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/ctype.h>
31#include <linux/errno.h>
32#include <linux/fs.h>
33#include <linux/kernel.h>
34#include <linux/list.h>
35#include <linux/mm.h>
36#include <linux/mutex.h>
37#include <linux/mount.h>
38#include <linux/pagemap.h>
39#include <linux/proc_fs.h>
40#include <linux/rcupdate.h>
41#include <linux/sched.h>
42#include <linux/backing-dev.h>
43#include <linux/seq_file.h>
44#include <linux/slab.h>
45#include <linux/magic.h>
46#include <linux/spinlock.h>
47#include <linux/string.h>
48#include <linux/sort.h>
49#include <linux/kmod.h>
50#include <linux/module.h>
51#include <linux/delayacct.h>
52#include <linux/cgroupstats.h>
53#include <linux/hash.h>
54#include <linux/namei.h>
55#include <linux/smp_lock.h>
56#include <linux/pid_namespace.h>
57#include <linux/idr.h>
58#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
59#include <linux/eventfd.h>
60#include <linux/poll.h>
61
62#include <asm/atomic.h>
63
64static DEFINE_MUTEX(cgroup_mutex);
65
66/*
67 * Generate an array of cgroup subsystem pointers. At boot time, this is
68 * populated up to CGROUP_BUILTIN_SUBSYS_COUNT, and modular subsystems are
69 * registered after that. The mutable section of this array is protected by
70 * cgroup_mutex.
71 */
72#define SUBSYS(_x) &_x ## _subsys,
73static struct cgroup_subsys *subsys[CGROUP_SUBSYS_COUNT] = {
74#include <linux/cgroup_subsys.h>
75};
76
77#define MAX_CGROUP_ROOT_NAMELEN 64
78
79/*
80 * A cgroupfs_root represents the root of a cgroup hierarchy,
81 * and may be associated with a superblock to form an active
82 * hierarchy
83 */
84struct cgroupfs_root {
85    struct super_block *sb;
86
87    /*
88     * The bitmask of subsystems intended to be attached to this
89     * hierarchy
90     */
91    unsigned long subsys_bits;
92
93    /* Unique id for this hierarchy. */
94    int hierarchy_id;
95
96    /* The bitmask of subsystems currently attached to this hierarchy */
97    unsigned long actual_subsys_bits;
98
99    /* A list running through the attached subsystems */
100    struct list_head subsys_list;
101
102    /* The root cgroup for this hierarchy */
103    struct cgroup top_cgroup;
104
105    /* Tracks how many cgroups are currently defined in hierarchy.*/
106    int number_of_cgroups;
107
108    /* A list running through the active hierarchies */
109    struct list_head root_list;
110
111    /* Hierarchy-specific flags */
112    unsigned long flags;
113
114    /* The path to use for release notifications. */
115    char release_agent_path[PATH_MAX];
116
117    /* The name for this hierarchy - may be empty */
118    char name[MAX_CGROUP_ROOT_NAMELEN];
119};
120
121/*
122 * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
123 * subsystems that are otherwise unattached - it never has more than a
124 * single cgroup, and all tasks are part of that cgroup.
125 */
126static struct cgroupfs_root rootnode;
127
128/*
129 * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
130 * cgroup_subsys->use_id != 0.
131 */
132#define CSS_ID_MAX (65535)
133struct css_id {
134    /*
135     * The css to which this ID points. This pointer is set to valid value
136     * after cgroup is populated. If cgroup is removed, this will be NULL.
137     * This pointer is expected to be RCU-safe because destroy()
138     * is called after synchronize_rcu(). But for safe use, css_is_removed()
139     * css_tryget() should be used for avoiding race.
140     */
141    struct cgroup_subsys_state *css;
142    /*
143     * ID of this css.
144     */
145    unsigned short id;
146    /*
147     * Depth in hierarchy which this ID belongs to.
148     */
149    unsigned short depth;
150    /*
151     * ID is freed by RCU. (and lookup routine is RCU safe.)
152     */
153    struct rcu_head rcu_head;
154    /*
155     * Hierarchy of CSS ID belongs to.
156     */
157    unsigned short stack[0]; /* Array of Length (depth+1) */
158};
159
160/*
161 * cgroup_event represents events which userspace want to recieve.
162 */
163struct cgroup_event {
164    /*
165     * Cgroup which the event belongs to.
166     */
167    struct cgroup *cgrp;
168    /*
169     * Control file which the event associated.
170     */
171    struct cftype *cft;
172    /*
173     * eventfd to signal userspace about the event.
174     */
175    struct eventfd_ctx *eventfd;
176    /*
177     * Each of these stored in a list by the cgroup.
178     */
179    struct list_head list;
180    /*
181     * All fields below needed to unregister event when
182     * userspace closes eventfd.
183     */
184    poll_table pt;
185    wait_queue_head_t *wqh;
186    wait_queue_t wait;
187    struct work_struct remove;
188};
189
190/* The list of hierarchy roots */
191
192static LIST_HEAD(roots);
193static int root_count;
194
195static DEFINE_IDA(hierarchy_ida);
196static int next_hierarchy_id;
197static DEFINE_SPINLOCK(hierarchy_id_lock);
198
199/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
200#define dummytop (&rootnode.top_cgroup)
201
202/* This flag indicates whether tasks in the fork and exit paths should
203 * check for fork/exit handlers to call. This avoids us having to do
204 * extra work in the fork/exit path if none of the subsystems need to
205 * be called.
206 */
207static int need_forkexit_callback __read_mostly;
208
209#ifdef CONFIG_PROVE_LOCKING
210int cgroup_lock_is_held(void)
211{
212    return lockdep_is_held(&cgroup_mutex);
213}
214#else /* #ifdef CONFIG_PROVE_LOCKING */
215int cgroup_lock_is_held(void)
216{
217    return mutex_is_locked(&cgroup_mutex);
218}
219#endif /* #else #ifdef CONFIG_PROVE_LOCKING */
220
221EXPORT_SYMBOL_GPL(cgroup_lock_is_held);
222
223/* convenient tests for these bits */
224inline int cgroup_is_removed(const struct cgroup *cgrp)
225{
226    return test_bit(CGRP_REMOVED, &cgrp->flags);
227}
228
229/* bits in struct cgroupfs_root flags field */
230enum {
231    ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
232};
233
234static int cgroup_is_releasable(const struct cgroup *cgrp)
235{
236    const int bits =
237        (1 << CGRP_RELEASABLE) |
238        (1 << CGRP_NOTIFY_ON_RELEASE);
239    return (cgrp->flags & bits) == bits;
240}
241
242static int notify_on_release(const struct cgroup *cgrp)
243{
244    return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
245}
246
247/*
248 * for_each_subsys() allows you to iterate on each subsystem attached to
249 * an active hierarchy
250 */
251#define for_each_subsys(_root, _ss) \
252list_for_each_entry(_ss, &_root->subsys_list, sibling)
253
254/* for_each_active_root() allows you to iterate across the active hierarchies */
255#define for_each_active_root(_root) \
256list_for_each_entry(_root, &roots, root_list)
257
258/* the list of cgroups eligible for automatic release. Protected by
259 * release_list_lock */
260static LIST_HEAD(release_list);
261static DEFINE_SPINLOCK(release_list_lock);
262static void cgroup_release_agent(struct work_struct *work);
263static DECLARE_WORK(release_agent_work, cgroup_release_agent);
264static void check_for_release(struct cgroup *cgrp);
265
266/* Link structure for associating css_set objects with cgroups */
267struct cg_cgroup_link {
268    /*
269     * List running through cg_cgroup_links associated with a
270     * cgroup, anchored on cgroup->css_sets
271     */
272    struct list_head cgrp_link_list;
273    struct cgroup *cgrp;
274    /*
275     * List running through cg_cgroup_links pointing at a
276     * single css_set object, anchored on css_set->cg_links
277     */
278    struct list_head cg_link_list;
279    struct css_set *cg;
280};
281
282/* The default css_set - used by init and its children prior to any
283 * hierarchies being mounted. It contains a pointer to the root state
284 * for each subsystem. Also used to anchor the list of css_sets. Not
285 * reference-counted, to improve performance when child cgroups
286 * haven't been created.
287 */
288
289static struct css_set init_css_set;
290static struct cg_cgroup_link init_css_set_link;
291
292static int cgroup_init_idr(struct cgroup_subsys *ss,
293               struct cgroup_subsys_state *css);
294
295/* css_set_lock protects the list of css_set objects, and the
296 * chain of tasks off each css_set. Nests outside task->alloc_lock
297 * due to cgroup_iter_start() */
298static DEFINE_RWLOCK(css_set_lock);
299static int css_set_count;
300
301/*
302 * hash table for cgroup groups. This improves the performance to find
303 * an existing css_set. This hash doesn't (currently) take into
304 * account cgroups in empty hierarchies.
305 */
306#define CSS_SET_HASH_BITS 7
307#define CSS_SET_TABLE_SIZE (1 << CSS_SET_HASH_BITS)
308static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];
309
310static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
311{
312    int i;
313    int index;
314    unsigned long tmp = 0UL;
315
316    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
317        tmp += (unsigned long)css[i];
318    tmp = (tmp >> 16) ^ tmp;
319
320    index = hash_long(tmp, CSS_SET_HASH_BITS);
321
322    return &css_set_table[index];
323}
324
325static void free_css_set_rcu(struct rcu_head *obj)
326{
327    struct css_set *cg = container_of(obj, struct css_set, rcu_head);
328    kfree(cg);
329}
330
331/* We don't maintain the lists running through each css_set to its
332 * task until after the first call to cgroup_iter_start(). This
333 * reduces the fork()/exit() overhead for people who have cgroups
334 * compiled into their kernel but not actually in use */
335static int use_task_css_set_links __read_mostly;
336
337static void __put_css_set(struct css_set *cg, int taskexit)
338{
339    struct cg_cgroup_link *link;
340    struct cg_cgroup_link *saved_link;
341    /*
342     * Ensure that the refcount doesn't hit zero while any readers
343     * can see it. Similar to atomic_dec_and_lock(), but for an
344     * rwlock
345     */
346    if (atomic_add_unless(&cg->refcount, -1, 1))
347        return;
348    write_lock(&css_set_lock);
349    if (!atomic_dec_and_test(&cg->refcount)) {
350        write_unlock(&css_set_lock);
351        return;
352    }
353
354    /* This css_set is dead. unlink it and release cgroup refcounts */
355    hlist_del(&cg->hlist);
356    css_set_count--;
357
358    list_for_each_entry_safe(link, saved_link, &cg->cg_links,
359                 cg_link_list) {
360        struct cgroup *cgrp = link->cgrp;
361        list_del(&link->cg_link_list);
362        list_del(&link->cgrp_link_list);
363        if (atomic_dec_and_test(&cgrp->count) &&
364            notify_on_release(cgrp)) {
365            if (taskexit)
366                set_bit(CGRP_RELEASABLE, &cgrp->flags);
367            check_for_release(cgrp);
368        }
369
370        kfree(link);
371    }
372
373    write_unlock(&css_set_lock);
374    call_rcu(&cg->rcu_head, free_css_set_rcu);
375}
376
377/*
378 * refcounted get/put for css_set objects
379 */
380static inline void get_css_set(struct css_set *cg)
381{
382    atomic_inc(&cg->refcount);
383}
384
385static inline void put_css_set(struct css_set *cg)
386{
387    __put_css_set(cg, 0);
388}
389
390static inline void put_css_set_taskexit(struct css_set *cg)
391{
392    __put_css_set(cg, 1);
393}
394
395/*
396 * compare_css_sets - helper function for find_existing_css_set().
397 * @cg: candidate css_set being tested
398 * @old_cg: existing css_set for a task
399 * @new_cgrp: cgroup that's being entered by the task
400 * @template: desired set of css pointers in css_set (pre-calculated)
401 *
402 * Returns true if "cg" matches "old_cg" except for the hierarchy
403 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
404 */
405static bool compare_css_sets(struct css_set *cg,
406                 struct css_set *old_cg,
407                 struct cgroup *new_cgrp,
408                 struct cgroup_subsys_state *template[])
409{
410    struct list_head *l1, *l2;
411
412    if (memcmp(template, cg->subsys, sizeof(cg->subsys))) {
413        /* Not all subsystems matched */
414        return false;
415    }
416
417    /*
418     * Compare cgroup pointers in order to distinguish between
419     * different cgroups in heirarchies with no subsystems. We
420     * could get by with just this check alone (and skip the
421     * memcmp above) but on most setups the memcmp check will
422     * avoid the need for this more expensive check on almost all
423     * candidates.
424     */
425
426    l1 = &cg->cg_links;
427    l2 = &old_cg->cg_links;
428    while (1) {
429        struct cg_cgroup_link *cgl1, *cgl2;
430        struct cgroup *cg1, *cg2;
431
432        l1 = l1->next;
433        l2 = l2->next;
434        /* See if we reached the end - both lists are equal length. */
435        if (l1 == &cg->cg_links) {
436            BUG_ON(l2 != &old_cg->cg_links);
437            break;
438        } else {
439            BUG_ON(l2 == &old_cg->cg_links);
440        }
441        /* Locate the cgroups associated with these links. */
442        cgl1 = list_entry(l1, struct cg_cgroup_link, cg_link_list);
443        cgl2 = list_entry(l2, struct cg_cgroup_link, cg_link_list);
444        cg1 = cgl1->cgrp;
445        cg2 = cgl2->cgrp;
446        /* Hierarchies should be linked in the same order. */
447        BUG_ON(cg1->root != cg2->root);
448
449        /*
450         * If this hierarchy is the hierarchy of the cgroup
451         * that's changing, then we need to check that this
452         * css_set points to the new cgroup; if it's any other
453         * hierarchy, then this css_set should point to the
454         * same cgroup as the old css_set.
455         */
456        if (cg1->root == new_cgrp->root) {
457            if (cg1 != new_cgrp)
458                return false;
459        } else {
460            if (cg1 != cg2)
461                return false;
462        }
463    }
464    return true;
465}
466
467/*
468 * find_existing_css_set() is a helper for
469 * find_css_set(), and checks to see whether an existing
470 * css_set is suitable.
471 *
472 * oldcg: the cgroup group that we're using before the cgroup
473 * transition
474 *
475 * cgrp: the cgroup that we're moving into
476 *
477 * template: location in which to build the desired set of subsystem
478 * state objects for the new cgroup group
479 */
480static struct css_set *find_existing_css_set(
481    struct css_set *oldcg,
482    struct cgroup *cgrp,
483    struct cgroup_subsys_state *template[])
484{
485    int i;
486    struct cgroupfs_root *root = cgrp->root;
487    struct hlist_head *hhead;
488    struct hlist_node *node;
489    struct css_set *cg;
490
491    /*
492     * Build the set of subsystem state objects that we want to see in the
493     * new css_set. while subsystems can change globally, the entries here
494     * won't change, so no need for locking.
495     */
496    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
497        if (root->subsys_bits & (1UL << i)) {
498            /* Subsystem is in this hierarchy. So we want
499             * the subsystem state from the new
500             * cgroup */
501            template[i] = cgrp->subsys[i];
502        } else {
503            /* Subsystem is not in this hierarchy, so we
504             * don't want to change the subsystem state */
505            template[i] = oldcg->subsys[i];
506        }
507    }
508
509    hhead = css_set_hash(template);
510    hlist_for_each_entry(cg, node, hhead, hlist) {
511        if (!compare_css_sets(cg, oldcg, cgrp, template))
512            continue;
513
514        /* This css_set matches what we need */
515        return cg;
516    }
517
518    /* No existing cgroup group matched */
519    return NULL;
520}
521
522static void free_cg_links(struct list_head *tmp)
523{
524    struct cg_cgroup_link *link;
525    struct cg_cgroup_link *saved_link;
526
527    list_for_each_entry_safe(link, saved_link, tmp, cgrp_link_list) {
528        list_del(&link->cgrp_link_list);
529        kfree(link);
530    }
531}
532
533/*
534 * allocate_cg_links() allocates "count" cg_cgroup_link structures
535 * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
536 * success or a negative error
537 */
538static int allocate_cg_links(int count, struct list_head *tmp)
539{
540    struct cg_cgroup_link *link;
541    int i;
542    INIT_LIST_HEAD(tmp);
543    for (i = 0; i < count; i++) {
544        link = kmalloc(sizeof(*link), GFP_KERNEL);
545        if (!link) {
546            free_cg_links(tmp);
547            return -ENOMEM;
548        }
549        list_add(&link->cgrp_link_list, tmp);
550    }
551    return 0;
552}
553
554/**
555 * link_css_set - a helper function to link a css_set to a cgroup
556 * @tmp_cg_links: cg_cgroup_link objects allocated by allocate_cg_links()
557 * @cg: the css_set to be linked
558 * @cgrp: the destination cgroup
559 */
560static void link_css_set(struct list_head *tmp_cg_links,
561             struct css_set *cg, struct cgroup *cgrp)
562{
563    struct cg_cgroup_link *link;
564
565    BUG_ON(list_empty(tmp_cg_links));
566    link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
567                cgrp_link_list);
568    link->cg = cg;
569    link->cgrp = cgrp;
570    atomic_inc(&cgrp->count);
571    list_move(&link->cgrp_link_list, &cgrp->css_sets);
572    /*
573     * Always add links to the tail of the list so that the list
574     * is sorted by order of hierarchy creation
575     */
576    list_add_tail(&link->cg_link_list, &cg->cg_links);
577}
578
579/*
580 * find_css_set() takes an existing cgroup group and a
581 * cgroup object, and returns a css_set object that's
582 * equivalent to the old group, but with the given cgroup
583 * substituted into the appropriate hierarchy. Must be called with
584 * cgroup_mutex held
585 */
586static struct css_set *find_css_set(
587    struct css_set *oldcg, struct cgroup *cgrp)
588{
589    struct css_set *res;
590    struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
591
592    struct list_head tmp_cg_links;
593
594    struct hlist_head *hhead;
595    struct cg_cgroup_link *link;
596
597    /* First see if we already have a cgroup group that matches
598     * the desired set */
599    read_lock(&css_set_lock);
600    res = find_existing_css_set(oldcg, cgrp, template);
601    if (res)
602        get_css_set(res);
603    read_unlock(&css_set_lock);
604
605    if (res)
606        return res;
607
608    res = kmalloc(sizeof(*res), GFP_KERNEL);
609    if (!res)
610        return NULL;
611
612    /* Allocate all the cg_cgroup_link objects that we'll need */
613    if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
614        kfree(res);
615        return NULL;
616    }
617
618    atomic_set(&res->refcount, 1);
619    INIT_LIST_HEAD(&res->cg_links);
620    INIT_LIST_HEAD(&res->tasks);
621    INIT_HLIST_NODE(&res->hlist);
622
623    /* Copy the set of subsystem state objects generated in
624     * find_existing_css_set() */
625    memcpy(res->subsys, template, sizeof(res->subsys));
626
627    write_lock(&css_set_lock);
628    /* Add reference counts and links from the new css_set. */
629    list_for_each_entry(link, &oldcg->cg_links, cg_link_list) {
630        struct cgroup *c = link->cgrp;
631        if (c->root == cgrp->root)
632            c = cgrp;
633        link_css_set(&tmp_cg_links, res, c);
634    }
635
636    BUG_ON(!list_empty(&tmp_cg_links));
637
638    css_set_count++;
639
640    /* Add this cgroup group to the hash table */
641    hhead = css_set_hash(res->subsys);
642    hlist_add_head(&res->hlist, hhead);
643
644    write_unlock(&css_set_lock);
645
646    return res;
647}
648
649/*
650 * Return the cgroup for "task" from the given hierarchy. Must be
651 * called with cgroup_mutex held.
652 */
653static struct cgroup *task_cgroup_from_root(struct task_struct *task,
654                        struct cgroupfs_root *root)
655{
656    struct css_set *css;
657    struct cgroup *res = NULL;
658
659    BUG_ON(!mutex_is_locked(&cgroup_mutex));
660    read_lock(&css_set_lock);
661    /*
662     * No need to lock the task - since we hold cgroup_mutex the
663     * task can't change groups, so the only thing that can happen
664     * is that it exits and its css is set back to init_css_set.
