Root/kernel/cgroup.c

1/*
2 * Generic process-grouping system.
3 *
4 * Based originally on the cpuset system, extracted by Paul Menage
5 * Copyright (C) 2006 Google, Inc
6 *
7 * Notifications support
8 * Copyright (C) 2009 Nokia Corporation
9 * Author: Kirill A. Shutemov
10 *
11 * Copyright notices from the original cpuset code:
12 * --------------------------------------------------
13 * Copyright (C) 2003 BULL SA.
14 * Copyright (C) 2004-2006 Silicon Graphics, Inc.
15 *
16 * Portions derived from Patrick Mochel's sysfs code.
17 * sysfs is Copyright (c) 2001-3 Patrick Mochel
18 *
19 * 2003-10-10 Written by Simon Derr.
20 * 2003-10-22 Updates by Stephen Hemminger.
21 * 2004 May-July Rework by Paul Jackson.
22 * ---------------------------------------------------
23 *
24 * This file is subject to the terms and conditions of the GNU General Public
25 * License. See the file COPYING in the main directory of the Linux
26 * distribution for more details.
27 */
28
29#include <linux/cgroup.h>
30#include <linux/cred.h>
31#include <linux/ctype.h>
32#include <linux/errno.h>
33#include <linux/fs.h>
34#include <linux/init_task.h>
35#include <linux/kernel.h>
36#include <linux/list.h>
37#include <linux/mm.h>
38#include <linux/mutex.h>
39#include <linux/mount.h>
40#include <linux/pagemap.h>
41#include <linux/proc_fs.h>
42#include <linux/rcupdate.h>
43#include <linux/sched.h>
44#include <linux/backing-dev.h>
45#include <linux/seq_file.h>
46#include <linux/slab.h>
47#include <linux/magic.h>
48#include <linux/spinlock.h>
49#include <linux/string.h>
50#include <linux/sort.h>
51#include <linux/kmod.h>
52#include <linux/module.h>
53#include <linux/delayacct.h>
54#include <linux/cgroupstats.h>
55#include <linux/hash.h>
56#include <linux/namei.h>
57#include <linux/pid_namespace.h>
58#include <linux/idr.h>
59#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
60#include <linux/eventfd.h>
61#include <linux/poll.h>
62#include <linux/flex_array.h> /* used in cgroup_attach_proc */
63#include <linux/kthread.h>
64
65#include <linux/atomic.h>
66
67/* css deactivation bias, makes css->refcnt negative to deny new trygets */
68#define CSS_DEACT_BIAS INT_MIN
69
70/*
71 * cgroup_mutex is the master lock. Any modification to cgroup or its
72 * hierarchy must be performed while holding it.
73 *
74 * cgroup_root_mutex nests inside cgroup_mutex and should be held to modify
75 * cgroupfs_root of any cgroup hierarchy - subsys list, flags,
76 * release_agent_path and so on. Modifying requires both cgroup_mutex and
77 * cgroup_root_mutex. Readers can acquire either of the two. This is to
78 * break the following locking order cycle.
79 *
80 * A. cgroup_mutex -> cred_guard_mutex -> s_type->i_mutex_key -> namespace_sem
81 * B. namespace_sem -> cgroup_mutex
82 *
83 * B happens only through cgroup_show_options() and using cgroup_root_mutex
84 * breaks it.
85 */
86static DEFINE_MUTEX(cgroup_mutex);
87static DEFINE_MUTEX(cgroup_root_mutex);
88
89/*
90 * Generate an array of cgroup subsystem pointers. At boot time, this is
91 * populated up to CGROUP_BUILTIN_SUBSYS_COUNT, and modular subsystems are
92 * registered after that. The mutable section of this array is protected by
93 * cgroup_mutex.
94 */
95#define SUBSYS(_x) &_x ## _subsys,
96static struct cgroup_subsys *subsys[CGROUP_SUBSYS_COUNT] = {
97#include <linux/cgroup_subsys.h>
98};
99
100#define MAX_CGROUP_ROOT_NAMELEN 64
101
102/*
103 * A cgroupfs_root represents the root of a cgroup hierarchy,
104 * and may be associated with a superblock to form an active
105 * hierarchy
106 */
107struct cgroupfs_root {
108    struct super_block *sb;
109
110    /*
111     * The bitmask of subsystems intended to be attached to this
112     * hierarchy
113     */
114    unsigned long subsys_bits;
115
116    /* Unique id for this hierarchy. */
117    int hierarchy_id;
118
119    /* The bitmask of subsystems currently attached to this hierarchy */
120    unsigned long actual_subsys_bits;
121
122    /* A list running through the attached subsystems */
123    struct list_head subsys_list;
124
125    /* The root cgroup for this hierarchy */
126    struct cgroup top_cgroup;
127
128    /* Tracks how many cgroups are currently defined in hierarchy.*/
129    int number_of_cgroups;
130
131    /* A list running through the active hierarchies */
132    struct list_head root_list;
133
134    /* All cgroups on this root, cgroup_mutex protected */
135    struct list_head allcg_list;
136
137    /* Hierarchy-specific flags */
138    unsigned long flags;
139
140    /* The path to use for release notifications. */
141    char release_agent_path[PATH_MAX];
142
143    /* The name for this hierarchy - may be empty */
144    char name[MAX_CGROUP_ROOT_NAMELEN];
145};
146
147/*
148 * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
149 * subsystems that are otherwise unattached - it never has more than a
150 * single cgroup, and all tasks are part of that cgroup.
151 */
152static struct cgroupfs_root rootnode;
153
154/*
155 * cgroupfs file entry, pointed to from leaf dentry->d_fsdata.
156 */
157struct cfent {
158    struct list_head node;
159    struct dentry *dentry;
160    struct cftype *type;
161};
162
163/*
164 * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
165 * cgroup_subsys->use_id != 0.
166 */
167#define CSS_ID_MAX (65535)
168struct css_id {
169    /*
170     * The css to which this ID points. This pointer is set to valid value
171     * after cgroup is populated. If cgroup is removed, this will be NULL.
172     * This pointer is expected to be RCU-safe because destroy()
173     * is called after synchronize_rcu(). But for safe use, css_is_removed()
174     * css_tryget() should be used for avoiding race.
175     */
176    struct cgroup_subsys_state __rcu *css;
177    /*
178     * ID of this css.
