Root/kernel/cgroup.c

1/*
2 * Generic process-grouping system.
3 *
4 * Based originally on the cpuset system, extracted by Paul Menage
5 * Copyright (C) 2006 Google, Inc
6 *
7 * Notifications support
8 * Copyright (C) 2009 Nokia Corporation
9 * Author: Kirill A. Shutemov
10 *
11 * Copyright notices from the original cpuset code:
12 * --------------------------------------------------
13 * Copyright (C) 2003 BULL SA.
14 * Copyright (C) 2004-2006 Silicon Graphics, Inc.
15 *
16 * Portions derived from Patrick Mochel's sysfs code.
17 * sysfs is Copyright (c) 2001-3 Patrick Mochel
18 *
19 * 2003-10-10 Written by Simon Derr.
20 * 2003-10-22 Updates by Stephen Hemminger.
21 * 2004 May-July Rework by Paul Jackson.
22 * ---------------------------------------------------
23 *
24 * This file is subject to the terms and conditions of the GNU General Public
25 * License. See the file COPYING in the main directory of the Linux
26 * distribution for more details.
27 */
28
29#include <linux/cgroup.h>
30#include <linux/cred.h>
31#include <linux/ctype.h>
32#include <linux/errno.h>
33#include <linux/init_task.h>
34#include <linux/kernel.h>
35#include <linux/list.h>
36#include <linux/magic.h>
37#include <linux/mm.h>
38#include <linux/mutex.h>
39#include <linux/mount.h>
40#include <linux/pagemap.h>
41#include <linux/proc_fs.h>
42#include <linux/rcupdate.h>
43#include <linux/sched.h>
44#include <linux/slab.h>
45#include <linux/spinlock.h>
46#include <linux/rwsem.h>
47#include <linux/string.h>
48#include <linux/sort.h>
49#include <linux/kmod.h>
50#include <linux/delayacct.h>
51#include <linux/cgroupstats.h>
52#include <linux/hashtable.h>
53#include <linux/pid_namespace.h>
54#include <linux/idr.h>
55#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
56#include <linux/kthread.h>
57#include <linux/delay.h>
58
59#include <linux/atomic.h>
60
61/*
62 * pidlists linger the following amount before being destroyed. The goal
63 * is avoiding frequent destruction in the middle of consecutive read calls
64 * Expiring in the middle is a performance problem not a correctness one.
65 * 1 sec should be enough.
66 */
67#define CGROUP_PIDLIST_DESTROY_DELAY HZ
68
69#define CGROUP_FILE_NAME_MAX (MAX_CGROUP_TYPE_NAMELEN + \
70                     MAX_CFTYPE_NAME + 2)
71
72/*
73 * cgroup_tree_mutex nests above cgroup_mutex and protects cftypes, file
74 * creation/removal and hierarchy changing operations including cgroup
75 * creation, removal, css association and controller rebinding. This outer
76 * lock is needed mainly to resolve the circular dependency between kernfs
77 * active ref and cgroup_mutex. cgroup_tree_mutex nests above both.
78 */
79static DEFINE_MUTEX(cgroup_tree_mutex);
80
81/*
82 * cgroup_mutex is the master lock. Any modification to cgroup or its
83 * hierarchy must be performed while holding it.
84 *
85 * css_set_rwsem protects task->cgroups pointer, the list of css_set
86 * objects, and the chain of tasks off each css_set.
87 *
88 * These locks are exported if CONFIG_PROVE_RCU so that accessors in
89 * cgroup.h can use them for lockdep annotations.
90 */
91#ifdef CONFIG_PROVE_RCU
92DEFINE_MUTEX(cgroup_mutex);
93DECLARE_RWSEM(css_set_rwsem);
94EXPORT_SYMBOL_GPL(cgroup_mutex);
95EXPORT_SYMBOL_GPL(css_set_rwsem);
96#else
97static DEFINE_MUTEX(cgroup_mutex);
98static DECLARE_RWSEM(css_set_rwsem);
99#endif
100
101/*
102 * Protects cgroup_subsys->release_agent_path. Modifying it also requires
103 * cgroup_mutex. Reading requires either cgroup_mutex or this spinlock.
104 */
105static DEFINE_SPINLOCK(release_agent_path_lock);
106
107#define cgroup_assert_mutexes_or_rcu_locked() \
108    rcu_lockdep_assert(rcu_read_lock_held() || \
109               lockdep_is_held(&cgroup_tree_mutex) || \
110               lockdep_is_held(&cgroup_mutex), \
111               "cgroup_[tree_]mutex or RCU read lock required");
112
113/*
114 * cgroup destruction makes heavy use of work items and there can be a lot
115 * of concurrent destructions. Use a separate workqueue so that cgroup
116 * destruction work items don't end up filling up max_active of system_wq
117 * which may lead to deadlock.
118 */
119static struct workqueue_struct *cgroup_destroy_wq;
120
121/*
122 * pidlist destructions need to be flushed on cgroup destruction. Use a
123 * separate workqueue as flush domain.
124 */
125static struct workqueue_struct *cgroup_pidlist_destroy_wq;
126
127/* generate an array of cgroup subsystem pointers */
128#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
129static struct cgroup_subsys *cgroup_subsys[] = {
130#include <linux/cgroup_subsys.h>
131};
132#undef SUBSYS
133
134/* array of cgroup subsystem names */
135#define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
136static const char *cgroup_subsys_name[] = {
137#include <linux/cgroup_subsys.h>
138};
139#undef SUBSYS
140
141/*
142 * The default hierarchy, reserved for the subsystems that are otherwise
143 * unattached - it never has more than a single cgroup, and all tasks are
144 * part of that cgroup.
145 */
146struct cgroup_root cgrp_dfl_root;
147
148/*
149 * The default hierarchy always exists but is hidden until mounted for the
150 * first time. This is for backward compatibility.
151 */
152static bool cgrp_dfl_root_visible;
153
154/* The list of hierarchy roots */
155
156static LIST_HEAD(cgroup_roots);
157static int cgroup_root_count;
158
159/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
160static DEFINE_IDR(cgroup_hierarchy_idr);
161
162/*
163 * Assign a monotonically increasing serial number to cgroups. It
164 * guarantees cgroups with bigger numbers are newer than those with smaller
165 * numbers. Also, as cgroups are always appended to the parent's
166 * ->children list, it guarantees that sibling cgroups are always sorted in
167 * the ascending serial number order on the list. Protected by
168 * cgroup_mutex.
169 */
170static u64 cgroup_serial_nr_next = 1;
171
172/* This flag indicates whether tasks in the fork and exit paths should
173 * check for fork/exit handlers to call. This avoids us having to do
174 * extra work in the fork/exit path if none of the subsystems need to
175 * be called.
176 */
177static int need_forkexit_callback __read_mostly;
178
179static struct cftype cgroup_base_files[];
180
181static void cgroup_put(struct cgroup *cgrp);
182static int rebind_subsystems(struct cgroup_root *dst_root,
183                 unsigned long ss_mask);
184static void cgroup_destroy_css_killed(struct cgroup *cgrp);
185static int cgroup_destroy_locked(struct cgroup *cgrp);
186static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
187                  bool is_add);
188static void cgroup_pidlist_destroy_all(struct cgroup *cgrp);
189
190/**
191 * cgroup_css - obtain a cgroup's css for the specified subsystem
192 * @cgrp: the cgroup of interest
193 * @ss: the subsystem of interest (%NULL returns the dummy_css)
194 *
195 * Return @cgrp's css (cgroup_subsys_state) associated with @ss. This
196 * function must be called either under cgroup_mutex or rcu_read_lock() and
197 * the caller is responsible for pinning the returned css if it wants to
198 * keep accessing it outside the said locks. This function may return
199 * %NULL if @cgrp doesn't have @subsys_id enabled.
200 */
201static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
202                          struct cgroup_subsys *ss)
203{
204    if (ss)
205        return rcu_dereference_check(cgrp->subsys[ss->id],
206                    lockdep_is_held(&cgroup_tree_mutex) ||
207                    lockdep_is_held(&cgroup_mutex));
208    else
209        return &cgrp->dummy_css;
210}
211
212/* convenient tests for these bits */
213static inline bool cgroup_is_dead(const struct cgroup *cgrp)
214{
215    return test_bit(CGRP_DEAD, &cgrp->flags);
216}
217
218struct cgroup_subsys_state *seq_css(struct seq_file *seq)
219{
220    struct kernfs_open_file *of = seq->private;
221    struct cgroup *cgrp = of->kn->parent->priv;
222    struct cftype *cft = seq_cft(seq);
223
224    /*
225     * This is open and unprotected implementation of cgroup_css().
226     * seq_css() is only called from a kernfs file operation which has
227     * an active reference on the file. Because all the subsystem
228     * files are drained before a css is disassociated with a cgroup,
229     * the matching css from the cgroup's subsys table is guaranteed to
230     * be and stay valid until the enclosing operation is complete.
231     */
232    if (cft->ss)
233        return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
234    else
235        return &cgrp->dummy_css;
236}
237EXPORT_SYMBOL_GPL(seq_css);
238
239/**
240 * cgroup_is_descendant - test ancestry
241 * @cgrp: the cgroup to be tested
242 * @ancestor: possible ancestor of @cgrp
243 *
244 * Test whether @cgrp is a descendant of @ancestor. It also returns %true
245 * if @cgrp == @ancestor. This function is safe to call as long as @cgrp
246 * and @ancestor are accessible.
247 */
248bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)
249{
250    while (cgrp) {
251        if (cgrp == ancestor)
252            return true;
253        cgrp = cgrp->parent;
254    }
255    return false;
256}
257
258static int cgroup_is_releasable(const struct cgroup *cgrp)
259{
260    const int bits =
261        (1 << CGRP_RELEASABLE) |
262        (1 << CGRP_NOTIFY_ON_RELEASE);
263    return (cgrp->flags & bits) == bits;
264}
265
266static int notify_on_release(const struct cgroup *cgrp)
267{
268    return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
269}
270
271/**
272 * for_each_css - iterate all css's of a cgroup
273 * @css: the iteration cursor
274 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
275 * @cgrp: the target cgroup to iterate css's of
276 *
277 * Should be called under cgroup_mutex.
278 */
279#define for_each_css(css, ssid, cgrp) \
280    for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++) \
281        if (!((css) = rcu_dereference_check( \
282                (cgrp)->subsys[(ssid)], \
283                lockdep_is_held(&cgroup_tree_mutex) || \
284                lockdep_is_held(&cgroup_mutex)))) { } \
285        else
286
287/**
288 * for_each_subsys - iterate all enabled cgroup subsystems
289 * @ss: the iteration cursor
290 * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
291 */
292#define for_each_subsys(ss, ssid) \
293    for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT && \
294         (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
295
296/* iterate across the hierarchies */
297#define for_each_root(root) \
298    list_for_each_entry((root), &cgroup_roots, root_list)
299
300/**
301 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
302 * @cgrp: the cgroup to be checked for liveness
303 *
304 * On success, returns true; the mutex should be later unlocked. On
305 * failure returns false with no lock held.
306 */
307static bool cgroup_lock_live_group(struct cgroup *cgrp)
308{
309    mutex_lock(&cgroup_mutex);
310    if (cgroup_is_dead(cgrp)) {
311        mutex_unlock(&cgroup_mutex);
312        return false;
313    }
314    return true;
315}
316
317/* the list of cgroups eligible for automatic release. Protected by
318 * release_list_lock */
319static LIST_HEAD(release_list);
320static DEFINE_RAW_SPINLOCK(release_list_lock);
321static void cgroup_release_agent(struct work_struct *work);
322static DECLARE_WORK(release_agent_work, cgroup_release_agent);
323static void check_for_release(struct cgroup *cgrp);
324
325/*
326 * A cgroup can be associated with multiple css_sets as different tasks may
327 * belong to different cgroups on different hierarchies. In the other
328 * direction, a css_set is naturally associated with multiple cgroups.
329 * This M:N relationship is represented by the following link structure
330 * which exists for each association and allows traversing the associations
331 * from both sides.
332 */
333struct cgrp_cset_link {
334    /* the cgroup and css_set this link associates */
335    struct cgroup *cgrp;
336    struct css_set *cset;
337
338    /* list of cgrp_cset_links anchored at cgrp->cset_links */
339    struct list_head cset_link;
340
341    /* list of cgrp_cset_links anchored at css_set->cgrp_links */
342    struct list_head cgrp_link;
343};
344
345/*
346 * The default css_set - used by init and its children prior to any
347 * hierarchies being mounted. It contains a pointer to the root state
348 * for each subsystem. Also used to anchor the list of css_sets. Not
349 * reference-counted, to improve performance when child cgroups
350 * haven't been created.
351 */
352struct css_set init_css_set = {
353    .refcount = ATOMIC_INIT(1),
354    .cgrp_links = LIST_HEAD_INIT(init_css_set.cgrp_links),
355    .tasks = LIST_HEAD_INIT(init_css_set.tasks),
356    .mg_tasks = LIST_HEAD_INIT(init_css_set.mg_tasks),
357    .mg_preload_node = LIST_HEAD_INIT(init_css_set.mg_preload_node),
358    .mg_node = LIST_HEAD_INIT(init_css_set.mg_node),
359};
360
361static int css_set_count = 1; /* 1 for init_css_set */
362
363/*
364 * hash table for cgroup groups. This improves the performance to find
365 * an existing css_set. This hash doesn't (currently) take into
366 * account cgroups in empty hierarchies.
367 */
368#define CSS_SET_HASH_BITS 7
369static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
370
371static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
372{
373    unsigned long key = 0UL;
374    struct cgroup_subsys *ss;
375    int i;
376
377    for_each_subsys(ss, i)
378        key += (unsigned long)css[i];
379    key = (key >> 16) ^ key;
380
381    return key;
382}
383
384static void put_css_set_locked(struct css_set *cset, bool taskexit)
385{
386    struct cgrp_cset_link *link, *tmp_link;
387
388    lockdep_assert_held(&css_set_rwsem);
389
390    if (!atomic_dec_and_test(&cset->refcount))
391        return;
392
393    /* This css_set is dead. unlink it and release cgroup refcounts */
394    hash_del(&cset->hlist);
395    css_set_count--;
396
397    list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
398        struct cgroup *cgrp = link->cgrp;
399
400        list_del(&link->cset_link);
401        list_del(&link->cgrp_link);
402
403        /* @cgrp can't go away while we're holding css_set_rwsem */
404        if (list_empty(&cgrp->cset_links) && notify_on_release(cgrp)) {
405            if (taskexit)
406                set_bit(CGRP_RELEASABLE, &cgrp->flags);
407            check_for_release(cgrp);
408        }
409
410        kfree(link);
411    }
412
413    kfree_rcu(cset, rcu_head);
414}
415
416static void put_css_set(struct css_set *cset, bool taskexit)
417{
418    /*
419     * Ensure that the refcount doesn't hit zero while any readers
420     * can see it. Similar to atomic_dec_and_lock(), but for an
421     * rwlock
422     */
423    if (atomic_add_unless(&cset->refcount, -1, 1))
424        return;
425
426    down_write(&css_set_rwsem);
427    put_css_set_locked(cset, taskexit);
428    up_write(&css_set_rwsem);
429}
430
431/*
432 * refcounted get/put for css_set objects
433 */
434static inline void get_css_set(struct css_set *cset)
435{
436    atomic_inc(&cset->refcount);
437}
438
439/**
440 * compare_css_sets - helper function for find_existing_css_set().
441 * @cset: candidate css_set being tested
442 * @old_cset: existing css_set for a task
443 * @new_cgrp: cgroup that's being entered by the task
444 * @template: desired set of css pointers in css_set (pre-calculated)
445 *
446 * Returns true if "cset" matches "old_cset" except for the hierarchy
447 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
448 */
449static bool compare_css_sets(struct css_set *cset,
450                 struct css_set *old_cset,
451                 struct cgroup *new_cgrp,
452                 struct cgroup_subsys_state *template[])
453{
454    struct list_head *l1, *l2;
455
456    if (memcmp(template, cset->subsys, sizeof(cset->subsys))) {
457        /* Not all subsystems matched */
458        return false;
459    }
460
461    /*
462     * Compare cgroup pointers in order to distinguish between
463     * different cgroups in heirarchies with no subsystems. We
464     * could get by with just this check alone (and skip the
465     * memcmp above) but on most setups the memcmp check will
466     * avoid the need for this more expensive check on almost all
467     * candidates.
468     */
469
470    l1 = &cset->cgrp_links;
471    l2 = &old_cset->cgrp_links;
472    while (1) {
473        struct cgrp_cset_link *link1, *link2;
474        struct cgroup *cgrp1, *cgrp2;
475
476        l1 = l1->next;
477        l2 = l2->next;
478        /* See if we reached the end - both lists are equal length. */
479        if (l1 == &cset->cgrp_links) {
480            BUG_ON(l2 != &old_cset->cgrp_links);
481            break;
482        } else {
483            BUG_ON(l2 == &old_cset->cgrp_links);
484        }
485        /* Locate the cgroups associated with these links. */
486        link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
487        link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
488        cgrp1 = link1->cgrp;
489        cgrp2 = link2->cgrp;
490        /* Hierarchies should be linked in the same order. */
491        BUG_ON(cgrp1->root != cgrp2->root);
492
493        /*
494         * If this hierarchy is the hierarchy of the cgroup
495         * that's changing, then we need to check that this
496         * css_set points to the new cgroup; if it's any other
497         * hierarchy, then this css_set should point to the
498         * same cgroup as the old css_set.
499         */
500        if (cgrp1->root == new_cgrp->root) {
501            if (cgrp1 != new_cgrp)
502                return false;
503        } else {
504            if (cgrp1 != cgrp2)
505                return false;
506        }
507    }
508    return true;
509}
510
511/**
512 * find_existing_css_set - init css array and find the matching css_set
513 * @old_cset: the css_set that we're using before the cgroup transition
514 * @cgrp: the cgroup that we're moving into
515 * @template: out param for the new set of csses, should be clear on entry
516 */
517static struct css_set *find_existing_css_set(struct css_set *old_cset,
518                    struct cgroup *cgrp,
519                    struct cgroup_subsys_state *template[])
520{
521    struct cgroup_root *root = cgrp->root;
522    struct cgroup_subsys *ss;
523    struct css_set *cset;
524    unsigned long key;
525    int i;
526
527    /*
528     * Build the set of subsystem state objects that we want to see in the
529     * new css_set. while subsystems can change globally, the entries here
530     * won't change, so no need for locking.
531     */
532    for_each_subsys(ss, i) {
533        if (root->cgrp.subsys_mask & (1UL << i)) {
534            /* Subsystem is in this hierarchy. So we want
535             * the subsystem state from the new
536             * cgroup */
537            template[i] = cgroup_css(cgrp, ss);
538        } else {
539            /* Subsystem is not in this hierarchy, so we
540             * don't want to change the subsystem state */
541            template[i] = old_cset->subsys[i];
542        }
543    }
544
545    key = css_set_hash(template);
546    hash_for_each_possible(css_set_table, cset, hlist, key) {
547        if (!compare_css_sets(cset, old_cset, cgrp, template))
548            continue;
549
550        /* This css_set matches what we need */
551        return cset;
552    }
553
554    /* No existing cgroup group matched */
555    return NULL;
556}
557
558static void free_cgrp_cset_links(struct list_head *links_to_free)
559{
560    struct cgrp_cset_link *link, *tmp_link;
561
562    list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
563        list_del(&link->cset_link);
564        kfree(link);
565    }
566}
567
568/**
569 * allocate_cgrp_cset_links - allocate cgrp_cset_links
570 * @count: the number of links to allocate
571 * @tmp_links: list_head the allocated links are put on
572 *
573 * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
574 * through ->cset_link. Returns 0 on success or -errno.