665     */
666    css = task->cgroups;
667    if (css == &init_css_set) {
668        res = &root->top_cgroup;
669    } else {
670        struct cg_cgroup_link *link;
671        list_for_each_entry(link, &css->cg_links, cg_link_list) {
672            struct cgroup *c = link->cgrp;
673            if (c->root == root) {
674                res = c;
675                break;
676            }
677        }
678    }
679    read_unlock(&css_set_lock);
680    BUG_ON(!res);
681    return res;
682}
683
684/*
685 * There is one global cgroup mutex. We also require taking
686 * task_lock() when dereferencing a task's cgroup subsys pointers.
687 * See "The task_lock() exception", at the end of this comment.
688 *
689 * A task must hold cgroup_mutex to modify cgroups.
690 *
691 * Any task can increment and decrement the count field without lock.
692 * So in general, code holding cgroup_mutex can't rely on the count
693 * field not changing. However, if the count goes to zero, then only
694 * cgroup_attach_task() can increment it again. Because a count of zero
695 * means that no tasks are currently attached, therefore there is no
696 * way a task attached to that cgroup can fork (the other way to
697 * increment the count). So code holding cgroup_mutex can safely
698 * assume that if the count is zero, it will stay zero. Similarly, if
699 * a task holds cgroup_mutex on a cgroup with zero count, it
700 * knows that the cgroup won't be removed, as cgroup_rmdir()
701 * needs that mutex.
702 *
703 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
704 * (usually) take cgroup_mutex. These are the two most performance
705 * critical pieces of code here. The exception occurs on cgroup_exit(),
706 * when a task in a notify_on_release cgroup exits. Then cgroup_mutex
707 * is taken, and if the cgroup count is zero, a usermode call made
708 * to the release agent with the name of the cgroup (path relative to
709 * the root of cgroup file system) as the argument.
710 *
711 * A cgroup can only be deleted if both its 'count' of using tasks
712 * is zero, and its list of 'children' cgroups is empty. Since all
713 * tasks in the system use _some_ cgroup, and since there is always at
714 * least one task in the system (init, pid == 1), therefore, top_cgroup
715 * always has either children cgroups and/or using tasks. So we don't
716 * need a special hack to ensure that top_cgroup cannot be deleted.
717 *
718 * The task_lock() exception
719 *
720 * The need for this exception arises from the action of
721 * cgroup_attach_task(), which overwrites one tasks cgroup pointer with
722 * another. It does so using cgroup_mutex, however there are
723 * several performance critical places that need to reference
724 * task->cgroup without the expense of grabbing a system global
725 * mutex. Therefore except as noted below, when dereferencing or, as
726 * in cgroup_attach_task(), modifying a task'ss cgroup pointer we use
727 * task_lock(), which acts on a spinlock (task->alloc_lock) already in
728 * the task_struct routinely used for such matters.
729 *
730 * P.S. One more locking exception. RCU is used to guard the
731 * update of a tasks cgroup pointer by cgroup_attach_task()
732 */
733
734/**
735 * cgroup_lock - lock out any changes to cgroup structures
736 *
737 */
738void cgroup_lock(void)
739{
740    mutex_lock(&cgroup_mutex);
741}
742EXPORT_SYMBOL_GPL(cgroup_lock);
743
744/**
745 * cgroup_unlock - release lock on cgroup changes
746 *
747 * Undo the lock taken in a previous cgroup_lock() call.
748 */
749void cgroup_unlock(void)
750{
751    mutex_unlock(&cgroup_mutex);
752}
753EXPORT_SYMBOL_GPL(cgroup_unlock);
754
755/*
756 * A couple of forward declarations required, due to cyclic reference loop:
757 * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
758 * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
759 * -> cgroup_mkdir.
760 */
761
762static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);
763static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
764static int cgroup_populate_dir(struct cgroup *cgrp);
765static const struct inode_operations cgroup_dir_inode_operations;
766static const struct file_operations proc_cgroupstats_operations;
767
768static struct backing_dev_info cgroup_backing_dev_info = {
769    .name = "cgroup",
770    .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK,
771};
772
773static int alloc_css_id(struct cgroup_subsys *ss,
774            struct cgroup *parent, struct cgroup *child);
775
776static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
777{
778    struct inode *inode = new_inode(sb);
779
780    if (inode) {
781        inode->i_mode = mode;
782        inode->i_uid = current_fsuid();
783        inode->i_gid = current_fsgid();
784        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
785        inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
786    }
787    return inode;
788}
789
790/*
791 * Call subsys's pre_destroy handler.
792 * This is called before css refcnt check.
793 */
794static int cgroup_call_pre_destroy(struct cgroup *cgrp)
795{
796    struct cgroup_subsys *ss;
797    int ret = 0;
798
799    for_each_subsys(cgrp->root, ss)
800        if (ss->pre_destroy) {
801            ret = ss->pre_destroy(ss, cgrp);
802            if (ret)
803                break;
804        }
805
806    return ret;
807}
808
809static void free_cgroup_rcu(struct rcu_head *obj)
810{
811    struct cgroup *cgrp = container_of(obj, struct cgroup, rcu_head);
812
813    kfree(cgrp);
814}
815
816static void cgroup_diput(struct dentry *dentry, struct inode *inode)
817{
818    /* is dentry a directory ? if so, kfree() associated cgroup */
819    if (S_ISDIR(inode->i_mode)) {
820        struct cgroup *cgrp = dentry->d_fsdata;
821        struct cgroup_subsys *ss;
822        BUG_ON(!(cgroup_is_removed(cgrp)));
823        /* It's possible for external users to be holding css
824         * reference counts on a cgroup; css_put() needs to
825         * be able to access the cgroup after decrementing
826         * the reference count in order to know if it needs to
827         * queue the cgroup to be handled by the release
828         * agent */
829        synchronize_rcu();
830
831        mutex_lock(&cgroup_mutex);
832        /*
833         * Release the subsystem state objects.
834         */
835        for_each_subsys(cgrp->root, ss)
836            ss->destroy(ss, cgrp);
837
838        cgrp->root->number_of_cgroups--;
839        mutex_unlock(&cgroup_mutex);
840
841        /*
842         * Drop the active superblock reference that we took when we
843         * created the cgroup
844         */
845        deactivate_super(cgrp->root->sb);
846
847        /*
848         * if we're getting rid of the cgroup, refcount should ensure
849         * that there are no pidlists left.
850         */
851        BUG_ON(!list_empty(&cgrp->pidlists));
852
853        call_rcu(&cgrp->rcu_head, free_cgroup_rcu);
854    }
855    iput(inode);
856}
857
858static void remove_dir(struct dentry *d)
859{
860    struct dentry *parent = dget(d->d_parent);
861
862    d_delete(d);
863    simple_rmdir(parent->d_inode, d);
864    dput(parent);
865}
866
867static void cgroup_clear_directory(struct dentry *dentry)
868{
869    struct list_head *node;
870
871    BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
872    spin_lock(&dcache_lock);
873    node = dentry->d_subdirs.next;
874    while (node != &dentry->d_subdirs) {
875        struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
876        list_del_init(node);
877        if (d->d_inode) {
878            /* This should never be called on a cgroup
879             * directory with child cgroups */
880            BUG_ON(d->d_inode->i_mode & S_IFDIR);
881            d = dget_locked(d);
882            spin_unlock(&dcache_lock);
883            d_delete(d);
884            simple_unlink(dentry->d_inode, d);
885            dput(d);
886            spin_lock(&dcache_lock);
887        }
888        node = dentry->d_subdirs.next;
889    }
890    spin_unlock(&dcache_lock);
891}
892
893/*
894 * NOTE : the dentry must have been dget()'ed
895 */
896static void cgroup_d_remove_dir(struct dentry *dentry)
897{
898    cgroup_clear_directory(dentry);
899
900    spin_lock(&dcache_lock);
901    list_del_init(&dentry->d_u.d_child);
902    spin_unlock(&dcache_lock);
903    remove_dir(dentry);
904}
905
906/*
907 * A queue for waiters to do rmdir() cgroup. A tasks will sleep when
908 * cgroup->count == 0 && list_empty(&cgroup->children) && subsys has some
909 * reference to css->refcnt. In general, this refcnt is expected to goes down
910 * to zero, soon.
911 *
912 * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
913 */
914DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
915
916static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
917{
918    if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
919        wake_up_all(&cgroup_rmdir_waitq);
920}
921
922void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
923{
924    css_get(css);
925}
926
927void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
928{
929    cgroup_wakeup_rmdir_waiter(css->cgroup);
930    css_put(css);
931}
932
933/*
934 * Call with cgroup_mutex held. Drops reference counts on modules, including
935 * any duplicate ones that parse_cgroupfs_options took. If this function
936 * returns an error, no reference counts are touched.
937 */
938static int rebind_subsystems(struct cgroupfs_root *root,
939                  unsigned long final_bits)
940{
941    unsigned long added_bits, removed_bits;
942    struct cgroup *cgrp = &root->top_cgroup;
943    int i;
944
945    BUG_ON(!mutex_is_locked(&cgroup_mutex));
946
947    removed_bits = root->actual_subsys_bits & ~final_bits;
948    added_bits = final_bits & ~root->actual_subsys_bits;
949    /* Check that any added subsystems are currently free */
950    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
951        unsigned long bit = 1UL << i;
952        struct cgroup_subsys *ss = subsys[i];
953        if (!(bit & added_bits))
954            continue;
955        /*
956         * Nobody should tell us to do a subsys that doesn't exist:
957         * parse_cgroupfs_options should catch that case and refcounts
958         * ensure that subsystems won't disappear once selected.
959         */
960        BUG_ON(ss == NULL);
961        if (ss->root != &rootnode) {
962            /* Subsystem isn't free */
963            return -EBUSY;
964        }
965    }
966
967    /* Currently we don't handle adding/removing subsystems when
968     * any child cgroups exist. This is theoretically supportable
969     * but involves complex error handling, so it's being left until
970     * later */
971    if (root->number_of_cgroups > 1)
972        return -EBUSY;
973
974    /* Process each subsystem */
975    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
976        struct cgroup_subsys *ss = subsys[i];
977        unsigned long bit = 1UL << i;
978        if (bit & added_bits) {
979            /* We're binding this subsystem to this hierarchy */
980            BUG_ON(ss == NULL);
981            BUG_ON(cgrp->subsys[i]);
982            BUG_ON(!dummytop->subsys[i]);
983            BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
984            mutex_lock(&ss->hierarchy_mutex);
985            cgrp->subsys[i] = dummytop->subsys[i];
986            cgrp->subsys[i]->cgroup = cgrp;
987            list_move(&ss->sibling, &root->subsys_list);
988            ss->root = root;
989            if (ss->bind)
990                ss->bind(ss, cgrp);
991            mutex_unlock(&ss->hierarchy_mutex);
992            /* refcount was already taken, and we're keeping it */
993        } else if (bit & removed_bits) {
994            /* We're removing this subsystem */
995            BUG_ON(ss == NULL);
996            BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
997            BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
998            mutex_lock(&ss->hierarchy_mutex);
999            if (ss->bind)
1000                ss->bind(ss, dummytop);
1001            dummytop->subsys[i]->cgroup = dummytop;
1002            cgrp->subsys[i] = NULL;
1003            subsys[i]->root = &rootnode;
1004            list_move(&ss->sibling, &rootnode.subsys_list);
1005            mutex_unlock(&ss->hierarchy_mutex);
1006            /* subsystem is now free - drop reference on module */
1007            module_put(ss->module);
1008        } else if (bit & final_bits) {
1009            /* Subsystem state should already exist */
1010            BUG_ON(ss == NULL);
1011            BUG_ON(!cgrp->subsys[i]);
1012            /*
1013             * a refcount was taken, but we already had one, so
1014             * drop the extra reference.
1015             */
1016            module_put(ss->module);
1017#ifdef CONFIG_MODULE_UNLOAD
1018            BUG_ON(ss->module && !module_refcount(ss->module));
1019#endif
1020        } else {
1021            /* Subsystem state shouldn't exist */
1022            BUG_ON(cgrp->subsys[i]);
1023        }
1024    }
1025    root->subsys_bits = root->actual_subsys_bits = final_bits;
1026    synchronize_rcu();
1027
1028    return 0;
1029}
1030
1031static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
1032{
1033    struct cgroupfs_root *root = vfs->mnt_sb->s_fs_info;
1034    struct cgroup_subsys *ss;
1035
1036    mutex_lock(&cgroup_mutex);
1037    for_each_subsys(root, ss)
1038        seq_printf(seq, ",%s", ss->name);
1039    if (test_bit(ROOT_NOPREFIX, &root->flags))
1040        seq_puts(seq, ",noprefix");
1041    if (strlen(root->release_agent_path))
1042        seq_printf(seq, ",release_agent=%s", root->release_agent_path);
1043    if (strlen(root->name))
1044        seq_printf(seq, ",name=%s", root->name);
1045    mutex_unlock(&cgroup_mutex);
1046    return 0;
1047}
1048
1049struct cgroup_sb_opts {
1050    unsigned long subsys_bits;
1051    unsigned long flags;
1052    char *release_agent;
1053    char *name;
1054    /* User explicitly requested empty subsystem */
1055    bool none;
1056
1057    struct cgroupfs_root *new_root;
1058
1059};
1060
1061/*
1062 * Convert a hierarchy specifier into a bitmask of subsystems and flags. Call
1063 * with cgroup_mutex held to protect the subsys[] array. This function takes
1064 * refcounts on subsystems to be used, unless it returns error, in which case
1065 * no refcounts are taken.
1066 */
1067static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1068{
1069    char *token, *o = data ?: "all";
1070    unsigned long mask = (unsigned long)-1;
1071    int i;
1072    bool module_pin_failed = false;
1073
1074    BUG_ON(!mutex_is_locked(&cgroup_mutex));
1075
1076#ifdef CONFIG_CPUSETS
1077    mask = ~(1UL << cpuset_subsys_id);
1078#endif
1079
1080    memset(opts, 0, sizeof(*opts));
1081
1082    while ((token = strsep(&o, ",")) != NULL) {
1083        if (!*token)
1084            return -EINVAL;
1085        if (!strcmp(token, "all")) {
1086            /* Add all non-disabled subsystems */
1087            opts->subsys_bits = 0;
1088            for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1089                struct cgroup_subsys *ss = subsys[i];
1090                if (ss == NULL)
1091                    continue;
1092                if (!ss->disabled)
1093                    opts->subsys_bits |= 1ul << i;
1094            }
1095        } else if (!strcmp(token, "none")) {
1096            /* Explicitly have no subsystems */
1097            opts->none = true;
1098        } else if (!strcmp(token, "noprefix")) {
1099            set_bit(ROOT_NOPREFIX, &opts->flags);
1100        } else if (!strncmp(token, "release_agent=", 14)) {
1101            /* Specifying two release agents is forbidden */
1102            if (opts->release_agent)
1103                return -EINVAL;
1104            opts->release_agent =
1105                kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1106            if (!opts->release_agent)
1107                return -ENOMEM;
1108        } else if (!strncmp(token, "name=", 5)) {
1109            const char *name = token + 5;
1110            /* Can't specify an empty name */
1111            if (!strlen(name))
1112                return -EINVAL;
1113            /* Must match [\w.-]+ */
1114            for (i = 0; i < strlen(name); i++) {
1115                char c = name[i];
1116                if (isalnum(c))
1117                    continue;
1118                if ((c == '.') || (c == '-') || (c == '_'))
1119                    continue;
1120                return -EINVAL;
1121            }
1122            /* Specifying two names is forbidden */
1123            if (opts->name)
1124                return -EINVAL;
1125            opts->name = kstrndup(name,
1126                          MAX_CGROUP_ROOT_NAMELEN - 1,
1127                          GFP_KERNEL);
1128            if (!opts->name)
1129                return -ENOMEM;
1130        } else {
1131            struct cgroup_subsys *ss;
1132            for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1133                ss = subsys[i];
1134                if (ss == NULL)
1135                    continue;
1136                if (!strcmp(token, ss->name)) {
1137                    if (!ss->disabled)
1138                        set_bit(i, &opts->subsys_bits);
1139                    break;
1140                }
1141            }
1142            if (i == CGROUP_SUBSYS_COUNT)
1143                return -ENOENT;
1144        }
1145    }
1146
1147    /* Consistency checks */
1148
1149    /*
1150     * Option noprefix was introduced just for backward compatibility
1151     * with the old cpuset, so we allow noprefix only if mounting just
1152     * the cpuset subsystem.
1153     */
1154    if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
1155        (opts->subsys_bits & mask))
1156        return -EINVAL;
1157
1158
1159    /* Can't specify "none" and some subsystems */
1160    if (opts->subsys_bits && opts->none)
1161        return -EINVAL;
1162
1163    /*
1164     * We either have to specify by name or by subsystems. (So all
1165     * empty hierarchies must have a name).
1166     */
1167    if (!opts->subsys_bits && !opts->name)
1168        return -EINVAL;
1169
1170    /*
1171     * Grab references on all the modules we'll need, so the subsystems
1172     * don't dance around before rebind_subsystems attaches them. This may
1173     * take duplicate reference counts on a subsystem that's already used,
1174     * but rebind_subsystems handles this case.
1175     */
1176    for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
1177        unsigned long bit = 1UL << i;
1178
1179        if (!(bit & opts->subsys_bits))
1180            continue;
1181        if (!try_module_get(subsys[i]->module)) {
1182            module_pin_failed = true;
1183            break;
1184        }
1185    }
1186    if (module_pin_failed) {
1187        /*
1188         * oops, one of the modules was going away. this means that we
1189         * raced with a module_delete call, and to the user this is
1190         * essentially a "subsystem doesn't exist" case.