179     */
180    unsigned short id;
181    /*
182     * Depth in hierarchy which this ID belongs to.
183     */
184    unsigned short depth;
185    /*
186     * ID is freed by RCU. (and lookup routine is RCU safe.)
187     */
188    struct rcu_head rcu_head;
189    /*
190     * Hierarchy of CSS ID belongs to.
191     */
192    unsigned short stack[0]; /* Array of Length (depth+1) */
193};
194
195/*
196 * cgroup_event represents events which userspace want to receive.
197 */
198struct cgroup_event {
199    /*
200     * Cgroup which the event belongs to.
201     */
202    struct cgroup *cgrp;
203    /*
204     * Control file which the event associated.
205     */
206    struct cftype *cft;
207    /*
208     * eventfd to signal userspace about the event.
209     */
210    struct eventfd_ctx *eventfd;
211    /*
212     * Each of these stored in a list by the cgroup.
213     */
214    struct list_head list;
215    /*
216     * All fields below needed to unregister event when
217     * userspace closes eventfd.
218     */
219    poll_table pt;
220    wait_queue_head_t *wqh;
221    wait_queue_t wait;
222    struct work_struct remove;
223};
224
225/* The list of hierarchy roots */
226
227static LIST_HEAD(roots);
228static int root_count;
229
230static DEFINE_IDA(hierarchy_ida);
231static int next_hierarchy_id;
232static DEFINE_SPINLOCK(hierarchy_id_lock);
233
234/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
235#define dummytop (&rootnode.top_cgroup)
236
237/* This flag indicates whether tasks in the fork and exit paths should
238 * check for fork/exit handlers to call. This avoids us having to do
239 * extra work in the fork/exit path if none of the subsystems need to
240 * be called.
241 */
242static int need_forkexit_callback __read_mostly;
243
244#ifdef CONFIG_PROVE_LOCKING
245int cgroup_lock_is_held(void)
246{
247    return lockdep_is_held(&cgroup_mutex);
248}
249#else /* #ifdef CONFIG_PROVE_LOCKING */
250int cgroup_lock_is_held(void)
251{
252    return mutex_is_locked(&cgroup_mutex);
253}
254#endif /* #else #ifdef CONFIG_PROVE_LOCKING */
255
256EXPORT_SYMBOL_GPL(cgroup_lock_is_held);
257
258static int css_unbias_refcnt(int refcnt)
259{
260    return refcnt >= 0 ? refcnt : refcnt - CSS_DEACT_BIAS;
261}
262
263/* the current nr of refs, always >= 0 whether @css is deactivated or not */
264static int css_refcnt(struct cgroup_subsys_state *css)
265{
266    int v = atomic_read(&css->refcnt);
267
268    return css_unbias_refcnt(v);
269}
270
271/* convenient tests for these bits */
272inline int cgroup_is_removed(const struct cgroup *cgrp)
273{
274    return test_bit(CGRP_REMOVED, &cgrp->flags);
275}
276
277/* bits in struct cgroupfs_root flags field */
278enum {
279    ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
280};
281
282static int cgroup_is_releasable(const struct cgroup *cgrp)
283{
284    const int bits =
285        (1 << CGRP_RELEASABLE) |
286        (1 << CGRP_NOTIFY_ON_RELEASE);
287    return (cgrp->flags & bits) == bits;
288}
289
290static int notify_on_release(const struct cgroup *cgrp)
291{
292    return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
293}
294
295static int clone_children(const struct cgroup *cgrp)
296{
297    return test_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
298}
299
300/*
301 * for_each_subsys() allows you to iterate on each subsystem attached to
302 * an active hierarchy
303 */
304#define for_each_subsys(_root, _ss) \
305list_for_each_entry(_ss, &_root->subsys_list, sibling)
306
307/* for_each_active_root() allows you to iterate across the active hierarchies */
308#define for_each_active_root(_root) \
309list_for_each_entry(_root, &roots, root_list)
310
311static inline struct cgroup *__d_cgrp(struct dentry *dentry)
312{
313    return dentry->d_fsdata;
314}
315
316static inline struct cfent *__d_cfe(struct dentry *dentry)
317{
318    return dentry->d_fsdata;
319}
320
321static inline struct cftype *__d_cft(struct dentry *dentry)
322{
323    return __d_cfe(dentry)->type;
324}
325
326/* the list of cgroups eligible for automatic release. Protected by
327 * release_list_lock */
328static LIST_HEAD(release_list);
329static DEFINE_RAW_SPINLOCK(release_list_lock);
330static void cgroup_release_agent(struct work_struct *work);
331static DECLARE_WORK(release_agent_work, cgroup_release_agent);
332static void check_for_release(struct cgroup *cgrp);
333
334/* Link structure for associating css_set objects with cgroups */
335struct cg_cgroup_link {
336    /*
337     * List running through cg_cgroup_links associated with a
338     * cgroup, anchored on cgroup->css_sets
339     */
340    struct list_head cgrp_link_list;
341    struct cgroup *cgrp;
342    /*
343     * List running through cg_cgroup_links pointing at a
344     * single css_set object, anchored on css_set->cg_links
345     */
346    struct list_head cg_link_list;
347    struct css_set *cg;
348};
349
350/* The default css_set - used by init and its children prior to any
351 * hierarchies being mounted. It contains a pointer to the root state
352 * for each subsystem. Also used to anchor the list of css_sets. Not
353 * reference-counted, to improve performance when child cgroups
354 * haven't been created.
355 */
356
357static struct css_set init_css_set;
358static struct cg_cgroup_link init_css_set_link;
359
360static int cgroup_init_idr(struct cgroup_subsys *ss,
361               struct cgroup_subsys_state *css);
362
363/* css_set_lock protects the list of css_set objects, and the
364 * chain of tasks off each css_set. Nests outside task->alloc_lock
365 * due to cgroup_iter_start() */
366static DEFINE_RWLOCK(css_set_lock);
367static int css_set_count;
368
369/*
370 * hash table for cgroup groups. This improves the performance to find
371 * an existing css_set. This hash doesn't (currently) take into
372 * account cgroups in empty hierarchies.