575 */
576static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
577{
578    struct cgrp_cset_link *link;
579    int i;
580
581    INIT_LIST_HEAD(tmp_links);
582
583    for (i = 0; i < count; i++) {
584        link = kzalloc(sizeof(*link), GFP_KERNEL);
585        if (!link) {
586            free_cgrp_cset_links(tmp_links);
587            return -ENOMEM;
588        }
589        list_add(&link->cset_link, tmp_links);
590    }
591    return 0;
592}
593
594/**
595 * link_css_set - a helper function to link a css_set to a cgroup
596 * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
597 * @cset: the css_set to be linked
598 * @cgrp: the destination cgroup
599 */
600static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
601             struct cgroup *cgrp)
602{
603    struct cgrp_cset_link *link;
604
605    BUG_ON(list_empty(tmp_links));
606    link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
607    link->cset = cset;
608    link->cgrp = cgrp;
609    list_move(&link->cset_link, &cgrp->cset_links);
610    /*
611     * Always add links to the tail of the list so that the list
612     * is sorted by order of hierarchy creation
613     */
614    list_add_tail(&link->cgrp_link, &cset->cgrp_links);
615}
616
617/**
618 * find_css_set - return a new css_set with one cgroup updated
619 * @old_cset: the baseline css_set
620 * @cgrp: the cgroup to be updated
621 *
622 * Return a new css_set that's equivalent to @old_cset, but with @cgrp
623 * substituted into the appropriate hierarchy.
624 */
625static struct css_set *find_css_set(struct css_set *old_cset,
626                    struct cgroup *cgrp)
627{
628    struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
629    struct css_set *cset;
630    struct list_head tmp_links;
631    struct cgrp_cset_link *link;
632    unsigned long key;
633
634    lockdep_assert_held(&cgroup_mutex);
635
636    /* First see if we already have a cgroup group that matches
637     * the desired set */
638    down_read(&css_set_rwsem);
639    cset = find_existing_css_set(old_cset, cgrp, template);
640    if (cset)
641        get_css_set(cset);
642    up_read(&css_set_rwsem);
643
644    if (cset)
645        return cset;
646
647    cset = kzalloc(sizeof(*cset), GFP_KERNEL);
648    if (!cset)
649        return NULL;
650
651    /* Allocate all the cgrp_cset_link objects that we'll need */
652    if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
653        kfree(cset);
654        return NULL;
655    }
656
657    atomic_set(&cset->refcount, 1);
658    INIT_LIST_HEAD(&cset->cgrp_links);
659    INIT_LIST_HEAD(&cset->tasks);
660    INIT_LIST_HEAD(&cset->mg_tasks);
661    INIT_LIST_HEAD(&cset->mg_preload_node);
662    INIT_LIST_HEAD(&cset->mg_node);
663    INIT_HLIST_NODE(&cset->hlist);
664
665    /* Copy the set of subsystem state objects generated in
666     * find_existing_css_set() */
667    memcpy(cset->subsys, template, sizeof(cset->subsys));
668
669    down_write(&css_set_rwsem);
670    /* Add reference counts and links from the new css_set. */
671    list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
672        struct cgroup *c = link->cgrp;
673
674        if (c->root == cgrp->root)
675            c = cgrp;
676        link_css_set(&tmp_links, cset, c);
677    }
678
679    BUG_ON(!list_empty(&tmp_links));
680
681    css_set_count++;
682
683    /* Add this cgroup group to the hash table */
684    key = css_set_hash(cset->subsys);
685    hash_add(css_set_table, &cset->hlist, key);
686
687    up_write(&css_set_rwsem);
688
689    return cset;
690}
691
692static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
693{
694    struct cgroup *root_cgrp = kf_root->kn->priv;
695
696    return root_cgrp->root;
697}
698
699static int cgroup_init_root_id(struct cgroup_root *root)
700{
701    int id;
702
703    lockdep_assert_held(&cgroup_mutex);
704
705    id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
706    if (id < 0)
707        return id;
708
709    root->hierarchy_id = id;
710    return 0;
711}
712
713static void cgroup_exit_root_id(struct cgroup_root *root)
714{
715    lockdep_assert_held(&cgroup_mutex);
716
717    if (root->hierarchy_id) {
718        idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
719        root->hierarchy_id = 0;
720    }
721}
722
723static void cgroup_free_root(struct cgroup_root *root)
724{
725    if (root) {
726        /* hierarhcy ID shoulid already have been released */
727        WARN_ON_ONCE(root->hierarchy_id);
728
729        idr_destroy(&root->cgroup_idr);
730        kfree(root);
731    }
732}
733
734static void cgroup_destroy_root(struct cgroup_root *root)
735{
736    struct cgroup *cgrp = &root->cgrp;
737    struct cgrp_cset_link *link, *tmp_link;
738
739    mutex_lock(&cgroup_tree_mutex);
740    mutex_lock(&cgroup_mutex);
741
742    BUG_ON(atomic_read(&root->nr_cgrps));
743    BUG_ON(!list_empty(&cgrp->children));
744
745    /* Rebind all subsystems back to the default hierarchy */
746    rebind_subsystems(&cgrp_dfl_root, cgrp->subsys_mask);
747
748    /*
749     * Release all the links from cset_links to this hierarchy's
750     * root cgroup
751     */
752    down_write(&css_set_rwsem);
753
754    list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
755        list_del(&link->cset_link);
756        list_del(&link->cgrp_link);
757        kfree(link);
758    }
759    up_write(&css_set_rwsem);
760
761    if (!list_empty(&root->root_list)) {
762        list_del(&root->root_list);
763        cgroup_root_count--;
764    }
765
766    cgroup_exit_root_id(root);
767
768    mutex_unlock(&cgroup_mutex);
769    mutex_unlock(&cgroup_tree_mutex);
770
771    kernfs_destroy_root(root->kf_root);
772    cgroup_free_root(root);
773}
774
775/* look up cgroup associated with given css_set on the specified hierarchy */
776static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
777                        struct cgroup_root *root)
778{
779    struct cgroup *res = NULL;
780
781    lockdep_assert_held(&cgroup_mutex);
782    lockdep_assert_held(&css_set_rwsem);
783
784    if (cset == &init_css_set) {
785        res = &root->cgrp;
786    } else {
787        struct cgrp_cset_link *link;
788
789        list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
790            struct cgroup *c = link->cgrp;
791
792            if (c->root == root) {
793                res = c;
794                break;
795            }
796        }
797    }
798
799    BUG_ON(!res);
800    return res;
801}
802
803/*
804 * Return the cgroup for "task" from the given hierarchy. Must be
805 * called with cgroup_mutex and css_set_rwsem held.
806 */
807static struct cgroup *task_cgroup_from_root(struct task_struct *task,
808                        struct cgroup_root *root)
809{
810    /*
811     * No need to lock the task - since we hold cgroup_mutex the
812     * task can't change groups, so the only thing that can happen
813     * is that it exits and its css is set back to init_css_set.
814     */
815    return cset_cgroup_from_root(task_css_set(task), root);
816}
817
818/*
819 * A task must hold cgroup_mutex to modify cgroups.
820 *
821 * Any task can increment and decrement the count field without lock.
822 * So in general, code holding cgroup_mutex can't rely on the count
823 * field not changing. However, if the count goes to zero, then only
824 * cgroup_attach_task() can increment it again. Because a count of zero
825 * means that no tasks are currently attached, therefore there is no
826 * way a task attached to that cgroup can fork (the other way to
827 * increment the count). So code holding cgroup_mutex can safely
828 * assume that if the count is zero, it will stay zero. Similarly, if
829 * a task holds cgroup_mutex on a cgroup with zero count, it
830 * knows that the cgroup won't be removed, as cgroup_rmdir()
831 * needs that mutex.
832 *
833 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
834 * (usually) take cgroup_mutex. These are the two most performance
835 * critical pieces of code here. The exception occurs on cgroup_exit(),
836 * when a task in a notify_on_release cgroup exits. Then cgroup_mutex
837 * is taken, and if the cgroup count is zero, a usermode call made
838 * to the release agent with the name of the cgroup (path relative to
839 * the root of cgroup file system) as the argument.
840 *
841 * A cgroup can only be deleted if both its 'count' of using tasks
842 * is zero, and its list of 'children' cgroups is empty. Since all
843 * tasks in the system use _some_ cgroup, and since there is always at
844 * least one task in the system (init, pid == 1), therefore, root cgroup
845 * always has either children cgroups and/or using tasks. So we don't
846 * need a special hack to ensure that root cgroup cannot be deleted.
847 *
848 * P.S. One more locking exception. RCU is used to guard the
849 * update of a tasks cgroup pointer by cgroup_attach_task()
850 */
851
852static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask);
853static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
854static const struct file_operations proc_cgroupstats_operations;
855
856static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
857                  char *buf)
858{
859    if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
860        !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
861        snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
862             cft->ss->name, cft->name);
863    else
864        strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
865    return buf;
866}
867
868/**
869 * cgroup_file_mode - deduce file mode of a control file
870 * @cft: the control file in question
871 *
872 * returns cft->mode if ->mode is not 0
873 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
874 * returns S_IRUGO if it has only a read handler
875 * returns S_IWUSR if it has only a write hander
876 */
877static umode_t cgroup_file_mode(const struct cftype *cft)
878{
879    umode_t mode = 0;
880
881    if (cft->mode)
882        return cft->mode;
883
884    if (cft->read_u64 || cft->read_s64 || cft->seq_show)
885        mode |= S_IRUGO;
886
887    if (cft->write_u64 || cft->write_s64 || cft->write_string ||
888        cft->trigger)
889        mode |= S_IWUSR;
890
891    return mode;
892}
893
894static void cgroup_free_fn(struct work_struct *work)
895{
896    struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
897
898    atomic_dec(&cgrp->root->nr_cgrps);
899    cgroup_pidlist_destroy_all(cgrp);
900
901    if (cgrp->parent) {
902        /*
903         * We get a ref to the parent, and put the ref when this
904         * cgroup is being freed, so it's guaranteed that the
905         * parent won't be destroyed before its children.
906         */
907        cgroup_put(cgrp->parent);
908        kernfs_put(cgrp->kn);
909        kfree(cgrp);
910    } else {
911        /*
912         * This is root cgroup's refcnt reaching zero, which
913         * indicates that the root should be released.
914         */
915        cgroup_destroy_root(cgrp->root);
916    }
917}
918
919static void cgroup_free_rcu(struct rcu_head *head)
920{
921    struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head);
922
923    INIT_WORK(&cgrp->destroy_work, cgroup_free_fn);
924    queue_work(cgroup_destroy_wq, &cgrp->destroy_work);
925}
926
927static void cgroup_get(struct cgroup *cgrp)
928{
929    WARN_ON_ONCE(cgroup_is_dead(cgrp));
930    WARN_ON_ONCE(atomic_read(&cgrp->refcnt) <= 0);
931    atomic_inc(&cgrp->refcnt);
932}
933
934static void cgroup_put(struct cgroup *cgrp)
935{
936    if (!atomic_dec_and_test(&cgrp->refcnt))
937        return;
938    if (WARN_ON_ONCE(cgrp->parent && !cgroup_is_dead(cgrp)))
939        return;
940
941    /*
942     * XXX: cgrp->id is only used to look up css's. As cgroup and
943     * css's lifetimes will be decoupled, it should be made
944     * per-subsystem and moved to css->id so that lookups are
945     * successful until the target css is released.
946     */
947    mutex_lock(&cgroup_mutex);
948    idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
949    mutex_unlock(&cgroup_mutex);
950    cgrp->id = -1;
951
952    call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
953}
954
955static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
956{
957    char name[CGROUP_FILE_NAME_MAX];
958
959    lockdep_assert_held(&cgroup_tree_mutex);
960    kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
961}
962
963/**
964 * cgroup_clear_dir - remove subsys files in a cgroup directory
965 * @cgrp: target cgroup
966 * @subsys_mask: mask of the subsystem ids whose files should be removed
967 */
968static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask)
969{
970    struct cgroup_subsys *ss;
971    int i;
972
973    for_each_subsys(ss, i) {
974        struct cftype *cfts;
975
976        if (!test_bit(i, &subsys_mask))
977            continue;
978        list_for_each_entry(cfts, &ss->cfts, node)
979            cgroup_addrm_files(cgrp, cfts, false);
980    }
981}
982
983static int rebind_subsystems(struct cgroup_root *dst_root,
984                 unsigned long ss_mask)
985{
986    struct cgroup_subsys *ss;
987    int ssid, ret;
988
989    lockdep_assert_held(&cgroup_tree_mutex);
990    lockdep_assert_held(&cgroup_mutex);
991
992    for_each_subsys(ss, ssid) {
993        if (!(ss_mask & (1 << ssid)))
994            continue;
995
996        /* if @ss is on the dummy_root, we can always move it */
997        if (ss->root == &cgrp_dfl_root)
998            continue;
999
1000        /* if @ss has non-root cgroups attached to it, can't move */
1001        if (!list_empty(&ss->root->cgrp.children))
1002            return -EBUSY;
1003
1004        /* can't move between two non-dummy roots either */
1005        if (dst_root != &cgrp_dfl_root)
1006            return -EBUSY;
1007    }
1008
1009    ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask);
1010    if (ret) {
1011        if (dst_root != &cgrp_dfl_root)
1012            return ret;
1013
1014        /*
1015         * Rebinding back to the default root is not allowed to
1016         * fail. Using both default and non-default roots should
1017         * be rare. Moving subsystems back and forth even more so.
1018         * Just warn about it and continue.
1019         */
1020        if (cgrp_dfl_root_visible) {
1021            pr_warning("cgroup: failed to create files (%d) while rebinding 0x%lx to default root\n",
1022                   ret, ss_mask);
1023            pr_warning("cgroup: you may retry by moving them to a different hierarchy and unbinding\n");
1024        }
1025    }
1026
1027    /*
1028     * Nothing can fail from this point on. Remove files for the
1029     * removed subsystems and rebind each subsystem.
1030     */
1031    mutex_unlock(&cgroup_mutex);
1032    for_each_subsys(ss, ssid)
1033        if (ss_mask & (1 << ssid))
1034            cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);
1035    mutex_lock(&cgroup_mutex);
1036
1037    for_each_subsys(ss, ssid) {
1038        struct cgroup_root *src_root;
1039        struct cgroup_subsys_state *css;
1040
1041        if (!(ss_mask & (1 << ssid)))
1042            continue;
1043
1044        src_root = ss->root;
1045        css = cgroup_css(&src_root->cgrp, ss);
1046
1047        WARN_ON(!css || cgroup_css(&dst_root->cgrp, ss));
1048
1049        RCU_INIT_POINTER(src_root->cgrp.subsys[ssid], NULL);
1050        rcu_assign_pointer(dst_root->cgrp.subsys[ssid], css);
1051        ss->root = dst_root;
1052        css->cgroup = &dst_root->cgrp;
1053
1054        src_root->cgrp.subsys_mask &= ~(1 << ssid);
1055        dst_root->cgrp.subsys_mask |= 1 << ssid;
1056
1057        if (ss->bind)
1058            ss->bind(css);
1059    }
1060
1061    kernfs_activate(dst_root->cgrp.kn);
1062    return 0;
1063}
1064
1065static int cgroup_show_options(struct seq_file *seq,
1066                   struct kernfs_root *kf_root)
1067{
1068    struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1069    struct cgroup_subsys *ss;
1070    int ssid;
1071
1072    for_each_subsys(ss, ssid)
1073        if (root->cgrp.subsys_mask & (1 << ssid))
1074            seq_printf(seq, ",%s", ss->name);
1075    if (root->flags & CGRP_ROOT_SANE_BEHAVIOR)
1076        seq_puts(seq, ",sane_behavior");
1077    if (root->flags & CGRP_ROOT_NOPREFIX)
1078        seq_puts(seq, ",noprefix");
1079    if (root->flags & CGRP_ROOT_XATTR)
1080        seq_puts(seq, ",xattr");
1081
1082    spin_lock(&release_agent_path_lock);
1083    if (strlen(root->release_agent_path))
1084        seq_printf(seq, ",release_agent=%s", root->release_agent_path);
1085    spin_unlock(&release_agent_path_lock);
1086
1087    if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1088        seq_puts(seq, ",clone_children");
1089    if (strlen(root->name))
1090        seq_printf(seq, ",name=%s", root->name);
1091    return 0;
1092}
1093
1094struct cgroup_sb_opts {
1095    unsigned long subsys_mask;
1096    unsigned long flags;
1097    char *release_agent;
1098    bool cpuset_clone_children;
1099    char *name;
1100    /* User explicitly requested empty subsystem */
1101    bool none;
1102};
1103
1104/*
1105 * Convert a hierarchy specifier into a bitmask of subsystems and
1106 * flags. Call with cgroup_mutex held to protect the cgroup_subsys[]
1107 * array. This function takes refcounts on subsystems to be used, unless it
1108 * returns error, in which case no refcounts are taken.
1109 */
1110static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1111{
1112    char *token, *o = data;
1113    bool all_ss = false, one_ss = false;
1114    unsigned long mask = (unsigned long)-1;
1115    struct cgroup_subsys *ss;
1116    int i;
1117
1118    BUG_ON(!mutex_is_locked(&cgroup_mutex));
1119
1120#ifdef CONFIG_CPUSETS
1121    mask = ~(1UL << cpuset_cgrp_id);
1122#endif
1123
1124    memset(opts, 0, sizeof(*opts));
1125
1126    while ((token = strsep(&o, ",")) != NULL) {
1127        if (!*token)
1128            return -EINVAL;
1129        if (!strcmp(token, "none")) {
1130            /* Explicitly have no subsystems */
1131            opts->none = true;
1132            continue;
1133        }
1134        if (!strcmp(token, "all")) {
1135            /* Mutually exclusive option 'all' + subsystem name */
1136            if (one_ss)
1137                return -EINVAL;
1138            all_ss = true;
1139            continue;
1140        }
1141        if (!strcmp(token, "__DEVEL__sane_behavior")) {
1142            opts->flags |= CGRP_ROOT_SANE_BEHAVIOR;
1143            continue;
1144        }
1145        if (!strcmp(token, "noprefix")) {
1146            opts->flags |= CGRP_ROOT_NOPREFIX;
1147            continue;
1148        }
1149        if (!strcmp(token, "clone_children")) {
1150            opts->cpuset_clone_children = true;
1151            continue;
1152        }
1153        if (!strcmp(token, "xattr")) {
1154            opts->flags |= CGRP_ROOT_XATTR;
1155            continue;
1156        }
1157        if (!strncmp(token, "release_agent=", 14)) {
1158            /* Specifying two release agents is forbidden */
1159            if (opts->release_agent)
1160                return -EINVAL;
1161            opts->release_agent =
1162                kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1163            if (!opts->release_agent)
1164                return -ENOMEM;
1165            continue;
1166        }
1167        if (!strncmp(token, "name=", 5)) {
1168            const char *name = token + 5;
1169            /* Can't specify an empty name */
1170            if (!strlen(name))
1171                return -EINVAL;
1172            /* Must match [\w.-]+ */
1173            for (i = 0; i < strlen(name); i++) {
1174                char c = name[i];
1175                if (isalnum(c))
1176                    continue;
1177                if ((c == '.') || (c == '-') || (c == '_'))
1178                    continue;
1179                return -EINVAL;
1180            }
1181            /* Specifying two names is forbidden */
1182            if (opts->name)
1183                return -EINVAL;
1184            opts->name = kstrndup(name,
1185                          MAX_CGROUP_ROOT_NAMELEN - 1,
1186                          GFP_KERNEL);
1187            if (!opts->name)
1188                return -ENOMEM;
1189
1190            continue;
1191        }
1192
1193        for_each_subsys(ss, i) {
1194            if (strcmp(token, ss->name))
1195                continue;
1196            if (ss->disabled)
1197                continue;
1198
1199            /* Mutually exclusive option 'all' + subsystem name */
1200            if (all_ss)
1201                return -EINVAL;
1202            set_bit(i, &opts->subsys_mask);
1203            one_ss = true;
1204
1205            break;
1206        }
1207        if (i == CGROUP_SUBSYS_COUNT)
1208            return -ENOENT;
1209    }
1210
1211    /* Consistency checks */
1212
1213    if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) {
1214        pr_warning("cgroup: sane_behavior: this is still under development and its behaviors will change, proceed at your own risk\n");
1215
1216        if ((opts->flags & (CGRP_ROOT_NOPREFIX | CGRP_ROOT_XATTR)) ||
1217            opts->cpuset_clone_children || opts->release_agent ||
1218            opts->name) {
1219            pr_err("cgroup: sane_behavior: noprefix, xattr, clone_children, release_agent and name are not allowed\n");
1220            return -EINVAL;
1221        }
1222    } else {
1223        /*
1224         * If the 'all' option was specified select all the
1225         * subsystems, otherwise if 'none', 'name=' and a subsystem
1226         * name options were not specified, let's default to 'all'
1227         */
1228        if (all_ss || (!one_ss && !opts->none && !opts->name))
1229            for_each_subsys(ss, i)
1230                if (!ss->disabled)
1231                    set_bit(i, &opts->subsys_mask);
1232
1233        /*
1234         * We either have to specify by name or by subsystems. (So
1235         * all empty hierarchies must have a name).