1191         */
1192        for (i--; i >= CGROUP_BUILTIN_SUBSYS_COUNT; i--) {
1193            /* drop refcounts only on the ones we took */
1194            unsigned long bit = 1UL << i;
1195
1196            if (!(bit & opts->subsys_bits))
1197                continue;
1198            module_put(subsys[i]->module);
1199        }
1200        return -ENOENT;
1201    }
1202
1203    return 0;
1204}
1205
1206static void drop_parsed_module_refcounts(unsigned long subsys_bits)
1207{
1208    int i;
1209    for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
1210        unsigned long bit = 1UL << i;
1211
1212        if (!(bit & subsys_bits))
1213            continue;
1214        module_put(subsys[i]->module);
1215    }
1216}
1217
1218static int cgroup_remount(struct super_block *sb, int *flags, char *data)
1219{
1220    int ret = 0;
1221    struct cgroupfs_root *root = sb->s_fs_info;
1222    struct cgroup *cgrp = &root->top_cgroup;
1223    struct cgroup_sb_opts opts;
1224
1225    lock_kernel();
1226    mutex_lock(&cgrp->dentry->d_inode->i_mutex);
1227    mutex_lock(&cgroup_mutex);
1228
1229    /* See what subsystems are wanted */
1230    ret = parse_cgroupfs_options(data, &opts);
1231    if (ret)
1232        goto out_unlock;
1233
1234    /* Don't allow flags or name to change at remount */
1235    if (opts.flags != root->flags ||
1236        (opts.name && strcmp(opts.name, root->name))) {
1237        ret = -EINVAL;
1238        drop_parsed_module_refcounts(opts.subsys_bits);
1239        goto out_unlock;
1240    }
1241
1242    ret = rebind_subsystems(root, opts.subsys_bits);
1243    if (ret) {
1244        drop_parsed_module_refcounts(opts.subsys_bits);
1245        goto out_unlock;
1246    }
1247
1248    /* (re)populate subsystem files */
1249    cgroup_populate_dir(cgrp);
1250
1251    if (opts.release_agent)
1252        strcpy(root->release_agent_path, opts.release_agent);
1253 out_unlock:
1254    kfree(opts.release_agent);
1255    kfree(opts.name);
1256    mutex_unlock(&cgroup_mutex);
1257    mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
1258    unlock_kernel();
1259    return ret;
1260}
1261
1262static const struct super_operations cgroup_ops = {
1263    .statfs = simple_statfs,
1264    .drop_inode = generic_delete_inode,
1265    .show_options = cgroup_show_options,
1266    .remount_fs = cgroup_remount,
1267};
1268
1269static void init_cgroup_housekeeping(struct cgroup *cgrp)
1270{
1271    INIT_LIST_HEAD(&cgrp->sibling);
1272    INIT_LIST_HEAD(&cgrp->children);
1273    INIT_LIST_HEAD(&cgrp->css_sets);
1274    INIT_LIST_HEAD(&cgrp->release_list);
1275    INIT_LIST_HEAD(&cgrp->pidlists);
1276    mutex_init(&cgrp->pidlist_mutex);
1277    INIT_LIST_HEAD(&cgrp->event_list);
1278    spin_lock_init(&cgrp->event_list_lock);
1279}
1280
1281static void init_cgroup_root(struct cgroupfs_root *root)
1282{
1283    struct cgroup *cgrp = &root->top_cgroup;
1284    INIT_LIST_HEAD(&root->subsys_list);
1285    INIT_LIST_HEAD(&root->root_list);
1286    root->number_of_cgroups = 1;
1287    cgrp->root = root;
1288    cgrp->top_cgroup = cgrp;
1289    init_cgroup_housekeeping(cgrp);
1290}
1291
1292static bool init_root_id(struct cgroupfs_root *root)
1293{
1294    int ret = 0;
1295
1296    do {
1297        if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))
1298            return false;
1299        spin_lock(&hierarchy_id_lock);
1300        /* Try to allocate the next unused ID */
1301        ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
1302                    &root->hierarchy_id);
1303        if (ret == -ENOSPC)
1304            /* Try again starting from 0 */
1305            ret = ida_get_new(&hierarchy_ida, &root->hierarchy_id);
1306        if (!ret) {
1307            next_hierarchy_id = root->hierarchy_id + 1;
1308        } else if (ret != -EAGAIN) {
1309            /* Can only get here if the 31-bit IDR is full ... */
1310            BUG_ON(ret);
1311        }
1312        spin_unlock(&hierarchy_id_lock);
1313    } while (ret);
1314    return true;
1315}
1316
1317static int cgroup_test_super(struct super_block *sb, void *data)
1318{
1319    struct cgroup_sb_opts *opts = data;
1320    struct cgroupfs_root *root = sb->s_fs_info;
1321
1322    /* If we asked for a name then it must match */
1323    if (opts->name && strcmp(opts->name, root->name))
1324        return 0;
1325
1326    /*
1327     * If we asked for subsystems (or explicitly for no
1328     * subsystems) then they must match
1329     */
1330    if ((opts->subsys_bits || opts->none)
1331        && (opts->subsys_bits != root->subsys_bits))
1332        return 0;
1333
1334    return 1;
1335}
1336
1337static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
1338{
1339    struct cgroupfs_root *root;
1340
1341    if (!opts->subsys_bits && !opts->none)
1342        return NULL;
1343
1344    root = kzalloc(sizeof(*root), GFP_KERNEL);
1345    if (!root)
1346        return ERR_PTR(-ENOMEM);
1347
1348    if (!init_root_id(root)) {
1349        kfree(root);
1350        return ERR_PTR(-ENOMEM);
1351    }
1352    init_cgroup_root(root);
1353
1354    root->subsys_bits = opts->subsys_bits;
1355    root->flags = opts->flags;
1356    if (opts->release_agent)
1357        strcpy(root->release_agent_path, opts->release_agent);
1358    if (opts->name)
1359        strcpy(root->name, opts->name);
1360    return root;
1361}
1362
1363static void cgroup_drop_root(struct cgroupfs_root *root)
1364{
1365    if (!root)
1366        return;
1367
1368    BUG_ON(!root->hierarchy_id);
1369    spin_lock(&hierarchy_id_lock);
1370    ida_remove(&hierarchy_ida, root->hierarchy_id);
1371    spin_unlock(&hierarchy_id_lock);
1372    kfree(root);
1373}
1374
1375static int cgroup_set_super(struct super_block *sb, void *data)
1376{
1377    int ret;
1378    struct cgroup_sb_opts *opts = data;
1379
1380    /* If we don't have a new root, we can't set up a new sb */
1381    if (!opts->new_root)
1382        return -EINVAL;
1383
1384    BUG_ON(!opts->subsys_bits && !opts->none);
1385
1386    ret = set_anon_super(sb, NULL);
1387    if (ret)
1388        return ret;
1389
1390    sb->s_fs_info = opts->new_root;
1391    opts->new_root->sb = sb;
1392
1393    sb->s_blocksize = PAGE_CACHE_SIZE;
1394    sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
1395    sb->s_magic = CGROUP_SUPER_MAGIC;
1396    sb->s_op = &cgroup_ops;
1397
1398    return 0;
1399}
1400
1401static int cgroup_get_rootdir(struct super_block *sb)
1402{
1403    struct inode *inode =
1404        cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
1405    struct dentry *dentry;
1406
1407    if (!inode)
1408        return -ENOMEM;
1409
1410    inode->i_fop = &simple_dir_operations;
1411    inode->i_op = &cgroup_dir_inode_operations;
1412    /* directories start off with i_nlink == 2 (for "." entry) */
1413    inc_nlink(inode);
1414    dentry = d_alloc_root(inode);
1415    if (!dentry) {
1416        iput(inode);
1417        return -ENOMEM;
1418    }
1419    sb->s_root = dentry;
1420    return 0;
1421}
1422
1423static int cgroup_get_sb(struct file_system_type *fs_type,
1424             int flags, const char *unused_dev_name,
1425             void *data, struct vfsmount *mnt)
1426{
1427    struct cgroup_sb_opts opts;
1428    struct cgroupfs_root *root;
1429    int ret = 0;
1430    struct super_block *sb;
1431    struct cgroupfs_root *new_root;
1432
1433    /* First find the desired set of subsystems */
1434    mutex_lock(&cgroup_mutex);
1435    ret = parse_cgroupfs_options(data, &opts);
1436    mutex_unlock(&cgroup_mutex);
1437    if (ret)
1438        goto out_err;
1439
1440    /*
1441     * Allocate a new cgroup root. We may not need it if we're
1442     * reusing an existing hierarchy.
1443     */
1444    new_root = cgroup_root_from_opts(&opts);
1445    if (IS_ERR(new_root)) {
1446        ret = PTR_ERR(new_root);
1447        goto drop_modules;
1448    }
1449    opts.new_root = new_root;
1450
1451    /* Locate an existing or new sb for this hierarchy */
1452    sb = sget(fs_type, cgroup_test_super, cgroup_set_super, &opts);
1453    if (IS_ERR(sb)) {
1454        ret = PTR_ERR(sb);
1455        cgroup_drop_root(opts.new_root);
1456        goto drop_modules;
1457    }
1458
1459    root = sb->s_fs_info;
1460    BUG_ON(!root);
1461    if (root == opts.new_root) {
1462        /* We used the new root structure, so this is a new hierarchy */
1463        struct list_head tmp_cg_links;
1464        struct cgroup *root_cgrp = &root->top_cgroup;
1465        struct inode *inode;
1466        struct cgroupfs_root *existing_root;
1467        int i;
1468
1469        BUG_ON(sb->s_root != NULL);
1470
1471        ret = cgroup_get_rootdir(sb);
1472        if (ret)
1473            goto drop_new_super;
1474        inode = sb->s_root->d_inode;
1475
1476        mutex_lock(&inode->i_mutex);
1477        mutex_lock(&cgroup_mutex);
1478
1479        if (strlen(root->name)) {
1480            /* Check for name clashes with existing mounts */
1481            for_each_active_root(existing_root) {
1482                if (!strcmp(existing_root->name, root->name)) {
1483                    ret = -EBUSY;
1484                    mutex_unlock(&cgroup_mutex);
1485                    mutex_unlock(&inode->i_mutex);
1486                    goto drop_new_super;
1487                }
1488            }
1489        }
1490
1491        /*
1492         * We're accessing css_set_count without locking
1493         * css_set_lock here, but that's OK - it can only be
1494         * increased by someone holding cgroup_lock, and
1495         * that's us. The worst that can happen is that we
1496         * have some link structures left over
1497         */
1498        ret = allocate_cg_links(css_set_count, &tmp_cg_links);
1499        if (ret) {
1500            mutex_unlock(&cgroup_mutex);
1501            mutex_unlock(&inode->i_mutex);
1502            goto drop_new_super;
1503        }
1504
1505        ret = rebind_subsystems(root, root->subsys_bits);
1506        if (ret == -EBUSY) {
1507            mutex_unlock(&cgroup_mutex);
1508            mutex_unlock(&inode->i_mutex);
1509            free_cg_links(&tmp_cg_links);
1510            goto drop_new_super;
1511        }
1512        /*
1513         * There must be no failure case after here, since rebinding
1514         * takes care of subsystems' refcounts, which are explicitly
1515         * dropped in the failure exit path.
1516         */
1517
1518        /* EBUSY should be the only error here */
1519        BUG_ON(ret);
1520
1521        list_add(&root->root_list, &roots);
1522        root_count++;
1523
1524        sb->s_root->d_fsdata = root_cgrp;
1525        root->top_cgroup.dentry = sb->s_root;
1526
1527        /* Link the top cgroup in this hierarchy into all
1528         * the css_set objects */
1529        write_lock(&css_set_lock);
1530        for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
1531            struct hlist_head *hhead = &css_set_table[i];
1532            struct hlist_node *node;
1533            struct css_set *cg;
1534
1535            hlist_for_each_entry(cg, node, hhead, hlist)
1536                link_css_set(&tmp_cg_links, cg, root_cgrp);
1537        }
1538        write_unlock(&css_set_lock);
1539
1540        free_cg_links(&tmp_cg_links);
1541
1542        BUG_ON(!list_empty(&root_cgrp->sibling));
1543        BUG_ON(!list_empty(&root_cgrp->children));
1544        BUG_ON(root->number_of_cgroups != 1);
1545
1546        cgroup_populate_dir(root_cgrp);
1547        mutex_unlock(&cgroup_mutex);
1548        mutex_unlock(&inode->i_mutex);
1549    } else {
1550        /*
1551         * We re-used an existing hierarchy - the new root (if
1552         * any) is not needed
1553         */
1554        cgroup_drop_root(opts.new_root);
1555        /* no subsys rebinding, so refcounts don't change */
1556        drop_parsed_module_refcounts(opts.subsys_bits);
1557    }
1558
1559    simple_set_mnt(mnt, sb);
1560    kfree(opts.release_agent);
1561    kfree(opts.name);
1562    return 0;
1563
1564 drop_new_super:
1565    deactivate_locked_super(sb);
1566 drop_modules:
1567    drop_parsed_module_refcounts(opts.subsys_bits);
1568 out_err:
1569    kfree(opts.release_agent);
1570    kfree(opts.name);
1571
1572    return ret;
1573}
1574
1575static void cgroup_kill_sb(struct super_block *sb) {
1576    struct cgroupfs_root *root = sb->s_fs_info;
1577    struct cgroup *cgrp = &root->top_cgroup;
1578    int ret;
1579    struct cg_cgroup_link *link;
1580    struct cg_cgroup_link *saved_link;
1581
1582    BUG_ON(!root);
1583
1584    BUG_ON(root->number_of_cgroups != 1);
1585    BUG_ON(!list_empty(&cgrp->children));
1586    BUG_ON(!list_empty(&cgrp->sibling));
1587
1588    mutex_lock(&cgroup_mutex);
1589
1590    /* Rebind all subsystems back to the default hierarchy */
1591    ret = rebind_subsystems(root, 0);
1592    /* Shouldn't be able to fail ... */
1593    BUG_ON(ret);
1594
1595    /*
1596     * Release all the links from css_sets to this hierarchy's
1597     * root cgroup
1598     */
1599    write_lock(&css_set_lock);
1600
1601    list_for_each_entry_safe(link, saved_link, &cgrp->css_sets,
1602                 cgrp_link_list) {
1603        list_del(&link->cg_link_list);
1604        list_del(&link->cgrp_link_list);
1605        kfree(link);
1606    }
1607    write_unlock(&css_set_lock);
1608
1609    if (!list_empty(&root->root_list)) {
1610        list_del(&root->root_list);
1611        root_count--;
1612    }
1613
1614    mutex_unlock(&cgroup_mutex);
1615
1616    kill_litter_super(sb);
1617    cgroup_drop_root(root);
1618}
1619
1620static struct file_system_type cgroup_fs_type = {
1621    .name = "cgroup",
1622    .get_sb = cgroup_get_sb,
1623    .kill_sb = cgroup_kill_sb,
1624};
1625
1626static struct kobject *cgroup_kobj;
1627
1628static inline struct cgroup *__d_cgrp(struct dentry *dentry)
1629{
1630    return dentry->d_fsdata;
1631}
1632
1633static inline struct cftype *__d_cft(struct dentry *dentry)
1634{
1635    return dentry->d_fsdata;
1636}
1637
1638/**
1639 * cgroup_path - generate the path of a cgroup
1640 * @cgrp: the cgroup in question
1641 * @buf: the buffer to write the path into
1642 * @buflen: the length of the buffer
1643 *
1644 * Called with cgroup_mutex held or else with an RCU-protected cgroup
1645 * reference. Writes path of cgroup into buf. Returns 0 on success,
1646 * -errno on error.
1647 */
1648int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
1649{
1650    char *start;
1651    struct dentry *dentry = rcu_dereference_check(cgrp->dentry,
1652                              rcu_read_lock_held() ||
1653                              cgroup_lock_is_held());
1654
1655    if (!dentry || cgrp == dummytop) {
1656        /*
1657         * Inactive subsystems have no dentry for their root
1658         * cgroup
1659         */
1660        strcpy(buf, "/");
1661        return 0;
1662    }
1663
1664    start = buf + buflen;
1665
1666    *--start = '\0';
1667    for (;;) {
1668        int len = dentry->d_name.len;
1669
1670        if ((start -= len) < buf)
1671            return -ENAMETOOLONG;
1672        memcpy(start, dentry->d_name.name, len);
1673        cgrp = cgrp->parent;
1674        if (!cgrp)
1675            break;
1676
1677        dentry = rcu_dereference_check(cgrp->dentry,
1678                           rcu_read_lock_held() ||
1679                           cgroup_lock_is_held());
1680        if (!cgrp->parent)
1681            continue;
1682        if (--start < buf)
1683            return -ENAMETOOLONG;
1684        *start = '/';
1685    }
1686    memmove(buf, start, buf + buflen - start);
1687    return 0;
1688}
1689EXPORT_SYMBOL_GPL(cgroup_path);
1690
1691/**
1692 * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
1693 * @cgrp: the cgroup the task is attaching to
1694 * @tsk: the task to be attached
1695 *
1696 * Call holding cgroup_mutex. May take task_lock of
1697 * the task 'tsk' during call.
1698 */
1699int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
1700{
1701    int retval = 0;
1702    struct cgroup_subsys *ss, *failed_ss = NULL;
1703    struct cgroup *oldcgrp;
1704    struct css_set *cg;
1705    struct css_set *newcg;
1706    struct cgroupfs_root *root = cgrp->root;
1707
1708    /* Nothing to do if the task is already in that cgroup */
1709    oldcgrp = task_cgroup_from_root(tsk, root);
1710    if (cgrp == oldcgrp)
1711        return 0;
1712
1713    for_each_subsys(root, ss) {
1714        if (ss->can_attach) {
1715            retval = ss->can_attach(ss, cgrp, tsk, false);
1716            if (retval) {
1717                /*
1718                 * Remember on which subsystem the can_attach()
1719                 * failed, so that we only call cancel_attach()
1720                 * against the subsystems whose can_attach()
1721                 * succeeded. (See below)
1722                 */
1723                failed_ss = ss;
1724                goto out;
1725            }
1726        }
1727    }
1728
1729    task_lock(tsk);
1730    cg = tsk->cgroups;
1731    get_css_set(cg);
1732    task_unlock(tsk);
1733    /*
1734     * Locate or allocate a new css_set for this task,
1735     * based on its final set of cgroups
1736     */
1737    newcg = find_css_set(cg, cgrp);
1738    put_css_set(cg);
1739    if (!newcg) {
1740        retval = -ENOMEM;
1741        goto out;
1742    }
1743
1744    task_lock(tsk);
1745    if (tsk->flags & PF_EXITING) {
1746        task_unlock(tsk);
1747        put_css_set(newcg);
1748        retval = -ESRCH;
1749        goto out;
1750    }
1751    rcu_assign_pointer(tsk->cgroups, newcg);
1752    task_unlock(tsk);
1753
1754    /* Update the css_set linked lists if we're using them */
1755    write_lock(&css_set_lock);
1756    if (!list_empty(&tsk->cg_list)) {
1757        list_del(&tsk->cg_list);
1758        list_add(&tsk->cg_list, &newcg->tasks);
1759    }
1760    write_unlock(&css_set_lock);
1761
1762    for_each_subsys(root, ss) {
1763        if (ss->attach)
1764            ss->attach(ss, cgrp, oldcgrp, tsk, false);
1765    }
1766    set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
1767    synchronize_rcu();
1768    put_css_set(cg);
1769
1770    /*
1771     * wake up rmdir() waiter. the rmdir should fail since the cgroup
1772     * is no longer empty.
1773     */
1774    cgroup_wakeup_rmdir_waiter(cgrp);
1775out:
1776    if (retval) {
1777        for_each_subsys(root, ss) {
1778            if (ss == failed_ss)
1779                /*
1780                 * This subsystem was the one that failed the
1781                 * can_attach() check earlier, so we don't need
1782                 * to call cancel_attach() against it or any
1783                 * remaining subsystems.
1784                 */
1785                break;
1786            if (ss->cancel_attach)
1787                ss->cancel_attach(ss, cgrp, tsk, false);
1788        }
1789    }
1790    return retval;
1791}
1792
1793/**
1794 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
1795 * @from: attach to all cgroups of a given task
1796 * @tsk: the task to be attached
1797 */
1798int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
1799{
1800    struct cgroupfs_root *root;
1801    int retval = 0;
1802
1803    cgroup_lock();
1804    for_each_active_root(root) {
1805        struct cgroup *from_cg = task_cgroup_from_root(from, root);
1806
1807        retval = cgroup_attach_task(from_cg, tsk);
1808        if (retval)
1809            break;
1810    }
1811    cgroup_unlock();
1812
1813    return retval;
1814}
1815EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
1816
1817/*
1818 * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
1819 * held. May take task_lock of task
1820 */
1821static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
1822{
1823    struct task_struct *tsk;
1824    const struct cred *cred = current_cred(), *tcred;
1825    int ret;
1826
1827    if (pid) {
1828        rcu_read_lock();
1829        tsk = find_task_by_vpid(pid);
1830        if (!tsk || tsk->flags & PF_EXITING) {
1831            rcu_read_unlock();
1832            return -ESRCH;
1833        }
1834
1835        tcred = __task_cred(tsk);
1836        if (cred->euid &&
1837            cred->euid != tcred->uid &&
1838            cred->euid != tcred->suid) {
1839            rcu_read_unlock();
1840            return -EACCES;
1841        }
1842        get_task_struct(tsk);
1843        rcu_read_unlock();
1844    } else {
1845        tsk = current;
1846        get_task_struct(tsk);
1847    }
1848
1849    ret = cgroup_attach_task(cgrp, tsk);
1850    put_task_struct(tsk);
1851    return ret;
1852}
1853
1854static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
1855{
1856    int ret;
1857    if (!cgroup_lock_live_group(cgrp))
1858        return -ENODEV;
1859    ret = attach_task_by_pid(cgrp, pid);
1860    cgroup_unlock();
1861    return ret;
1862}
1863
1864/**
1865 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
1866 * @cgrp: the cgroup to be checked for liveness
1867 *
1868 * On success, returns true; the lock should be later released with
1869 * cgroup_unlock(). On failure returns false with no lock held.