373 */
374#define CSS_SET_HASH_BITS 7
375#define CSS_SET_TABLE_SIZE (1 << CSS_SET_HASH_BITS)
376static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];
377
378static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
379{
380    int i;
381    int index;
382    unsigned long tmp = 0UL;
383
384    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
385        tmp += (unsigned long)css[i];
386    tmp = (tmp >> 16) ^ tmp;
387
388    index = hash_long(tmp, CSS_SET_HASH_BITS);
389
390    return &css_set_table[index];
391}
392
393/* We don't maintain the lists running through each css_set to its
394 * task until after the first call to cgroup_iter_start(). This
395 * reduces the fork()/exit() overhead for people who have cgroups
396 * compiled into their kernel but not actually in use */
397static int use_task_css_set_links __read_mostly;
398
399static void __put_css_set(struct css_set *cg, int taskexit)
400{
401    struct cg_cgroup_link *link;
402    struct cg_cgroup_link *saved_link;
403    /*
404     * Ensure that the refcount doesn't hit zero while any readers
405     * can see it. Similar to atomic_dec_and_lock(), but for an
406     * rwlock
407     */
408    if (atomic_add_unless(&cg->refcount, -1, 1))
409        return;
410    write_lock(&css_set_lock);
411    if (!atomic_dec_and_test(&cg->refcount)) {
412        write_unlock(&css_set_lock);
413        return;
414    }
415
416    /* This css_set is dead. unlink it and release cgroup refcounts */
417    hlist_del(&cg->hlist);
418    css_set_count--;
419
420    list_for_each_entry_safe(link, saved_link, &cg->cg_links,
421                 cg_link_list) {
422        struct cgroup *cgrp = link->cgrp;
423        list_del(&link->cg_link_list);
424        list_del(&link->cgrp_link_list);
425        if (atomic_dec_and_test(&cgrp->count) &&
426            notify_on_release(cgrp)) {
427            if (taskexit)
428                set_bit(CGRP_RELEASABLE, &cgrp->flags);
429            check_for_release(cgrp);
430        }
431
432        kfree(link);
433    }
434
435    write_unlock(&css_set_lock);
436    kfree_rcu(cg, rcu_head);
437}
438
439/*
440 * refcounted get/put for css_set objects
441 */
442static inline void get_css_set(struct css_set *cg)
443{
444    atomic_inc(&cg->refcount);
445}
446
447static inline void put_css_set(struct css_set *cg)
448{
449    __put_css_set(cg, 0);
450}
451
452static inline void put_css_set_taskexit(struct css_set *cg)
453{
454    __put_css_set(cg, 1);
455}
456
457/*
458 * compare_css_sets - helper function for find_existing_css_set().
459 * @cg: candidate css_set being tested
460 * @old_cg: existing css_set for a task
461 * @new_cgrp: cgroup that's being entered by the task
462 * @template: desired set of css pointers in css_set (pre-calculated)
463 *
464 * Returns true if "cg" matches "old_cg" except for the hierarchy
465 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
466 */
467static bool compare_css_sets(struct css_set *cg,
468                 struct css_set *old_cg,
469                 struct cgroup *new_cgrp,
470                 struct cgroup_subsys_state *template[])
471{
472    struct list_head *l1, *l2;
473
474    if (memcmp(template, cg->subsys, sizeof(cg->subsys))) {
475        /* Not all subsystems matched */
476        return false;
477    }
478
479    /*
480     * Compare cgroup pointers in order to distinguish between
481     * different cgroups in heirarchies with no subsystems. We
482     * could get by with just this check alone (and skip the
483     * memcmp above) but on most setups the memcmp check will
484     * avoid the need for this more expensive check on almost all
485     * candidates.
486     */
487
488    l1 = &cg->cg_links;
489    l2 = &old_cg->cg_links;
490    while (1) {
491        struct cg_cgroup_link *cgl1, *cgl2;
492        struct cgroup *cg1, *cg2;
493
494        l1 = l1->next;
495        l2 = l2->next;
496        /* See if we reached the end - both lists are equal length. */
497        if (l1 == &cg->cg_links) {
498            BUG_ON(l2 != &old_cg->cg_links);
499            break;
500        } else {
501            BUG_ON(l2 == &old_cg->cg_links);
502        }
503        /* Locate the cgroups associated with these links. */
504        cgl1 = list_entry(l1, struct cg_cgroup_link, cg_link_list);
505        cgl2 = list_entry(l2, struct cg_cgroup_link, cg_link_list);
506        cg1 = cgl1->cgrp;
507        cg2 = cgl2->cgrp;
508        /* Hierarchies should be linked in the same order. */
509        BUG_ON(cg1->root != cg2->root);
510
511        /*
512         * If this hierarchy is the hierarchy of the cgroup
513         * that's changing, then we need to check that this
514         * css_set points to the new cgroup; if it's any other
515         * hierarchy, then this css_set should point to the
516         * same cgroup as the old css_set.
517         */
518        if (cg1->root == new_cgrp->root) {
519            if (cg1 != new_cgrp)
520                return false;
521        } else {
522            if (cg1 != cg2)
523                return false;
524        }
525    }
526    return true;
527}
528
529/*
530 * find_existing_css_set() is a helper for
531 * find_css_set(), and checks to see whether an existing
532 * css_set is suitable.
533 *
534 * oldcg: the cgroup group that we're using before the cgroup
535 * transition
536 *
537 * cgrp: the cgroup that we're moving into
538 *
539 * template: location in which to build the desired set of subsystem
540 * state objects for the new cgroup group
541 */
542static struct css_set *find_existing_css_set(
543    struct css_set *oldcg,
544    struct cgroup *cgrp,
545    struct cgroup_subsys_state *template[])
546{
547    int i;
548    struct cgroupfs_root *root = cgrp->root;
549    struct hlist_head *hhead;
550    struct hlist_node *node;
551    struct css_set *cg;
552
553    /*
554     * Build the set of subsystem state objects that we want to see in the
555     * new css_set. while subsystems can change globally, the entries here
556     * won't change, so no need for locking.