1236         */
1237        if (!opts->subsys_mask && !opts->name)
1238            return -EINVAL;
1239    }
1240
1241    /*
1242     * Option noprefix was introduced just for backward compatibility
1243     * with the old cpuset, so we allow noprefix only if mounting just
1244     * the cpuset subsystem.
1245     */
1246    if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1247        return -EINVAL;
1248
1249
1250    /* Can't specify "none" and some subsystems */
1251    if (opts->subsys_mask && opts->none)
1252        return -EINVAL;
1253
1254    return 0;
1255}
1256
1257static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1258{
1259    int ret = 0;
1260    struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1261    struct cgroup_sb_opts opts;
1262    unsigned long added_mask, removed_mask;
1263
1264    if (root->flags & CGRP_ROOT_SANE_BEHAVIOR) {
1265        pr_err("cgroup: sane_behavior: remount is not allowed\n");
1266        return -EINVAL;
1267    }
1268
1269    mutex_lock(&cgroup_tree_mutex);
1270    mutex_lock(&cgroup_mutex);
1271
1272    /* See what subsystems are wanted */
1273    ret = parse_cgroupfs_options(data, &opts);
1274    if (ret)
1275        goto out_unlock;
1276
1277    if (opts.subsys_mask != root->cgrp.subsys_mask || opts.release_agent)
1278        pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
1279               task_tgid_nr(current), current->comm);
1280
1281    added_mask = opts.subsys_mask & ~root->cgrp.subsys_mask;
1282    removed_mask = root->cgrp.subsys_mask & ~opts.subsys_mask;
1283
1284    /* Don't allow flags or name to change at remount */
1285    if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) ||
1286        (opts.name && strcmp(opts.name, root->name))) {
1287        pr_err("cgroup: option or name mismatch, new: 0x%lx \"%s\", old: 0x%lx \"%s\"\n",
1288               opts.flags & CGRP_ROOT_OPTION_MASK, opts.name ?: "",
1289               root->flags & CGRP_ROOT_OPTION_MASK, root->name);
1290        ret = -EINVAL;
1291        goto out_unlock;
1292    }
1293
1294    /* remounting is not allowed for populated hierarchies */
1295    if (!list_empty(&root->cgrp.children)) {
1296        ret = -EBUSY;
1297        goto out_unlock;
1298    }
1299
1300    ret = rebind_subsystems(root, added_mask);
1301    if (ret)
1302        goto out_unlock;
1303
1304    rebind_subsystems(&cgrp_dfl_root, removed_mask);
1305
1306    if (opts.release_agent) {
1307        spin_lock(&release_agent_path_lock);
1308        strcpy(root->release_agent_path, opts.release_agent);
1309        spin_unlock(&release_agent_path_lock);
1310    }
1311 out_unlock:
1312    kfree(opts.release_agent);
1313    kfree(opts.name);
1314    mutex_unlock(&cgroup_mutex);
1315    mutex_unlock(&cgroup_tree_mutex);
1316    return ret;
1317}
1318
1319/*
1320 * To reduce the fork() overhead for systems that are not actually using
1321 * their cgroups capability, we don't maintain the lists running through
1322 * each css_set to its tasks until we see the list actually used - in other
1323 * words after the first mount.
1324 */
1325static bool use_task_css_set_links __read_mostly;
1326
1327static void cgroup_enable_task_cg_lists(void)
1328{
1329    struct task_struct *p, *g;
1330
1331    down_write(&css_set_rwsem);
1332
1333    if (use_task_css_set_links)
1334        goto out_unlock;
1335
1336    use_task_css_set_links = true;
1337
1338    /*
1339     * We need tasklist_lock because RCU is not safe against
1340     * while_each_thread(). Besides, a forking task that has passed
1341     * cgroup_post_fork() without seeing use_task_css_set_links = 1
1342     * is not guaranteed to have its child immediately visible in the
1343     * tasklist if we walk through it with RCU.
1344     */
1345    read_lock(&tasklist_lock);
1346    do_each_thread(g, p) {
1347        WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1348                 task_css_set(p) != &init_css_set);
1349
1350        /*
1351         * We should check if the process is exiting, otherwise
1352         * it will race with cgroup_exit() in that the list
1353         * entry won't be deleted though the process has exited.
1354         * Do it while holding siglock so that we don't end up
1355         * racing against cgroup_exit().
1356         */
1357        spin_lock_irq(&p->sighand->siglock);
1358        if (!(p->flags & PF_EXITING)) {
1359            struct css_set *cset = task_css_set(p);
1360
1361            list_add(&p->cg_list, &cset->tasks);
1362            get_css_set(cset);
1363        }
1364        spin_unlock_irq(&p->sighand->siglock);
1365    } while_each_thread(g, p);
1366    read_unlock(&tasklist_lock);
1367out_unlock:
1368    up_write(&css_set_rwsem);
1369}
1370
1371static void init_cgroup_housekeeping(struct cgroup *cgrp)
1372{
1373    atomic_set(&cgrp->refcnt, 1);
1374    INIT_LIST_HEAD(&cgrp->sibling);
1375    INIT_LIST_HEAD(&cgrp->children);
1376    INIT_LIST_HEAD(&cgrp->cset_links);
1377    INIT_LIST_HEAD(&cgrp->release_list);
1378    INIT_LIST_HEAD(&cgrp->pidlists);
1379    mutex_init(&cgrp->pidlist_mutex);
1380    cgrp->dummy_css.cgroup = cgrp;
1381}
1382
1383static void init_cgroup_root(struct cgroup_root *root,
1384                 struct cgroup_sb_opts *opts)
1385{
1386    struct cgroup *cgrp = &root->cgrp;
1387
1388    INIT_LIST_HEAD(&root->root_list);
1389    atomic_set(&root->nr_cgrps, 1);
1390    cgrp->root = root;
1391    init_cgroup_housekeeping(cgrp);
1392    idr_init(&root->cgroup_idr);
1393
1394    root->flags = opts->flags;
1395    if (opts->release_agent)
1396        strcpy(root->release_agent_path, opts->release_agent);
1397    if (opts->name)
1398        strcpy(root->name, opts->name);
1399    if (opts->cpuset_clone_children)
1400        set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1401}
1402
1403static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
1404{
1405    LIST_HEAD(tmp_links);
1406    struct cgroup *root_cgrp = &root->cgrp;
1407    struct css_set *cset;
1408    int i, ret;
1409
1410    lockdep_assert_held(&cgroup_tree_mutex);
1411    lockdep_assert_held(&cgroup_mutex);
1412
1413    ret = idr_alloc(&root->cgroup_idr, root_cgrp, 0, 1, GFP_KERNEL);
1414    if (ret < 0)
1415        goto out;
1416    root_cgrp->id = ret;
1417
1418    /*
1419     * We're accessing css_set_count without locking css_set_rwsem here,
1420     * but that's OK - it can only be increased by someone holding
1421     * cgroup_lock, and that's us. The worst that can happen is that we
1422     * have some link structures left over
1423     */
1424    ret = allocate_cgrp_cset_links(css_set_count, &tmp_links);
1425    if (ret)
1426        goto out;
1427
1428    ret = cgroup_init_root_id(root);
1429    if (ret)
1430        goto out;
1431
1432    root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
1433                       KERNFS_ROOT_CREATE_DEACTIVATED,
1434                       root_cgrp);
1435    if (IS_ERR(root->kf_root)) {
1436        ret = PTR_ERR(root->kf_root);
1437        goto exit_root_id;
1438    }
1439    root_cgrp->kn = root->kf_root->kn;
1440
1441    ret = cgroup_addrm_files(root_cgrp, cgroup_base_files, true);
1442    if (ret)
1443        goto destroy_root;
1444
1445    ret = rebind_subsystems(root, ss_mask);
1446    if (ret)
1447        goto destroy_root;
1448
1449    /*
1450     * There must be no failure case after here, since rebinding takes
1451     * care of subsystems' refcounts, which are explicitly dropped in
1452     * the failure exit path.
1453     */
1454    list_add(&root->root_list, &cgroup_roots);
1455    cgroup_root_count++;
1456
1457    /*
1458     * Link the root cgroup in this hierarchy into all the css_set
1459     * objects.
1460     */
1461    down_write(&css_set_rwsem);
1462    hash_for_each(css_set_table, i, cset, hlist)
1463        link_css_set(&tmp_links, cset, root_cgrp);
1464    up_write(&css_set_rwsem);
1465
1466    BUG_ON(!list_empty(&root_cgrp->children));
1467    BUG_ON(atomic_read(&root->nr_cgrps) != 1);
1468
1469    kernfs_activate(root_cgrp->kn);
1470    ret = 0;
1471    goto out;
1472
1473destroy_root:
1474    kernfs_destroy_root(root->kf_root);
1475    root->kf_root = NULL;
1476exit_root_id:
1477    cgroup_exit_root_id(root);
1478out:
1479    free_cgrp_cset_links(&tmp_links);
1480    return ret;
1481}
1482
1483static struct dentry *cgroup_mount(struct file_system_type *fs_type,
1484             int flags, const char *unused_dev_name,
1485             void *data)
1486{
1487    struct cgroup_root *root;
1488    struct cgroup_sb_opts opts;
1489    struct dentry *dentry;
1490    int ret;
1491    bool new_sb;
1492
1493    /*
1494     * The first time anyone tries to mount a cgroup, enable the list
1495     * linking each css_set to its tasks and fix up all existing tasks.
1496     */
1497    if (!use_task_css_set_links)
1498        cgroup_enable_task_cg_lists();
1499
1500    mutex_lock(&cgroup_tree_mutex);
1501    mutex_lock(&cgroup_mutex);
1502
1503    /* First find the desired set of subsystems */
1504    ret = parse_cgroupfs_options(data, &opts);
1505    if (ret)
1506        goto out_unlock;
1507retry:
1508    /* look for a matching existing root */
1509    if (!opts.subsys_mask && !opts.none && !opts.name) {
1510        cgrp_dfl_root_visible = true;
1511        root = &cgrp_dfl_root;
1512        cgroup_get(&root->cgrp);
1513        ret = 0;
1514        goto out_unlock;
1515    }
1516
1517    for_each_root(root) {
1518        bool name_match = false;
1519
1520        if (root == &cgrp_dfl_root)
1521            continue;
1522
1523        /*
1524         * If we asked for a name then it must match. Also, if
1525         * name matches but sybsys_mask doesn't, we should fail.
1526         * Remember whether name matched.
1527         */
1528        if (opts.name) {
1529            if (strcmp(opts.name, root->name))
1530                continue;
1531            name_match = true;
1532        }
1533
1534        /*
1535         * If we asked for subsystems (or explicitly for no
1536         * subsystems) then they must match.
1537         */
1538        if ((opts.subsys_mask || opts.none) &&
1539            (opts.subsys_mask != root->cgrp.subsys_mask)) {
1540            if (!name_match)
1541                continue;
1542            ret = -EBUSY;
1543            goto out_unlock;
1544        }
1545
1546        if ((root->flags ^ opts.flags) & CGRP_ROOT_OPTION_MASK) {
1547            if ((root->flags | opts.flags) & CGRP_ROOT_SANE_BEHAVIOR) {
1548                pr_err("cgroup: sane_behavior: new mount options should match the existing superblock\n");
1549                ret = -EINVAL;
1550                goto out_unlock;
1551            } else {
1552                pr_warning("cgroup: new mount options do not match the existing superblock, will be ignored\n");
1553            }
1554        }
1555
1556        /*
1557         * A root's lifetime is governed by its root cgroup. Zero
1558         * ref indicate that the root is being destroyed. Wait for
1559         * destruction to complete so that the subsystems are free.
1560         * We can use wait_queue for the wait but this path is
1561         * super cold. Let's just sleep for a bit and retry.
1562         */
1563        if (!atomic_inc_not_zero(&root->cgrp.refcnt)) {
1564            mutex_unlock(&cgroup_mutex);
1565            mutex_unlock(&cgroup_tree_mutex);
1566            msleep(10);
1567            mutex_lock(&cgroup_tree_mutex);
1568            mutex_lock(&cgroup_mutex);
1569            goto retry;
1570        }
1571
1572        ret = 0;
1573        goto out_unlock;
1574    }
1575
1576    /*
1577     * No such thing, create a new one. name= matching without subsys
1578     * specification is allowed for already existing hierarchies but we
1579     * can't create new one without subsys specification.
1580     */
1581    if (!opts.subsys_mask && !opts.none) {
1582        ret = -EINVAL;
1583        goto out_unlock;
1584    }
1585
1586    root = kzalloc(sizeof(*root), GFP_KERNEL);
1587    if (!root) {
1588        ret = -ENOMEM;
1589        goto out_unlock;
1590    }
1591
1592    init_cgroup_root(root, &opts);
1593
1594    ret = cgroup_setup_root(root, opts.subsys_mask);
1595    if (ret)
1596        cgroup_free_root(root);
1597
1598out_unlock:
1599    mutex_unlock(&cgroup_mutex);
1600    mutex_unlock(&cgroup_tree_mutex);
1601
1602    kfree(opts.release_agent);
1603    kfree(opts.name);
1604
1605    if (ret)
1606        return ERR_PTR(ret);
1607
1608    dentry = kernfs_mount(fs_type, flags, root->kf_root,
1609                CGROUP_SUPER_MAGIC, &new_sb);
1610    if (IS_ERR(dentry) || !new_sb)
1611        cgroup_put(&root->cgrp);
1612    return dentry;
1613}
1614
1615static void cgroup_kill_sb(struct super_block *sb)
1616{
1617    struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
1618    struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1619
1620    cgroup_put(&root->cgrp);
1621    kernfs_kill_sb(sb);
1622}
1623
1624static struct file_system_type cgroup_fs_type = {
1625    .name = "cgroup",
1626    .mount = cgroup_mount,
1627    .kill_sb = cgroup_kill_sb,
1628};
1629
1630static struct kobject *cgroup_kobj;
1631
1632/**
1633 * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
1634 * @task: target task
1635 * @buf: the buffer to write the path into
1636 * @buflen: the length of the buffer
1637 *
1638 * Determine @task's cgroup on the first (the one with the lowest non-zero
1639 * hierarchy_id) cgroup hierarchy and copy its path into @buf. This
1640 * function grabs cgroup_mutex and shouldn't be used inside locks used by
1641 * cgroup controller callbacks.
1642 *
1643 * Return value is the same as kernfs_path().
1644 */
1645char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
1646{
1647    struct cgroup_root *root;
1648    struct cgroup *cgrp;
1649    int hierarchy_id = 1;
1650    char *path = NULL;
1651
1652    mutex_lock(&cgroup_mutex);
1653    down_read(&css_set_rwsem);
1654
1655    root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
1656
1657    if (root) {
1658        cgrp = task_cgroup_from_root(task, root);
1659        path = cgroup_path(cgrp, buf, buflen);
1660    } else {
1661        /* if no hierarchy exists, everyone is in "/" */
1662        if (strlcpy(buf, "/", buflen) < buflen)
1663            path = buf;
1664    }
1665
1666    up_read(&css_set_rwsem);
1667    mutex_unlock(&cgroup_mutex);
1668    return path;
1669}
1670EXPORT_SYMBOL_GPL(task_cgroup_path);
1671
1672/* used to track tasks and other necessary states during migration */
1673struct cgroup_taskset {
1674    /* the src and dst cset list running through cset->mg_node */
1675    struct list_head src_csets;
1676    struct list_head dst_csets;
1677
1678    /*
1679     * Fields for cgroup_taskset_*() iteration.
1680     *
1681     * Before migration is committed, the target migration tasks are on
1682     * ->mg_tasks of the csets on ->src_csets. After, on ->mg_tasks of
1683     * the csets on ->dst_csets. ->csets point to either ->src_csets
1684     * or ->dst_csets depending on whether migration is committed.
1685     *
1686     * ->cur_csets and ->cur_task point to the current task position
1687     * during iteration.
1688     */
1689    struct list_head *csets;
1690    struct css_set *cur_cset;
1691    struct task_struct *cur_task;
1692};
1693
1694/**
1695 * cgroup_taskset_first - reset taskset and return the first task
1696 * @tset: taskset of interest
1697 *
1698 * @tset iteration is initialized and the first task is returned.
1699 */
1700struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset)
1701{
1702    tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
1703    tset->cur_task = NULL;
1704
1705    return cgroup_taskset_next(tset);
1706}
1707
1708/**
1709 * cgroup_taskset_next - iterate to the next task in taskset
1710 * @tset: taskset of interest
1711 *
1712 * Return the next task in @tset. Iteration must have been initialized
1713 * with cgroup_taskset_first().
1714 */
1715struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
1716{
1717    struct css_set *cset = tset->cur_cset;
1718    struct task_struct *task = tset->cur_task;
1719
1720    while (&cset->mg_node != tset->csets) {
1721        if (!task)
1722            task = list_first_entry(&cset->mg_tasks,
1723                        struct task_struct, cg_list);
1724        else
1725            task = list_next_entry(task, cg_list);
1726
1727        if (&task->cg_list != &cset->mg_tasks) {
1728            tset->cur_cset = cset;
1729            tset->cur_task = task;
1730            return task;
1731        }
1732
1733        cset = list_next_entry(cset, mg_node);
1734        task = NULL;
1735    }
1736
1737    return NULL;
1738}
1739
1740/**
1741 * cgroup_task_migrate - move a task from one cgroup to another.
1742 * @old_cgrp; the cgroup @tsk is being migrated from
1743 * @tsk: the task being migrated
1744 * @new_cset: the new css_set @tsk is being attached to
1745 *
1746 * Must be called with cgroup_mutex, threadgroup and css_set_rwsem locked.
1747 */
1748static void cgroup_task_migrate(struct cgroup *old_cgrp,
1749                struct task_struct *tsk,
1750                struct css_set *new_cset)
1751{
1752    struct css_set *old_cset;
1753
1754    lockdep_assert_held(&cgroup_mutex);
1755    lockdep_assert_held(&css_set_rwsem);
1756
1757    /*
1758     * We are synchronized through threadgroup_lock() against PF_EXITING
1759     * setting such that we can't race against cgroup_exit() changing the
1760     * css_set to init_css_set and dropping the old one.
1761     */
1762    WARN_ON_ONCE(tsk->flags & PF_EXITING);
1763    old_cset = task_css_set(tsk);
1764
1765    get_css_set(new_cset);
1766    rcu_assign_pointer(tsk->cgroups, new_cset);
1767
1768    /*
1769     * Use move_tail so that cgroup_taskset_first() still returns the
1770     * leader after migration. This works because cgroup_migrate()
1771     * ensures that the dst_cset of the leader is the first on the
1772     * tset's dst_csets list.
1773     */
1774    list_move_tail(&tsk->cg_list, &new_cset->mg_tasks);
1775
1776    /*
1777     * We just gained a reference on old_cset by taking it from the
1778     * task. As trading it for new_cset is protected by cgroup_mutex,
1779     * we're safe to drop it here; it will be freed under RCU.
1780     */
1781    set_bit(CGRP_RELEASABLE, &old_cgrp->flags);
1782    put_css_set_locked(old_cset, false);
1783}
1784
1785/**
1786 * cgroup_migrate_finish - cleanup after attach
1787 * @preloaded_csets: list of preloaded css_sets
1788 *
1789 * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst(). See
1790 * those functions for details.
1791 */
1792static void cgroup_migrate_finish(struct list_head *preloaded_csets)
1793{
1794    struct css_set *cset, *tmp_cset;
1795
1796    lockdep_assert_held(&cgroup_mutex);
1797
1798    down_write(&css_set_rwsem);
1799    list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
1800        cset->mg_src_cgrp = NULL;
1801        cset->mg_dst_cset = NULL;
1802        list_del_init(&cset->mg_preload_node);
1803        put_css_set_locked(cset, false);
1804    }
1805    up_write(&css_set_rwsem);
1806}
1807
1808/**
1809 * cgroup_migrate_add_src - add a migration source css_set
1810 * @src_cset: the source css_set to add
1811 * @dst_cgrp: the destination cgroup
1812 * @preloaded_csets: list of preloaded css_sets
1813 *
1814 * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp. Pin
1815 * @src_cset and add it to @preloaded_csets, which should later be cleaned
1816 * up by cgroup_migrate_finish().