1870 */
1871bool cgroup_lock_live_group(struct cgroup *cgrp)
1872{
1873    mutex_lock(&cgroup_mutex);
1874    if (cgroup_is_removed(cgrp)) {
1875        mutex_unlock(&cgroup_mutex);
1876        return false;
1877    }
1878    return true;
1879}
1880EXPORT_SYMBOL_GPL(cgroup_lock_live_group);
1881
1882static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
1883                      const char *buffer)
1884{
1885    BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
1886    if (!cgroup_lock_live_group(cgrp))
1887        return -ENODEV;
1888    strcpy(cgrp->root->release_agent_path, buffer);
1889    cgroup_unlock();
1890    return 0;
1891}
1892
1893static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
1894                     struct seq_file *seq)
1895{
1896    if (!cgroup_lock_live_group(cgrp))
1897        return -ENODEV;
1898    seq_puts(seq, cgrp->root->release_agent_path);
1899    seq_putc(seq, '\n');
1900    cgroup_unlock();
1901    return 0;
1902}
1903
1904/* A buffer size big enough for numbers or short strings */
1905#define CGROUP_LOCAL_BUFFER_SIZE 64
1906
1907static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
1908                struct file *file,
1909                const char __user *userbuf,
1910                size_t nbytes, loff_t *unused_ppos)
1911{
1912    char buffer[CGROUP_LOCAL_BUFFER_SIZE];
1913    int retval = 0;
1914    char *end;
1915
1916    if (!nbytes)
1917        return -EINVAL;
1918    if (nbytes >= sizeof(buffer))
1919        return -E2BIG;
1920    if (copy_from_user(buffer, userbuf, nbytes))
1921        return -EFAULT;
1922
1923    buffer[nbytes] = 0; /* nul-terminate */
1924    if (cft->write_u64) {
1925        u64 val = simple_strtoull(strstrip(buffer), &end, 0);
1926        if (*end)
1927            return -EINVAL;
1928        retval = cft->write_u64(cgrp, cft, val);
1929    } else {
1930        s64 val = simple_strtoll(strstrip(buffer), &end, 0);
1931        if (*end)
1932            return -EINVAL;
1933        retval = cft->write_s64(cgrp, cft, val);
1934    }
1935    if (!retval)
1936        retval = nbytes;
1937    return retval;
1938}
1939
1940static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
1941                   struct file *file,
1942                   const char __user *userbuf,
1943                   size_t nbytes, loff_t *unused_ppos)
1944{
1945    char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
1946    int retval = 0;
1947    size_t max_bytes = cft->max_write_len;
1948    char *buffer = local_buffer;
1949
1950    if (!max_bytes)
1951        max_bytes = sizeof(local_buffer) - 1;
1952    if (nbytes >= max_bytes)
1953        return -E2BIG;
1954    /* Allocate a dynamic buffer if we need one */
1955    if (nbytes >= sizeof(local_buffer)) {
1956        buffer = kmalloc(nbytes + 1, GFP_KERNEL);
1957        if (buffer == NULL)
1958            return -ENOMEM;
1959    }
1960    if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
1961        retval = -EFAULT;
1962        goto out;
1963    }
1964
1965    buffer[nbytes] = 0; /* nul-terminate */
1966    retval = cft->write_string(cgrp, cft, strstrip(buffer));
1967    if (!retval)
1968        retval = nbytes;
1969out:
1970    if (buffer != local_buffer)
1971        kfree(buffer);
1972    return retval;
1973}
1974
1975static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
1976                        size_t nbytes, loff_t *ppos)
1977{
1978    struct cftype *cft = __d_cft(file->f_dentry);
1979    struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
1980
1981    if (cgroup_is_removed(cgrp))
1982        return -ENODEV;
1983    if (cft->write)
1984        return cft->write(cgrp, cft, file, buf, nbytes, ppos);
1985    if (cft->write_u64 || cft->write_s64)
1986        return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
1987    if (cft->write_string)
1988        return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
1989    if (cft->trigger) {
1990        int ret = cft->trigger(cgrp, (unsigned int)cft->private);
1991        return ret ? ret : nbytes;
1992    }
1993    return -EINVAL;
1994}
1995
1996static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
1997                   struct file *file,
1998                   char __user *buf, size_t nbytes,
1999                   loff_t *ppos)
2000{
2001    char tmp[CGROUP_LOCAL_BUFFER_SIZE];
2002    u64 val = cft->read_u64(cgrp, cft);
2003    int len = sprintf(tmp, "%llu\n", (unsigned long long) val);
2004
2005    return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
2006}
2007
2008static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
2009                   struct file *file,
2010                   char __user *buf, size_t nbytes,
2011                   loff_t *ppos)
2012{
2013    char tmp[CGROUP_LOCAL_BUFFER_SIZE];
2014    s64 val = cft->read_s64(cgrp, cft);
2015    int len = sprintf(tmp, "%lld\n", (long long) val);
2016
2017    return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
2018}
2019
2020static ssize_t cgroup_file_read(struct file *file, char __user *buf,
2021                   size_t nbytes, loff_t *ppos)
2022{
2023    struct cftype *cft = __d_cft(file->f_dentry);
2024    struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2025
2026    if (cgroup_is_removed(cgrp))
2027        return -ENODEV;
2028
2029    if (cft->read)
2030        return cft->read(cgrp, cft, file, buf, nbytes, ppos);
2031    if (cft->read_u64)
2032        return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
2033    if (cft->read_s64)
2034        return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
2035    return -EINVAL;
2036}
2037
2038/*
2039 * seqfile ops/methods for returning structured data. Currently just
2040 * supports string->u64 maps, but can be extended in future.
2041 */
2042
2043struct cgroup_seqfile_state {
2044    struct cftype *cft;
2045    struct cgroup *cgroup;
2046};
2047
2048static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
2049{
2050    struct seq_file *sf = cb->state;
2051    return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
2052}
2053
2054static int cgroup_seqfile_show(struct seq_file *m, void *arg)
2055{
2056    struct cgroup_seqfile_state *state = m->private;
2057    struct cftype *cft = state->cft;
2058    if (cft->read_map) {
2059        struct cgroup_map_cb cb = {
2060            .fill = cgroup_map_add,
2061            .state = m,
2062        };
2063        return cft->read_map(state->cgroup, cft, &cb);
2064    }
2065    return cft->read_seq_string(state->cgroup, cft, m);
2066}
2067
2068static int cgroup_seqfile_release(struct inode *inode, struct file *file)
2069{
2070    struct seq_file *seq = file->private_data;
2071    kfree(seq->private);
2072    return single_release(inode, file);
2073}
2074
2075static const struct file_operations cgroup_seqfile_operations = {
2076    .read = seq_read,
2077    .write = cgroup_file_write,
2078    .llseek = seq_lseek,
2079    .release = cgroup_seqfile_release,
2080};
2081
2082static int cgroup_file_open(struct inode *inode, struct file *file)
2083{
2084    int err;
2085    struct cftype *cft;
2086
2087    err = generic_file_open(inode, file);
2088    if (err)
2089        return err;
2090    cft = __d_cft(file->f_dentry);
2091
2092    if (cft->read_map || cft->read_seq_string) {
2093        struct cgroup_seqfile_state *state =
2094            kzalloc(sizeof(*state), GFP_USER);
2095        if (!state)
2096            return -ENOMEM;
2097        state->cft = cft;
2098        state->cgroup = __d_cgrp(file->f_dentry->d_parent);
2099        file->f_op = &cgroup_seqfile_operations;
2100        err = single_open(file, cgroup_seqfile_show, state);
2101        if (err < 0)
2102            kfree(state);
2103    } else if (cft->open)
2104        err = cft->open(inode, file);
2105    else
2106        err = 0;
2107
2108    return err;
2109}
2110
2111static int cgroup_file_release(struct inode *inode, struct file *file)
2112{
2113    struct cftype *cft = __d_cft(file->f_dentry);
2114    if (cft->release)
2115        return cft->release(inode, file);
2116    return 0;
2117}
2118
2119/*
2120 * cgroup_rename - Only allow simple rename of directories in place.
2121 */
2122static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
2123                struct inode *new_dir, struct dentry *new_dentry)
2124{
2125    if (!S_ISDIR(old_dentry->d_inode->i_mode))
2126        return -ENOTDIR;
2127    if (new_dentry->d_inode)
2128        return -EEXIST;
2129    if (old_dir != new_dir)
2130        return -EIO;
2131    return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
2132}
2133
2134static const struct file_operations cgroup_file_operations = {
2135    .read = cgroup_file_read,
2136    .write = cgroup_file_write,
2137    .llseek = generic_file_llseek,
2138    .open = cgroup_file_open,
2139    .release = cgroup_file_release,
2140};
2141
2142static const struct inode_operations cgroup_dir_inode_operations = {
2143    .lookup = simple_lookup,
2144    .mkdir = cgroup_mkdir,
2145    .rmdir = cgroup_rmdir,
2146    .rename = cgroup_rename,
2147};
2148
2149/*
2150 * Check if a file is a control file
2151 */
2152static inline struct cftype *__file_cft(struct file *file)
2153{
2154    if (file->f_dentry->d_inode->i_fop != &cgroup_file_operations)
2155        return ERR_PTR(-EINVAL);
2156    return __d_cft(file->f_dentry);
2157}
2158
2159static int cgroup_create_file(struct dentry *dentry, mode_t mode,
2160                struct super_block *sb)
2161{
2162    static const struct dentry_operations cgroup_dops = {
2163        .d_iput = cgroup_diput,
2164    };
2165
2166    struct inode *inode;
2167
2168    if (!dentry)
2169        return -ENOENT;
2170    if (dentry->d_inode)
2171        return -EEXIST;
2172
2173    inode = cgroup_new_inode(mode, sb);
2174    if (!inode)
2175        return -ENOMEM;
2176
2177    if (S_ISDIR(mode)) {
2178        inode->i_op = &cgroup_dir_inode_operations;
2179        inode->i_fop = &simple_dir_operations;
2180
2181        /* start off with i_nlink == 2 (for "." entry) */
2182        inc_nlink(inode);
2183
2184        /* start with the directory inode held, so that we can
2185         * populate it without racing with another mkdir */
2186        mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
2187    } else if (S_ISREG(mode)) {
2188        inode->i_size = 0;
2189        inode->i_fop = &cgroup_file_operations;
2190    }
2191    dentry->d_op = &cgroup_dops;
2192    d_instantiate(dentry, inode);
2193    dget(dentry); /* Extra count - pin the dentry in core */
2194    return 0;
2195}
2196
2197/*
2198 * cgroup_create_dir - create a directory for an object.
2199 * @cgrp: the cgroup we create the directory for. It must have a valid
2200 * ->parent field. And we are going to fill its ->dentry field.
2201 * @dentry: dentry of the new cgroup
2202 * @mode: mode to set on new directory.
2203 */
2204static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
2205                mode_t mode)
2206{
2207    struct dentry *parent;
2208    int error = 0;
2209
2210    parent = cgrp->parent->dentry;
2211    error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb);
2212    if (!error) {
2213        dentry->d_fsdata = cgrp;
2214        inc_nlink(parent->d_inode);
2215        rcu_assign_pointer(cgrp->dentry, dentry);
2216        dget(dentry);
2217    }
2218    dput(dentry);
2219
2220    return error;
2221}
2222
2223/**
2224 * cgroup_file_mode - deduce file mode of a control file
2225 * @cft: the control file in question
2226 *
2227 * returns cft->mode if ->mode is not 0
2228 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
2229 * returns S_IRUGO if it has only a read handler
2230 * returns S_IWUSR if it has only a write hander
2231 */
2232static mode_t cgroup_file_mode(const struct cftype *cft)
2233{
2234    mode_t mode = 0;
2235
2236    if (cft->mode)
2237        return cft->mode;
2238
2239    if (cft->read || cft->read_u64 || cft->read_s64 ||
2240        cft->read_map || cft->read_seq_string)
2241        mode |= S_IRUGO;
2242
2243    if (cft->write || cft->write_u64 || cft->write_s64 ||
2244        cft->write_string || cft->trigger)
2245        mode |= S_IWUSR;
2246
2247    return mode;
2248}
2249
2250int cgroup_add_file(struct cgroup *cgrp,
2251               struct cgroup_subsys *subsys,
2252               const struct cftype *cft)
2253{
2254    struct dentry *dir = cgrp->dentry;
2255    struct dentry *dentry;
2256    int error;
2257    mode_t mode;
2258
2259    char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
2260    if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
2261        strcpy(name, subsys->name);
2262        strcat(name, ".");
2263    }
2264    strcat(name, cft->name);
2265    BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
2266    dentry = lookup_one_len(name, dir, strlen(name));
2267    if (!IS_ERR(dentry)) {
2268        mode = cgroup_file_mode(cft);
2269        error = cgroup_create_file(dentry, mode | S_IFREG,
2270                        cgrp->root->sb);
2271        if (!error)
2272            dentry->d_fsdata = (void *)cft;
2273        dput(dentry);
2274    } else
2275        error = PTR_ERR(dentry);
2276    return error;
2277}
2278EXPORT_SYMBOL_GPL(cgroup_add_file);
2279
2280int cgroup_add_files(struct cgroup *cgrp,
2281            struct cgroup_subsys *subsys,
2282            const struct cftype cft[],
2283            int count)
2284{
2285    int i, err;
2286    for (i = 0; i < count; i++) {
2287        err = cgroup_add_file(cgrp, subsys, &cft[i]);
2288        if (err)
2289            return err;
2290    }
2291    return 0;
2292}
2293EXPORT_SYMBOL_GPL(cgroup_add_files);
2294
2295/**
2296 * cgroup_task_count - count the number of tasks in a cgroup.
2297 * @cgrp: the cgroup in question
2298 *
2299 * Return the number of tasks in the cgroup.
2300 */
2301int cgroup_task_count(const struct cgroup *cgrp)
2302{
2303    int count = 0;
2304    struct cg_cgroup_link *link;
2305
2306    read_lock(&css_set_lock);
2307    list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
2308        count += atomic_read(&link->cg->refcount);
2309    }
2310    read_unlock(&css_set_lock);
2311    return count;
2312}
2313
2314/*
2315 * Advance a list_head iterator. The iterator should be positioned at
2316 * the start of a css_set
2317 */
2318static void cgroup_advance_iter(struct cgroup *cgrp,
2319                struct cgroup_iter *it)
2320{
2321    struct list_head *l = it->cg_link;
2322    struct cg_cgroup_link *link;
2323    struct css_set *cg;
2324
2325    /* Advance to the next non-empty css_set */
2326    do {
2327        l = l->next;
2328        if (l == &cgrp->css_sets) {
2329            it->cg_link = NULL;
2330            return;
2331        }
2332        link = list_entry(l, struct cg_cgroup_link, cgrp_link_list);
2333        cg = link->cg;
2334    } while (list_empty(&cg->tasks));
2335    it->cg_link = l;
2336    it->task = cg->tasks.next;
2337}
2338
2339/*
2340 * To reduce the fork() overhead for systems that are not actually
2341 * using their cgroups capability, we don't maintain the lists running
2342 * through each css_set to its tasks until we see the list actually
2343 * used - in other words after the first call to cgroup_iter_start().
2344 *
2345 * The tasklist_lock is not held here, as do_each_thread() and
2346 * while_each_thread() are protected by RCU.
2347 */
2348static void cgroup_enable_task_cg_lists(void)
2349{
2350    struct task_struct *p, *g;
2351    write_lock(&css_set_lock);
2352    use_task_css_set_links = 1;
2353    do_each_thread(g, p) {
2354        task_lock(p);
2355        /*
2356         * We should check if the process is exiting, otherwise
2357         * it will race with cgroup_exit() in that the list
2358         * entry won't be deleted though the process has exited.
2359         */
2360        if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
2361            list_add(&p->cg_list, &p->cgroups->tasks);
2362        task_unlock(p);
2363    } while_each_thread(g, p);
2364    write_unlock(&css_set_lock);
2365}
2366
2367void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
2368{
2369    /*
2370     * The first time anyone tries to iterate across a cgroup,
2371     * we need to enable the list linking each css_set to its
2372     * tasks, and fix up all existing tasks.
2373     */
2374    if (!use_task_css_set_links)
2375        cgroup_enable_task_cg_lists();
2376
2377    read_lock(&css_set_lock);
2378    it->cg_link = &cgrp->css_sets;
2379    cgroup_advance_iter(cgrp, it);
2380}
2381
2382struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
2383                    struct cgroup_iter *it)
2384{
2385    struct task_struct *res;
2386    struct list_head *l = it->task;
2387    struct cg_cgroup_link *link;
2388
2389    /* If the iterator cg is NULL, we have no tasks */
2390    if (!it->cg_link)
2391        return NULL;
2392    res = list_entry(l, struct task_struct, cg_list);
2393    /* Advance iterator to find next entry */
2394    l = l->next;
2395    link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list);
2396    if (l == &link->cg->tasks) {
2397        /* We reached the end of this task list - move on to
2398         * the next cg_cgroup_link */
2399        cgroup_advance_iter(cgrp, it);
2400    } else {
2401        it->task = l;
2402    }
2403    return res;
2404}
2405
2406void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
2407{
2408    read_unlock(&css_set_lock);
2409}
2410
2411static inline int started_after_time(struct task_struct *t1,
2412                     struct timespec *time,
2413                     struct task_struct *t2)
2414{
2415    int start_diff = timespec_compare(&t1->start_time, time);
2416    if (start_diff > 0) {
2417        return 1;
2418    } else if (start_diff < 0) {
2419        return 0;
2420    } else {
2421        /*
2422         * Arbitrarily, if two processes started at the same
2423         * time, we'll say that the lower pointer value
2424         * started first. Note that t2 may have exited by now
2425         * so this may not be a valid pointer any longer, but
2426         * that's fine - it still serves to distinguish
2427         * between two tasks started (effectively) simultaneously.
2428         */
2429        return t1 > t2;
2430    }
2431}
2432
2433/*
2434 * This function is a callback from heap_insert() and is used to order
2435 * the heap.
2436 * In this case we order the heap in descending task start time.
2437 */
2438static inline int started_after(void *p1, void *p2)
2439{
2440    struct task_struct *t1 = p1;
2441    struct task_struct *t2 = p2;
2442    return started_after_time(t1, &t2->start_time, t2);
2443}
2444
2445/**
2446 * cgroup_scan_tasks - iterate though all the tasks in a cgroup
2447 * @scan: struct cgroup_scanner containing arguments for the scan
2448 *
2449 * Arguments include pointers to callback functions test_task() and
2450 * process_task().
2451 * Iterate through all the tasks in a cgroup, calling test_task() for each,
2452 * and if it returns true, call process_task() for it also.
2453 * The test_task pointer may be NULL, meaning always true (select all tasks).
2454 * Effectively duplicates cgroup_iter_{start,next,end}()
2455 * but does not lock css_set_lock for the call to process_task().
2456 * The struct cgroup_scanner may be embedded in any structure of the caller's
2457 * creation.
2458 * It is guaranteed that process_task() will act on every task that
2459 * is a member of the cgroup for the duration of this call. This
2460 * function may or may not call process_task() for tasks that exit
2461 * or move to a different cgroup during the call, or are forked or
2462 * move into the cgroup during the call.
2463 *
2464 * Note that test_task() may be called with locks held, and may in some
2465 * situations be called multiple times for the same task, so it should
2466 * be cheap.
2467 * If the heap pointer in the struct cgroup_scanner is non-NULL, a heap has been
2468 * pre-allocated and will be used for heap operations (and its "gt" member will
2469 * be overwritten), else a temporary heap will be used (allocation of which
2470 * may cause this function to fail).
2471 */
2472int cgroup_scan_tasks(struct cgroup_scanner *scan)
2473{
2474    int retval, i;
2475    struct cgroup_iter it;
2476    struct task_struct *p, *dropped;
2477    /* Never dereference latest_task, since it's not refcounted */
2478    struct task_struct *latest_task = NULL;
2479    struct ptr_heap tmp_heap;
2480    struct ptr_heap *heap;
2481    struct timespec latest_time = { 0, 0 };
2482
2483    if (scan->heap) {
2484        /* The caller supplied our heap and pre-allocated its memory */
2485        heap = scan->heap;
2486        heap->gt = &started_after;
2487    } else {
2488        /* We need to allocate our own heap memory */
2489        heap = &tmp_heap;
2490        retval = heap_init(heap, PAGE_SIZE, GFP_KERNEL, &started_after);
2491        if (retval)
2492            /* cannot allocate the heap */
2493            return retval;
2494    }
2495
2496 again:
2497    /*
2498     * Scan tasks in the cgroup, using the scanner's "test_task" callback
2499     * to determine which are of interest, and using the scanner's
2500     * "process_task" callback to process any of them that need an update.