557     */
558    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
559        if (root->subsys_bits & (1UL << i)) {
560            /* Subsystem is in this hierarchy. So we want
561             * the subsystem state from the new
562             * cgroup */
563            template[i] = cgrp->subsys[i];
564        } else {
565            /* Subsystem is not in this hierarchy, so we
566             * don't want to change the subsystem state */
567            template[i] = oldcg->subsys[i];
568        }
569    }
570
571    hhead = css_set_hash(template);
572    hlist_for_each_entry(cg, node, hhead, hlist) {
573        if (!compare_css_sets(cg, oldcg, cgrp, template))
574            continue;
575
576        /* This css_set matches what we need */
577        return cg;
578    }
579
580    /* No existing cgroup group matched */
581    return NULL;
582}
583
584static void free_cg_links(struct list_head *tmp)
585{
586    struct cg_cgroup_link *link;
587    struct cg_cgroup_link *saved_link;
588
589    list_for_each_entry_safe(link, saved_link, tmp, cgrp_link_list) {
590        list_del(&link->cgrp_link_list);
591        kfree(link);
592    }
593}
594
595/*
596 * allocate_cg_links() allocates "count" cg_cgroup_link structures
597 * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
598 * success or a negative error
599 */
600static int allocate_cg_links(int count, struct list_head *tmp)
601{
602    struct cg_cgroup_link *link;
603    int i;
604    INIT_LIST_HEAD(tmp);
605    for (i = 0; i < count; i++) {
606        link = kmalloc(sizeof(*link), GFP_KERNEL);
607        if (!link) {
608            free_cg_links(tmp);
609            return -ENOMEM;
610        }
611        list_add(&link->cgrp_link_list, tmp);
612    }
613    return 0;
614}
615
616/**
617 * link_css_set - a helper function to link a css_set to a cgroup
618 * @tmp_cg_links: cg_cgroup_link objects allocated by allocate_cg_links()
619 * @cg: the css_set to be linked
620 * @cgrp: the destination cgroup
621 */
622static void link_css_set(struct list_head *tmp_cg_links,
623             struct css_set *cg, struct cgroup *cgrp)
624{
625    struct cg_cgroup_link *link;
626
627    BUG_ON(list_empty(tmp_cg_links));
628    link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
629                cgrp_link_list);
630    link->cg = cg;
631    link->cgrp = cgrp;
632    atomic_inc(&cgrp->count);
633    list_move(&link->cgrp_link_list, &cgrp->css_sets);
634    /*
635     * Always add links to the tail of the list so that the list
636     * is sorted by order of hierarchy creation
637     */
638    list_add_tail(&link->cg_link_list, &cg->cg_links);
639}
640
641/*
642 * find_css_set() takes an existing cgroup group and a
643 * cgroup object, and returns a css_set object that's
644 * equivalent to the old group, but with the given cgroup
645 * substituted into the appropriate hierarchy. Must be called with
646 * cgroup_mutex held
647 */
648static struct css_set *find_css_set(
649    struct css_set *oldcg, struct cgroup *cgrp)
650{
651    struct css_set *res;
652    struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
653
654    struct list_head tmp_cg_links;
655
656    struct hlist_head *hhead;
657    struct cg_cgroup_link *link;
658
659    /* First see if we already have a cgroup group that matches
660     * the desired set */
661    read_lock(&css_set_lock);
662    res = find_existing_css_set(oldcg, cgrp, template);
663    if (res)
664        get_css_set(res);
665    read_unlock(&css_set_lock);
666
667    if (res)
668        return res;
669
670    res = kmalloc(sizeof(*res), GFP_KERNEL);
671    if (!res)
672        return NULL;
673
674    /* Allocate all the cg_cgroup_link objects that we'll need */
675    if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
676        kfree(res);
677        return NULL;
678    }
679
680    atomic_set(&res->refcount, 1);
681    INIT_LIST_HEAD(&res->cg_links);
682    INIT_LIST_HEAD(&res->tasks);
683    INIT_HLIST_NODE(&res->hlist);
684
685    /* Copy the set of subsystem state objects generated in
686     * find_existing_css_set() */
687    memcpy(res->subsys, template, sizeof(res->subsys));
688
689    write_lock(&css_set_lock);
690    /* Add reference counts and links from the new css_set. */
691    list_for_each_entry(link, &oldcg->cg_links, cg_link_list) {
692        struct cgroup *c = link->cgrp;
693        if (c->root == cgrp->root)
694            c = cgrp;
695        link_css_set(&tmp_cg_links, res, c);
696    }
697
698    BUG_ON(!list_empty(&tmp_cg_links));
699
700    css_set_count++;
701
702    /* Add this cgroup group to the hash table */
703    hhead = css_set_hash(res->subsys);
704    hlist_add_head(&res->hlist, hhead);
705
706    write_unlock(&css_set_lock);
707
708    return res;
709}
710
711/*
712 * Return the cgroup for "task" from the given hierarchy. Must be
713 * called with cgroup_mutex held.
714 */
715static struct cgroup *task_cgroup_from_root(struct task_struct *task,
716                        struct cgroupfs_root *root)
717{
718    struct css_set *css;
719    struct cgroup *res = NULL;
720
721    BUG_ON(!mutex_is_locked(&cgroup_mutex));
722    read_lock(&css_set_lock);
723    /*
724     * No need to lock the task - since we hold cgroup_mutex the
725     * task can't change groups, so the only thing that can happen
726     * is that it exits and its css is set back to init_css_set.
727     */
728    css = task->cgroups;
729    if (css == &init_css_set) {
730        res = &root->top_cgroup;
731    } else {
732        struct cg_cgroup_link *link;
733        list_for_each_entry(link, &css->cg_links, cg_link_list) {
734            struct cgroup *c = link->cgrp;
735            if (c->root == root) {
736                res = c;
737                break;
738            }
739        }
740    }
741    read_unlock(&css_set_lock);
742    BUG_ON(!res);
743    return res;
744}
745
746/*
747 * There is one global cgroup mutex. We also require taking
748 * task_lock() when dereferencing a task's cgroup subsys pointers.
749 * See "The task_lock() exception", at the end of this comment.
750 *
751 * A task must hold cgroup_mutex to modify cgroups.
752 *
753 * Any task can increment and decrement the count field without lock.
754 * So in general, code holding cgroup_mutex can't rely on the count
755 * field not changing. However, if the count goes to zero, then only
756 * cgroup_attach_task() can increment it again. Because a count of zero
757 * means that no tasks are currently attached, therefore there is no
758 * way a task attached to that cgroup can fork (the other way to
759 * increment the count). So code holding cgroup_mutex can safely
760 * assume that if the count is zero, it will stay zero. Similarly, if
761 * a task holds cgroup_mutex on a cgroup with zero count, it
762 * knows that the cgroup won't be removed, as cgroup_rmdir()
763 * needs that mutex.