1817 *
1818 * This function may be called without holding threadgroup_lock even if the
1819 * target is a process. Threads may be created and destroyed but as long
1820 * as cgroup_mutex is not dropped, no new css_set can be put into play and
1821 * the preloaded css_sets are guaranteed to cover all migrations.
1822 */
1823static void cgroup_migrate_add_src(struct css_set *src_cset,
1824                   struct cgroup *dst_cgrp,
1825                   struct list_head *preloaded_csets)
1826{
1827    struct cgroup *src_cgrp;
1828
1829    lockdep_assert_held(&cgroup_mutex);
1830    lockdep_assert_held(&css_set_rwsem);
1831
1832    src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
1833
1834    /* nothing to do if this cset already belongs to the cgroup */
1835    if (src_cgrp == dst_cgrp)
1836        return;
1837
1838    if (!list_empty(&src_cset->mg_preload_node))
1839        return;
1840
1841    WARN_ON(src_cset->mg_src_cgrp);
1842    WARN_ON(!list_empty(&src_cset->mg_tasks));
1843    WARN_ON(!list_empty(&src_cset->mg_node));
1844
1845    src_cset->mg_src_cgrp = src_cgrp;
1846    get_css_set(src_cset);
1847    list_add(&src_cset->mg_preload_node, preloaded_csets);
1848}
1849
1850/**
1851 * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
1852 * @dst_cgrp: the destination cgroup
1853 * @preloaded_csets: list of preloaded source css_sets
1854 *
1855 * Tasks are about to be moved to @dst_cgrp and all the source css_sets
1856 * have been preloaded to @preloaded_csets. This function looks up and
1857 * pins all destination css_sets, links each to its source, and put them on
1858 * @preloaded_csets.
1859 *
1860 * This function must be called after cgroup_migrate_add_src() has been
1861 * called on each migration source css_set. After migration is performed
1862 * using cgroup_migrate(), cgroup_migrate_finish() must be called on
1863 * @preloaded_csets.
1864 */
1865static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
1866                      struct list_head *preloaded_csets)
1867{
1868    LIST_HEAD(csets);
1869    struct css_set *src_cset;
1870
1871    lockdep_assert_held(&cgroup_mutex);
1872
1873    /* look up the dst cset for each src cset and link it to src */
1874    list_for_each_entry(src_cset, preloaded_csets, mg_preload_node) {
1875        struct css_set *dst_cset;
1876
1877        dst_cset = find_css_set(src_cset, dst_cgrp);
1878        if (!dst_cset)
1879            goto err;
1880
1881        WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
1882        src_cset->mg_dst_cset = dst_cset;
1883
1884        if (list_empty(&dst_cset->mg_preload_node))
1885            list_add(&dst_cset->mg_preload_node, &csets);
1886        else
1887            put_css_set(dst_cset, false);
1888    }
1889
1890    list_splice(&csets, preloaded_csets);
1891    return 0;
1892err:
1893    cgroup_migrate_finish(&csets);
1894    return -ENOMEM;
1895}
1896
1897/**
1898 * cgroup_migrate - migrate a process or task to a cgroup
1899 * @cgrp: the destination cgroup
1900 * @leader: the leader of the process or the task to migrate
1901 * @threadgroup: whether @leader points to the whole process or a single task
1902 *
1903 * Migrate a process or task denoted by @leader to @cgrp. If migrating a
1904 * process, the caller must be holding threadgroup_lock of @leader. The
1905 * caller is also responsible for invoking cgroup_migrate_add_src() and
1906 * cgroup_migrate_prepare_dst() on the targets before invoking this
1907 * function and following up with cgroup_migrate_finish().
1908 *
1909 * As long as a controller's ->can_attach() doesn't fail, this function is
1910 * guaranteed to succeed. This means that, excluding ->can_attach()
1911 * failure, when migrating multiple targets, the success or failure can be
1912 * decided for all targets by invoking group_migrate_prepare_dst() before
1913 * actually starting migrating.
1914 */
1915static int cgroup_migrate(struct cgroup *cgrp, struct task_struct *leader,
1916              bool threadgroup)
1917{
1918    struct cgroup_taskset tset = {
1919        .src_csets = LIST_HEAD_INIT(tset.src_csets),
1920        .dst_csets = LIST_HEAD_INIT(tset.dst_csets),
1921        .csets = &tset.src_csets,
1922    };
1923    struct cgroup_subsys_state *css, *failed_css = NULL;
1924    struct css_set *cset, *tmp_cset;
1925    struct task_struct *task, *tmp_task;
1926    int i, ret;
1927
1928    /*
1929     * Prevent freeing of tasks while we take a snapshot. Tasks that are
1930     * already PF_EXITING could be freed from underneath us unless we
1931     * take an rcu_read_lock.
1932     */
1933    down_write(&css_set_rwsem);
1934    rcu_read_lock();
1935    task = leader;
1936    do {
1937        /* @task either already exited or can't exit until the end */
1938        if (task->flags & PF_EXITING)
1939            goto next;
1940
1941        /* leave @task alone if post_fork() hasn't linked it yet */
1942        if (list_empty(&task->cg_list))
1943            goto next;
1944
1945        cset = task_css_set(task);
1946        if (!cset->mg_src_cgrp)
1947            goto next;
1948
1949        /*
1950         * cgroup_taskset_first() must always return the leader.
1951         * Take care to avoid disturbing the ordering.
1952         */
1953        list_move_tail(&task->cg_list, &cset->mg_tasks);
1954        if (list_empty(&cset->mg_node))
1955            list_add_tail(&cset->mg_node, &tset.src_csets);
1956        if (list_empty(&cset->mg_dst_cset->mg_node))
1957            list_move_tail(&cset->mg_dst_cset->mg_node,
1958                       &tset.dst_csets);
1959    next:
1960        if (!threadgroup)
1961            break;
1962    } while_each_thread(leader, task);
1963    rcu_read_unlock();
1964    up_write(&css_set_rwsem);
1965
1966    /* methods shouldn't be called if no task is actually migrating */
1967    if (list_empty(&tset.src_csets))
1968        return 0;
1969
1970    /* check that we can legitimately attach to the cgroup */
1971    for_each_css(css, i, cgrp) {
1972        if (css->ss->can_attach) {
1973            ret = css->ss->can_attach(css, &tset);
1974            if (ret) {
1975                failed_css = css;
1976                goto out_cancel_attach;
1977            }
1978        }
1979    }
1980
1981    /*
1982     * Now that we're guaranteed success, proceed to move all tasks to
1983     * the new cgroup. There are no failure cases after here, so this
1984     * is the commit point.
1985     */
1986    down_write(&css_set_rwsem);
1987    list_for_each_entry(cset, &tset.src_csets, mg_node) {
1988        list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list)
1989            cgroup_task_migrate(cset->mg_src_cgrp, task,
1990                        cset->mg_dst_cset);
1991    }
1992    up_write(&css_set_rwsem);
1993
1994    /*
1995     * Migration is committed, all target tasks are now on dst_csets.
1996     * Nothing is sensitive to fork() after this point. Notify
1997     * controllers that migration is complete.
1998     */
1999    tset.csets = &tset.dst_csets;
2000
2001    for_each_css(css, i, cgrp)
2002        if (css->ss->attach)
2003            css->ss->attach(css, &tset);
2004
2005    ret = 0;
2006    goto out_release_tset;
2007
2008out_cancel_attach:
2009    for_each_css(css, i, cgrp) {
2010        if (css == failed_css)
2011            break;
2012        if (css->ss->cancel_attach)
2013            css->ss->cancel_attach(css, &tset);
2014    }
2015out_release_tset:
2016    down_write(&css_set_rwsem);
2017    list_splice_init(&tset.dst_csets, &tset.src_csets);
2018    list_for_each_entry_safe(cset, tmp_cset, &tset.src_csets, mg_node) {
2019        list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2020        list_del_init(&cset->mg_node);
2021    }
2022    up_write(&css_set_rwsem);
2023    return ret;
2024}
2025
2026/**
2027 * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2028 * @dst_cgrp: the cgroup to attach to
2029 * @leader: the task or the leader of the threadgroup to be attached
2030 * @threadgroup: attach the whole threadgroup?
2031 *
2032 * Call holding cgroup_mutex and threadgroup_lock of @leader.
2033 */
2034static int cgroup_attach_task(struct cgroup *dst_cgrp,
2035                  struct task_struct *leader, bool threadgroup)
2036{
2037    LIST_HEAD(preloaded_csets);
2038    struct task_struct *task;
2039    int ret;
2040
2041    /* look up all src csets */
2042    down_read(&css_set_rwsem);
2043    rcu_read_lock();
2044    task = leader;
2045    do {
2046        cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
2047                       &preloaded_csets);
2048        if (!threadgroup)
2049            break;
2050    } while_each_thread(leader, task);
2051    rcu_read_unlock();
2052    up_read(&css_set_rwsem);
2053
2054    /* prepare dst csets and commit */
2055    ret = cgroup_migrate_prepare_dst(dst_cgrp, &preloaded_csets);
2056    if (!ret)
2057        ret = cgroup_migrate(dst_cgrp, leader, threadgroup);
2058
2059    cgroup_migrate_finish(&preloaded_csets);
2060    return ret;
2061}
2062
2063/*
2064 * Find the task_struct of the task to attach by vpid and pass it along to the
2065 * function to attach either it or all tasks in its threadgroup. Will lock
2066 * cgroup_mutex and threadgroup.
2067 */
2068static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
2069{
2070    struct task_struct *tsk;
2071    const struct cred *cred = current_cred(), *tcred;
2072    int ret;
2073
2074    if (!cgroup_lock_live_group(cgrp))
2075        return -ENODEV;
2076
2077retry_find_task:
2078    rcu_read_lock();
2079    if (pid) {
2080        tsk = find_task_by_vpid(pid);
2081        if (!tsk) {
2082            rcu_read_unlock();
2083            ret = -ESRCH;
2084            goto out_unlock_cgroup;
2085        }
2086        /*
2087         * even if we're attaching all tasks in the thread group, we
2088         * only need to check permissions on one of them.
2089         */
2090        tcred = __task_cred(tsk);
2091        if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2092            !uid_eq(cred->euid, tcred->uid) &&
2093            !uid_eq(cred->euid, tcred->suid)) {
2094            rcu_read_unlock();
2095            ret = -EACCES;
2096            goto out_unlock_cgroup;
2097        }
2098    } else
2099        tsk = current;
2100
2101    if (threadgroup)
2102        tsk = tsk->group_leader;
2103
2104    /*
2105     * Workqueue threads may acquire PF_NO_SETAFFINITY and become
2106     * trapped in a cpuset, or RT worker may be born in a cgroup
2107     * with no rt_runtime allocated. Just say no.
2108     */
2109    if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
2110        ret = -EINVAL;
2111        rcu_read_unlock();
2112        goto out_unlock_cgroup;
2113    }
2114
2115    get_task_struct(tsk);
2116    rcu_read_unlock();
2117
2118    threadgroup_lock(tsk);
2119    if (threadgroup) {
2120        if (!thread_group_leader(tsk)) {
2121            /*
2122             * a race with de_thread from another thread's exec()
2123             * may strip us of our leadership, if this happens,
2124             * there is no choice but to throw this task away and
2125             * try again; this is
2126             * "double-double-toil-and-trouble-check locking".
2127             */
2128            threadgroup_unlock(tsk);
2129            put_task_struct(tsk);
2130            goto retry_find_task;
2131        }
2132    }
2133
2134    ret = cgroup_attach_task(cgrp, tsk, threadgroup);
2135
2136    threadgroup_unlock(tsk);
2137
2138    put_task_struct(tsk);
2139out_unlock_cgroup:
2140    mutex_unlock(&cgroup_mutex);
2141    return ret;
2142}
2143
2144/**
2145 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2146 * @from: attach to all cgroups of a given task
2147 * @tsk: the task to be attached
2148 */
2149int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2150{
2151    struct cgroup_root *root;
2152    int retval = 0;
2153
2154    mutex_lock(&cgroup_mutex);
2155    for_each_root(root) {
2156        struct cgroup *from_cgrp;
2157
2158        if (root == &cgrp_dfl_root)
2159            continue;
2160
2161        down_read(&css_set_rwsem);
2162        from_cgrp = task_cgroup_from_root(from, root);
2163        up_read(&css_set_rwsem);
2164
2165        retval = cgroup_attach_task(from_cgrp, tsk, false);
2166        if (retval)
2167            break;
2168    }
2169    mutex_unlock(&cgroup_mutex);
2170
2171    return retval;
2172}
2173EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2174
2175static int cgroup_tasks_write(struct cgroup_subsys_state *css,
2176                  struct cftype *cft, u64 pid)
2177{
2178    return attach_task_by_pid(css->cgroup, pid, false);
2179}
2180
2181static int cgroup_procs_write(struct cgroup_subsys_state *css,
2182                  struct cftype *cft, u64 tgid)
2183{
2184    return attach_task_by_pid(css->cgroup, tgid, true);
2185}
2186
2187static int cgroup_release_agent_write(struct cgroup_subsys_state *css,
2188                      struct cftype *cft, char *buffer)
2189{
2190    struct cgroup_root *root = css->cgroup->root;
2191
2192    BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX);
2193    if (!cgroup_lock_live_group(css->cgroup))
2194        return -ENODEV;
2195    spin_lock(&release_agent_path_lock);
2196    strlcpy(root->release_agent_path, buffer,
2197        sizeof(root->release_agent_path));
2198    spin_unlock(&release_agent_path_lock);
2199    mutex_unlock(&cgroup_mutex);
2200    return 0;
2201}
2202
2203static int cgroup_release_agent_show(struct seq_file *seq, void *v)
2204{
2205    struct cgroup *cgrp = seq_css(seq)->cgroup;
2206
2207    if (!cgroup_lock_live_group(cgrp))
2208        return -ENODEV;
2209    seq_puts(seq, cgrp->root->release_agent_path);
2210    seq_putc(seq, '\n');
2211    mutex_unlock(&cgroup_mutex);
2212    return 0;
2213}
2214
2215static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
2216{
2217    struct cgroup *cgrp = seq_css(seq)->cgroup;
2218
2219    seq_printf(seq, "%d\n", cgroup_sane_behavior(cgrp));
2220    return 0;
2221}
2222
2223static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
2224                 size_t nbytes, loff_t off)
2225{
2226    struct cgroup *cgrp = of->kn->parent->priv;
2227    struct cftype *cft = of->kn->priv;
2228    struct cgroup_subsys_state *css;
2229    int ret;
2230
2231    /*
2232     * kernfs guarantees that a file isn't deleted with operations in
2233     * flight, which means that the matching css is and stays alive and
2234     * doesn't need to be pinned. The RCU locking is not necessary
2235     * either. It's just for the convenience of using cgroup_css().
2236     */
2237    rcu_read_lock();
2238    css = cgroup_css(cgrp, cft->ss);
2239    rcu_read_unlock();
2240
2241    if (cft->write_string) {
2242        ret = cft->write_string(css, cft, strstrip(buf));
2243    } else if (cft->write_u64) {
2244        unsigned long long v;
2245        ret = kstrtoull(buf, 0, &v);
2246        if (!ret)
2247            ret = cft->write_u64(css, cft, v);
2248    } else if (cft->write_s64) {
2249        long long v;
2250        ret = kstrtoll(buf, 0, &v);
2251        if (!ret)
2252            ret = cft->write_s64(css, cft, v);
2253    } else if (cft->trigger) {
2254        ret = cft->trigger(css, (unsigned int)cft->private);
2255    } else {
2256        ret = -EINVAL;
2257    }
2258
2259    return ret ?: nbytes;
2260}
2261
2262static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
2263{
2264    return seq_cft(seq)->seq_start(seq, ppos);
2265}
2266
2267static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
2268{
2269    return seq_cft(seq)->seq_next(seq, v, ppos);
2270}
2271
2272static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
2273{
2274    seq_cft(seq)->seq_stop(seq, v);
2275}
2276
2277static int cgroup_seqfile_show(struct seq_file *m, void *arg)
2278{
2279    struct cftype *cft = seq_cft(m);
2280    struct cgroup_subsys_state *css = seq_css(m);
2281
2282    if (cft->seq_show)
2283        return cft->seq_show(m, arg);
2284
2285    if (cft->read_u64)
2286        seq_printf(m, "%llu\n", cft->read_u64(css, cft));
2287    else if (cft->read_s64)
2288        seq_printf(m, "%lld\n", cft->read_s64(css, cft));
2289    else
2290        return -EINVAL;
2291    return 0;
2292}
2293
2294static struct kernfs_ops cgroup_kf_single_ops = {
2295    .atomic_write_len = PAGE_SIZE,
2296    .write = cgroup_file_write,
2297    .seq_show = cgroup_seqfile_show,
2298};
2299
2300static struct kernfs_ops cgroup_kf_ops = {
2301    .atomic_write_len = PAGE_SIZE,
2302    .write = cgroup_file_write,
2303    .seq_start = cgroup_seqfile_start,
2304    .seq_next = cgroup_seqfile_next,
2305    .seq_stop = cgroup_seqfile_stop,
2306    .seq_show = cgroup_seqfile_show,
2307};
2308
2309/*
2310 * cgroup_rename - Only allow simple rename of directories in place.
2311 */
2312static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
2313             const char *new_name_str)
2314{
2315    struct cgroup *cgrp = kn->priv;
2316    int ret;
2317
2318    if (kernfs_type(kn) != KERNFS_DIR)
2319        return -ENOTDIR;
2320    if (kn->parent != new_parent)
2321        return -EIO;
2322
2323    /*
2324     * This isn't a proper migration and its usefulness is very
2325     * limited. Disallow if sane_behavior.
2326     */
2327    if (cgroup_sane_behavior(cgrp))
2328        return -EPERM;
2329
2330    /*
2331     * We're gonna grab cgroup_tree_mutex which nests outside kernfs
2332     * active_ref. kernfs_rename() doesn't require active_ref
2333     * protection. Break them before grabbing cgroup_tree_mutex.
2334     */
2335    kernfs_break_active_protection(new_parent);
2336    kernfs_break_active_protection(kn);
2337
2338    mutex_lock(&cgroup_tree_mutex);
2339    mutex_lock(&cgroup_mutex);
2340
2341    ret = kernfs_rename(kn, new_parent, new_name_str);
2342
2343    mutex_unlock(&cgroup_mutex);
2344    mutex_unlock(&cgroup_tree_mutex);
2345
2346    kernfs_unbreak_active_protection(kn);
2347    kernfs_unbreak_active_protection(new_parent);
2348    return ret;
2349}
2350
2351/* set uid and gid of cgroup dirs and files to that of the creator */
2352static int cgroup_kn_set_ugid(struct kernfs_node *kn)
2353{
2354    struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
2355                   .ia_uid = current_fsuid(),
2356                   .ia_gid = current_fsgid(), };
2357
2358    if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
2359        gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
2360        return 0;
2361
2362    return kernfs_setattr(kn, &iattr);
2363}
2364
2365static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
2366{
2367    char name[CGROUP_FILE_NAME_MAX];
2368    struct kernfs_node *kn;
2369    struct lock_class_key *key = NULL;
2370    int ret;
2371
2372#ifdef CONFIG_DEBUG_LOCK_ALLOC
2373    key = &cft->lockdep_key;
2374#endif
2375    kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
2376                  cgroup_file_mode(cft), 0, cft->kf_ops, cft,
2377                  NULL, false, key);
2378    if (IS_ERR(kn))
2379        return PTR_ERR(kn);
2380
2381    ret = cgroup_kn_set_ugid(kn);
2382    if (ret)
2383        kernfs_remove(kn);
2384    return ret;
2385}
2386
2387/**
2388 * cgroup_addrm_files - add or remove files to a cgroup directory
2389 * @cgrp: the target cgroup
2390 * @cfts: array of cftypes to be added
2391 * @is_add: whether to add or remove
2392 *
2393 * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
2394 * For removals, this function never fails. If addition fails, this
2395 * function doesn't remove files already added. The caller is responsible
2396 * for cleaning up.
