
5918	static int current_css_set_cg_links_read(struct seq_file seq, void v)
5919	{
5920	struct cgrp_cset_link *link;
5921	struct css_set *cset;
5922	char *name_buf;
5923
5924	name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
5925	if (!name_buf)
5926	return -ENOMEM;
5927
5928	spin_lock_bh(&css_set_lock);
5929	rcu_read_lock();
5930	cset = rcu_dereference(current->cgroups);
5931	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
5932	struct cgroup *c = link->cgrp;
5933
5934	cgroup_name(c, name_buf, NAME_MAX + 1);
5935	seq_printf(seq, "Root %d group %s\n",
5936	c->root->hierarchy_id, name_buf);
5937	}
5938	rcu_read_unlock();
5939	spin_unlock_bh(&css_set_lock);
5940	kfree(name_buf);
5941	return 0;
5942	}
5943
5944	#define MAX_TASKS_SHOWN_PER_CSS 25
5945	static int cgroup_css_links_read(struct seq_file seq, void v)
5946	{
5947	struct cgroup_subsys_state *css = seq_css(seq);
5948	struct cgrp_cset_link *link;
5949
5950	spin_lock_bh(&css_set_lock);
5951	list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
5952	struct css_set *cset = link->cset;
5953	struct task_struct *task;
5954	int count = 0;
5955
5956	seq_printf(seq, "css_set %p\n", cset);
5957
5958	list_for_each_entry(task, &cset->tasks, cg_list) {
5959	if (count++ > MAX_TASKS_SHOWN_PER_CSS)
5960	goto overflow;
5961	seq_printf(seq, " task %d\n", task_pid_vnr(task));
5962	}
5963
5964	list_for_each_entry(task, &cset->mg_tasks, cg_list) {
5965	if (count++ > MAX_TASKS_SHOWN_PER_CSS)
5966	goto overflow;
5967	seq_printf(seq, " task %d\n", task_pid_vnr(task));
5968	}
5969	continue;
5970	overflow:
5971	seq_puts(seq, " ...\n");
5972	}
5973	spin_unlock_bh(&css_set_lock);
5974	return 0;
5975	}
5976
5977	static u64 releasable_read(struct cgroup_subsys_state css, struct cftype cft)
5978	{
5979	return (!cgroup_is_populated(css->cgroup) &&
5980	!css_has_online_children(&css->cgroup->self));
5981	}
5982
5983	static struct cftype debug_files[] = {
5984	{
5985	.name = "taskcount",
5986	.read_u64 = debug_taskcount_read,
5987	},
5988
5989	{
5990	.name = "current_css_set",
5991	.read_u64 = current_css_set_read,
5992	},
5993
5994	{
5995	.name = "current_css_set_refcount",
5996	.read_u64 = current_css_set_refcount_read,
5997	},
5998
5999	{
6000	.name = "current_css_set_cg_links",
6001	.seq_show = current_css_set_cg_links_read,
6002	},
6003
6004	{
6005	.name = "cgroup_css_links",
6006	.seq_show = cgroup_css_links_read,
6007	},
6008
6009	{
6010	.name = "releasable",
6011	.read_u64 = releasable_read,
6012	},
6013
6014	{ } /* terminate */
6015	};
6016
6017	struct cgroup_subsys debug_cgrp_subsys = {
6018	.css_alloc = debug_css_alloc,
6019	.css_free = debug_css_free,
6020	.legacy_cftypes = debug_files,
6021	};
6022	#endif /* CONFIG_CGROUP_DEBUG */