764 *
765 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
766 * (usually) take cgroup_mutex. These are the two most performance
767 * critical pieces of code here. The exception occurs on cgroup_exit(),
768 * when a task in a notify_on_release cgroup exits. Then cgroup_mutex
769 * is taken, and if the cgroup count is zero, a usermode call made
770 * to the release agent with the name of the cgroup (path relative to
771 * the root of cgroup file system) as the argument.
772 *
773 * A cgroup can only be deleted if both its 'count' of using tasks
774 * is zero, and its list of 'children' cgroups is empty. Since all
775 * tasks in the system use _some_ cgroup, and since there is always at
776 * least one task in the system (init, pid == 1), therefore, top_cgroup
777 * always has either children cgroups and/or using tasks. So we don't
778 * need a special hack to ensure that top_cgroup cannot be deleted.
779 *
780 * The task_lock() exception
781 *
782 * The need for this exception arises from the action of
783 * cgroup_attach_task(), which overwrites one tasks cgroup pointer with
784 * another. It does so using cgroup_mutex, however there are
785 * several performance critical places that need to reference
786 * task->cgroup without the expense of grabbing a system global
787 * mutex. Therefore except as noted below, when dereferencing or, as
788 * in cgroup_attach_task(), modifying a task'ss cgroup pointer we use
789 * task_lock(), which acts on a spinlock (task->alloc_lock) already in
790 * the task_struct routinely used for such matters.
791 *
792 * P.S. One more locking exception. RCU is used to guard the
793 * update of a tasks cgroup pointer by cgroup_attach_task()
794 */
795
796/**
797 * cgroup_lock - lock out any changes to cgroup structures
798 *
799 */
800void cgroup_lock(void)
801{
802    mutex_lock(&cgroup_mutex);
803}
804EXPORT_SYMBOL_GPL(cgroup_lock);
805
806/**
807 * cgroup_unlock - release lock on cgroup changes
808 *
809 * Undo the lock taken in a previous cgroup_lock() call.
810 */
811void cgroup_unlock(void)
812{
813    mutex_unlock(&cgroup_mutex);
814}
815EXPORT_SYMBOL_GPL(cgroup_unlock);
816
817/*
818 * A couple of forward declarations required, due to cyclic reference loop:
819 * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
820 * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
821 * -> cgroup_mkdir.
822 */
823
824static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode);
825static struct dentry *cgroup_lookup(struct inode *, struct dentry *, struct nameidata *);
826static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
827static int cgroup_populate_dir(struct cgroup *cgrp);
828static const struct inode_operations cgroup_dir_inode_operations;
829static const struct file_operations proc_cgroupstats_operations;
830
831static struct backing_dev_info cgroup_backing_dev_info = {
832    .name = "cgroup",
833    .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK,
834};
835
836static int alloc_css_id(struct cgroup_subsys *ss,
837            struct cgroup *parent, struct cgroup *child);
838
839static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
840{
841    struct inode *inode = new_inode(sb);
842
843    if (inode) {
844        inode->i_ino = get_next_ino();
845        inode->i_mode = mode;
846        inode->i_uid = current_fsuid();
847        inode->i_gid = current_fsgid();
848        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
849        inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
850    }
851    return inode;
852}
853
854/*
855 * Call subsys's pre_destroy handler.
856 * This is called before css refcnt check.
857 */
858static int cgroup_call_pre_destroy(struct cgroup *cgrp)
859{
860    struct cgroup_subsys *ss;
861    int ret = 0;
862
863    for_each_subsys(cgrp->root, ss) {
864        if (!ss->pre_destroy)
865            continue;
866
867        ret = ss->pre_destroy(cgrp);
868        if (ret) {
869            /* ->pre_destroy() failure is being deprecated */
870            WARN_ON_ONCE(!ss->__DEPRECATED_clear_css_refs);
871            break;
872        }
873    }
874
875    return ret;
876}
877
878static void cgroup_diput(struct dentry *dentry, struct inode *inode)
879{
880    /* is dentry a directory ? if so, kfree() associated cgroup */
881    if (S_ISDIR(inode->i_mode)) {
882        struct cgroup *cgrp = dentry->d_fsdata;
883        struct cgroup_subsys *ss;
884        BUG_ON(!(cgroup_is_removed(cgrp)));
885        /* It's possible for external users to be holding css
886         * reference counts on a cgroup; css_put() needs to
887         * be able to access the cgroup after decrementing
888         * the reference count in order to know if it needs to
889         * queue the cgroup to be handled by the release
890         * agent */
891        synchronize_rcu();
892
893        mutex_lock(&cgroup_mutex);
894        /*
895         * Release the subsystem state objects.
896         */
897        for_each_subsys(cgrp->root, ss)
898            ss->destroy(cgrp);
899
900        cgrp->root->number_of_cgroups--;
901        mutex_unlock(&cgroup_mutex);
902
903        /*
904         * Drop the active superblock reference that we took when we
905         * created the cgroup
906         */
907        deactivate_super(cgrp->root->sb);
908
909        /*
910         * if we're getting rid of the cgroup, refcount should ensure
911         * that there are no pidlists left.