2397 */
2398static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
2399                  bool is_add)
2400{
2401    struct cftype *cft;
2402    int ret;
2403
2404    lockdep_assert_held(&cgroup_tree_mutex);
2405
2406    for (cft = cfts; cft->name[0] != '\0'; cft++) {
2407        /* does cft->flags tell us to skip this file on @cgrp? */
2408        if ((cft->flags & CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
2409            continue;
2410        if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp))
2411            continue;
2412        if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
2413            continue;
2414        if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgrp->parent)
2415            continue;
2416
2417        if (is_add) {
2418            ret = cgroup_add_file(cgrp, cft);
2419            if (ret) {
2420                pr_warn("cgroup_addrm_files: failed to add %s, err=%d\n",
2421                    cft->name, ret);
2422                return ret;
2423            }
2424        } else {
2425            cgroup_rm_file(cgrp, cft);
2426        }
2427    }
2428    return 0;
2429}
2430
2431static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
2432{
2433    LIST_HEAD(pending);
2434    struct cgroup_subsys *ss = cfts[0].ss;
2435    struct cgroup *root = &ss->root->cgrp;
2436    struct cgroup_subsys_state *css;
2437    int ret = 0;
2438
2439    lockdep_assert_held(&cgroup_tree_mutex);
2440
2441    /* don't bother if @ss isn't attached */
2442    if (ss->root == &cgrp_dfl_root)
2443        return 0;
2444
2445    /* add/rm files for all cgroups created before */
2446    css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
2447        struct cgroup *cgrp = css->cgroup;
2448
2449        if (cgroup_is_dead(cgrp))
2450            continue;
2451
2452        ret = cgroup_addrm_files(cgrp, cfts, is_add);
2453        if (ret)
2454            break;
2455    }
2456
2457    if (is_add && !ret)
2458        kernfs_activate(root->kn);
2459    return ret;
2460}
2461
2462static void cgroup_exit_cftypes(struct cftype *cfts)
2463{
2464    struct cftype *cft;
2465
2466    for (cft = cfts; cft->name[0] != '\0'; cft++) {
2467        /* free copy for custom atomic_write_len, see init_cftypes() */
2468        if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
2469            kfree(cft->kf_ops);
2470        cft->kf_ops = NULL;
2471        cft->ss = NULL;
2472    }
2473}
2474
2475static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
2476{
2477    struct cftype *cft;
2478
2479    for (cft = cfts; cft->name[0] != '\0'; cft++) {
2480        struct kernfs_ops *kf_ops;
2481
2482        WARN_ON(cft->ss || cft->kf_ops);
2483
2484        if (cft->seq_start)
2485            kf_ops = &cgroup_kf_ops;
2486        else
2487            kf_ops = &cgroup_kf_single_ops;
2488
2489        /*
2490         * Ugh... if @cft wants a custom max_write_len, we need to
2491         * make a copy of kf_ops to set its atomic_write_len.
2492         */
2493        if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
2494            kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
2495            if (!kf_ops) {
2496                cgroup_exit_cftypes(cfts);
2497                return -ENOMEM;
2498            }
2499            kf_ops->atomic_write_len = cft->max_write_len;
2500        }
2501
2502        cft->kf_ops = kf_ops;
2503        cft->ss = ss;
2504    }
2505
2506    return 0;
2507}
2508
2509static int cgroup_rm_cftypes_locked(struct cftype *cfts)
2510{
2511    lockdep_assert_held(&cgroup_tree_mutex);
2512
2513    if (!cfts || !cfts[0].ss)
2514        return -ENOENT;
2515
2516    list_del(&cfts->node);
2517    cgroup_apply_cftypes(cfts, false);
2518    cgroup_exit_cftypes(cfts);
2519    return 0;
2520}
2521
2522/**
2523 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
2524 * @cfts: zero-length name terminated array of cftypes
2525 *
2526 * Unregister @cfts. Files described by @cfts are removed from all
2527 * existing cgroups and all future cgroups won't have them either. This
2528 * function can be called anytime whether @cfts' subsys is attached or not.
2529 *
2530 * Returns 0 on successful unregistration, -ENOENT if @cfts is not
2531 * registered.
2532 */
2533int cgroup_rm_cftypes(struct cftype *cfts)
2534{
2535    int ret;
2536
2537    mutex_lock(&cgroup_tree_mutex);
2538    ret = cgroup_rm_cftypes_locked(cfts);
2539    mutex_unlock(&cgroup_tree_mutex);
2540    return ret;
2541}
2542
2543/**
2544 * cgroup_add_cftypes - add an array of cftypes to a subsystem
2545 * @ss: target cgroup subsystem
2546 * @cfts: zero-length name terminated array of cftypes
2547 *
2548 * Register @cfts to @ss. Files described by @cfts are created for all
2549 * existing cgroups to which @ss is attached and all future cgroups will
2550 * have them too. This function can be called anytime whether @ss is
2551 * attached or not.
2552 *
2553 * Returns 0 on successful registration, -errno on failure. Note that this
2554 * function currently returns 0 as long as @cfts registration is successful
2555 * even if some file creation attempts on existing cgroups fail.
2556 */
2557int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
2558{
2559    int ret;
2560
2561    if (!cfts || cfts[0].name[0] == '\0')
2562        return 0;
2563
2564    ret = cgroup_init_cftypes(ss, cfts);
2565    if (ret)
2566        return ret;
2567
2568    mutex_lock(&cgroup_tree_mutex);
2569
2570    list_add_tail(&cfts->node, &ss->cfts);
2571    ret = cgroup_apply_cftypes(cfts, true);
2572    if (ret)
2573        cgroup_rm_cftypes_locked(cfts);
2574
2575    mutex_unlock(&cgroup_tree_mutex);
2576    return ret;
2577}
2578
2579/**
2580 * cgroup_task_count - count the number of tasks in a cgroup.
2581 * @cgrp: the cgroup in question
2582 *
2583 * Return the number of tasks in the cgroup.
2584 */
2585static int cgroup_task_count(const struct cgroup *cgrp)
2586{
2587    int count = 0;
2588    struct cgrp_cset_link *link;
2589
2590    down_read(&css_set_rwsem);
2591    list_for_each_entry(link, &cgrp->cset_links, cset_link)
2592        count += atomic_read(&link->cset->refcount);
2593    up_read(&css_set_rwsem);
2594    return count;
2595}
2596
2597/**
2598 * css_next_child - find the next child of a given css
2599 * @pos_css: the current position (%NULL to initiate traversal)
2600 * @parent_css: css whose children to walk
2601 *
2602 * This function returns the next child of @parent_css and should be called
2603 * under either cgroup_mutex or RCU read lock. The only requirement is
2604 * that @parent_css and @pos_css are accessible. The next sibling is
2605 * guaranteed to be returned regardless of their states.
2606 */
2607struct cgroup_subsys_state *
2608css_next_child(struct cgroup_subsys_state *pos_css,
2609           struct cgroup_subsys_state *parent_css)
2610{
2611    struct cgroup *pos = pos_css ? pos_css->cgroup : NULL;
2612    struct cgroup *cgrp = parent_css->cgroup;
2613    struct cgroup *next;
2614
2615    cgroup_assert_mutexes_or_rcu_locked();
2616
2617    /*
2618     * @pos could already have been removed. Once a cgroup is removed,
2619     * its ->sibling.next is no longer updated when its next sibling
2620     * changes. As CGRP_DEAD assertion is serialized and happens
2621     * before the cgroup is taken off the ->sibling list, if we see it
2622     * unasserted, it's guaranteed that the next sibling hasn't
2623     * finished its grace period even if it's already removed, and thus
2624     * safe to dereference from this RCU critical section. If
2625     * ->sibling.next is inaccessible, cgroup_is_dead() is guaranteed
2626     * to be visible as %true here.
2627     *
2628     * If @pos is dead, its next pointer can't be dereferenced;
2629     * however, as each cgroup is given a monotonically increasing
2630     * unique serial number and always appended to the sibling list,
2631     * the next one can be found by walking the parent's children until
2632     * we see a cgroup with higher serial number than @pos's. While
2633     * this path can be slower, it's taken only when either the current
2634     * cgroup is removed or iteration and removal race.
2635     */
2636    if (!pos) {
2637        next = list_entry_rcu(cgrp->children.next, struct cgroup, sibling);
2638    } else if (likely(!cgroup_is_dead(pos))) {
2639        next = list_entry_rcu(pos->sibling.next, struct cgroup, sibling);
2640    } else {
2641        list_for_each_entry_rcu(next, &cgrp->children, sibling)
2642            if (next->serial_nr > pos->serial_nr)
2643                break;
2644    }
2645
2646    if (&next->sibling == &cgrp->children)
2647        return NULL;
2648
2649    return cgroup_css(next, parent_css->ss);
2650}
2651
2652/**
2653 * css_next_descendant_pre - find the next descendant for pre-order walk
2654 * @pos: the current position (%NULL to initiate traversal)
2655 * @root: css whose descendants to walk
2656 *
2657 * To be used by css_for_each_descendant_pre(). Find the next descendant
2658 * to visit for pre-order traversal of @root's descendants. @root is
2659 * included in the iteration and the first node to be visited.
2660 *
2661 * While this function requires cgroup_mutex or RCU read locking, it
2662 * doesn't require the whole traversal to be contained in a single critical
2663 * section. This function will return the correct next descendant as long
2664 * as both @pos and @root are accessible and @pos is a descendant of @root.
2665 */
2666struct cgroup_subsys_state *
2667css_next_descendant_pre(struct cgroup_subsys_state *pos,
2668            struct cgroup_subsys_state *root)
2669{
2670    struct cgroup_subsys_state *next;
2671
2672    cgroup_assert_mutexes_or_rcu_locked();
2673
2674    /* if first iteration, visit @root */
2675    if (!pos)
2676        return root;
2677
2678    /* visit the first child if exists */
2679    next = css_next_child(NULL, pos);
2680    if (next)
2681        return next;
2682
2683    /* no child, visit my or the closest ancestor's next sibling */
2684    while (pos != root) {
2685        next = css_next_child(pos, css_parent(pos));
2686        if (next)
2687            return next;
2688        pos = css_parent(pos);
2689    }
2690
2691    return NULL;
2692}
2693
2694/**
2695 * css_rightmost_descendant - return the rightmost descendant of a css
2696 * @pos: css of interest
2697 *
2698 * Return the rightmost descendant of @pos. If there's no descendant, @pos
2699 * is returned. This can be used during pre-order traversal to skip
2700 * subtree of @pos.
2701 *
2702 * While this function requires cgroup_mutex or RCU read locking, it
2703 * doesn't require the whole traversal to be contained in a single critical
2704 * section. This function will return the correct rightmost descendant as
2705 * long as @pos is accessible.
2706 */
2707struct cgroup_subsys_state *
2708css_rightmost_descendant(struct cgroup_subsys_state *pos)
2709{
2710    struct cgroup_subsys_state *last, *tmp;
2711
2712    cgroup_assert_mutexes_or_rcu_locked();
2713
2714    do {
2715        last = pos;
2716        /* ->prev isn't RCU safe, walk ->next till the end */
2717        pos = NULL;
2718        css_for_each_child(tmp, last)
2719            pos = tmp;
2720    } while (pos);
2721
2722    return last;
2723}
2724
2725static struct cgroup_subsys_state *
2726css_leftmost_descendant(struct cgroup_subsys_state *pos)
2727{
2728    struct cgroup_subsys_state *last;
2729
2730    do {
2731        last = pos;
2732        pos = css_next_child(NULL, pos);
2733    } while (pos);
2734
2735    return last;
2736}
2737
2738/**
2739 * css_next_descendant_post - find the next descendant for post-order walk
2740 * @pos: the current position (%NULL to initiate traversal)
2741 * @root: css whose descendants to walk
2742 *
2743 * To be used by css_for_each_descendant_post(). Find the next descendant
2744 * to visit for post-order traversal of @root's descendants. @root is
2745 * included in the iteration and the last node to be visited.
2746 *
2747 * While this function requires cgroup_mutex or RCU read locking, it
2748 * doesn't require the whole traversal to be contained in a single critical
2749 * section. This function will return the correct next descendant as long
2750 * as both @pos and @cgroup are accessible and @pos is a descendant of
2751 * @cgroup.
2752 */
2753struct cgroup_subsys_state *
2754css_next_descendant_post(struct cgroup_subsys_state *pos,
2755             struct cgroup_subsys_state *root)
2756{
2757    struct cgroup_subsys_state *next;
2758
2759    cgroup_assert_mutexes_or_rcu_locked();
2760
2761    /* if first iteration, visit leftmost descendant which may be @root */
2762    if (!pos)
2763        return css_leftmost_descendant(root);
2764
2765    /* if we visited @root, we're done */
2766    if (pos == root)
2767        return NULL;
2768
2769    /* if there's an unvisited sibling, visit its leftmost descendant */
2770    next = css_next_child(pos, css_parent(pos));
2771    if (next)
2772        return css_leftmost_descendant(next);
2773
2774    /* no sibling left, visit parent */
2775    return css_parent(pos);
2776}
2777
2778/**
2779 * css_advance_task_iter - advance a task itererator to the next css_set
2780 * @it: the iterator to advance
2781 *
2782 * Advance @it to the next css_set to walk.
2783 */
2784static void css_advance_task_iter(struct css_task_iter *it)
2785{
2786    struct list_head *l = it->cset_link;
2787    struct cgrp_cset_link *link;
2788    struct css_set *cset;
2789
2790    /* Advance to the next non-empty css_set */
2791    do {
2792        l = l->next;
2793        if (l == &it->origin_css->cgroup->cset_links) {
2794            it->cset_link = NULL;
2795            return;
2796        }
2797        link = list_entry(l, struct cgrp_cset_link, cset_link);
2798        cset = link->cset;
2799    } while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks));
2800
2801    it->cset_link = l;
2802
2803    if (!list_empty(&cset->tasks))
2804        it->task = cset->tasks.next;
2805    else
2806        it->task = cset->mg_tasks.next;
2807}
2808
2809/**
2810 * css_task_iter_start - initiate task iteration
2811 * @css: the css to walk tasks of
2812 * @it: the task iterator to use
2813 *
2814 * Initiate iteration through the tasks of @css. The caller can call
2815 * css_task_iter_next() to walk through the tasks until the function
2816 * returns NULL. On completion of iteration, css_task_iter_end() must be
2817 * called.
2818 *
2819 * Note that this function acquires a lock which is released when the
2820 * iteration finishes. The caller can't sleep while iteration is in
2821 * progress.
2822 */
2823void css_task_iter_start(struct cgroup_subsys_state *css,
2824             struct css_task_iter *it)
2825    __acquires(css_set_rwsem)
2826{
2827    /* no one should try to iterate before mounting cgroups */
2828    WARN_ON_ONCE(!use_task_css_set_links);
2829
2830    down_read(&css_set_rwsem);
2831
2832    it->origin_css = css;
2833    it->cset_link = &css->cgroup->cset_links;
2834
2835    css_advance_task_iter(it);
2836}
2837
2838/**
2839 * css_task_iter_next - return the next task for the iterator
2840 * @it: the task iterator being iterated
2841 *
2842 * The "next" function for task iteration. @it should have been
2843 * initialized via css_task_iter_start(). Returns NULL when the iteration
2844 * reaches the end.
2845 */
2846struct task_struct *css_task_iter_next(struct css_task_iter *it)
2847{
2848    struct task_struct *res;
2849    struct list_head *l = it->task;
2850    struct cgrp_cset_link *link = list_entry(it->cset_link,
2851                    struct cgrp_cset_link, cset_link);
2852
2853    /* If the iterator cg is NULL, we have no tasks */
2854    if (!it->cset_link)
2855        return NULL;
2856    res = list_entry(l, struct task_struct, cg_list);
2857
2858    /*
2859     * Advance iterator to find next entry. cset->tasks is consumed
2860     * first and then ->mg_tasks. After ->mg_tasks, we move onto the
2861     * next cset.
2862     */
2863    l = l->next;
2864
2865    if (l == &link->cset->tasks)
2866        l = link->cset->mg_tasks.next;
2867
2868    if (l == &link->cset->mg_tasks)
2869        css_advance_task_iter(it);
2870    else
2871        it->task = l;
2872
2873    return res;
2874}
2875
2876/**
2877 * css_task_iter_end - finish task iteration
2878 * @it: the task iterator to finish
2879 *
2880 * Finish task iteration started by css_task_iter_start().
2881 */
2882void css_task_iter_end(struct css_task_iter *it)
2883    __releases(css_set_rwsem)
2884{
2885    up_read(&css_set_rwsem);
2886}
2887
2888/**
2889 * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
2890 * @to: cgroup to which the tasks will be moved
2891 * @from: cgroup in which the tasks currently reside
2892 *
2893 * Locking rules between cgroup_post_fork() and the migration path
2894 * guarantee that, if a task is forking while being migrated, the new child
2895 * is guaranteed to be either visible in the source cgroup after the
2896 * parent's migration is complete or put into the target cgroup. No task
2897 * can slip out of migration through forking.
2898 */
2899int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
2900{
2901    LIST_HEAD(preloaded_csets);
2902    struct cgrp_cset_link *link;
2903    struct css_task_iter it;
2904    struct task_struct *task;
2905    int ret;
2906
2907    mutex_lock(&cgroup_mutex);
2908
2909    /* all tasks in @from are being moved, all csets are source */
2910    down_read(&css_set_rwsem);
2911    list_for_each_entry(link, &from->cset_links, cset_link)
2912        cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
2913    up_read(&css_set_rwsem);
2914
2915    ret = cgroup_migrate_prepare_dst(to, &preloaded_csets);
2916    if (ret)
2917        goto out_err;
2918
2919    /*
2920     * Migrate tasks one-by-one until @form is empty. This fails iff
2921     * ->can_attach() fails.
2922     */
2923    do {
2924        css_task_iter_start(&from->dummy_css, &it);
2925        task = css_task_iter_next(&it);
2926        if (task)
2927            get_task_struct(task);
2928        css_task_iter_end(&it);
2929
2930        if (task) {
2931            ret = cgroup_migrate(to, task, false);
2932            put_task_struct(task);
2933        }
2934    } while (task && !ret);
2935out_err:
2936    cgroup_migrate_finish(&preloaded_csets);
2937    mutex_unlock(&cgroup_mutex);
2938    return ret;
2939}
2940
2941/*
2942 * Stuff for reading the 'tasks'/'procs' files.
2943 *
2944 * Reading this file can return large amounts of data if a cgroup has
2945 * *lots* of attached tasks. So it may need several calls to read(),
2946 * but we cannot guarantee that the information we produce is correct
2947 * unless we produce it entirely atomically.
2948 *
2949 */
2950
2951/* which pidlist file are we talking about? */
2952enum cgroup_filetype {
2953    CGROUP_FILE_PROCS,
2954    CGROUP_FILE_TASKS,
2955};
2956
2957/*
2958 * A pidlist is a list of pids that virtually represents the contents of one
2959 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
2960 * a pair (one each for procs, tasks) for each pid namespace that's relevant
2961 * to the cgroup.
2962 */
2963struct cgroup_pidlist {
2964    /*
2965     * used to find which pidlist is wanted. doesn't change as long as
2966     * this particular list stays in the list.
2967    */
2968    struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
2969    /* array of xids */
2970    pid_t *list;
2971    /* how many elements the above list has */
2972    int length;
2973    /* each of these stored in a list by its cgroup */
2974    struct list_head links;
2975    /* pointer to the cgroup we belong to, for list removal purposes */
2976    struct cgroup *owner;
2977    /* for delayed destruction */
2978    struct delayed_work destroy_dwork;
2979};
2980
2981/*
2982 * The following two functions "fix" the issue where there are more pids
2983 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
2984 * TODO: replace with a kernel-wide solution to this problem
2985 */
2986#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
2987static void *pidlist_allocate(int count)
2988{
2989    if (PIDLIST_TOO_LARGE(count))
2990        return vmalloc(count * sizeof(pid_t));
2991    else
2992        return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
2993}
2994
2995static void pidlist_free(void *p)
2996{
2997    if (is_vmalloc_addr(p))
2998        vfree(p);
2999    else
3000        kfree(p);
3001}
3002
3003/*
3004 * Used to destroy all pidlists lingering waiting for destroy timer. None
3005 * should be left afterwards.