2501     * Since we don't want to hold any locks during the task updates,
2502     * gather tasks to be processed in a heap structure.
2503     * The heap is sorted by descending task start time.
2504     * If the statically-sized heap fills up, we overflow tasks that
2505     * started later, and in future iterations only consider tasks that
2506     * started after the latest task in the previous pass. This
2507     * guarantees forward progress and that we don't miss any tasks.
2508     */
2509    heap->size = 0;
2510    cgroup_iter_start(scan->cg, &it);
2511    while ((p = cgroup_iter_next(scan->cg, &it))) {
2512        /*
2513         * Only affect tasks that qualify per the caller's callback,
2514         * if he provided one
2515         */
2516        if (scan->test_task && !scan->test_task(p, scan))
2517            continue;
2518        /*
2519         * Only process tasks that started after the last task
2520         * we processed
2521         */
2522        if (!started_after_time(p, &latest_time, latest_task))
2523            continue;
2524        dropped = heap_insert(heap, p);
2525        if (dropped == NULL) {
2526            /*
2527             * The new task was inserted; the heap wasn't
2528             * previously full
2529             */
2530            get_task_struct(p);
2531        } else if (dropped != p) {
2532            /*
2533             * The new task was inserted, and pushed out a
2534             * different task
2535             */
2536            get_task_struct(p);
2537            put_task_struct(dropped);
2538        }
2539        /*
2540         * Else the new task was newer than anything already in
2541         * the heap and wasn't inserted
2542         */
2543    }
2544    cgroup_iter_end(scan->cg, &it);
2545
2546    if (heap->size) {
2547        for (i = 0; i < heap->size; i++) {
2548            struct task_struct *q = heap->ptrs[i];
2549            if (i == 0) {
2550                latest_time = q->start_time;
2551                latest_task = q;
2552            }
2553            /* Process the task per the caller's callback */
2554            scan->process_task(q, scan);
2555            put_task_struct(q);
2556        }
2557        /*
2558         * If we had to process any tasks at all, scan again
2559         * in case some of them were in the middle of forking
2560         * children that didn't get processed.
2561         * Not the most efficient way to do it, but it avoids
2562         * having to take callback_mutex in the fork path
2563         */
2564        goto again;
2565    }
2566    if (heap == &tmp_heap)
2567        heap_free(&tmp_heap);
2568    return 0;
2569}
2570
2571/*
2572 * Stuff for reading the 'tasks'/'procs' files.
2573 *
2574 * Reading this file can return large amounts of data if a cgroup has
2575 * *lots* of attached tasks. So it may need several calls to read(),
2576 * but we cannot guarantee that the information we produce is correct
2577 * unless we produce it entirely atomically.
2578 *
2579 */
2580
2581/*
2582 * The following two functions "fix" the issue where there are more pids
2583 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
2584 * TODO: replace with a kernel-wide solution to this problem
2585 */
2586#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
2587static void *pidlist_allocate(int count)
2588{
2589    if (PIDLIST_TOO_LARGE(count))
2590        return vmalloc(count * sizeof(pid_t));
2591    else
2592        return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
2593}
2594static void pidlist_free(void *p)
2595{
2596    if (is_vmalloc_addr(p))
2597        vfree(p);
2598    else
2599        kfree(p);
2600}
2601static void *pidlist_resize(void *p, int newcount)
2602{
2603    void *newlist;
2604    /* note: if new alloc fails, old p will still be valid either way */
2605    if (is_vmalloc_addr(p)) {
2606        newlist = vmalloc(newcount * sizeof(pid_t));
2607        if (!newlist)
2608            return NULL;
2609        memcpy(newlist, p, newcount * sizeof(pid_t));
2610        vfree(p);
2611    } else {
2612        newlist = krealloc(p, newcount * sizeof(pid_t), GFP_KERNEL);
2613    }
2614    return newlist;
2615}
2616
2617/*
2618 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
2619 * If the new stripped list is sufficiently smaller and there's enough memory
2620 * to allocate a new buffer, will let go of the unneeded memory. Returns the
2621 * number of unique elements.
2622 */
2623/* is the size difference enough that we should re-allocate the array? */
2624#define PIDLIST_REALLOC_DIFFERENCE(old, new) ((old) - PAGE_SIZE >= (new))
2625static int pidlist_uniq(pid_t **p, int length)
2626{
2627    int src, dest = 1;
2628    pid_t *list = *p;
2629    pid_t *newlist;
2630
2631    /*
2632     * we presume the 0th element is unique, so i starts at 1. trivial
2633     * edge cases first; no work needs to be done for either
2634     */
2635    if (length == 0 || length == 1)
2636        return length;
2637    /* src and dest walk down the list; dest counts unique elements */
2638    for (src = 1; src < length; src++) {
2639        /* find next unique element */
2640        while (list[src] == list[src-1]) {
2641            src++;
2642            if (src == length)
2643                goto after;
2644        }
2645        /* dest always points to where the next unique element goes */
2646        list[dest] = list[src];
2647        dest++;
2648    }
2649after:
2650    /*
2651     * if the length difference is large enough, we want to allocate a
2652     * smaller buffer to save memory. if this fails due to out of memory,
2653     * we'll just stay with what we've got.
2654     */
2655    if (PIDLIST_REALLOC_DIFFERENCE(length, dest)) {
2656        newlist = pidlist_resize(list, dest);
2657        if (newlist)
2658            *p = newlist;
2659    }
2660    return dest;
2661}
2662
2663static int cmppid(const void *a, const void *b)
2664{
2665    return *(pid_t *)a - *(pid_t *)b;
2666}
2667
2668/*
2669 * find the appropriate pidlist for our purpose (given procs vs tasks)
2670 * returns with the lock on that pidlist already held, and takes care
2671 * of the use count, or returns NULL with no locks held if we're out of
2672 * memory.
2673 */
2674static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
2675                          enum cgroup_filetype type)
2676{
2677    struct cgroup_pidlist *l;
2678    /* don't need task_nsproxy() if we're looking at ourself */
2679    struct pid_namespace *ns = current->nsproxy->pid_ns;
2680
2681    /*
2682     * We can't drop the pidlist_mutex before taking the l->mutex in case
2683     * the last ref-holder is trying to remove l from the list at the same
2684     * time. Holding the pidlist_mutex precludes somebody taking whichever
2685     * list we find out from under us - compare release_pid_array().
2686     */
2687    mutex_lock(&cgrp->pidlist_mutex);
2688    list_for_each_entry(l, &cgrp->pidlists, links) {
2689        if (l->key.type == type && l->key.ns == ns) {
2690            /* make sure l doesn't vanish out from under us */
2691            down_write(&l->mutex);
2692            mutex_unlock(&cgrp->pidlist_mutex);
2693            return l;
2694        }
2695    }
2696    /* entry not found; create a new one */
2697    l = kmalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
2698    if (!l) {
2699        mutex_unlock(&cgrp->pidlist_mutex);
2700        return l;
2701    }
2702    init_rwsem(&l->mutex);
2703    down_write(&l->mutex);
2704    l->key.type = type;
2705    l->key.ns = get_pid_ns(ns);
2706    l->use_count = 0; /* don't increment here */
2707    l->list = NULL;
2708    l->owner = cgrp;
2709    list_add(&l->links, &cgrp->pidlists);
2710    mutex_unlock(&cgrp->pidlist_mutex);
2711    return l;
2712}
2713
2714/*
2715 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
2716 */
2717static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
2718                  struct cgroup_pidlist **lp)
2719{
2720    pid_t *array;
2721    int length;
2722    int pid, n = 0; /* used for populating the array */
2723    struct cgroup_iter it;
2724    struct task_struct *tsk;
2725    struct cgroup_pidlist *l;
2726
2727    /*
2728     * If cgroup gets more users after we read count, we won't have
2729     * enough space - tough. This race is indistinguishable to the
2730     * caller from the case that the additional cgroup users didn't
2731     * show up until sometime later on.
2732     */
2733    length = cgroup_task_count(cgrp);
2734    array = pidlist_allocate(length);
2735    if (!array)
2736        return -ENOMEM;
2737    /* now, populate the array */
2738    cgroup_iter_start(cgrp, &it);
2739    while ((tsk = cgroup_iter_next(cgrp, &it))) {
2740        if (unlikely(n == length))
2741            break;
2742        /* get tgid or pid for procs or tasks file respectively */
2743        if (type == CGROUP_FILE_PROCS)
2744            pid = task_tgid_vnr(tsk);
2745        else
2746            pid = task_pid_vnr(tsk);
2747        if (pid > 0) /* make sure to only use valid results */
2748            array[n++] = pid;
2749    }
2750    cgroup_iter_end(cgrp, &it);
2751    length = n;
2752    /* now sort & (if procs) strip out duplicates */
2753    sort(array, length, sizeof(pid_t), cmppid, NULL);
2754    if (type == CGROUP_FILE_PROCS)
2755        length = pidlist_uniq(&array, length);
2756    l = cgroup_pidlist_find(cgrp, type);
2757    if (!l) {
2758        pidlist_free(array);
2759        return -ENOMEM;
2760    }
2761    /* store array, freeing old if necessary - lock already held */
2762    pidlist_free(l->list);
2763    l->list = array;
2764    l->length = length;
2765    l->use_count++;
2766    up_write(&l->mutex);
2767    *lp = l;
2768    return 0;
2769}
2770
2771/**
2772 * cgroupstats_build - build and fill cgroupstats
2773 * @stats: cgroupstats to fill information into
2774 * @dentry: A dentry entry belonging to the cgroup for which stats have
2775 * been requested.
2776 *
2777 * Build and fill cgroupstats so that taskstats can export it to user
2778 * space.
2779 */
2780int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
2781{
2782    int ret = -EINVAL;
2783    struct cgroup *cgrp;
2784    struct cgroup_iter it;
2785    struct task_struct *tsk;
2786
2787    /*
2788     * Validate dentry by checking the superblock operations,
2789     * and make sure it's a directory.
2790     */
2791    if (dentry->d_sb->s_op != &cgroup_ops ||
2792        !S_ISDIR(dentry->d_inode->i_mode))
2793         goto err;
2794
2795    ret = 0;
2796    cgrp = dentry->d_fsdata;
2797
2798    cgroup_iter_start(cgrp, &it);
2799    while ((tsk = cgroup_iter_next(cgrp, &it))) {
2800        switch (tsk->state) {
2801        case TASK_RUNNING:
2802            stats->nr_running++;
2803            break;
2804        case TASK_INTERRUPTIBLE:
2805            stats->nr_sleeping++;
2806            break;
2807        case TASK_UNINTERRUPTIBLE:
2808            stats->nr_uninterruptible++;
2809            break;
2810        case TASK_STOPPED:
2811            stats->nr_stopped++;
2812            break;
2813        default:
2814            if (delayacct_is_task_waiting_on_io(tsk))
2815                stats->nr_io_wait++;
2816            break;
2817        }
2818    }
2819    cgroup_iter_end(cgrp, &it);
2820
2821err:
2822    return ret;
2823}
2824
2825
2826/*
2827 * seq_file methods for the tasks/procs files. The seq_file position is the
2828 * next pid to display; the seq_file iterator is a pointer to the pid
2829 * in the cgroup->l->list array.
2830 */
2831
2832static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
2833{
2834    /*
2835     * Initially we receive a position value that corresponds to
2836     * one more than the last pid shown (or 0 on the first call or
2837     * after a seek to the start). Use a binary-search to find the
2838     * next pid to display, if any
2839     */
2840    struct cgroup_pidlist *l = s->private;
2841    int index = 0, pid = *pos;
2842    int *iter;
2843
2844    down_read(&l->mutex);
2845    if (pid) {
2846        int end = l->length;
2847
2848        while (index < end) {
2849            int mid = (index + end) / 2;
2850            if (l->list[mid] == pid) {
2851                index = mid;
2852                break;
2853            } else if (l->list[mid] <= pid)
2854                index = mid + 1;
2855            else
2856                end = mid;
2857        }
2858    }
2859    /* If we're off the end of the array, we're done */
2860    if (index >= l->length)
2861        return NULL;
2862    /* Update the abstract position to be the actual pid that we found */
2863    iter = l->list + index;
2864    *pos = *iter;
2865    return iter;
2866}
2867
2868static void cgroup_pidlist_stop(struct seq_file *s, void *v)
2869{
2870    struct cgroup_pidlist *l = s->private;
2871    up_read(&l->mutex);
2872}
2873
2874static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
2875{
2876    struct cgroup_pidlist *l = s->private;
2877    pid_t *p = v;
2878    pid_t *end = l->list + l->length;
2879    /*
2880     * Advance to the next pid in the array. If this goes off the
2881     * end, we're done
2882     */
2883    p++;
2884    if (p >= end) {
2885        return NULL;
2886    } else {
2887        *pos = *p;
2888        return p;
2889    }
2890}
2891
2892static int cgroup_pidlist_show(struct seq_file *s, void *v)
2893{
2894    return seq_printf(s, "%d\n", *(int *)v);
2895}
2896
2897/*
2898 * seq_operations functions for iterating on pidlists through seq_file -
2899 * independent of whether it's tasks or procs
2900 */
2901static const struct seq_operations cgroup_pidlist_seq_operations = {
2902    .start = cgroup_pidlist_start,
2903    .stop = cgroup_pidlist_stop,
2904    .next = cgroup_pidlist_next,
2905    .show = cgroup_pidlist_show,
2906};
2907
2908static void cgroup_release_pid_array(struct cgroup_pidlist *l)
2909{
2910    /*
2911     * the case where we're the last user of this particular pidlist will
2912     * have us remove it from the cgroup's list, which entails taking the
2913     * mutex. since in pidlist_find the pidlist->lock depends on cgroup->
2914     * pidlist_mutex, we have to take pidlist_mutex first.
2915     */
2916    mutex_lock(&l->owner->pidlist_mutex);
2917    down_write(&l->mutex);
2918    BUG_ON(!l->use_count);
2919    if (!--l->use_count) {
2920        /* we're the last user if refcount is 0; remove and free */
2921        list_del(&l->links);
2922        mutex_unlock(&l->owner->pidlist_mutex);
2923        pidlist_free(l->list);
2924        put_pid_ns(l->key.ns);
2925        up_write(&l->mutex);
2926        kfree(l);
2927        return;
2928    }
2929    mutex_unlock(&l->owner->pidlist_mutex);
2930    up_write(&l->mutex);
2931}
2932
2933static int cgroup_pidlist_release(struct inode *inode, struct file *file)
2934{
2935    struct cgroup_pidlist *l;
2936    if (!(file->f_mode & FMODE_READ))
2937        return 0;
2938    /*
2939     * the seq_file will only be initialized if the file was opened for
2940     * reading; hence we check if it's not null only in that case.
2941     */
2942    l = ((struct seq_file *)file->private_data)->private;
2943    cgroup_release_pid_array(l);
2944    return seq_release(inode, file);
2945}
2946
2947static const struct file_operations cgroup_pidlist_operations = {
2948    .read = seq_read,
2949    .llseek = seq_lseek,
2950    .write = cgroup_file_write,
2951    .release = cgroup_pidlist_release,
2952};
2953
2954/*
2955 * The following functions handle opens on a file that displays a pidlist
2956 * (tasks or procs). Prepare an array of the process/thread IDs of whoever's
2957 * in the cgroup.
2958 */
2959/* helper function for the two below it */
2960static int cgroup_pidlist_open(struct file *file, enum cgroup_filetype type)
2961{
2962    struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2963    struct cgroup_pidlist *l;
2964    int retval;
2965
2966    /* Nothing to do for write-only files */
2967    if (!(file->f_mode & FMODE_READ))
2968        return 0;
2969
2970    /* have the array populated */
2971    retval = pidlist_array_load(cgrp, type, &l);
2972    if (retval)
2973        return retval;
2974    /* configure file information */
2975    file->f_op = &cgroup_pidlist_operations;
2976
2977    retval = seq_open(file, &cgroup_pidlist_seq_operations);
2978    if (retval) {
2979        cgroup_release_pid_array(l);
2980        return retval;
2981    }
2982    ((struct seq_file *)file->private_data)->private = l;
2983    return 0;
2984}
2985static int cgroup_tasks_open(struct inode *unused, struct file *file)
2986{
2987    return cgroup_pidlist_open(file, CGROUP_FILE_TASKS);
2988}
2989static int cgroup_procs_open(struct inode *unused, struct file *file)
2990{
2991    return cgroup_pidlist_open(file, CGROUP_FILE_PROCS);
2992}
2993
2994static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
2995                        struct cftype *cft)
2996{
2997    return notify_on_release(cgrp);
2998}
2999
3000static int cgroup_write_notify_on_release(struct cgroup *cgrp,
3001                      struct cftype *cft,
3002                      u64 val)
3003{
3004    clear_bit(CGRP_RELEASABLE, &cgrp->flags);
3005    if (val)
3006        set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3007    else
3008        clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3009    return 0;
3010}
3011
3012/*
3013 * Unregister event and free resources.
3014 *
3015 * Gets called from workqueue.
3016 */
3017static void cgroup_event_remove(struct work_struct *work)
3018{
3019    struct cgroup_event *event = container_of(work, struct cgroup_event,
3020            remove);
3021    struct cgroup *cgrp = event->cgrp;
3022
3023    event->cft->unregister_event(cgrp, event->cft, event->eventfd);
3024
3025    eventfd_ctx_put(event->eventfd);
3026    kfree(event);
3027    dput(cgrp->dentry);
3028}
3029
3030/*
3031 * Gets called on POLLHUP on eventfd when user closes it.
3032 *
3033 * Called with wqh->lock held and interrupts disabled.
3034 */
3035static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
3036        int sync, void *key)
3037{
3038    struct cgroup_event *event = container_of(wait,
3039            struct cgroup_event, wait);
3040    struct cgroup *cgrp = event->cgrp;
3041    unsigned long flags = (unsigned long)key;
3042
3043    if (flags & POLLHUP) {
3044        __remove_wait_queue(event->wqh, &event->wait);
3045        spin_lock(&cgrp->event_list_lock);
3046        list_del(&event->list);
3047        spin_unlock(&cgrp->event_list_lock);
3048        /*
3049         * We are in atomic context, but cgroup_event_remove() may
3050         * sleep, so we have to call it in workqueue.
3051         */
3052        schedule_work(&event->remove);
3053    }
3054
3055    return 0;
3056}
3057
3058static void cgroup_event_ptable_queue_proc(struct file *file,
3059        wait_queue_head_t *wqh, poll_table *pt)
3060{
3061    struct cgroup_event *event = container_of(pt,
3062            struct cgroup_event, pt);
3063
3064    event->wqh = wqh;
3065    add_wait_queue(wqh, &event->wait);
3066}
3067
3068/*
3069 * Parse input and register new cgroup event handler.
3070 *
3071 * Input must be in format '<event_fd> <control_fd> <args>'.
3072 * Interpretation of args is defined by control file implementation.