912         */
913        BUG_ON(!list_empty(&cgrp->pidlists));
914
915        kfree_rcu(cgrp, rcu_head);
916    } else {
917        struct cfent *cfe = __d_cfe(dentry);
918        struct cgroup *cgrp = dentry->d_parent->d_fsdata;
919
920        WARN_ONCE(!list_empty(&cfe->node) &&
921              cgrp != &cgrp->root->top_cgroup,
922              "cfe still linked for %s\n", cfe->type->name);
923        kfree(cfe);
924    }
925    iput(inode);
926}
927
928static int cgroup_delete(const struct dentry *d)
929{
930    return 1;
931}
932
933static void remove_dir(struct dentry *d)
934{
935    struct dentry *parent = dget(d->d_parent);
936
937    d_delete(d);
938    simple_rmdir(parent->d_inode, d);
939    dput(parent);
940}
941
942static int cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
943{
944    struct cfent *cfe;
945
946    lockdep_assert_held(&cgrp->dentry->d_inode->i_mutex);
947    lockdep_assert_held(&cgroup_mutex);
948
949    list_for_each_entry(cfe, &cgrp->files, node) {
950        struct dentry *d = cfe->dentry;
951
952        if (cft && cfe->type != cft)
953            continue;
954
955        dget(d);
956        d_delete(d);
957        simple_unlink(d->d_inode, d);
958        list_del_init(&cfe->node);
959        dput(d);
960
961        return 0;
962    }
963    return -ENOENT;
964}
965
966static void cgroup_clear_directory(struct dentry *dir)
967{
968    struct cgroup *cgrp = __d_cgrp(dir);
969
970    while (!list_empty(&cgrp->files))
971        cgroup_rm_file(cgrp, NULL);
972}
973
974/*
975 * NOTE : the dentry must have been dget()'ed
976 */
977static void cgroup_d_remove_dir(struct dentry *dentry)
978{
979    struct dentry *parent;
980
981    cgroup_clear_directory(dentry);
982
983    parent = dentry->d_parent;
984    spin_lock(&parent->d_lock);
985    spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
986    list_del_init(&dentry->d_u.d_child);
987    spin_unlock(&dentry->d_lock);
988    spin_unlock(&parent->d_lock);
989    remove_dir(dentry);
990}
991
992/*
993 * A queue for waiters to do rmdir() cgroup. A tasks will sleep when
994 * cgroup->count == 0 && list_empty(&cgroup->children) && subsys has some
995 * reference to css->refcnt. In general, this refcnt is expected to goes down
996 * to zero, soon.
997 *
998 * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
999 */
1000static DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
1001
1002static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
1003{
1004    if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
1005        wake_up_all(&cgroup_rmdir_waitq);
1006}
1007
1008void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
1009{
1010    css_get(css);
1011}
1012
1013void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
1014{
1015    cgroup_wakeup_rmdir_waiter(css->cgroup);
1016    css_put(css);
1017}
1018
1019/*
1020 * Call with cgroup_mutex held. Drops reference counts on modules, including
1021 * any duplicate ones that parse_cgroupfs_options took. If this function
1022 * returns an error, no reference counts are touched.
1023 */
1024static int rebind_subsystems(struct cgroupfs_root *root,
1025                  unsigned long final_bits)
1026{
1027    unsigned long added_bits, removed_bits;
1028    struct cgroup *cgrp = &root->top_cgroup;
1029    int i;
1030
1031    BUG_ON(!mutex_is_locked(&cgroup_mutex));
1032    BUG_ON(!mutex_is_locked(&cgroup_root_mutex));
1033
1034    removed_bits = root->actual_subsys_bits & ~final_bits;
1035    added_bits = final_bits & ~root->actual_subsys_bits;
1036    /* Check that any added subsystems are currently free */
1037    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1038        unsigned long bit = 1UL << i;
1039        struct cgroup_subsys *ss = subsys[i];
1040        if (!(bit & added_bits))
1041            continue;
1042        /*
1043         * Nobody should tell us to do a subsys that doesn't exist:
1044         * parse_cgroupfs_options should catch that case and refcounts
1045         * ensure that subsystems won't disappear once selected.
1046         */
1047        BUG_ON(ss == NULL);
1048        if (ss->root != &rootnode) {
1049            /* Subsystem isn't free */
1050            return -EBUSY;
1051        }
1052    }
1053
1054    /* Currently we don't handle adding/removing subsystems when
1055     * any child cgroups exist. This is theoretically supportable
1056     * but involves complex error handling, so it's being left until
1057     * later */
1058    if (root->number_of_cgroups > 1)
1059        return -EBUSY;
1060
1061    /* Process each subsystem */
1062    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1063        struct cgroup_subsys *ss = subsys[i];
1064        unsigned long bit = 1UL << i;
1065        if (bit & added_bits) {
1066            /* We're binding this subsystem to this hierarchy */
1067            BUG_ON(ss == NULL);
1068            BUG_ON(cgrp->subsys[i]);
1069            BUG_ON(!dummytop->subsys[i]);
1070            BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
1071            mutex_lock(&ss->hierarchy_mutex);
1072            cgrp->subsys[i] = dummytop->subsys[i];
1073            cgrp->subsys[i]->cgroup = cgrp;
1074            list_move(&ss->sibling, &root->subsys_list);
1075            ss->root = root;
1076            if (ss->bind)
1077                ss->bind(cgrp);
1078            mutex_unlock(&ss->hierarchy_mutex);
1079            /* refcount was already taken, and we're keeping it */
1080        } else if (bit & removed_bits) {
1081            /* We're removing this subsystem */
1082            BUG_ON(ss == NULL);
1083            BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
1084            BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
1085            mutex_lock(&ss->hierarchy_mutex);
1086            if (ss->bind)
1087                ss->bind(dummytop);
1088            dummytop->subsys[i]->cgroup = dummytop;
1089            cgrp->subsys[i] = NULL;
1090            subsys[i]->root = &rootnode;
1091            list_move(&ss->sibling, &rootnode.subsys_list);
1092            mutex_unlock(&ss->hierarchy_mutex);
1093            /* subsystem is now free - drop reference on module */
1094            module_put(ss->module);
1095        } else if (bit & final_bits) {
1096            /* Subsystem state should already exist */
1097            BUG_ON(ss == NULL);
1098            BUG_ON(!cgrp->subsys[i]);
1099            /*
1100             * a refcount was taken, but we already had one, so
1101             * drop the extra reference.
1102             */
1103            module_put(ss->module);
1104#ifdef CONFIG_MODULE_UNLOAD
1105            BUG_ON(ss->module && !module_refcount(ss->module));
1106#endif
1107        } else {
1108            /* Subsystem state shouldn't exist */
1109            BUG_ON(cgrp->subsys[i]);
1110        }
1111    }
1112    root->subsys_bits = root->actual_subsys_bits = final_bits;
1113    synchronize_rcu();
1114
1115    return 0;
1116}
1117
1118static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
1119{
1120    struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
1121    struct cgroup_subsys *ss;
1122
1123    mutex_lock(&cgroup_root_mutex);
1124    for_each_subsys(root, ss)
1125        seq_printf(seq, ",%s", ss->name);
1126    if (test_bit(ROOT_NOPREFIX, &root->flags))
1127        seq_puts(seq, ",noprefix");
1128    if (strlen(root->release_agent_path))
1129        seq_printf(seq, ",release_agent=%s", root->release_agent_path);
1130    if (clone_children(&root->top_cgroup))
1131        seq_puts(seq, ",clone_children");
1132    if (strlen(root->name))
1133        seq_printf(seq, ",name=%s", root->name);
1134    mutex_unlock(&cgroup_root_mutex);
1135    return 0;
1136}
1137
1138struct cgroup_sb_opts {
1139    unsigned long subsys_bits;
1140    unsigned long flags;
1141    char *release_agent;
1142    bool clone_children;
1143    char *name;
1144    /* User explicitly requested empty subsystem */
1145    bool none;
1146
1147    struct cgroupfs_root *new_root;
1148
1149};
1150
1151/*
1152 * Convert a hierarchy specifier into a bitmask of subsystems and flags. Call
1153 * with cgroup_mutex held to protect the subsys[] array. This function takes
1154 * refcounts on subsystems to be used, unless it returns error, in which case
1155 * no refcounts are taken.