3006 */
3007static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
3008{
3009    struct cgroup_pidlist *l, *tmp_l;
3010
3011    mutex_lock(&cgrp->pidlist_mutex);
3012    list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
3013        mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
3014    mutex_unlock(&cgrp->pidlist_mutex);
3015
3016    flush_workqueue(cgroup_pidlist_destroy_wq);
3017    BUG_ON(!list_empty(&cgrp->pidlists));
3018}
3019
3020static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
3021{
3022    struct delayed_work *dwork = to_delayed_work(work);
3023    struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
3024                        destroy_dwork);
3025    struct cgroup_pidlist *tofree = NULL;
3026
3027    mutex_lock(&l->owner->pidlist_mutex);
3028
3029    /*
3030     * Destroy iff we didn't get queued again. The state won't change
3031     * as destroy_dwork can only be queued while locked.
3032     */
3033    if (!delayed_work_pending(dwork)) {
3034        list_del(&l->links);
3035        pidlist_free(l->list);
3036        put_pid_ns(l->key.ns);
3037        tofree = l;
3038    }
3039
3040    mutex_unlock(&l->owner->pidlist_mutex);
3041    kfree(tofree);
3042}
3043
3044/*
3045 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
3046 * Returns the number of unique elements.
3047 */
3048static int pidlist_uniq(pid_t *list, int length)
3049{
3050    int src, dest = 1;
3051
3052    /*
3053     * we presume the 0th element is unique, so i starts at 1. trivial
3054     * edge cases first; no work needs to be done for either
3055     */
3056    if (length == 0 || length == 1)
3057        return length;
3058    /* src and dest walk down the list; dest counts unique elements */
3059    for (src = 1; src < length; src++) {
3060        /* find next unique element */
3061        while (list[src] == list[src-1]) {
3062            src++;
3063            if (src == length)
3064                goto after;
3065        }
3066        /* dest always points to where the next unique element goes */
3067        list[dest] = list[src];
3068        dest++;
3069    }
3070after:
3071    return dest;
3072}
3073
3074/*
3075 * The two pid files - task and cgroup.procs - guaranteed that the result
3076 * is sorted, which forced this whole pidlist fiasco. As pid order is
3077 * different per namespace, each namespace needs differently sorted list,
3078 * making it impossible to use, for example, single rbtree of member tasks
3079 * sorted by task pointer. As pidlists can be fairly large, allocating one
3080 * per open file is dangerous, so cgroup had to implement shared pool of
3081 * pidlists keyed by cgroup and namespace.
3082 *
3083 * All this extra complexity was caused by the original implementation
3084 * committing to an entirely unnecessary property. In the long term, we
3085 * want to do away with it. Explicitly scramble sort order if
3086 * sane_behavior so that no such expectation exists in the new interface.
3087 *
3088 * Scrambling is done by swapping every two consecutive bits, which is
3089 * non-identity one-to-one mapping which disturbs sort order sufficiently.
3090 */
3091static pid_t pid_fry(pid_t pid)
3092{
3093    unsigned a = pid & 0x55555555;
3094    unsigned b = pid & 0xAAAAAAAA;
3095
3096    return (a << 1) | (b >> 1);
3097}
3098
3099static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
3100{
3101    if (cgroup_sane_behavior(cgrp))
3102        return pid_fry(pid);
3103    else
3104        return pid;
3105}
3106
3107static int cmppid(const void *a, const void *b)
3108{
3109    return *(pid_t *)a - *(pid_t *)b;
3110}
3111
3112static int fried_cmppid(const void *a, const void *b)
3113{
3114    return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b);
3115}
3116
3117static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
3118                          enum cgroup_filetype type)
3119{
3120    struct cgroup_pidlist *l;
3121    /* don't need task_nsproxy() if we're looking at ourself */
3122    struct pid_namespace *ns = task_active_pid_ns(current);
3123
3124    lockdep_assert_held(&cgrp->pidlist_mutex);
3125
3126    list_for_each_entry(l, &cgrp->pidlists, links)
3127        if (l->key.type == type && l->key.ns == ns)
3128            return l;
3129    return NULL;
3130}
3131
3132/*
3133 * find the appropriate pidlist for our purpose (given procs vs tasks)
3134 * returns with the lock on that pidlist already held, and takes care
3135 * of the use count, or returns NULL with no locks held if we're out of
3136 * memory.
3137 */
3138static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
3139                        enum cgroup_filetype type)
3140{
3141    struct cgroup_pidlist *l;
3142
3143    lockdep_assert_held(&cgrp->pidlist_mutex);
3144
3145    l = cgroup_pidlist_find(cgrp, type);
3146    if (l)
3147        return l;
3148
3149    /* entry not found; create a new one */
3150    l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
3151    if (!l)
3152        return l;
3153
3154    INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
3155    l->key.type = type;
3156    /* don't need task_nsproxy() if we're looking at ourself */
3157    l->key.ns = get_pid_ns(task_active_pid_ns(current));
3158    l->owner = cgrp;
3159    list_add(&l->links, &cgrp->pidlists);
3160    return l;
3161}
3162
3163/*
3164 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
3165 */
3166static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
3167                  struct cgroup_pidlist **lp)
3168{
3169    pid_t *array;
3170    int length;
3171    int pid, n = 0; /* used for populating the array */
3172    struct css_task_iter it;
3173    struct task_struct *tsk;
3174    struct cgroup_pidlist *l;
3175
3176    lockdep_assert_held(&cgrp->pidlist_mutex);
3177
3178    /*
3179     * If cgroup gets more users after we read count, we won't have
3180     * enough space - tough. This race is indistinguishable to the
3181     * caller from the case that the additional cgroup users didn't
3182     * show up until sometime later on.
3183     */
3184    length = cgroup_task_count(cgrp);
3185    array = pidlist_allocate(length);
3186    if (!array)
3187        return -ENOMEM;
3188    /* now, populate the array */
3189    css_task_iter_start(&cgrp->dummy_css, &it);
3190    while ((tsk = css_task_iter_next(&it))) {
3191        if (unlikely(n == length))
3192            break;
3193        /* get tgid or pid for procs or tasks file respectively */
3194        if (type == CGROUP_FILE_PROCS)
3195            pid = task_tgid_vnr(tsk);
3196        else
3197            pid = task_pid_vnr(tsk);
3198        if (pid > 0) /* make sure to only use valid results */
3199            array[n++] = pid;
3200    }
3201    css_task_iter_end(&it);
3202    length = n;
3203    /* now sort & (if procs) strip out duplicates */
3204    if (cgroup_sane_behavior(cgrp))
3205        sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
3206    else
3207        sort(array, length, sizeof(pid_t), cmppid, NULL);
3208    if (type == CGROUP_FILE_PROCS)
3209        length = pidlist_uniq(array, length);
3210
3211    l = cgroup_pidlist_find_create(cgrp, type);
3212    if (!l) {
3213        mutex_unlock(&cgrp->pidlist_mutex);
3214        pidlist_free(array);
3215        return -ENOMEM;
3216    }
3217
3218    /* store array, freeing old if necessary */
3219    pidlist_free(l->list);
3220    l->list = array;
3221    l->length = length;
3222    *lp = l;
3223    return 0;
3224}
3225
3226/**
3227 * cgroupstats_build - build and fill cgroupstats
3228 * @stats: cgroupstats to fill information into
3229 * @dentry: A dentry entry belonging to the cgroup for which stats have
3230 * been requested.
3231 *
3232 * Build and fill cgroupstats so that taskstats can export it to user
3233 * space.
3234 */
3235int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
3236{
3237    struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
3238    struct cgroup *cgrp;
3239    struct css_task_iter it;
3240    struct task_struct *tsk;
3241
3242    /* it should be kernfs_node belonging to cgroupfs and is a directory */
3243    if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
3244        kernfs_type(kn) != KERNFS_DIR)
3245        return -EINVAL;
3246
3247    mutex_lock(&cgroup_mutex);
3248
3249    /*
3250     * We aren't being called from kernfs and there's no guarantee on
3251     * @kn->priv's validity. For this and css_tryget_from_dir(),
3252     * @kn->priv is RCU safe. Let's do the RCU dancing.
3253     */
3254    rcu_read_lock();
3255    cgrp = rcu_dereference(kn->priv);
3256    if (!cgrp || cgroup_is_dead(cgrp)) {
3257        rcu_read_unlock();
3258        mutex_unlock(&cgroup_mutex);
3259        return -ENOENT;
3260    }
3261    rcu_read_unlock();
3262
3263    css_task_iter_start(&cgrp->dummy_css, &it);
3264    while ((tsk = css_task_iter_next(&it))) {
3265        switch (tsk->state) {
3266        case TASK_RUNNING:
3267            stats->nr_running++;
3268            break;
3269        case TASK_INTERRUPTIBLE:
3270            stats->nr_sleeping++;
3271            break;
3272        case TASK_UNINTERRUPTIBLE:
3273            stats->nr_uninterruptible++;
3274            break;
3275        case TASK_STOPPED:
3276            stats->nr_stopped++;
3277            break;
3278        default:
3279            if (delayacct_is_task_waiting_on_io(tsk))
3280                stats->nr_io_wait++;
3281            break;
3282        }
3283    }
3284    css_task_iter_end(&it);
3285
3286    mutex_unlock(&cgroup_mutex);
3287    return 0;
3288}
3289
3290
3291/*
3292 * seq_file methods for the tasks/procs files. The seq_file position is the
3293 * next pid to display; the seq_file iterator is a pointer to the pid
3294 * in the cgroup->l->list array.
3295 */
3296
3297static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
3298{
3299    /*
3300     * Initially we receive a position value that corresponds to
3301     * one more than the last pid shown (or 0 on the first call or
3302     * after a seek to the start). Use a binary-search to find the
3303     * next pid to display, if any
3304     */
3305    struct kernfs_open_file *of = s->private;
3306    struct cgroup *cgrp = seq_css(s)->cgroup;
3307    struct cgroup_pidlist *l;
3308    enum cgroup_filetype type = seq_cft(s)->private;
3309    int index = 0, pid = *pos;
3310    int *iter, ret;
3311
3312    mutex_lock(&cgrp->pidlist_mutex);
3313
3314    /*
3315     * !NULL @of->priv indicates that this isn't the first start()
3316     * after open. If the matching pidlist is around, we can use that.
3317     * Look for it. Note that @of->priv can't be used directly. It
3318     * could already have been destroyed.
3319     */
3320    if (of->priv)
3321        of->priv = cgroup_pidlist_find(cgrp, type);
3322
3323    /*
3324     * Either this is the first start() after open or the matching
3325     * pidlist has been destroyed inbetween. Create a new one.
3326     */
3327    if (!of->priv) {
3328        ret = pidlist_array_load(cgrp, type,
3329                     (struct cgroup_pidlist **)&of->priv);
3330        if (ret)
3331            return ERR_PTR(ret);
3332    }
3333    l = of->priv;
3334
3335    if (pid) {
3336        int end = l->length;
3337
3338        while (index < end) {
3339            int mid = (index + end) / 2;
3340            if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
3341                index = mid;
3342                break;
3343            } else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
3344                index = mid + 1;
3345            else
3346                end = mid;
3347        }
3348    }
3349    /* If we're off the end of the array, we're done */
3350    if (index >= l->length)
3351        return NULL;
3352    /* Update the abstract position to be the actual pid that we found */
3353    iter = l->list + index;
3354    *pos = cgroup_pid_fry(cgrp, *iter);
3355    return iter;
3356}
3357
3358static void cgroup_pidlist_stop(struct seq_file *s, void *v)
3359{
3360    struct kernfs_open_file *of = s->private;
3361    struct cgroup_pidlist *l = of->priv;
3362
3363    if (l)
3364        mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
3365                 CGROUP_PIDLIST_DESTROY_DELAY);
3366    mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
3367}
3368
3369static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
3370{
3371    struct kernfs_open_file *of = s->private;
3372    struct cgroup_pidlist *l = of->priv;
3373    pid_t *p = v;
3374    pid_t *end = l->list + l->length;
3375    /*
3376     * Advance to the next pid in the array. If this goes off the
3377     * end, we're done
3378     */
3379    p++;
3380    if (p >= end) {
3381        return NULL;
3382    } else {
3383        *pos = cgroup_pid_fry(seq_css(s)->cgroup, *p);
3384        return p;
3385    }
3386}
3387
3388static int cgroup_pidlist_show(struct seq_file *s, void *v)
3389{
3390    return seq_printf(s, "%d\n", *(int *)v);
3391}
3392
3393/*
3394 * seq_operations functions for iterating on pidlists through seq_file -
3395 * independent of whether it's tasks or procs
3396 */
3397static const struct seq_operations cgroup_pidlist_seq_operations = {
3398    .start = cgroup_pidlist_start,
3399    .stop = cgroup_pidlist_stop,
3400    .next = cgroup_pidlist_next,
3401    .show = cgroup_pidlist_show,
3402};
3403
3404static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
3405                     struct cftype *cft)
3406{
3407    return notify_on_release(css->cgroup);
3408}
3409
3410static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
3411                      struct cftype *cft, u64 val)
3412{
3413    clear_bit(CGRP_RELEASABLE, &css->cgroup->flags);
3414    if (val)
3415        set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
3416    else
3417        clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
3418    return 0;
3419}
3420
3421static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
3422                      struct cftype *cft)
3423{
3424    return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3425}
3426
3427static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
3428                       struct cftype *cft, u64 val)
3429{
3430    if (val)
3431        set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3432    else
3433        clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
3434    return 0;
3435}
3436
3437static struct cftype cgroup_base_files[] = {
3438    {
3439        .name = "cgroup.procs",
3440        .seq_start = cgroup_pidlist_start,
3441        .seq_next = cgroup_pidlist_next,
3442        .seq_stop = cgroup_pidlist_stop,
3443        .seq_show = cgroup_pidlist_show,
3444        .private = CGROUP_FILE_PROCS,
3445        .write_u64 = cgroup_procs_write,
3446        .mode = S_IRUGO | S_IWUSR,
3447    },
3448    {
3449        .name = "cgroup.clone_children",
3450        .flags = CFTYPE_INSANE,
3451        .read_u64 = cgroup_clone_children_read,
3452        .write_u64 = cgroup_clone_children_write,
3453    },
3454    {
3455        .name = "cgroup.sane_behavior",
3456        .flags = CFTYPE_ONLY_ON_ROOT,
3457        .seq_show = cgroup_sane_behavior_show,
3458    },
3459
3460    /*
3461     * Historical crazy stuff. These don't have "cgroup." prefix and
3462     * don't exist if sane_behavior. If you're depending on these, be
3463     * prepared to be burned.
3464     */
3465    {
3466        .name = "tasks",
3467        .flags = CFTYPE_INSANE, /* use "procs" instead */
3468        .seq_start = cgroup_pidlist_start,
3469        .seq_next = cgroup_pidlist_next,
3470        .seq_stop = cgroup_pidlist_stop,
3471        .seq_show = cgroup_pidlist_show,
3472        .private = CGROUP_FILE_TASKS,
3473        .write_u64 = cgroup_tasks_write,
3474        .mode = S_IRUGO | S_IWUSR,
3475    },
3476    {
3477        .name = "notify_on_release",
3478        .flags = CFTYPE_INSANE,
3479        .read_u64 = cgroup_read_notify_on_release,
3480        .write_u64 = cgroup_write_notify_on_release,
3481    },
3482    {
3483        .name = "release_agent",
3484        .flags = CFTYPE_INSANE | CFTYPE_ONLY_ON_ROOT,
3485        .seq_show = cgroup_release_agent_show,
3486        .write_string = cgroup_release_agent_write,
3487        .max_write_len = PATH_MAX - 1,
3488    },
3489    { } /* terminate */
3490};
3491
3492/**
3493 * cgroup_populate_dir - create subsys files in a cgroup directory
3494 * @cgrp: target cgroup
3495 * @subsys_mask: mask of the subsystem ids whose files should be added
3496 *
3497 * On failure, no file is added.
3498 */
3499static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
3500{
3501    struct cgroup_subsys *ss;
3502    int i, ret = 0;
3503
3504    /* process cftsets of each subsystem */
3505    for_each_subsys(ss, i) {
3506        struct cftype *cfts;
3507
3508        if (!test_bit(i, &subsys_mask))
3509            continue;
3510
3511        list_for_each_entry(cfts, &ss->cfts, node) {
3512            ret = cgroup_addrm_files(cgrp, cfts, true);
3513            if (ret < 0)
3514                goto err;
3515        }
3516    }
3517    return 0;
3518err:
3519    cgroup_clear_dir(cgrp, subsys_mask);
3520    return ret;
3521}
3522
3523/*
3524 * css destruction is four-stage process.
3525 *
3526 * 1. Destruction starts. Killing of the percpu_ref is initiated.
3527 * Implemented in kill_css().
3528 *
3529 * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
3530 * and thus css_tryget() is guaranteed to fail, the css can be offlined
3531 * by invoking offline_css(). After offlining, the base ref is put.
3532 * Implemented in css_killed_work_fn().
3533 *
3534 * 3. When the percpu_ref reaches zero, the only possible remaining
3535 * accessors are inside RCU read sections. css_release() schedules the
3536 * RCU callback.
3537 *
3538 * 4. After the grace period, the css can be freed. Implemented in
3539 * css_free_work_fn().
3540 *
3541 * It is actually hairier because both step 2 and 4 require process context
3542 * and thus involve punting to css->destroy_work adding two additional
3543 * steps to the already complex sequence.
3544 */
3545static void css_free_work_fn(struct work_struct *work)
3546{
3547    struct cgroup_subsys_state *css =
3548        container_of(work, struct cgroup_subsys_state, destroy_work);
3549    struct cgroup *cgrp = css->cgroup;
3550
3551    if (css->parent)
3552        css_put(css->parent);
3553
3554    css->ss->css_free(css);
3555    cgroup_put(cgrp);
3556}
3557
3558static void css_free_rcu_fn(struct rcu_head *rcu_head)
3559{
3560    struct cgroup_subsys_state *css =
3561        container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
3562
3563    INIT_WORK(&css->destroy_work, css_free_work_fn);
3564    queue_work(cgroup_destroy_wq, &css->destroy_work);
3565}
3566
3567static void css_release(struct percpu_ref *ref)
3568{
3569    struct cgroup_subsys_state *css =
3570        container_of(ref, struct cgroup_subsys_state, refcnt);
3571
3572    RCU_INIT_POINTER(css->cgroup->subsys[css->ss->id], NULL);
3573    call_rcu(&css->rcu_head, css_free_rcu_fn);
3574}
3575
3576static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss,
3577             struct cgroup *cgrp)
3578{
3579    css->cgroup = cgrp;
3580    css->ss = ss;
3581    css->flags = 0;
3582
3583    if (cgrp->parent)
3584        css->parent = cgroup_css(cgrp->parent, ss);
3585    else
3586        css->flags |= CSS_ROOT;
3587
3588    BUG_ON(cgroup_css(cgrp, ss));
3589}
3590
3591/* invoke ->css_online() on a new CSS and mark it online if successful */
3592static int online_css(struct cgroup_subsys_state *css)
3593{
3594    struct cgroup_subsys *ss = css->ss;
3595    int ret = 0;
3596
3597    lockdep_assert_held(&cgroup_tree_mutex);
3598    lockdep_assert_held(&cgroup_mutex);
3599
3600    if (ss->css_online)
3601        ret = ss->css_online(css);
3602    if (!ret) {
3603        css->flags |= CSS_ONLINE;
3604        css->cgroup->nr_css++;
3605        rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
3606    }
3607    return ret;
3608}
3609
3610/* if the CSS is online, invoke ->css_offline() on it and mark it offline */
3611static void offline_css(struct cgroup_subsys_state *css)
3612{
3613    struct cgroup_subsys *ss = css->ss;
3614
3615    lockdep_assert_held(&cgroup_tree_mutex);
3616    lockdep_assert_held(&cgroup_mutex);
3617
3618    if (!(css->flags & CSS_ONLINE))
3619        return;
3620
3621    if (ss->css_offline)
3622        ss->css_offline(css);
3623
3624    css->flags &= ~CSS_ONLINE;
3625    css->cgroup->nr_css--;
3626    RCU_INIT_POINTER(css->cgroup->subsys[ss->id], css);
3627}
3628
3629/**
3630 * create_css - create a cgroup_subsys_state
3631 * @cgrp: the cgroup new css will be associated with
3632 * @ss: the subsys of new css
3633 *
3634 * Create a new css associated with @cgrp - @ss pair. On success, the new
3635 * css is online and installed in @cgrp with all interface files created.