3073 */
3074static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
3075                      const char *buffer)
3076{
3077    struct cgroup_event *event = NULL;
3078    unsigned int efd, cfd;
3079    struct file *efile = NULL;
3080    struct file *cfile = NULL;
3081    char *endp;
3082    int ret;
3083
3084    efd = simple_strtoul(buffer, &endp, 10);
3085    if (*endp != ' ')
3086        return -EINVAL;
3087    buffer = endp + 1;
3088
3089    cfd = simple_strtoul(buffer, &endp, 10);
3090    if ((*endp != ' ') && (*endp != '\0'))
3091        return -EINVAL;
3092    buffer = endp + 1;
3093
3094    event = kzalloc(sizeof(*event), GFP_KERNEL);
3095    if (!event)
3096        return -ENOMEM;
3097    event->cgrp = cgrp;
3098    INIT_LIST_HEAD(&event->list);
3099    init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
3100    init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
3101    INIT_WORK(&event->remove, cgroup_event_remove);
3102
3103    efile = eventfd_fget(efd);
3104    if (IS_ERR(efile)) {
3105        ret = PTR_ERR(efile);
3106        goto fail;
3107    }
3108
3109    event->eventfd = eventfd_ctx_fileget(efile);
3110    if (IS_ERR(event->eventfd)) {
3111        ret = PTR_ERR(event->eventfd);
3112        goto fail;
3113    }
3114
3115    cfile = fget(cfd);
3116    if (!cfile) {
3117        ret = -EBADF;
3118        goto fail;
3119    }
3120
3121    /* the process need read permission on control file */
3122    ret = file_permission(cfile, MAY_READ);
3123    if (ret < 0)
3124        goto fail;
3125
3126    event->cft = __file_cft(cfile);
3127    if (IS_ERR(event->cft)) {
3128        ret = PTR_ERR(event->cft);
3129        goto fail;
3130    }
3131
3132    if (!event->cft->register_event || !event->cft->unregister_event) {
3133        ret = -EINVAL;
3134        goto fail;
3135    }
3136
3137    ret = event->cft->register_event(cgrp, event->cft,
3138            event->eventfd, buffer);
3139    if (ret)
3140        goto fail;
3141
3142    if (efile->f_op->poll(efile, &event->pt) & POLLHUP) {
3143        event->cft->unregister_event(cgrp, event->cft, event->eventfd);
3144        ret = 0;
3145        goto fail;
3146    }
3147
3148    /*
3149     * Events should be removed after rmdir of cgroup directory, but before
3150     * destroying subsystem state objects. Let's take reference to cgroup
3151     * directory dentry to do that.
3152     */
3153    dget(cgrp->dentry);
3154
3155    spin_lock(&cgrp->event_list_lock);
3156    list_add(&event->list, &cgrp->event_list);
3157    spin_unlock(&cgrp->event_list_lock);
3158
3159    fput(cfile);
3160    fput(efile);
3161
3162    return 0;
3163
3164fail:
3165    if (cfile)
3166        fput(cfile);
3167
3168    if (event && event->eventfd && !IS_ERR(event->eventfd))
3169        eventfd_ctx_put(event->eventfd);
3170
3171    if (!IS_ERR_OR_NULL(efile))
3172        fput(efile);
3173
3174    kfree(event);
3175
3176    return ret;
3177}
3178
3179/*
3180 * for the common functions, 'private' gives the type of file
3181 */
3182/* for hysterical raisins, we can't put this on the older files */
3183#define CGROUP_FILE_GENERIC_PREFIX "cgroup."
3184static struct cftype files[] = {
3185    {
3186        .name = "tasks",
3187        .open = cgroup_tasks_open,
3188        .write_u64 = cgroup_tasks_write,
3189        .release = cgroup_pidlist_release,
3190        .mode = S_IRUGO | S_IWUSR,
3191    },
3192    {
3193        .name = CGROUP_FILE_GENERIC_PREFIX "procs",
3194        .open = cgroup_procs_open,
3195        /* .write_u64 = cgroup_procs_write, TODO */
3196        .release = cgroup_pidlist_release,
3197        .mode = S_IRUGO,
3198    },
3199    {
3200        .name = "notify_on_release",
3201        .read_u64 = cgroup_read_notify_on_release,
3202        .write_u64 = cgroup_write_notify_on_release,
3203    },
3204    {
3205        .name = CGROUP_FILE_GENERIC_PREFIX "event_control",
3206        .write_string = cgroup_write_event_control,
3207        .mode = S_IWUGO,
3208    },
3209};
3210
3211static struct cftype cft_release_agent = {
3212    .name = "release_agent",
3213    .read_seq_string = cgroup_release_agent_show,
3214    .write_string = cgroup_release_agent_write,
3215    .max_write_len = PATH_MAX,
3216};
3217
3218static int cgroup_populate_dir(struct cgroup *cgrp)
3219{
3220    int err;
3221    struct cgroup_subsys *ss;
3222
3223    /* First clear out any existing files */
3224    cgroup_clear_directory(cgrp->dentry);
3225
3226    err = cgroup_add_files(cgrp, NULL, files, ARRAY_SIZE(files));
3227    if (err < 0)
3228        return err;
3229
3230    if (cgrp == cgrp->top_cgroup) {
3231        if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0)
3232            return err;
3233    }
3234
3235    for_each_subsys(cgrp->root, ss) {
3236        if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
3237            return err;
3238    }
3239    /* This cgroup is ready now */
3240    for_each_subsys(cgrp->root, ss) {
3241        struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
3242        /*
3243         * Update id->css pointer and make this css visible from
3244         * CSS ID functions. This pointer will be dereferened
3245         * from RCU-read-side without locks.
3246         */
3247        if (css->id)
3248            rcu_assign_pointer(css->id->css, css);
3249    }
3250
3251    return 0;
3252}
3253
3254static void init_cgroup_css(struct cgroup_subsys_state *css,
3255                   struct cgroup_subsys *ss,
3256                   struct cgroup *cgrp)
3257{
3258    css->cgroup = cgrp;
3259    atomic_set(&css->refcnt, 1);
3260    css->flags = 0;
3261    css->id = NULL;
3262    if (cgrp == dummytop)
3263        set_bit(CSS_ROOT, &css->flags);
3264    BUG_ON(cgrp->subsys[ss->subsys_id]);
3265    cgrp->subsys[ss->subsys_id] = css;
3266}
3267
3268static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
3269{
3270    /* We need to take each hierarchy_mutex in a consistent order */
3271    int i;
3272
3273    /*
3274     * No worry about a race with rebind_subsystems that might mess up the
3275     * locking order, since both parties are under cgroup_mutex.
3276     */
3277    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3278        struct cgroup_subsys *ss = subsys[i];
3279        if (ss == NULL)
3280            continue;
3281        if (ss->root == root)
3282            mutex_lock(&ss->hierarchy_mutex);
3283    }
3284}
3285
3286static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
3287{
3288    int i;
3289
3290    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3291        struct cgroup_subsys *ss = subsys[i];
3292        if (ss == NULL)
3293            continue;
3294        if (ss->root == root)
3295            mutex_unlock(&ss->hierarchy_mutex);
3296    }
3297}
3298
3299/*
3300 * cgroup_create - create a cgroup
3301 * @parent: cgroup that will be parent of the new cgroup
3302 * @dentry: dentry of the new cgroup
3303 * @mode: mode to set on new inode
3304 *
3305 * Must be called with the mutex on the parent inode held
3306 */
3307static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
3308                 mode_t mode)
3309{
3310    struct cgroup *cgrp;
3311    struct cgroupfs_root *root = parent->root;
3312    int err = 0;
3313    struct cgroup_subsys *ss;
3314    struct super_block *sb = root->sb;
3315
3316    cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
3317    if (!cgrp)
3318        return -ENOMEM;
3319
3320    /* Grab a reference on the superblock so the hierarchy doesn't
3321     * get deleted on unmount if there are child cgroups. This
3322     * can be done outside cgroup_mutex, since the sb can't
3323     * disappear while someone has an open control file on the
3324     * fs */
3325    atomic_inc(&sb->s_active);
3326
3327    mutex_lock(&cgroup_mutex);
3328
3329    init_cgroup_housekeeping(cgrp);
3330
3331    cgrp->parent = parent;
3332    cgrp->root = parent->root;
3333    cgrp->top_cgroup = parent->top_cgroup;
3334
3335    if (notify_on_release(parent))
3336        set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3337
3338    for_each_subsys(root, ss) {
3339        struct cgroup_subsys_state *css = ss->create(ss, cgrp);
3340
3341        if (IS_ERR(css)) {
3342            err = PTR_ERR(css);
3343            goto err_destroy;
3344        }
3345        init_cgroup_css(css, ss, cgrp);
3346        if (ss->use_id) {
3347            err = alloc_css_id(ss, parent, cgrp);
3348            if (err)
3349                goto err_destroy;
3350        }
3351        /* At error, ->destroy() callback has to free assigned ID. */
3352    }
3353
3354    cgroup_lock_hierarchy(root);
3355    list_add(&cgrp->sibling, &cgrp->parent->children);
3356    cgroup_unlock_hierarchy(root);
3357    root->number_of_cgroups++;
3358
3359    err = cgroup_create_dir(cgrp, dentry, mode);
3360    if (err < 0)
3361        goto err_remove;
3362
3363    /* The cgroup directory was pre-locked for us */
3364    BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
3365
3366    err = cgroup_populate_dir(cgrp);
3367    /* If err < 0, we have a half-filled directory - oh well ;) */
3368
3369    mutex_unlock(&cgroup_mutex);
3370    mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
3371
3372    return 0;
3373
3374 err_remove:
3375
3376    cgroup_lock_hierarchy(root);
3377    list_del(&cgrp->sibling);
3378    cgroup_unlock_hierarchy(root);
3379    root->number_of_cgroups--;
3380
3381 err_destroy:
3382
3383    for_each_subsys(root, ss) {
3384        if (cgrp->subsys[ss->subsys_id])
3385            ss->destroy(ss, cgrp);
3386    }
3387
3388    mutex_unlock(&cgroup_mutex);
3389
3390    /* Release the reference count that we took on the superblock */
3391    deactivate_super(sb);
3392
3393    kfree(cgrp);
3394    return err;
3395}
3396
3397static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)
3398{
3399    struct cgroup *c_parent = dentry->d_parent->d_fsdata;
3400
3401    /* the vfs holds inode->i_mutex already */
3402    return cgroup_create(c_parent, dentry, mode | S_IFDIR);
3403}
3404
3405static int cgroup_has_css_refs(struct cgroup *cgrp)
3406{
3407    /* Check the reference count on each subsystem. Since we
3408     * already established that there are no tasks in the
3409     * cgroup, if the css refcount is also 1, then there should
3410     * be no outstanding references, so the subsystem is safe to
3411     * destroy. We scan across all subsystems rather than using
3412     * the per-hierarchy linked list of mounted subsystems since
3413     * we can be called via check_for_release() with no
3414     * synchronization other than RCU, and the subsystem linked
3415     * list isn't RCU-safe */
3416    int i;
3417    /*
3418     * We won't need to lock the subsys array, because the subsystems
3419     * we're concerned about aren't going anywhere since our cgroup root
3420     * has a reference on them.
3421     */
3422    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3423        struct cgroup_subsys *ss = subsys[i];
3424        struct cgroup_subsys_state *css;
3425        /* Skip subsystems not present or not in this hierarchy */
3426        if (ss == NULL || ss->root != cgrp->root)
3427            continue;
3428        css = cgrp->subsys[ss->subsys_id];
3429        /* When called from check_for_release() it's possible
3430         * that by this point the cgroup has been removed
3431         * and the css deleted. But a false-positive doesn't
3432         * matter, since it can only happen if the cgroup
3433         * has been deleted and hence no longer needs the
3434         * release agent to be called anyway. */
3435        if (css && (atomic_read(&css->refcnt) > 1))
3436            return 1;
3437    }
3438    return 0;
3439}
3440
3441/*
3442 * Atomically mark all (or else none) of the cgroup's CSS objects as
3443 * CSS_REMOVED. Return true on success, or false if the cgroup has
3444 * busy subsystems. Call with cgroup_mutex held
3445 */
3446
3447static int cgroup_clear_css_refs(struct cgroup *cgrp)
3448{
3449    struct cgroup_subsys *ss;
3450    unsigned long flags;
3451    bool failed = false;
3452    local_irq_save(flags);
3453    for_each_subsys(cgrp->root, ss) {
3454        struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
3455        int refcnt;
3456        while (1) {
3457            /* We can only remove a CSS with a refcnt==1 */
3458            refcnt = atomic_read(&css->refcnt);
3459            if (refcnt > 1) {
3460                failed = true;
3461                goto done;
3462            }
3463            BUG_ON(!refcnt);
3464            /*
3465             * Drop the refcnt to 0 while we check other
3466             * subsystems. This will cause any racing
3467             * css_tryget() to spin until we set the
3468             * CSS_REMOVED bits or abort
3469             */
3470            if (atomic_cmpxchg(&css->refcnt, refcnt, 0) == refcnt)
3471                break;
3472            cpu_relax();
3473        }
3474    }
3475 done:
3476    for_each_subsys(cgrp->root, ss) {
3477        struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
3478        if (failed) {
3479            /*
3480             * Restore old refcnt if we previously managed
3481             * to clear it from 1 to 0
3482             */
3483            if (!atomic_read(&css->refcnt))
3484                atomic_set(&css->refcnt, 1);
3485        } else {
3486            /* Commit the fact that the CSS is removed */
3487            set_bit(CSS_REMOVED, &css->flags);
3488        }
3489    }
3490    local_irq_restore(flags);
3491    return !failed;
3492}
3493
3494static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
3495{
3496    struct cgroup *cgrp = dentry->d_fsdata;
3497    struct dentry *d;
3498    struct cgroup *parent;
3499    DEFINE_WAIT(wait);
3500    struct cgroup_event *event, *tmp;
3501    int ret;
3502
3503    /* the vfs holds both inode->i_mutex already */
3504again:
3505    mutex_lock(&cgroup_mutex);
3506    if (atomic_read(&cgrp->count) != 0) {
3507        mutex_unlock(&cgroup_mutex);
3508        return -EBUSY;
3509    }
3510    if (!list_empty(&cgrp->children)) {
3511        mutex_unlock(&cgroup_mutex);
3512        return -EBUSY;
3513    }
3514    mutex_unlock(&cgroup_mutex);
3515
3516    /*
3517     * In general, subsystem has no css->refcnt after pre_destroy(). But
3518     * in racy cases, subsystem may have to get css->refcnt after
3519     * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
3520     * make rmdir return -EBUSY too often. To avoid that, we use waitqueue
3521     * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
3522     * and subsystem's reference count handling. Please see css_get/put
3523     * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
3524     */
3525    set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3526
3527    /*
3528     * Call pre_destroy handlers of subsys. Notify subsystems
3529     * that rmdir() request comes.
3530     */
3531    ret = cgroup_call_pre_destroy(cgrp);
3532    if (ret) {
3533        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3534        return ret;
3535    }
3536
3537    mutex_lock(&cgroup_mutex);
3538    parent = cgrp->parent;
3539    if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
3540        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3541        mutex_unlock(&cgroup_mutex);
3542        return -EBUSY;
3543    }
3544    prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
3545    if (!cgroup_clear_css_refs(cgrp)) {
3546        mutex_unlock(&cgroup_mutex);
3547        /*
3548         * Because someone may call cgroup_wakeup_rmdir_waiter() before
3549         * prepare_to_wait(), we need to check this flag.
3550         */
3551        if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
3552            schedule();
3553        finish_wait(&cgroup_rmdir_waitq, &wait);
3554        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3555        if (signal_pending(current))
3556            return -EINTR;
3557        goto again;
3558    }
3559    /* NO css_tryget() can success after here. */
3560    finish_wait(&cgroup_rmdir_waitq, &wait);
3561    clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3562
3563    spin_lock(&release_list_lock);
3564    set_bit(CGRP_REMOVED, &cgrp->flags);
3565    if (!list_empty(&cgrp->release_list))
3566        list_del(&cgrp->release_list);
3567    spin_unlock(&release_list_lock);
3568
3569    cgroup_lock_hierarchy(cgrp->root);
3570    /* delete this cgroup from parent->children */
3571    list_del(&cgrp->sibling);
3572    cgroup_unlock_hierarchy(cgrp->root);
3573
3574    spin_lock(&cgrp->dentry->d_lock);
3575    d = dget(cgrp->dentry);
3576    spin_unlock(&d->d_lock);
3577
3578    cgroup_d_remove_dir(d);
3579    dput(d);
3580
3581    set_bit(CGRP_RELEASABLE, &parent->flags);
3582    check_for_release(parent);
3583
3584    /*
3585     * Unregister events and notify userspace.
3586     * Notify userspace about cgroup removing only after rmdir of cgroup
3587     * directory to avoid race between userspace and kernelspace
3588     */
3589    spin_lock(&cgrp->event_list_lock);
3590    list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
3591        list_del(&event->list);
3592        remove_wait_queue(event->wqh, &event->wait);
3593        eventfd_signal(event->eventfd, 1);
3594        schedule_work(&event->remove);
3595    }
3596    spin_unlock(&cgrp->event_list_lock);
3597
3598    mutex_unlock(&cgroup_mutex);
3599    return 0;
3600}
3601
3602static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
3603{
3604    struct cgroup_subsys_state *css;
3605
3606    printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
3607
3608    /* Create the top cgroup state for this subsystem */
3609    list_add(&ss->sibling, &rootnode.subsys_list);
3610    ss->root = &rootnode;
3611    css = ss->create(ss, dummytop);
3612    /* We don't handle early failures gracefully */
3613    BUG_ON(IS_ERR(css));
3614    init_cgroup_css(css, ss, dummytop);
3615
3616    /* Update the init_css_set to contain a subsys
3617     * pointer to this state - since the subsystem is
3618     * newly registered, all tasks and hence the
3619     * init_css_set is in the subsystem's top cgroup. */
3620    init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
3621
3622    need_forkexit_callback |= ss->fork || ss->exit;
3623
3624    /* At system boot, before all subsystems have been
3625     * registered, no tasks have been forked, so we don't
3626     * need to invoke fork callbacks here. */
3627    BUG_ON(!list_empty(&init_task.tasks));
3628
3629    mutex_init(&ss->hierarchy_mutex);
3630    lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
3631    ss->active = 1;
3632
3633    /* this function shouldn't be used with modular subsystems, since they
3634     * need to register a subsys_id, among other things */
3635    BUG_ON(ss->module);
3636}
3637
3638/**
3639 * cgroup_load_subsys: load and register a modular subsystem at runtime
3640 * @ss: the subsystem to load
3641 *
3642 * This function should be called in a modular subsystem's initcall. If the
3643 * subsystem is built as a module, it will be assigned a new subsys_id and set
3644 * up for use. If the subsystem is built-in anyway, work is delegated to the
3645 * simpler cgroup_init_subsys.
3646 */
3647int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
3648{
3649    int i;
3650    struct cgroup_subsys_state *css;
3651
3652    /* check name and function validity */
3653    if (ss->name == NULL || strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN ||
3654        ss->create == NULL || ss->destroy == NULL)
3655        return -EINVAL;
3656
3657    /*
3658     * we don't support callbacks in modular subsystems. this check is
3659     * before the ss->module check for consistency; a subsystem that could
3660     * be a module should still have no callbacks even if the user isn't
3661     * compiling it as one.
3662     */
3663    if (ss->fork || ss->exit)
3664        return -EINVAL;
3665
3666    /*
3667     * an optionally modular subsystem is built-in: we want to do nothing,
3668     * since cgroup_init_subsys will have already taken care of it.
3669     */
3670    if (ss->module == NULL) {
3671        /* a few sanity checks */
3672        BUG_ON(ss->subsys_id >= CGROUP_BUILTIN_SUBSYS_COUNT);
3673        BUG_ON(subsys[ss->subsys_id] != ss);
3674        return 0;
3675    }
3676
3677    /*
3678     * need to register a subsys id before anything else - for example,
3679     * init_cgroup_css needs it.
3680     */
3681    mutex_lock(&cgroup_mutex);
3682    /* find the first empty slot in the array */
3683    for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
3684        if (subsys[i] == NULL)
3685            break;
3686    }
3687    if (i == CGROUP_SUBSYS_COUNT) {
3688        /* maximum number of subsystems already registered! */
3689        mutex_unlock(&cgroup_mutex);
3690        return -EBUSY;
3691    }
3692    /* assign ourselves the subsys_id */
3693    ss->subsys_id = i;
3694    subsys[i] = ss;
3695
3696    /*
3697     * no ss->create seems to need anything important in the ss struct, so
3698     * this can happen first (i.e. before the rootnode attachment).