1156 */
1157static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1158{
1159    char *token, *o = data;
1160    bool all_ss = false, one_ss = false;
1161    unsigned long mask = (unsigned long)-1;
1162    int i;
1163    bool module_pin_failed = false;
1164
1165    BUG_ON(!mutex_is_locked(&cgroup_mutex));
1166
1167#ifdef CONFIG_CPUSETS
1168    mask = ~(1UL << cpuset_subsys_id);
1169#endif
1170
1171    memset(opts, 0, sizeof(*opts));
1172
1173    while ((token = strsep(&o, ",")) != NULL) {
1174        if (!*token)
1175            return -EINVAL;
1176        if (!strcmp(token, "none")) {
1177            /* Explicitly have no subsystems */
1178            opts->none = true;
1179            continue;
1180        }
1181        if (!strcmp(token, "all")) {
1182            /* Mutually exclusive option 'all' + subsystem name */
1183            if (one_ss)
1184                return -EINVAL;
1185            all_ss = true;
1186            continue;
1187        }
1188        if (!strcmp(token, "noprefix")) {
1189            set_bit(ROOT_NOPREFIX, &opts->flags);
1190            continue;
1191        }
1192        if (!strcmp(token, "clone_children")) {
1193            opts->clone_children = true;
1194            continue;
1195        }
1196        if (!strncmp(token, "release_agent=", 14)) {
1197            /* Specifying two release agents is forbidden */
1198            if (opts->release_agent)
1199                return -EINVAL;
1200            opts->release_agent =
1201                kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1202            if (!opts->release_agent)
1203                return -ENOMEM;
1204            continue;
1205        }
1206        if (!strncmp(token, "name=", 5)) {
1207            const char *name = token + 5;
1208            /* Can't specify an empty name */
1209            if (!strlen(name))
1210                return -EINVAL;
1211            /* Must match [\w.-]+ */
1212            for (i = 0; i < strlen(name); i++) {
1213                char c = name[i];
1214                if (isalnum(c))
1215                    continue;
1216                if ((c == '.') || (c == '-') || (c == '_'))
1217                    continue;
1218                return -EINVAL;
1219            }
1220            /* Specifying two names is forbidden */
1221            if (opts->name)
1222                return -EINVAL;
1223            opts->name = kstrndup(name,
1224                          MAX_CGROUP_ROOT_NAMELEN - 1,
1225                          GFP_KERNEL);
1226            if (!opts->name)
1227                return -ENOMEM;
1228
1229            continue;
1230        }
1231
1232        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1233            struct cgroup_subsys *ss = subsys[i];
1234            if (ss == NULL)
1235                continue;
1236            if (strcmp(token, ss->name))
1237                continue;
1238            if (ss->disabled)
1239                continue;
1240
1241            /* Mutually exclusive option 'all' + subsystem name */
1242            if (all_ss)
1243                return -EINVAL;
1244            set_bit(i, &opts->subsys_bits);
1245            one_ss = true;
1246
1247            break;
1248        }
1249        if (i == CGROUP_SUBSYS_COUNT)
1250            return -ENOENT;
1251    }
1252
1253    /*
1254     * If the 'all' option was specified select all the subsystems,
1255     * otherwise if 'none', 'name=' and a subsystem name options
1256     * were not specified, let's default to 'all'
1257     */
1258    if (all_ss || (!one_ss && !opts->none && !opts->name)) {
1259        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1260            struct cgroup_subsys *ss = subsys[i];
1261            if (ss == NULL)
1262                continue;
1263            if (ss->disabled)
1264                continue;
1265            set_bit(i, &opts->subsys_bits);
1266        }
1267    }
1268
1269    /* Consistency checks */
1270
1271    /*
1272     * Option noprefix was introduced just for backward compatibility
1273     * with the old cpuset, so we allow noprefix only if mounting just
1274     * the cpuset subsystem.
1275     */
1276    if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
1277        (opts->subsys_bits & mask))
1278        return -EINVAL;
1279
1280
1281    /* Can't specify "none" and some subsystems */
1282    if (opts->subsys_bits && opts->none)
1283        return -EINVAL;
1284
1285    /*
1286     * We either have to specify by name or by subsystems. (So all
1287     * empty hierarchies must have a name).
1288     */
1289    if (!opts->subsys_bits && !opts->name)
1290        return -EINVAL;
1291
1292    /*
1293     * Grab references on all the modules we'll need, so the subsystems
1294     * don't dance around before rebind_subsystems attaches them. This may
1295     * take duplicate reference counts on a subsystem that's already used,
1296     * but rebind_subsystems handles this case.
1297     */
1298    for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
1299        unsigned long bit = 1UL << i;
1300
1301        if (!(bit & opts->subsys_bits))
1302            continue;
1303        if (!try_module_get(subsys[i]->module)) {
1304            module_pin_failed = true;
1305            break;
1306        }
1307    }
1308    if (module_pin_failed) {
1309        /*
1310         * oops, one of the modules was going away. this means that we
1311         * raced with a module_delete call, and to the user this is
1312         * essentially a "subsystem doesn't exist" case.