3636 * Returns 0 on success, -errno on failure.
3637 */
3638static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
3639{
3640    struct cgroup *parent = cgrp->parent;
3641    struct cgroup_subsys_state *css;
3642    int err;
3643
3644    lockdep_assert_held(&cgroup_mutex);
3645
3646    css = ss->css_alloc(cgroup_css(parent, ss));
3647    if (IS_ERR(css))
3648        return PTR_ERR(css);
3649
3650    err = percpu_ref_init(&css->refcnt, css_release);
3651    if (err)
3652        goto err_free_css;
3653
3654    init_css(css, ss, cgrp);
3655
3656    err = cgroup_populate_dir(cgrp, 1 << ss->id);
3657    if (err)
3658        goto err_free_percpu_ref;
3659
3660    err = online_css(css);
3661    if (err)
3662        goto err_clear_dir;
3663
3664    cgroup_get(cgrp);
3665    css_get(css->parent);
3666
3667    cgrp->subsys_mask |= 1 << ss->id;
3668
3669    if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
3670        parent->parent) {
3671        pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
3672               current->comm, current->pid, ss->name);
3673        if (!strcmp(ss->name, "memory"))
3674            pr_warning("cgroup: \"memory\" requires setting use_hierarchy to 1 on the root.\n");
3675        ss->warned_broken_hierarchy = true;
3676    }
3677
3678    return 0;
3679
3680err_clear_dir:
3681    cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
3682err_free_percpu_ref:
3683    percpu_ref_cancel_init(&css->refcnt);
3684err_free_css:
3685    ss->css_free(css);
3686    return err;
3687}
3688
3689/**
3690 * cgroup_create - create a cgroup
3691 * @parent: cgroup that will be parent of the new cgroup
3692 * @name: name of the new cgroup
3693 * @mode: mode to set on new cgroup
3694 */
3695static long cgroup_create(struct cgroup *parent, const char *name,
3696              umode_t mode)
3697{
3698    struct cgroup *cgrp;
3699    struct cgroup_root *root = parent->root;
3700    int ssid, err;
3701    struct cgroup_subsys *ss;
3702    struct kernfs_node *kn;
3703
3704    /*
3705     * XXX: The default hierarchy isn't fully implemented yet. Block
3706     * !root cgroup creation on it for now.
3707     */
3708    if (root == &cgrp_dfl_root)
3709        return -EINVAL;
3710
3711    /* allocate the cgroup and its ID, 0 is reserved for the root */
3712    cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
3713    if (!cgrp)
3714        return -ENOMEM;
3715
3716    mutex_lock(&cgroup_tree_mutex);
3717
3718    /*
3719     * Only live parents can have children. Note that the liveliness
3720     * check isn't strictly necessary because cgroup_mkdir() and
3721     * cgroup_rmdir() are fully synchronized by i_mutex; however, do it
3722     * anyway so that locking is contained inside cgroup proper and we
3723     * don't get nasty surprises if we ever grow another caller.
3724     */
3725    if (!cgroup_lock_live_group(parent)) {
3726        err = -ENODEV;
3727        goto err_unlock_tree;
3728    }
3729
3730    /*
3731     * Temporarily set the pointer to NULL, so idr_find() won't return
3732     * a half-baked cgroup.
3733     */
3734    cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 1, 0, GFP_KERNEL);
3735    if (cgrp->id < 0) {
3736        err = -ENOMEM;
3737        goto err_unlock;
3738    }
3739
3740    init_cgroup_housekeeping(cgrp);
3741
3742    cgrp->parent = parent;
3743    cgrp->dummy_css.parent = &parent->dummy_css;
3744    cgrp->root = parent->root;
3745
3746    if (notify_on_release(parent))
3747        set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3748
3749    if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
3750        set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
3751
3752    /* create the directory */
3753    kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
3754    if (IS_ERR(kn)) {
3755        err = PTR_ERR(kn);
3756        goto err_free_id;
3757    }
3758    cgrp->kn = kn;
3759
3760    /*
3761     * This extra ref will be put in cgroup_free_fn() and guarantees
3762     * that @cgrp->kn is always accessible.
3763     */
3764    kernfs_get(kn);
3765
3766    cgrp->serial_nr = cgroup_serial_nr_next++;
3767
3768    /* allocation complete, commit to creation */
3769    list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
3770    atomic_inc(&root->nr_cgrps);
3771    cgroup_get(parent);
3772
3773    /*
3774     * @cgrp is now fully operational. If something fails after this
3775     * point, it'll be released via the normal destruction path.
3776     */
3777    idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
3778
3779    err = cgroup_kn_set_ugid(kn);
3780    if (err)
3781        goto err_destroy;
3782
3783    err = cgroup_addrm_files(cgrp, cgroup_base_files, true);
3784    if (err)
3785        goto err_destroy;
3786
3787    /* let's create and online css's */
3788    for_each_subsys(ss, ssid) {
3789        if (root->cgrp.subsys_mask & (1 << ssid)) {
3790            err = create_css(cgrp, ss);
3791            if (err)
3792                goto err_destroy;
3793        }
3794    }
3795
3796    kernfs_activate(kn);
3797
3798    mutex_unlock(&cgroup_mutex);
3799    mutex_unlock(&cgroup_tree_mutex);
3800
3801    return 0;
3802
3803err_free_id:
3804    idr_remove(&root->cgroup_idr, cgrp->id);
3805err_unlock:
3806    mutex_unlock(&cgroup_mutex);
3807err_unlock_tree:
3808    mutex_unlock(&cgroup_tree_mutex);
3809    kfree(cgrp);
3810    return err;
3811
3812err_destroy:
3813    cgroup_destroy_locked(cgrp);
3814    mutex_unlock(&cgroup_mutex);
3815    mutex_unlock(&cgroup_tree_mutex);
3816    return err;
3817}
3818
3819static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
3820            umode_t mode)
3821{
3822    struct cgroup *parent = parent_kn->priv;
3823    int ret;
3824
3825    /*
3826     * cgroup_create() grabs cgroup_tree_mutex which nests outside
3827     * kernfs active_ref and cgroup_create() already synchronizes
3828     * properly against removal through cgroup_lock_live_group().
3829     * Break it before calling cgroup_create().
3830     */
3831    cgroup_get(parent);
3832    kernfs_break_active_protection(parent_kn);
3833
3834    ret = cgroup_create(parent, name, mode);
3835
3836    kernfs_unbreak_active_protection(parent_kn);
3837    cgroup_put(parent);
3838    return ret;
3839}
3840
3841/*
3842 * This is called when the refcnt of a css is confirmed to be killed.
3843 * css_tryget() is now guaranteed to fail.
3844 */
3845static void css_killed_work_fn(struct work_struct *work)
3846{
3847    struct cgroup_subsys_state *css =
3848        container_of(work, struct cgroup_subsys_state, destroy_work);
3849    struct cgroup *cgrp = css->cgroup;
3850
3851    mutex_lock(&cgroup_tree_mutex);
3852    mutex_lock(&cgroup_mutex);
3853
3854    /*
3855     * css_tryget() is guaranteed to fail now. Tell subsystems to
3856     * initate destruction.
3857     */
3858    offline_css(css);
3859
3860    /*
3861     * If @cgrp is marked dead, it's waiting for refs of all css's to
3862     * be disabled before proceeding to the second phase of cgroup
3863     * destruction. If we are the last one, kick it off.
3864     */
3865    if (!cgrp->nr_css && cgroup_is_dead(cgrp))
3866        cgroup_destroy_css_killed(cgrp);
3867
3868    mutex_unlock(&cgroup_mutex);
3869    mutex_unlock(&cgroup_tree_mutex);
3870
3871    /*
3872     * Put the css refs from kill_css(). Each css holds an extra
3873     * reference to the cgroup's dentry and cgroup removal proceeds
3874     * regardless of css refs. On the last put of each css, whenever
3875     * that may be, the extra dentry ref is put so that dentry
3876     * destruction happens only after all css's are released.
3877     */
3878    css_put(css);
3879}
3880
3881/* css kill confirmation processing requires process context, bounce */
3882static void css_killed_ref_fn(struct percpu_ref *ref)
3883{
3884    struct cgroup_subsys_state *css =
3885        container_of(ref, struct cgroup_subsys_state, refcnt);
3886
3887    INIT_WORK(&css->destroy_work, css_killed_work_fn);
3888    queue_work(cgroup_destroy_wq, &css->destroy_work);
3889}
3890
3891static void __kill_css(struct cgroup_subsys_state *css)
3892{
3893    lockdep_assert_held(&cgroup_tree_mutex);
3894
3895    /*
3896     * This must happen before css is disassociated with its cgroup.
3897     * See seq_css() for details.
3898     */
3899    cgroup_clear_dir(css->cgroup, 1 << css->ss->id);
3900
3901    /*
3902     * Killing would put the base ref, but we need to keep it alive
3903     * until after ->css_offline().
3904     */
3905    css_get(css);
3906
3907    /*
3908     * cgroup core guarantees that, by the time ->css_offline() is
3909     * invoked, no new css reference will be given out via
3910     * css_tryget(). We can't simply call percpu_ref_kill() and
3911     * proceed to offlining css's because percpu_ref_kill() doesn't
3912     * guarantee that the ref is seen as killed on all CPUs on return.
3913     *
3914     * Use percpu_ref_kill_and_confirm() to get notifications as each
3915     * css is confirmed to be seen as killed on all CPUs.
3916     */
3917    percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
3918}
3919
3920/**
3921 * kill_css - destroy a css
3922 * @css: css to destroy
3923 *
3924 * This function initiates destruction of @css by removing cgroup interface
3925 * files and putting its base reference. ->css_offline() will be invoked
3926 * asynchronously once css_tryget() is guaranteed to fail and when the
3927 * reference count reaches zero, @css will be released.
3928 */
3929static void kill_css(struct cgroup_subsys_state *css)
3930{
3931    struct cgroup *cgrp = css->cgroup;
3932
3933    lockdep_assert_held(&cgroup_tree_mutex);
3934
3935    /* if already killed, noop */
3936    if (cgrp->subsys_mask & (1 << css->ss->id)) {
3937        cgrp->subsys_mask &= ~(1 << css->ss->id);
3938        __kill_css(css);
3939    }
3940}
3941
3942/**
3943 * cgroup_destroy_locked - the first stage of cgroup destruction
3944 * @cgrp: cgroup to be destroyed
3945 *
3946 * css's make use of percpu refcnts whose killing latency shouldn't be
3947 * exposed to userland and are RCU protected. Also, cgroup core needs to
3948 * guarantee that css_tryget() won't succeed by the time ->css_offline() is
3949 * invoked. To satisfy all the requirements, destruction is implemented in
3950 * the following two steps.
3951 *
3952 * s1. Verify @cgrp can be destroyed and mark it dying. Remove all
3953 * userland visible parts and start killing the percpu refcnts of
3954 * css's. Set up so that the next stage will be kicked off once all
3955 * the percpu refcnts are confirmed to be killed.
3956 *
3957 * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
3958 * rest of destruction. Once all cgroup references are gone, the
3959 * cgroup is RCU-freed.
3960 *
3961 * This function implements s1. After this step, @cgrp is gone as far as
3962 * the userland is concerned and a new cgroup with the same name may be
3963 * created. As cgroup doesn't care about the names internally, this
3964 * doesn't cause any problem.
3965 */
3966static int cgroup_destroy_locked(struct cgroup *cgrp)
3967    __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
3968{
3969    struct cgroup *child;
3970    struct cgroup_subsys_state *css;
3971    bool empty;
3972    int ssid;
3973
3974    lockdep_assert_held(&cgroup_tree_mutex);
3975    lockdep_assert_held(&cgroup_mutex);
3976
3977    /*
3978     * css_set_rwsem synchronizes access to ->cset_links and prevents
3979     * @cgrp from being removed while put_css_set() is in progress.
3980     */
3981    down_read(&css_set_rwsem);
3982    empty = list_empty(&cgrp->cset_links);
3983    up_read(&css_set_rwsem);
3984    if (!empty)
3985        return -EBUSY;
3986
3987    /*
3988     * Make sure there's no live children. We can't test ->children
3989     * emptiness as dead children linger on it while being destroyed;
3990     * otherwise, "rmdir parent/child parent" may fail with -EBUSY.
3991     */
3992    empty = true;
3993    rcu_read_lock();
3994    list_for_each_entry_rcu(child, &cgrp->children, sibling) {
3995        empty = cgroup_is_dead(child);
3996        if (!empty)
3997            break;
3998    }
3999    rcu_read_unlock();
4000    if (!empty)
4001        return -EBUSY;
4002
4003    /*
4004     * Mark @cgrp dead. This prevents further task migration and child
4005     * creation by disabling cgroup_lock_live_group(). Note that
4006     * CGRP_DEAD assertion is depended upon by css_next_child() to
4007     * resume iteration after dropping RCU read lock. See
4008     * css_next_child() for details.
4009     */
4010    set_bit(CGRP_DEAD, &cgrp->flags);
4011
4012    /*
4013     * Initiate massacre of all css's. cgroup_destroy_css_killed()
4014     * will be invoked to perform the rest of destruction once the
4015     * percpu refs of all css's are confirmed to be killed. This
4016     * involves removing the subsystem's files, drop cgroup_mutex.
4017     */
4018    mutex_unlock(&cgroup_mutex);
4019    for_each_css(css, ssid, cgrp)
4020        kill_css(css);
4021    mutex_lock(&cgroup_mutex);
4022
4023    /* CGRP_DEAD is set, remove from ->release_list for the last time */
4024    raw_spin_lock(&release_list_lock);
4025    if (!list_empty(&cgrp->release_list))
4026        list_del_init(&cgrp->release_list);
4027    raw_spin_unlock(&release_list_lock);
4028
4029    /*
4030     * If @cgrp has css's attached, the second stage of cgroup
4031     * destruction is kicked off from css_killed_work_fn() after the
4032     * refs of all attached css's are killed. If @cgrp doesn't have
4033     * any css, we kick it off here.
4034     */
4035    if (!cgrp->nr_css)
4036        cgroup_destroy_css_killed(cgrp);
4037
4038    /* remove @cgrp directory along with the base files */
4039    mutex_unlock(&cgroup_mutex);
4040
4041    /*
4042     * There are two control paths which try to determine cgroup from
4043     * dentry without going through kernfs - cgroupstats_build() and
4044     * css_tryget_from_dir(). Those are supported by RCU protecting
4045     * clearing of cgrp->kn->priv backpointer, which should happen
4046     * after all files under it have been removed.
4047     */
4048    kernfs_remove(cgrp->kn); /* @cgrp has an extra ref on its kn */
4049    RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);
4050
4051    mutex_lock(&cgroup_mutex);
4052
4053    return 0;
4054};
4055
4056/**
4057 * cgroup_destroy_css_killed - the second step of cgroup destruction
4058 * @work: cgroup->destroy_free_work
4059 *
4060 * This function is invoked from a work item for a cgroup which is being
4061 * destroyed after all css's are offlined and performs the rest of
4062 * destruction. This is the second step of destruction described in the
4063 * comment above cgroup_destroy_locked().
4064 */
4065static void cgroup_destroy_css_killed(struct cgroup *cgrp)
4066{
4067    struct cgroup *parent = cgrp->parent;
4068
4069    lockdep_assert_held(&cgroup_tree_mutex);
4070    lockdep_assert_held(&cgroup_mutex);
4071
4072    /* delete this cgroup from parent->children */
4073    list_del_rcu(&cgrp->sibling);
4074
4075    cgroup_put(cgrp);
4076
4077    set_bit(CGRP_RELEASABLE, &parent->flags);
4078    check_for_release(parent);
4079}
4080
4081static int cgroup_rmdir(struct kernfs_node *kn)
4082{
4083    struct cgroup *cgrp = kn->priv;
4084    int ret = 0;
4085
4086    /*
4087     * This is self-destruction but @kn can't be removed while this
4088     * callback is in progress. Let's break active protection. Once
4089     * the protection is broken, @cgrp can be destroyed at any point.
4090     * Pin it so that it stays accessible.
4091     */
4092    cgroup_get(cgrp);
4093    kernfs_break_active_protection(kn);
4094
4095    mutex_lock(&cgroup_tree_mutex);
4096    mutex_lock(&cgroup_mutex);
4097
4098    /*
4099     * @cgrp might already have been destroyed while we're trying to
4100     * grab the mutexes.
4101     */
4102    if (!cgroup_is_dead(cgrp))
4103        ret = cgroup_destroy_locked(cgrp);
4104
4105    mutex_unlock(&cgroup_mutex);
4106    mutex_unlock(&cgroup_tree_mutex);
4107
4108    kernfs_unbreak_active_protection(kn);
4109    cgroup_put(cgrp);
4110    return ret;
4111}
4112
4113static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
4114    .remount_fs = cgroup_remount,
4115    .show_options = cgroup_show_options,
4116    .mkdir = cgroup_mkdir,
4117    .rmdir = cgroup_rmdir,
4118    .rename = cgroup_rename,
4119};
4120
4121static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
4122{
4123    struct cgroup_subsys_state *css;
4124
4125    printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
4126
4127    mutex_lock(&cgroup_tree_mutex);
4128    mutex_lock(&cgroup_mutex);
4129
4130    INIT_LIST_HEAD(&ss->cfts);
4131
4132    /* Create the root cgroup state for this subsystem */
4133    ss->root = &cgrp_dfl_root;
4134    css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
4135    /* We don't handle early failures gracefully */
4136    BUG_ON(IS_ERR(css));
4137    init_css(css, ss, &cgrp_dfl_root.cgrp);
4138
4139    /* Update the init_css_set to contain a subsys
4140     * pointer to this state - since the subsystem is
4141     * newly registered, all tasks and hence the
4142     * init_css_set is in the subsystem's root cgroup. */
4143    init_css_set.subsys[ss->id] = css;
4144
4145    need_forkexit_callback |= ss->fork || ss->exit;
4146
4147    /* At system boot, before all subsystems have been
4148     * registered, no tasks have been forked, so we don't
4149     * need to invoke fork callbacks here. */
4150    BUG_ON(!list_empty(&init_task.tasks));
4151
4152    BUG_ON(online_css(css));
4153
4154    cgrp_dfl_root.cgrp.subsys_mask |= 1 << ss->id;
4155
4156    mutex_unlock(&cgroup_mutex);
4157    mutex_unlock(&cgroup_tree_mutex);
4158}
4159
4160/**
4161 * cgroup_init_early - cgroup initialization at system boot
4162 *
4163 * Initialize cgroups at system boot, and initialize any
4164 * subsystems that request early init.
4165 */
4166int __init cgroup_init_early(void)
4167{
4168    static struct cgroup_sb_opts __initdata opts =
4169        { .flags = CGRP_ROOT_SANE_BEHAVIOR };
4170    struct cgroup_subsys *ss;
4171    int i;
4172
4173    init_cgroup_root(&cgrp_dfl_root, &opts);
4174    RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
4175
4176    for_each_subsys(ss, i) {
4177        WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
4178             "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p name:id=%d:%s\n",
4179             i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
4180             ss->id, ss->name);
4181        WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
4182             "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
4183
4184        ss->id = i;
4185        ss->name = cgroup_subsys_name[i];
4186
4187        if (ss->early_init)
4188            cgroup_init_subsys(ss);
4189    }
4190    return 0;
4191}
4192
4193/**
4194 * cgroup_init - cgroup initialization
4195 *
4196 * Register cgroup filesystem and /proc file, and initialize
4197 * any subsystems that didn't request early init.
4198 */
4199int __init cgroup_init(void)
4200{
4201    struct cgroup_subsys *ss;
4202    unsigned long key;
4203    int ssid, err;
4204
4205    BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
4206
4207    mutex_lock(&cgroup_tree_mutex);
4208    mutex_lock(&cgroup_mutex);
4209
4210    /* Add init_css_set to the hash table */
4211    key = css_set_hash(init_css_set.subsys);
4212    hash_add(css_set_table, &init_css_set.hlist, key);
4213
4214    BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
4215
4216    mutex_unlock(&cgroup_mutex);
4217    mutex_unlock(&cgroup_tree_mutex);
4218
4219    for_each_subsys(ss, ssid) {
4220        if (!ss->early_init)
4221            cgroup_init_subsys(ss);
4222
4223        /*
4224         * cftype registration needs kmalloc and can't be done
4225         * during early_init. Register base cftypes separately.