3699     */
3700    css = ss->create(ss, dummytop);
3701    if (IS_ERR(css)) {
3702        /* failure case - need to deassign the subsys[] slot. */
3703        subsys[i] = NULL;
3704        mutex_unlock(&cgroup_mutex);
3705        return PTR_ERR(css);
3706    }
3707
3708    list_add(&ss->sibling, &rootnode.subsys_list);
3709    ss->root = &rootnode;
3710
3711    /* our new subsystem will be attached to the dummy hierarchy. */
3712    init_cgroup_css(css, ss, dummytop);
3713    /* init_idr must be after init_cgroup_css because it sets css->id. */
3714    if (ss->use_id) {
3715        int ret = cgroup_init_idr(ss, css);
3716        if (ret) {
3717            dummytop->subsys[ss->subsys_id] = NULL;
3718            ss->destroy(ss, dummytop);
3719            subsys[i] = NULL;
3720            mutex_unlock(&cgroup_mutex);
3721            return ret;
3722        }
3723    }
3724
3725    /*
3726     * Now we need to entangle the css into the existing css_sets. unlike
3727     * in cgroup_init_subsys, there are now multiple css_sets, so each one
3728     * will need a new pointer to it; done by iterating the css_set_table.
3729     * furthermore, modifying the existing css_sets will corrupt the hash
3730     * table state, so each changed css_set will need its hash recomputed.
3731     * this is all done under the css_set_lock.
3732     */
3733    write_lock(&css_set_lock);
3734    for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
3735        struct css_set *cg;
3736        struct hlist_node *node, *tmp;
3737        struct hlist_head *bucket = &css_set_table[i], *new_bucket;
3738
3739        hlist_for_each_entry_safe(cg, node, tmp, bucket, hlist) {
3740            /* skip entries that we already rehashed */
3741            if (cg->subsys[ss->subsys_id])
3742                continue;
3743            /* remove existing entry */
3744            hlist_del(&cg->hlist);
3745            /* set new value */
3746            cg->subsys[ss->subsys_id] = css;
3747            /* recompute hash and restore entry */
3748            new_bucket = css_set_hash(cg->subsys);
3749            hlist_add_head(&cg->hlist, new_bucket);
3750        }
3751    }
3752    write_unlock(&css_set_lock);
3753
3754    mutex_init(&ss->hierarchy_mutex);
3755    lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
3756    ss->active = 1;
3757
3758    /* success! */
3759    mutex_unlock(&cgroup_mutex);
3760    return 0;
3761}
3762EXPORT_SYMBOL_GPL(cgroup_load_subsys);
3763
3764/**
3765 * cgroup_unload_subsys: unload a modular subsystem
3766 * @ss: the subsystem to unload
3767 *
3768 * This function should be called in a modular subsystem's exitcall. When this
3769 * function is invoked, the refcount on the subsystem's module will be 0, so
3770 * the subsystem will not be attached to any hierarchy.
3771 */
3772void cgroup_unload_subsys(struct cgroup_subsys *ss)
3773{
3774    struct cg_cgroup_link *link;
3775    struct hlist_head *hhead;
3776
3777    BUG_ON(ss->module == NULL);
3778
3779    /*
3780     * we shouldn't be called if the subsystem is in use, and the use of
3781     * try_module_get in parse_cgroupfs_options should ensure that it
3782     * doesn't start being used while we're killing it off.
3783     */
3784    BUG_ON(ss->root != &rootnode);
3785
3786    mutex_lock(&cgroup_mutex);
3787    /* deassign the subsys_id */
3788    BUG_ON(ss->subsys_id < CGROUP_BUILTIN_SUBSYS_COUNT);
3789    subsys[ss->subsys_id] = NULL;
3790
3791    /* remove subsystem from rootnode's list of subsystems */
3792    list_del(&ss->sibling);
3793
3794    /*
3795     * disentangle the css from all css_sets attached to the dummytop. as
3796     * in loading, we need to pay our respects to the hashtable gods.
3797     */
3798    write_lock(&css_set_lock);
3799    list_for_each_entry(link, &dummytop->css_sets, cgrp_link_list) {
3800        struct css_set *cg = link->cg;
3801
3802        hlist_del(&cg->hlist);
3803        BUG_ON(!cg->subsys[ss->subsys_id]);
3804        cg->subsys[ss->subsys_id] = NULL;
3805        hhead = css_set_hash(cg->subsys);
3806        hlist_add_head(&cg->hlist, hhead);
3807    }
3808    write_unlock(&css_set_lock);
3809
3810    /*
3811     * remove subsystem's css from the dummytop and free it - need to free
3812     * before marking as null because ss->destroy needs the cgrp->subsys
3813     * pointer to find their state. note that this also takes care of
3814     * freeing the css_id.
3815     */
3816    ss->destroy(ss, dummytop);
3817    dummytop->subsys[ss->subsys_id] = NULL;
3818
3819    mutex_unlock(&cgroup_mutex);
3820}
3821EXPORT_SYMBOL_GPL(cgroup_unload_subsys);
3822
3823/**
3824 * cgroup_init_early - cgroup initialization at system boot
3825 *
3826 * Initialize cgroups at system boot, and initialize any
3827 * subsystems that request early init.
3828 */
3829int __init cgroup_init_early(void)
3830{
3831    int i;
3832    atomic_set(&init_css_set.refcount, 1);
3833    INIT_LIST_HEAD(&init_css_set.cg_links);
3834    INIT_LIST_HEAD(&init_css_set.tasks);
3835    INIT_HLIST_NODE(&init_css_set.hlist);
3836    css_set_count = 1;
3837    init_cgroup_root(&rootnode);
3838    root_count = 1;
3839    init_task.cgroups = &init_css_set;
3840
3841    init_css_set_link.cg = &init_css_set;
3842    init_css_set_link.cgrp = dummytop;
3843    list_add(&init_css_set_link.cgrp_link_list,
3844         &rootnode.top_cgroup.css_sets);
3845    list_add(&init_css_set_link.cg_link_list,
3846         &init_css_set.cg_links);
3847
3848    for (i = 0; i < CSS_SET_TABLE_SIZE; i++)
3849        INIT_HLIST_HEAD(&css_set_table[i]);
3850
3851    /* at bootup time, we don't worry about modular subsystems */
3852    for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
3853        struct cgroup_subsys *ss = subsys[i];
3854
3855        BUG_ON(!ss->name);
3856        BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
3857        BUG_ON(!ss->create);
3858        BUG_ON(!ss->destroy);
3859        if (ss->subsys_id != i) {
3860            printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
3861                   ss->name, ss->subsys_id);
3862            BUG();
3863        }
3864
3865        if (ss->early_init)
3866            cgroup_init_subsys(ss);
3867    }
3868    return 0;
3869}
3870
3871/**
3872 * cgroup_init - cgroup initialization
3873 *
3874 * Register cgroup filesystem and /proc file, and initialize
3875 * any subsystems that didn't request early init.
3876 */
3877int __init cgroup_init(void)
3878{
3879    int err;
3880    int i;
3881    struct hlist_head *hhead;
3882
3883    err = bdi_init(&cgroup_backing_dev_info);
3884    if (err)
3885        return err;
3886
3887    /* at bootup time, we don't worry about modular subsystems */
3888    for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
3889        struct cgroup_subsys *ss = subsys[i];
3890        if (!ss->early_init)
3891            cgroup_init_subsys(ss);
3892        if (ss->use_id)
3893            cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
3894    }
3895
3896    /* Add init_css_set to the hash table */
3897    hhead = css_set_hash(init_css_set.subsys);
3898    hlist_add_head(&init_css_set.hlist, hhead);
3899    BUG_ON(!init_root_id(&rootnode));
3900
3901    cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
3902    if (!cgroup_kobj) {
3903        err = -ENOMEM;
3904        goto out;
3905    }
3906
3907    err = register_filesystem(&cgroup_fs_type);
3908    if (err < 0) {
3909        kobject_put(cgroup_kobj);
3910        goto out;
3911    }
3912
3913    proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
3914
3915out:
3916    if (err)
3917        bdi_destroy(&cgroup_backing_dev_info);
3918
3919    return err;
3920}
3921
3922/*
3923 * proc_cgroup_show()
3924 * - Print task's cgroup paths into seq_file, one line for each hierarchy
3925 * - Used for /proc/<pid>/cgroup.
3926 * - No need to task_lock(tsk) on this tsk->cgroup reference, as it
3927 * doesn't really matter if tsk->cgroup changes after we read it,
3928 * and we take cgroup_mutex, keeping cgroup_attach_task() from changing it
3929 * anyway. No need to check that tsk->cgroup != NULL, thanks to
3930 * the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
3931 * cgroup to top_cgroup.
3932 */
3933
3934/* TODO: Use a proper seq_file iterator */
3935static int proc_cgroup_show(struct seq_file *m, void *v)
3936{
3937    struct pid *pid;
3938    struct task_struct *tsk;
3939    char *buf;
3940    int retval;
3941    struct cgroupfs_root *root;
3942
3943    retval = -ENOMEM;
3944    buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
3945    if (!buf)
3946        goto out;
3947
3948    retval = -ESRCH;
3949    pid = m->private;
3950    tsk = get_pid_task(pid, PIDTYPE_PID);
3951    if (!tsk)
3952        goto out_free;
3953
3954    retval = 0;
3955
3956    mutex_lock(&cgroup_mutex);
3957
3958    for_each_active_root(root) {
3959        struct cgroup_subsys *ss;
3960        struct cgroup *cgrp;
3961        int count = 0;
3962
3963        seq_printf(m, "%d:", root->hierarchy_id);
3964        for_each_subsys(root, ss)
3965            seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
3966        if (strlen(root->name))
3967            seq_printf(m, "%sname=%s", count ? "," : "",
3968                   root->name);
3969        seq_putc(m, ':');
3970        cgrp = task_cgroup_from_root(tsk, root);
3971        retval = cgroup_path(cgrp, buf, PAGE_SIZE);
3972        if (retval < 0)
3973            goto out_unlock;
3974        seq_puts(m, buf);
3975        seq_putc(m, '\n');
3976    }
3977
3978out_unlock:
3979    mutex_unlock(&cgroup_mutex);
3980    put_task_struct(tsk);
3981out_free:
3982    kfree(buf);
3983out:
3984    return retval;
3985}
3986
3987static int cgroup_open(struct inode *inode, struct file *file)
3988{
3989    struct pid *pid = PROC_I(inode)->pid;
3990    return single_open(file, proc_cgroup_show, pid);
3991}
3992
3993const struct file_operations proc_cgroup_operations = {
3994    .open = cgroup_open,
3995    .read = seq_read,
3996    .llseek = seq_lseek,
3997    .release = single_release,
3998};
3999
4000/* Display information about each subsystem and each hierarchy */
4001static int proc_cgroupstats_show(struct seq_file *m, void *v)
4002{
4003    int i;
4004
4005    seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
4006    /*
4007     * ideally we don't want subsystems moving around while we do this.
4008     * cgroup_mutex is also necessary to guarantee an atomic snapshot of
4009     * subsys/hierarchy state.
4010     */
4011    mutex_lock(&cgroup_mutex);
4012    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4013        struct cgroup_subsys *ss = subsys[i];
4014        if (ss == NULL)
4015            continue;
4016        seq_printf(m, "%s\t%d\t%d\t%d\n",
4017               ss->name, ss->root->hierarchy_id,
4018               ss->root->number_of_cgroups, !ss->disabled);
4019    }
4020    mutex_unlock(&cgroup_mutex);
4021    return 0;
4022}
4023
4024static int cgroupstats_open(struct inode *inode, struct file *file)
4025{
4026    return single_open(file, proc_cgroupstats_show, NULL);
4027}
4028
4029static const struct file_operations proc_cgroupstats_operations = {
4030    .open = cgroupstats_open,
4031    .read = seq_read,
4032    .llseek = seq_lseek,
4033    .release = single_release,
4034};
4035
4036/**
4037 * cgroup_fork - attach newly forked task to its parents cgroup.
4038 * @child: pointer to task_struct of forking parent process.
4039 *
4040 * Description: A task inherits its parent's cgroup at fork().
4041 *
4042 * A pointer to the shared css_set was automatically copied in
4043 * fork.c by dup_task_struct(). However, we ignore that copy, since
4044 * it was not made under the protection of RCU or cgroup_mutex, so
4045 * might no longer be a valid cgroup pointer. cgroup_attach_task() might
4046 * have already changed current->cgroups, allowing the previously
4047 * referenced cgroup group to be removed and freed.
4048 *
4049 * At the point that cgroup_fork() is called, 'current' is the parent
4050 * task, and the passed argument 'child' points to the child task.
4051 */
4052void cgroup_fork(struct task_struct *child)
4053{
4054    task_lock(current);
4055    child->cgroups = current->cgroups;
4056    get_css_set(child->cgroups);
4057    task_unlock(current);
4058    INIT_LIST_HEAD(&child->cg_list);
4059}
4060
4061/**
4062 * cgroup_fork_callbacks - run fork callbacks
4063 * @child: the new task
4064 *
4065 * Called on a new task very soon before adding it to the
4066 * tasklist. No need to take any locks since no-one can
4067 * be operating on this task.
4068 */
4069void cgroup_fork_callbacks(struct task_struct *child)
4070{
4071    if (need_forkexit_callback) {
4072        int i;
4073        /*
4074         * forkexit callbacks are only supported for builtin
4075         * subsystems, and the builtin section of the subsys array is
4076         * immutable, so we don't need to lock the subsys array here.
4077         */
4078        for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4079            struct cgroup_subsys *ss = subsys[i];
4080            if (ss->fork)
4081                ss->fork(ss, child);
4082        }
4083    }
4084}
4085
4086/**
4087 * cgroup_post_fork - called on a new task after adding it to the task list
4088 * @child: the task in question
4089 *
4090 * Adds the task to the list running through its css_set if necessary.
4091 * Has to be after the task is visible on the task list in case we race
4092 * with the first call to cgroup_iter_start() - to guarantee that the
4093 * new task ends up on its list.
4094 */
4095void cgroup_post_fork(struct task_struct *child)
4096{
4097    if (use_task_css_set_links) {
4098        write_lock(&css_set_lock);
4099        task_lock(child);
4100        if (list_empty(&child->cg_list))
4101            list_add(&child->cg_list, &child->cgroups->tasks);
4102        task_unlock(child);
4103        write_unlock(&css_set_lock);
4104    }
4105}
4106/**
4107 * cgroup_exit - detach cgroup from exiting task
4108 * @tsk: pointer to task_struct of exiting process
4109 * @run_callback: run exit callbacks?
4110 *
4111 * Description: Detach cgroup from @tsk and release it.
4112 *
4113 * Note that cgroups marked notify_on_release force every task in
4114 * them to take the global cgroup_mutex mutex when exiting.
4115 * This could impact scaling on very large systems. Be reluctant to
4116 * use notify_on_release cgroups where very high task exit scaling
4117 * is required on large systems.
4118 *
4119 * the_top_cgroup_hack:
4120 *
4121 * Set the exiting tasks cgroup to the root cgroup (top_cgroup).
4122 *
4123 * We call cgroup_exit() while the task is still competent to
4124 * handle notify_on_release(), then leave the task attached to the
4125 * root cgroup in each hierarchy for the remainder of its exit.
4126 *
4127 * To do this properly, we would increment the reference count on
4128 * top_cgroup, and near the very end of the kernel/exit.c do_exit()
4129 * code we would add a second cgroup function call, to drop that
4130 * reference. This would just create an unnecessary hot spot on
4131 * the top_cgroup reference count, to no avail.
4132 *
4133 * Normally, holding a reference to a cgroup without bumping its
4134 * count is unsafe. The cgroup could go away, or someone could
4135 * attach us to a different cgroup, decrementing the count on
4136 * the first cgroup that we never incremented. But in this case,
4137 * top_cgroup isn't going away, and either task has PF_EXITING set,
4138 * which wards off any cgroup_attach_task() attempts, or task is a failed
4139 * fork, never visible to cgroup_attach_task.
4140 */
4141void cgroup_exit(struct task_struct *tsk, int run_callbacks)
4142{
4143    int i;
4144    struct css_set *cg;
4145
4146    if (run_callbacks && need_forkexit_callback) {
4147        /*
4148         * modular subsystems can't use callbacks, so no need to lock
4149         * the subsys array
4150         */
4151        for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4152            struct cgroup_subsys *ss = subsys[i];
4153            if (ss->exit)
4154                ss->exit(ss, tsk);
4155        }
4156    }
4157
4158    /*
4159     * Unlink from the css_set task list if necessary.
4160     * Optimistically check cg_list before taking
4161     * css_set_lock
4162     */
4163    if (!list_empty(&tsk->cg_list)) {
4164        write_lock(&css_set_lock);
4165        if (!list_empty(&tsk->cg_list))
4166            list_del(&tsk->cg_list);
4167        write_unlock(&css_set_lock);
4168    }
4169
4170    /* Reassign the task to the init_css_set. */
4171    task_lock(tsk);
4172    cg = tsk->cgroups;
4173    tsk->cgroups = &init_css_set;
4174    task_unlock(tsk);
4175    if (cg)
4176        put_css_set_taskexit(cg);
4177}
4178
4179/**
4180 * cgroup_clone - clone the cgroup the given subsystem is attached to
4181 * @tsk: the task to be moved
4182 * @subsys: the given subsystem
4183 * @nodename: the name for the new cgroup
4184 *
4185 * Duplicate the current cgroup in the hierarchy that the given
4186 * subsystem is attached to, and move this task into the new
4187 * child.
4188 */
4189int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
4190                            char *nodename)
4191{
4192    struct dentry *dentry;
4193    int ret = 0;
4194    struct cgroup *parent, *child;
4195    struct inode *inode;
4196    struct css_set *cg;
4197    struct cgroupfs_root *root;
4198    struct cgroup_subsys *ss;
4199
4200    /* We shouldn't be called by an unregistered subsystem */
4201    BUG_ON(!subsys->active);
4202
4203    /* First figure out what hierarchy and cgroup we're dealing
4204     * with, and pin them so we can drop cgroup_mutex */
4205    mutex_lock(&cgroup_mutex);
4206 again:
4207    root = subsys->root;
4208    if (root == &rootnode) {
4209        mutex_unlock(&cgroup_mutex);
4210        return 0;
4211    }
4212
4213    /* Pin the hierarchy */
4214    if (!atomic_inc_not_zero(&root->sb->s_active)) {
4215        /* We race with the final deactivate_super() */
4216        mutex_unlock(&cgroup_mutex);
4217        return 0;
4218    }
4219
4220    /* Keep the cgroup alive */
4221    task_lock(tsk);
4222    parent = task_cgroup(tsk, subsys->subsys_id);
4223    cg = tsk->cgroups;
4224    get_css_set(cg);
4225    task_unlock(tsk);
4226
4227    mutex_unlock(&cgroup_mutex);
4228
4229    /* Now do the VFS work to create a cgroup */
4230    inode = parent->dentry->d_inode;
4231
4232    /* Hold the parent directory mutex across this operation to
4233     * stop anyone else deleting the new cgroup */
4234    mutex_lock(&inode->i_mutex);
4235    dentry = lookup_one_len(nodename, parent->dentry, strlen(nodename));
4236    if (IS_ERR(dentry)) {
4237        printk(KERN_INFO
4238               "cgroup: Couldn't allocate dentry for %s: %ld\n", nodename,
4239               PTR_ERR(dentry));
4240        ret = PTR_ERR(dentry);
4241        goto out_release;
4242    }
4243
4244    /* Create the cgroup directory, which also creates the cgroup */
4245    ret = vfs_mkdir(inode, dentry, 0755);
4246    child = __d_cgrp(dentry);
4247    dput(dentry);
4248    if (ret) {
4249        printk(KERN_INFO
4250               "Failed to create cgroup %s: %d\n", nodename,
4251               ret);
4252        goto out_release;
4253    }
4254
4255    /* The cgroup now exists. Retake cgroup_mutex and check
4256     * that we're still in the same state that we thought we
4257     * were. */
4258    mutex_lock(&cgroup_mutex);
4259    if ((root != subsys->root) ||
4260        (parent != task_cgroup(tsk, subsys->subsys_id))) {
4261        /* Aargh, we raced ... */
4262        mutex_unlock(&inode->i_mutex);
4263        put_css_set(cg);
4264
4265        deactivate_super(root->sb);
4266        /* The cgroup is still accessible in the VFS, but
4267         * we're not going to try to rmdir() it at this
4268         * point. */
4269        printk(KERN_INFO
4270               "Race in cgroup_clone() - leaking cgroup %s\n",
4271               nodename);
4272        goto again;
4273    }
4274
4275    /* do any required auto-setup */
4276    for_each_subsys(root, ss) {
4277        if (ss->post_clone)
4278            ss->post_clone(ss, child);
4279    }
4280
4281    /* All seems fine. Finish by moving the task into the new cgroup */
4282    ret = cgroup_attach_task(child, tsk);
4283    mutex_unlock(&cgroup_mutex);
4284
4285 out_release:
4286    mutex_unlock(&inode->i_mutex);
4287
4288    mutex_lock(&cgroup_mutex);
4289    put_css_set(cg);
4290    mutex_unlock(&cgroup_mutex);
4291    deactivate_super(root->sb);
4292    return ret;
4293}
4294
4295/**
4296 * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp
4297 * @cgrp: the cgroup in question
4298 * @task: the task in question
4299 *
4300 * See if @cgrp is a descendant of @task's cgroup in the appropriate
4301 * hierarchy.
4302 *
4303 * If we are sending in dummytop, then presumably we are creating
4304 * the top cgroup in the subsystem.
4305 *
4306 * Called only by the ns (nsproxy) cgroup.
4307 */
4308int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
4309{
4310    int ret;
4311    struct cgroup *target;
4312
4313    if (cgrp == dummytop)
4314        return 1;
4315
4316    target = task_cgroup_from_root(task, cgrp->root);
4317    while (cgrp != target && cgrp!= cgrp->top_cgroup)
4318        cgrp = cgrp->parent;
4319    ret = (cgrp == target);
4320    return ret;
4321}
4322
4323static void check_for_release(struct cgroup *cgrp)
4324{
4325    /* All of these checks rely on RCU to keep the cgroup
4326     * structure alive */
4327    if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count)
4328        && list_empty(&cgrp->children) && !cgroup_has_css_refs(cgrp)) {
4329        /* Control Group is currently removeable. If it's not
4330         * already queued for a userspace notification, queue
4331         * it now */
4332        int need_schedule_work = 0;
4333        spin_lock(&release_list_lock);
4334        if (!cgroup_is_removed(cgrp) &&
4335            list_empty(&cgrp->release_list)) {
4336            list_add(&cgrp->release_list, &release_list);
4337            need_schedule_work = 1;
4338        }
4339        spin_unlock(&release_list_lock);
4340        if (need_schedule_work)
4341            schedule_work(&release_agent_work);
4342    }
4343}
4344
4345/* Caller must verify that the css is not for root cgroup */
4346void __css_put(struct cgroup_subsys_state *css, int count)
4347{
4348    struct cgroup *cgrp = css->cgroup;
4349    int val;
4350    rcu_read_lock();
4351    val = atomic_sub_return(count, &css->refcnt);
4352    if (val == 1) {
4353        if (notify_on_release(cgrp)) {
4354            set_bit(CGRP_RELEASABLE, &cgrp->flags);
4355            check_for_release(cgrp);
4356        }
4357        cgroup_wakeup_rmdir_waiter(cgrp);
4358    }
4359    rcu_read_unlock();
4360    WARN_ON_ONCE(val < 1);
4361}
4362EXPORT_SYMBOL_GPL(__css_put);
4363
4364/*
4365 * Notify userspace when a cgroup is released, by running the
4366 * configured release agent with the name of the cgroup (path
4367 * relative to the root of cgroup file system) as the argument.
4368 *
4369 * Most likely, this user command will try to rmdir this cgroup.
4370 *
4371 * This races with the possibility that some other task will be
4372 * attached to this cgroup before it is removed, or that some other
4373 * user task will 'mkdir' a child cgroup of this cgroup. That's ok.
4374 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
4375 * unused, and this cgroup will be reprieved from its death sentence,
4376 * to continue to serve a useful existence. Next time it's released,
4377 * we will get notified again, if it still has 'notify_on_release' set.
4378 *
4379 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
4380 * means only wait until the task is successfully execve()'d. The
4381 * separate release agent task is forked by call_usermodehelper(),
4382 * then control in this thread returns here, without waiting for the
4383 * release agent task. We don't bother to wait because the caller of
4384 * this routine has no use for the exit status of the release agent
4385 * task, so no sense holding our caller up for that.
4386 */
4387static void cgroup_release_agent(struct work_struct *work)
4388{
4389    BUG_ON(work != &release_agent_work);
4390    mutex_lock(&cgroup_mutex);
4391    spin_lock(&release_list_lock);
4392    while (!list_empty(&release_list)) {
4393        char *argv[3], *envp[3];
4394        int i;
4395        char *pathbuf = NULL, *agentbuf = NULL;
4396        struct cgroup *cgrp = list_entry(release_list.next,
4397                            struct cgroup,
4398                            release_list);
4399        list_del_init(&cgrp->release_list);
4400        spin_unlock(&release_list_lock);
4401        pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
4402        if (!pathbuf)
4403            goto continue_free;
4404        if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
4405            goto continue_free;
4406        agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
4407        if (!agentbuf)
4408            goto continue_free;
4409
4410        i = 0;
4411        argv[i++] = agentbuf;
4412        argv[i++] = pathbuf;
4413        argv[i] = NULL;
4414
4415        i = 0;
4416        /* minimal command environment */
4417        envp[i++] = "HOME=/";
4418        envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
4419        envp[i] = NULL;
4420
4421        /* Drop the lock while we invoke the usermode helper,
4422         * since the exec could involve hitting disk and hence
4423         * be a slow process */
4424        mutex_unlock(&cgroup_mutex);
4425        call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
4426        mutex_lock(&cgroup_mutex);
4427 continue_free:
4428        kfree(pathbuf);
4429        kfree(agentbuf);
4430        spin_lock(&release_list_lock);
4431    }
4432    spin_unlock(&release_list_lock);
4433    mutex_unlock(&cgroup_mutex);
4434}
4435
4436static int __init cgroup_disable(char *str)
4437{
4438    int i;
4439    char *token;
4440
4441    while ((token = strsep(&str, ",")) != NULL) {
4442        if (!*token)
4443            continue;
4444        /*
4445         * cgroup_disable, being at boot time, can't know about module
4446         * subsystems, so we don't worry about them.
4447         */
4448        for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4449            struct cgroup_subsys *ss = subsys[i];
4450
4451            if (!strcmp(token, ss->name)) {
4452                ss->disabled = 1;
4453                printk(KERN_INFO "Disabling %s control group"
4454                    " subsystem\n", ss->name);
4455                break;
4456            }
4457        }
4458    }
4459    return 1;
4460}
4461__setup("cgroup_disable=", cgroup_disable);
4462
4463/*
4464 * Functons for CSS ID.
4465 */
4466
4467/*
4468 *To get ID other than 0, this should be called when !cgroup_is_removed().
4469 */
4470unsigned short css_id(struct cgroup_subsys_state *css)
4471{
4472    struct css_id *cssid;
4473
4474    /*
4475     * This css_id() can return correct value when somone has refcnt
4476     * on this or this is under rcu_read_lock(). Once css->id is allocated,
4477     * it's unchanged until freed.
4478     */
4479    cssid = rcu_dereference_check(css->id,
4480            rcu_read_lock_held() || atomic_read(&css->refcnt));
4481
4482    if (cssid)
4483        return cssid->id;
4484    return 0;
4485}
4486EXPORT_SYMBOL_GPL(css_id);
4487
4488unsigned short css_depth(struct cgroup_subsys_state *css)
4489{
4490    struct css_id *cssid;
4491
4492    cssid = rcu_dereference_check(css->id,
4493            rcu_read_lock_held() || atomic_read(&css->refcnt));
4494
4495    if (cssid)
4496        return cssid->depth;
4497    return 0;
4498}
4499EXPORT_SYMBOL_GPL(css_depth);
4500
4501/**
4502 * css_is_ancestor - test "root" css is an ancestor of "child"
4503 * @child: the css to be tested.
4504 * @root: the css supporsed to be an ancestor of the child.
4505 *
4506 * Returns true if "root" is an ancestor of "child" in its hierarchy. Because
4507 * this function reads css->id, this use rcu_dereference() and rcu_read_lock().
4508 * But, considering usual usage, the csses should be valid objects after test.
4509 * Assuming that the caller will do some action to the child if this returns
4510 * returns true, the caller must take "child";s reference count.
4511 * If "child" is valid object and this returns true, "root" is valid, too.
4512 */
4513
4514bool css_is_ancestor(struct cgroup_subsys_state *child,
4515            const struct cgroup_subsys_state *root)
4516{
4517    struct css_id *child_id;
4518    struct css_id *root_id;
4519    bool ret = true;
4520
4521    rcu_read_lock();
4522    child_id = rcu_dereference(child->id);
4523    root_id = rcu_dereference(root->id);
4524    if (!child_id
4525        || !root_id
4526        || (child_id->depth < root_id->depth)
4527        || (child_id->stack[root_id->depth] != root_id->id))
4528        ret = false;
4529    rcu_read_unlock();
4530    return ret;
4531}
4532
4533static void __free_css_id_cb(struct rcu_head *head)
4534{
4535    struct css_id *id;
4536
4537    id = container_of(head, struct css_id, rcu_head);
4538    kfree(id);
4539}
4540
4541void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
4542{
4543    struct css_id *id = css->id;
4544    /* When this is called before css_id initialization, id can be NULL */
4545    if (!id)
4546        return;
4547
4548    BUG_ON(!ss->use_id);
4549
4550    rcu_assign_pointer(id->css, NULL);
4551    rcu_assign_pointer(css->id, NULL);
4552    spin_lock(&ss->id_lock);
4553    idr_remove(&ss->idr, id->id);
4554    spin_unlock(&ss->id_lock);
4555    call_rcu(&id->rcu_head, __free_css_id_cb);
4556}
4557EXPORT_SYMBOL_GPL(free_css_id);
4558
4559/*
4560 * This is called by init or create(). Then, calls to this function are
4561 * always serialized (By cgroup_mutex() at create()).
4562 */
4563
4564static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
4565{
4566    struct css_id *newid;
4567    int myid, error, size;
4568
4569    BUG_ON(!ss->use_id);
4570
4571    size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
4572    newid = kzalloc(size, GFP_KERNEL);
4573    if (!newid)
4574        return ERR_PTR(-ENOMEM);
4575    /* get id */
4576    if (unlikely(!idr_pre_get(&ss->idr, GFP_KERNEL))) {
4577        error = -ENOMEM;
4578        goto err_out;
4579    }
4580    spin_lock(&ss->id_lock);
4581    /* Don't use 0. allocates an ID of 1-65535 */
4582    error = idr_get_new_above(&ss->idr, newid, 1, &myid);
4583    spin_unlock(&ss->id_lock);
4584
4585    /* Returns error when there are no free spaces for new ID.*/
4586    if (error) {
4587        error = -ENOSPC;
4588        goto err_out;
4589    }
4590    if (myid > CSS_ID_MAX)
4591        goto remove_idr;
4592
4593    newid->id = myid;
4594    newid->depth = depth;
4595    return newid;
4596remove_idr:
4597    error = -ENOSPC;
4598    spin_lock(&ss->id_lock);
4599    idr_remove(&ss->idr, myid);
4600    spin_unlock(&ss->id_lock);
4601err_out:
4602    kfree(newid);
4603    return ERR_PTR(error);
4604
4605}
4606
4607static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
4608                        struct cgroup_subsys_state *rootcss)
4609{
4610    struct css_id *newid;
4611
4612    spin_lock_init(&ss->id_lock);
4613    idr_init(&ss->idr);
4614
4615    newid = get_new_cssid(ss, 0);
4616    if (IS_ERR(newid))
4617        return PTR_ERR(newid);
4618
4619    newid->stack[0] = newid->id;
4620    newid->css = rootcss;
4621    rootcss->id = newid;
4622    return 0;
4623}
4624
4625static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
4626            struct cgroup *child)
4627{
4628    int subsys_id, i, depth = 0;
4629    struct cgroup_subsys_state *parent_css, *child_css;
4630    struct css_id *child_id, *parent_id;
4631
4632    subsys_id = ss->subsys_id;
4633    parent_css = parent->subsys[subsys_id];
4634    child_css = child->subsys[subsys_id];
4635    parent_id = parent_css->id;
4636    depth = parent_id->depth + 1;
4637
4638    child_id = get_new_cssid(ss, depth);
4639    if (IS_ERR(child_id))
4640        return PTR_ERR(child_id);
4641
4642    for (i = 0; i < depth; i++)
4643        child_id->stack[i] = parent_id->stack[i];
4644    child_id->stack[depth] = child_id->id;
4645    /*
4646     * child_id->css pointer will be set after this cgroup is available
4647     * see cgroup_populate_dir()
4648     */
4649    rcu_assign_pointer(child_css->id, child_id);
4650
4651    return 0;
4652}
4653
4654/**
4655 * css_lookup - lookup css by id
4656 * @ss: cgroup subsys to be looked into.
4657 * @id: the id
4658 *
4659 * Returns pointer to cgroup_subsys_state if there is valid one with id.
4660 * NULL if not. Should be called under rcu_read_lock()
4661 */
4662struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
4663{
4664    struct css_id *cssid = NULL;
4665
4666    BUG_ON(!ss->use_id);
4667    cssid = idr_find(&ss->idr, id);
4668
4669    if (unlikely(!cssid))
4670        return NULL;
4671
4672    return rcu_dereference(cssid->css);
4673}
4674EXPORT_SYMBOL_GPL(css_lookup);
4675
4676/**
4677 * css_get_next - lookup next cgroup under specified hierarchy.
4678 * @ss: pointer to subsystem
4679 * @id: current position of iteration.
4680 * @root: pointer to css. search tree under this.
4681 * @foundid: position of found object.
4682 *
4683 * Search next css under the specified hierarchy of rootid. Calling under
4684 * rcu_read_lock() is necessary. Returns NULL if it reaches the end.
4685 */
4686struct cgroup_subsys_state *
4687css_get_next(struct cgroup_subsys *ss, int id,
4688         struct cgroup_subsys_state *root, int *foundid)
4689{
4690    struct cgroup_subsys_state *ret = NULL;
4691    struct css_id *tmp;
4692    int tmpid;
4693    int rootid = css_id(root);
4694    int depth = css_depth(root);
4695
4696    if (!rootid)
4697        return NULL;
4698
4699    BUG_ON(!ss->use_id);
4700    /* fill start point for scan */
4701    tmpid = id;
4702    while (1) {
4703        /*
4704         * scan next entry from bitmap(tree), tmpid is updated after
4705         * idr_get_next().
4706         */
4707        spin_lock(&ss->id_lock);
4708        tmp = idr_get_next(&ss->idr, &tmpid);
4709        spin_unlock(&ss->id_lock);
4710
4711        if (!tmp)
4712            break;
4713        if (tmp->depth >= depth && tmp->stack[depth] == rootid) {
4714            ret = rcu_dereference(tmp->css);
4715            if (ret) {
4716                *foundid = tmpid;
4717                break;
4718            }
4719        }
4720        /* continue to scan from next id */
4721        tmpid = tmpid + 1;
4722    }
4723    return ret;
4724}
4725
4726#ifdef CONFIG_CGROUP_DEBUG
4727static struct cgroup_subsys_state *debug_create(struct cgroup_subsys *ss,
4728                           struct cgroup *cont)
4729{
4730    struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
4731
4732    if (!css)
4733        return ERR_PTR(-ENOMEM);
4734
4735    return css;
4736}
4737
4738static void debug_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
4739{
4740    kfree(cont->subsys[debug_subsys_id]);
4741}
4742
4743static u64 cgroup_refcount_read(struct cgroup *cont, struct cftype *cft)
4744{
4745    return atomic_read(&cont->count);
4746}
4747
4748static u64 debug_taskcount_read(struct cgroup *cont, struct cftype *cft)
4749{
4750    return cgroup_task_count(cont);
4751}
4752
4753static u64 current_css_set_read(struct cgroup *cont, struct cftype *cft)
4754{
4755    return (u64)(unsigned long)current->cgroups;
4756}
4757
4758static u64 current_css_set_refcount_read(struct cgroup *cont,
4759                       struct cftype *cft)
4760{
4761    u64 count;
4762
4763    rcu_read_lock();
4764    count = atomic_read(&current->cgroups->refcount);
4765    rcu_read_unlock();
4766    return count;
4767}
4768
4769static int current_css_set_cg_links_read(struct cgroup *cont,
4770                     struct cftype *cft,
4771                     struct seq_file *seq)
4772{
4773    struct cg_cgroup_link *link;
4774    struct css_set *cg;
4775
4776    read_lock(&css_set_lock);
4777    rcu_read_lock();
4778    cg = rcu_dereference(current->cgroups);
4779    list_for_each_entry(link, &cg->cg_links, cg_link_list) {
4780        struct cgroup *c = link->cgrp;
4781        const char *name;
4782
4783        if (c->dentry)
4784            name = c->dentry->d_name.name;
4785        else
4786            name = "?";
4787        seq_printf(seq, "Root %d group %s\n",
4788               c->root->hierarchy_id, name);
4789    }
4790    rcu_read_unlock();
4791    read_unlock(&css_set_lock);
4792    return 0;
4793}
4794
4795#define MAX_TASKS_SHOWN_PER_CSS 25
4796static int cgroup_css_links_read(struct cgroup *cont,
4797                 struct cftype *cft,
4798                 struct seq_file *seq)
4799{
4800    struct cg_cgroup_link *link;
4801
4802    read_lock(&css_set_lock);
4803    list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
4804        struct css_set *cg = link->cg;
4805        struct task_struct *task;
4806        int count = 0;
4807        seq_printf(seq, "css_set %p\n", cg);
4808        list_for_each_entry(task, &cg->tasks, cg_list) {
4809            if (count++ > MAX_TASKS_SHOWN_PER_CSS) {
4810                seq_puts(seq, " ...\n");
4811                break;
4812            } else {
4813                seq_printf(seq, " task %d\n",
4814                       task_pid_vnr(task));
4815            }
4816        }
4817    }
4818    read_unlock(&css_set_lock);
4819    return 0;
4820}
4821
4822static u64 releasable_read(struct cgroup *cgrp, struct cftype *cft)
4823{
4824    return test_bit(CGRP_RELEASABLE, &cgrp->flags);
4825}
4826
4827static struct cftype debug_files[] = {
4828    {
4829        .name = "cgroup_refcount",
4830        .read_u64 = cgroup_refcount_read,
4831    },
4832    {
4833        .name = "taskcount",
4834        .read_u64 = debug_taskcount_read,
4835    },
4836
4837    {
4838        .name = "current_css_set",
4839        .read_u64 = current_css_set_read,
4840    },
4841
4842    {
4843        .name = "current_css_set_refcount",
4844        .read_u64 = current_css_set_refcount_read,
4845    },
4846
4847    {
4848        .name = "current_css_set_cg_links",
4849        .read_seq_string = current_css_set_cg_links_read,
4850    },
4851
4852    {
4853        .name = "cgroup_css_links",
4854        .read_seq_string = cgroup_css_links_read,
4855    },
4856
4857    {
4858        .name = "releasable",
4859        .read_u64 = releasable_read,
4860    },
4861};
4862
4863static int debug_populate(struct cgroup_subsys *ss, struct cgroup *cont)
4864{
4865    return cgroup_add_files(cont, ss, debug_files,
4866                ARRAY_SIZE(debug_files));
4867}
4868
4869struct cgroup_subsys debug_subsys = {
4870    .name = "debug",
4871    .create = debug_create,
4872    .destroy = debug_destroy,
4873    .populate = debug_populate,
4874    .subsys_id = debug_subsys_id,
4875};
4876#endif /* CONFIG_CGROUP_DEBUG */
4877

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