4226         */
4227        if (ss->base_cftypes)
4228            WARN_ON(cgroup_add_cftypes(ss, ss->base_cftypes));
4229    }
4230
4231    cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
4232    if (!cgroup_kobj)
4233        return -ENOMEM;
4234
4235    err = register_filesystem(&cgroup_fs_type);
4236    if (err < 0) {
4237        kobject_put(cgroup_kobj);
4238        return err;
4239    }
4240
4241    proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
4242    return 0;
4243}
4244
4245static int __init cgroup_wq_init(void)
4246{
4247    /*
4248     * There isn't much point in executing destruction path in
4249     * parallel. Good chunk is serialized with cgroup_mutex anyway.
4250     * Use 1 for @max_active.
4251     *
4252     * We would prefer to do this in cgroup_init() above, but that
4253     * is called before init_workqueues(): so leave this until after.
4254     */
4255    cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
4256    BUG_ON(!cgroup_destroy_wq);
4257
4258    /*
4259     * Used to destroy pidlists and separate to serve as flush domain.
4260     * Cap @max_active to 1 too.
4261     */
4262    cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
4263                            0, 1);
4264    BUG_ON(!cgroup_pidlist_destroy_wq);
4265
4266    return 0;
4267}
4268core_initcall(cgroup_wq_init);
4269
4270/*
4271 * proc_cgroup_show()
4272 * - Print task's cgroup paths into seq_file, one line for each hierarchy
4273 * - Used for /proc/<pid>/cgroup.
4274 */
4275
4276/* TODO: Use a proper seq_file iterator */
4277int proc_cgroup_show(struct seq_file *m, void *v)
4278{
4279    struct pid *pid;
4280    struct task_struct *tsk;
4281    char *buf, *path;
4282    int retval;
4283    struct cgroup_root *root;
4284
4285    retval = -ENOMEM;
4286    buf = kmalloc(PATH_MAX, GFP_KERNEL);
4287    if (!buf)
4288        goto out;
4289
4290    retval = -ESRCH;
4291    pid = m->private;
4292    tsk = get_pid_task(pid, PIDTYPE_PID);
4293    if (!tsk)
4294        goto out_free;
4295
4296    retval = 0;
4297
4298    mutex_lock(&cgroup_mutex);
4299    down_read(&css_set_rwsem);
4300
4301    for_each_root(root) {
4302        struct cgroup_subsys *ss;
4303        struct cgroup *cgrp;
4304        int ssid, count = 0;
4305
4306        if (root == &cgrp_dfl_root && !cgrp_dfl_root_visible)
4307            continue;
4308
4309        seq_printf(m, "%d:", root->hierarchy_id);
4310        for_each_subsys(ss, ssid)
4311            if (root->cgrp.subsys_mask & (1 << ssid))
4312                seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
4313        if (strlen(root->name))
4314            seq_printf(m, "%sname=%s", count ? "," : "",
4315                   root->name);
4316        seq_putc(m, ':');
4317        cgrp = task_cgroup_from_root(tsk, root);
4318        path = cgroup_path(cgrp, buf, PATH_MAX);
4319        if (!path) {
4320            retval = -ENAMETOOLONG;
4321            goto out_unlock;
4322        }
4323        seq_puts(m, path);
4324        seq_putc(m, '\n');
4325    }
4326
4327out_unlock:
4328    up_read(&css_set_rwsem);
4329    mutex_unlock(&cgroup_mutex);
4330    put_task_struct(tsk);
4331out_free:
4332    kfree(buf);
4333out:
4334    return retval;
4335}
4336
4337/* Display information about each subsystem and each hierarchy */
4338static int proc_cgroupstats_show(struct seq_file *m, void *v)
4339{
4340    struct cgroup_subsys *ss;
4341    int i;
4342
4343    seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
4344    /*
4345     * ideally we don't want subsystems moving around while we do this.
4346     * cgroup_mutex is also necessary to guarantee an atomic snapshot of
4347     * subsys/hierarchy state.
4348     */
4349    mutex_lock(&cgroup_mutex);
4350
4351    for_each_subsys(ss, i)
4352        seq_printf(m, "%s\t%d\t%d\t%d\n",
4353               ss->name, ss->root->hierarchy_id,
4354               atomic_read(&ss->root->nr_cgrps), !ss->disabled);
4355
4356    mutex_unlock(&cgroup_mutex);
4357    return 0;
4358}
4359
4360static int cgroupstats_open(struct inode *inode, struct file *file)
4361{
4362    return single_open(file, proc_cgroupstats_show, NULL);
4363}
4364
4365static const struct file_operations proc_cgroupstats_operations = {
4366    .open = cgroupstats_open,
4367    .read = seq_read,
4368    .llseek = seq_lseek,
4369    .release = single_release,
4370};
4371
4372/**
4373 * cgroup_fork - initialize cgroup related fields during copy_process()
4374 * @child: pointer to task_struct of forking parent process.
4375 *
4376 * A task is associated with the init_css_set until cgroup_post_fork()
4377 * attaches it to the parent's css_set. Empty cg_list indicates that
4378 * @child isn't holding reference to its css_set.
4379 */
4380void cgroup_fork(struct task_struct *child)
4381{
4382    RCU_INIT_POINTER(child->cgroups, &init_css_set);
4383    INIT_LIST_HEAD(&child->cg_list);
4384}
4385
4386/**
4387 * cgroup_post_fork - called on a new task after adding it to the task list
4388 * @child: the task in question
4389 *
4390 * Adds the task to the list running through its css_set if necessary and
4391 * call the subsystem fork() callbacks. Has to be after the task is
4392 * visible on the task list in case we race with the first call to
4393 * cgroup_task_iter_start() - to guarantee that the new task ends up on its
4394 * list.
4395 */
4396void cgroup_post_fork(struct task_struct *child)
4397{
4398    struct cgroup_subsys *ss;
4399    int i;
4400
4401    /*
4402     * This may race against cgroup_enable_task_cg_links(). As that
4403     * function sets use_task_css_set_links before grabbing
4404     * tasklist_lock and we just went through tasklist_lock to add
4405     * @child, it's guaranteed that either we see the set
4406     * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
4407     * @child during its iteration.
4408     *
4409     * If we won the race, @child is associated with %current's
4410     * css_set. Grabbing css_set_rwsem guarantees both that the
4411     * association is stable, and, on completion of the parent's
4412     * migration, @child is visible in the source of migration or
4413     * already in the destination cgroup. This guarantee is necessary
4414     * when implementing operations which need to migrate all tasks of
4415     * a cgroup to another.
4416     *
4417     * Note that if we lose to cgroup_enable_task_cg_links(), @child
4418     * will remain in init_css_set. This is safe because all tasks are
4419     * in the init_css_set before cg_links is enabled and there's no
4420     * operation which transfers all tasks out of init_css_set.
4421     */
4422    if (use_task_css_set_links) {
4423        struct css_set *cset;
4424
4425        down_write(&css_set_rwsem);
4426        cset = task_css_set(current);
4427        if (list_empty(&child->cg_list)) {
4428            rcu_assign_pointer(child->cgroups, cset);
4429            list_add(&child->cg_list, &cset->tasks);
4430            get_css_set(cset);
4431        }
4432        up_write(&css_set_rwsem);
4433    }
4434
4435    /*
4436     * Call ss->fork(). This must happen after @child is linked on
4437     * css_set; otherwise, @child might change state between ->fork()
4438     * and addition to css_set.
4439     */
4440    if (need_forkexit_callback) {
4441        for_each_subsys(ss, i)
4442            if (ss->fork)
4443                ss->fork(child);
4444    }
4445}
4446
4447/**
4448 * cgroup_exit - detach cgroup from exiting task
4449 * @tsk: pointer to task_struct of exiting process
4450 *
4451 * Description: Detach cgroup from @tsk and release it.
4452 *
4453 * Note that cgroups marked notify_on_release force every task in
4454 * them to take the global cgroup_mutex mutex when exiting.
4455 * This could impact scaling on very large systems. Be reluctant to
4456 * use notify_on_release cgroups where very high task exit scaling
4457 * is required on large systems.
4458 *
4459 * We set the exiting tasks cgroup to the root cgroup (top_cgroup). We
4460 * call cgroup_exit() while the task is still competent to handle
4461 * notify_on_release(), then leave the task attached to the root cgroup in
4462 * each hierarchy for the remainder of its exit. No need to bother with
4463 * init_css_set refcnting. init_css_set never goes away and we can't race
4464 * with migration path - PF_EXITING is visible to migration path.
4465 */
4466void cgroup_exit(struct task_struct *tsk)
4467{
4468    struct cgroup_subsys *ss;
4469    struct css_set *cset;
4470    bool put_cset = false;
4471    int i;
4472
4473    /*
4474     * Unlink from @tsk from its css_set. As migration path can't race
4475     * with us, we can check cg_list without grabbing css_set_rwsem.
4476     */
4477    if (!list_empty(&tsk->cg_list)) {
4478        down_write(&css_set_rwsem);
4479        list_del_init(&tsk->cg_list);
4480        up_write(&css_set_rwsem);
4481        put_cset = true;
4482    }
4483
4484    /* Reassign the task to the init_css_set. */
4485    cset = task_css_set(tsk);
4486    RCU_INIT_POINTER(tsk->cgroups, &init_css_set);
4487
4488    if (need_forkexit_callback) {
4489        /* see cgroup_post_fork() for details */
4490        for_each_subsys(ss, i) {
4491            if (ss->exit) {
4492                struct cgroup_subsys_state *old_css = cset->subsys[i];
4493                struct cgroup_subsys_state *css = task_css(tsk, i);
4494
4495                ss->exit(css, old_css, tsk);
4496            }
4497        }
4498    }
4499
4500    if (put_cset)
4501        put_css_set(cset, true);
4502}
4503
4504static void check_for_release(struct cgroup *cgrp)
4505{
4506    if (cgroup_is_releasable(cgrp) &&
4507        list_empty(&cgrp->cset_links) && list_empty(&cgrp->children)) {
4508        /*
4509         * Control Group is currently removeable. If it's not
4510         * already queued for a userspace notification, queue
4511         * it now
4512         */
4513        int need_schedule_work = 0;
4514
4515        raw_spin_lock(&release_list_lock);
4516        if (!cgroup_is_dead(cgrp) &&
4517            list_empty(&cgrp->release_list)) {
4518            list_add(&cgrp->release_list, &release_list);
4519            need_schedule_work = 1;
4520        }
4521        raw_spin_unlock(&release_list_lock);
4522        if (need_schedule_work)
4523            schedule_work(&release_agent_work);
4524    }
4525}
4526
4527/*
4528 * Notify userspace when a cgroup is released, by running the
4529 * configured release agent with the name of the cgroup (path
4530 * relative to the root of cgroup file system) as the argument.
4531 *
4532 * Most likely, this user command will try to rmdir this cgroup.
4533 *
4534 * This races with the possibility that some other task will be
4535 * attached to this cgroup before it is removed, or that some other
4536 * user task will 'mkdir' a child cgroup of this cgroup. That's ok.
4537 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
4538 * unused, and this cgroup will be reprieved from its death sentence,
4539 * to continue to serve a useful existence. Next time it's released,
4540 * we will get notified again, if it still has 'notify_on_release' set.
4541 *
4542 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
4543 * means only wait until the task is successfully execve()'d. The
4544 * separate release agent task is forked by call_usermodehelper(),
4545 * then control in this thread returns here, without waiting for the
4546 * release agent task. We don't bother to wait because the caller of
4547 * this routine has no use for the exit status of the release agent
4548 * task, so no sense holding our caller up for that.
4549 */
4550static void cgroup_release_agent(struct work_struct *work)
4551{
4552    BUG_ON(work != &release_agent_work);
4553    mutex_lock(&cgroup_mutex);
4554    raw_spin_lock(&release_list_lock);
4555    while (!list_empty(&release_list)) {
4556        char *argv[3], *envp[3];
4557        int i;
4558        char *pathbuf = NULL, *agentbuf = NULL, *path;
4559        struct cgroup *cgrp = list_entry(release_list.next,
4560                            struct cgroup,
4561                            release_list);
4562        list_del_init(&cgrp->release_list);
4563        raw_spin_unlock(&release_list_lock);
4564        pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
4565        if (!pathbuf)
4566            goto continue_free;
4567        path = cgroup_path(cgrp, pathbuf, PATH_MAX);
4568        if (!path)
4569            goto continue_free;
4570        agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
4571        if (!agentbuf)
4572            goto continue_free;
4573
4574        i = 0;
4575        argv[i++] = agentbuf;
4576        argv[i++] = path;
4577        argv[i] = NULL;
4578
4579        i = 0;
4580        /* minimal command environment */
4581        envp[i++] = "HOME=/";
4582        envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
4583        envp[i] = NULL;
4584
4585        /* Drop the lock while we invoke the usermode helper,
4586         * since the exec could involve hitting disk and hence
4587         * be a slow process */
4588        mutex_unlock(&cgroup_mutex);
4589        call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
4590        mutex_lock(&cgroup_mutex);
4591 continue_free:
4592        kfree(pathbuf);
4593        kfree(agentbuf);
4594        raw_spin_lock(&release_list_lock);
4595    }
4596    raw_spin_unlock(&release_list_lock);
4597    mutex_unlock(&cgroup_mutex);
4598}
4599
4600static int __init cgroup_disable(char *str)
4601{
4602    struct cgroup_subsys *ss;
4603    char *token;
4604    int i;
4605
4606    while ((token = strsep(&str, ",")) != NULL) {
4607        if (!*token)
4608            continue;
4609
4610        for_each_subsys(ss, i) {
4611            if (!strcmp(token, ss->name)) {
4612                ss->disabled = 1;
4613                printk(KERN_INFO "Disabling %s control group"
4614                    " subsystem\n", ss->name);
4615                break;
4616            }
4617        }
4618    }
4619    return 1;
4620}
4621__setup("cgroup_disable=", cgroup_disable);
4622
4623/**
4624 * css_tryget_from_dir - get corresponding css from the dentry of a cgroup dir
4625 * @dentry: directory dentry of interest
4626 * @ss: subsystem of interest
4627 *
4628 * If @dentry is a directory for a cgroup which has @ss enabled on it, try
4629 * to get the corresponding css and return it. If such css doesn't exist
4630 * or can't be pinned, an ERR_PTR value is returned.
4631 */
4632struct cgroup_subsys_state *css_tryget_from_dir(struct dentry *dentry,
4633                        struct cgroup_subsys *ss)
4634{
4635    struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
4636    struct cgroup_subsys_state *css = NULL;
4637    struct cgroup *cgrp;
4638
4639    /* is @dentry a cgroup dir? */
4640    if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
4641        kernfs_type(kn) != KERNFS_DIR)
4642        return ERR_PTR(-EBADF);
4643
4644    rcu_read_lock();
4645
4646    /*
4647     * This path doesn't originate from kernfs and @kn could already
4648     * have been or be removed at any point. @kn->priv is RCU
4649     * protected for this access. See destroy_locked() for details.
4650     */
4651    cgrp = rcu_dereference(kn->priv);
4652    if (cgrp)
4653        css = cgroup_css(cgrp, ss);
4654
4655    if (!css || !css_tryget(css))
4656        css = ERR_PTR(-ENOENT);
4657
4658    rcu_read_unlock();
4659    return css;
4660}
4661
4662/**
4663 * css_from_id - lookup css by id
4664 * @id: the cgroup id
4665 * @ss: cgroup subsys to be looked into
4666 *
4667 * Returns the css if there's valid one with @id, otherwise returns NULL.
4668 * Should be called under rcu_read_lock().
4669 */
4670struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
4671{
4672    struct cgroup *cgrp;
4673
4674    cgroup_assert_mutexes_or_rcu_locked();
4675
4676    cgrp = idr_find(&ss->root->cgroup_idr, id);
4677    if (cgrp)
4678        return cgroup_css(cgrp, ss);
4679    return NULL;
4680}
4681
4682#ifdef CONFIG_CGROUP_DEBUG
4683static struct cgroup_subsys_state *
4684debug_css_alloc(struct cgroup_subsys_state *parent_css)
4685{
4686    struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
4687
4688    if (!css)
4689        return ERR_PTR(-ENOMEM);
4690
4691    return css;
4692}
4693
4694static void debug_css_free(struct cgroup_subsys_state *css)
4695{
4696    kfree(css);
4697}
4698
4699static u64 debug_taskcount_read(struct cgroup_subsys_state *css,
4700                struct cftype *cft)
4701{
4702    return cgroup_task_count(css->cgroup);
4703}
4704
4705static u64 current_css_set_read(struct cgroup_subsys_state *css,
4706                struct cftype *cft)
4707{
4708    return (u64)(unsigned long)current->cgroups;
4709}
4710
4711static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
4712                     struct cftype *cft)
4713{
4714    u64 count;
4715
4716    rcu_read_lock();
4717    count = atomic_read(&task_css_set(current)->refcount);
4718    rcu_read_unlock();
4719    return count;
4720}
4721
4722static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
4723{
4724    struct cgrp_cset_link *link;
4725    struct css_set *cset;
4726    char *name_buf;
4727
4728    name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
4729    if (!name_buf)
4730        return -ENOMEM;
4731
4732    down_read(&css_set_rwsem);
4733    rcu_read_lock();
4734    cset = rcu_dereference(current->cgroups);
4735    list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
4736        struct cgroup *c = link->cgrp;
4737
4738        cgroup_name(c, name_buf, NAME_MAX + 1);
4739        seq_printf(seq, "Root %d group %s\n",
4740               c->root->hierarchy_id, name_buf);
4741    }
4742    rcu_read_unlock();
4743    up_read(&css_set_rwsem);
4744    kfree(name_buf);
4745    return 0;
4746}
4747
4748#define MAX_TASKS_SHOWN_PER_CSS 25
4749static int cgroup_css_links_read(struct seq_file *seq, void *v)
4750{
4751    struct cgroup_subsys_state *css = seq_css(seq);
4752    struct cgrp_cset_link *link;
4753
4754    down_read(&css_set_rwsem);
4755    list_for_each_entry(link, &css->cgroup->cset_links, cset_link) {
4756        struct css_set *cset = link->cset;
4757        struct task_struct *task;
4758        int count = 0;
4759
4760        seq_printf(seq, "css_set %p\n", cset);
4761
4762        list_for_each_entry(task, &cset->tasks, cg_list) {
4763            if (count++ > MAX_TASKS_SHOWN_PER_CSS)
4764                goto overflow;
4765            seq_printf(seq, " task %d\n", task_pid_vnr(task));
4766        }
4767
4768        list_for_each_entry(task, &cset->mg_tasks, cg_list) {
4769            if (count++ > MAX_TASKS_SHOWN_PER_CSS)
4770                goto overflow;
4771            seq_printf(seq, " task %d\n", task_pid_vnr(task));
4772        }
4773        continue;
4774    overflow:
4775        seq_puts(seq, " ...\n");
4776    }
4777    up_read(&css_set_rwsem);
4778    return 0;
4779}
4780
4781static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
4782{
4783    return test_bit(CGRP_RELEASABLE, &css->cgroup->flags);
4784}
4785
4786static struct cftype debug_files[] = {
4787    {
4788        .name = "taskcount",
4789        .read_u64 = debug_taskcount_read,
4790    },
4791
4792    {
4793        .name = "current_css_set",
4794        .read_u64 = current_css_set_read,
4795    },
4796
4797    {
4798        .name = "current_css_set_refcount",
4799        .read_u64 = current_css_set_refcount_read,
4800    },
4801
4802    {
4803        .name = "current_css_set_cg_links",
4804        .seq_show = current_css_set_cg_links_read,
4805    },
4806
4807    {
4808        .name = "cgroup_css_links",
4809        .seq_show = cgroup_css_links_read,
4810    },
4811
4812    {
4813        .name = "releasable",
4814        .read_u64 = releasable_read,
4815    },
4816
4817    { } /* terminate */
4818};
4819
4820struct cgroup_subsys debug_cgrp_subsys = {
4821    .css_alloc = debug_css_alloc,
4822    .css_free = debug_css_free,
4823    .base_cftypes = debug_files,
4824};
4825#endif /* CONFIG_CGROUP_DEBUG */
4826

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