1313         */
1314        for (i--; i >= CGROUP_BUILTIN_SUBSYS_COUNT; i--) {
1315            /* drop refcounts only on the ones we took */
1316            unsigned long bit = 1UL << i;
1317
1318            if (!(bit & opts->subsys_bits))
1319                continue;
1320            module_put(subsys[i]->module);
1321        }
1322        return -ENOENT;
1323    }
1324
1325    return 0;
1326}
1327
1328static void drop_parsed_module_refcounts(unsigned long subsys_bits)
1329{
1330    int i;
1331    for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
1332        unsigned long bit = 1UL << i;
1333
1334        if (!(bit & subsys_bits))
1335            continue;
1336        module_put(subsys[i]->module);
1337    }
1338}
1339
1340static int cgroup_remount(struct super_block *sb, int *flags, char *data)
1341{
1342    int ret = 0;
1343    struct cgroupfs_root *root = sb->s_fs_info;
1344    struct cgroup *cgrp = &root->top_cgroup;
1345    struct cgroup_sb_opts opts;
1346
1347    mutex_lock(&cgrp->dentry->d_inode->i_mutex);
1348    mutex_lock(&cgroup_mutex);
1349    mutex_lock(&cgroup_root_mutex);
1350
1351    /* See what subsystems are wanted */
1352    ret = parse_cgroupfs_options(data, &opts);
1353    if (ret)
1354        goto out_unlock;
1355
1356    /* See feature-removal-schedule.txt */
1357    if (opts.subsys_bits != root->actual_subsys_bits || opts.release_agent)
1358        pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
1359               task_tgid_nr(current), current->comm);
1360
1361    /* Don't allow flags or name to change at remount */
1362    if (opts.flags != root->flags ||
1363        (opts.name && strcmp(opts.name, root->name))) {
1364        ret = -EINVAL;
1365        drop_parsed_module_refcounts(opts.subsys_bits);
1366        goto out_unlock;
1367    }
1368
1369    ret = rebind_subsystems(root, opts.subsys_bits);
1370    if (ret) {
1371        drop_parsed_module_refcounts(opts.subsys_bits);
1372        goto out_unlock;
1373    }
1374
1375    /* clear out any existing files and repopulate subsystem files */
1376    cgroup_clear_directory(cgrp->dentry);
1377    cgroup_populate_dir(cgrp);
1378
1379    if (opts.release_agent)
1380        strcpy(root->release_agent_path, opts.release_agent);
1381 out_unlock:
1382    kfree(opts.release_agent);
1383    kfree(opts.name);
1384    mutex_unlock(&cgroup_root_mutex);
1385    mutex_unlock(&cgroup_mutex);
1386    mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
1387    return ret;
1388}
1389
1390static const struct super_operations cgroup_ops = {
1391    .statfs = simple_statfs,
1392    .drop_inode = generic_delete_inode,
1393    .show_options = cgroup_show_options,
1394    .remount_fs = cgroup_remount,
1395};
1396
1397static void init_cgroup_housekeeping(struct cgroup *cgrp)
1398{
1399    INIT_LIST_HEAD(&cgrp->sibling);
1400    INIT_LIST_HEAD(&cgrp->children);
1401    INIT_LIST_HEAD(&cgrp->files);
1402    INIT_LIST_HEAD(&cgrp->css_sets);
1403    INIT_LIST_HEAD(&cgrp->release_list);
1404    INIT_LIST_HEAD(&cgrp->pidlists);
1405    mutex_init(&cgrp->pidlist_mutex);
1406    INIT_LIST_HEAD(&cgrp->event_list);
1407    spin_lock_init(&cgrp->event_list_lock);
1408}
1409
1410static void init_cgroup_root(struct cgroupfs_root *root)
1411{
1412    struct cgroup *cgrp = &root->top_cgroup;
1413
1414    INIT_LIST_HEAD(&root->subsys_list);
1415    INIT_LIST_HEAD(&root->root_list);
1416    INIT_LIST_HEAD(&root->allcg_list);
1417    root->number_of_cgroups = 1;
1418    cgrp->root = root;
1419    cgrp->top_cgroup = cgrp;
1420    list_add_tail(&cgrp->allcg_node, &root->allcg_list);
1421    init_cgroup_housekeeping(cgrp);
1422}
1423
1424static bool init_root_id(struct cgroupfs_root *root)
1425{
1426    int ret = 0;
1427
1428    do {
1429        if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))
1430            return false;
1431        spin_lock(&hierarchy_id_lock);
1432        /* Try to allocate the next unused ID */
1433        ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
1434                    &root->hierarchy_id);
1435        if (ret == -ENOSPC)
1436            /* Try again starting from 0 */
1437            ret = ida_get_new(&hierarchy_ida, &root->hierarchy_id);
1438        if (!ret) {
1439            next_hierarchy_id = root->hierarchy_id + 1;
1440        } else if (ret != -EAGAIN) {
1441            /* Can only get here if the 31-bit IDR is full ... */
1442            BUG_ON(ret);
1443        }
1444        spin_unlock(&hierarchy_id_lock);
1445    } while (ret);
1446    return true;
1447}
1448
1449static int cgroup_test_super(struct super_block *sb, void *data)
1450{
1451    struct cgroup_sb_opts *opts = data;
1452    struct cgroupfs_root *root = sb->s_fs_info;
1453
1454    /* If we asked for a name then it must match */
1455    if (opts->name && strcmp(opts->name, root->name))
1456        return 0;
1457
1458    /*
1459     * If we asked for subsystems (or explicitly for no
1460     * subsystems) then they must match
1461     */
1462    if ((opts->subsys_bits || opts->none)
1463        && (opts->subsys_bits != root->subsys_bits))
1464        return 0;
1465
1466    return 1;
1467}
1468
1469static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
1470{
1471    struct cgroupfs_root *root;
1472
1473    if (!opts->subsys_bits && !opts->none)
1474        return NULL;
1475
1476    root = kzalloc(sizeof(*root), GFP_KERNEL);
1477    if (!root)
1478        return ERR_PTR(-ENOMEM);
1479
1480    if (!init_root_id(root)) {
1481        kfree(root);
1482        return ERR_PTR(-ENOMEM);
1483    }
1484    init_cgroup_root(root);
1485
1486    root->subsys_bits = opts->subsys_bits;
1487    root->flags = opts->flags;
1488    if (opts->release_agent)
1489        strcpy(root->release_agent_path, opts->release_agent);
1490    if (opts->name)
1491        strcpy(root->name, opts->name);
1492    if (opts->clone_children)
1493        set_bit(CGRP_CLONE_CHILDREN, &root->top_cgroup.flags);
1494    return root;
1495}
1496
1497static void cgroup_drop_root(struct cgroupfs_root *root)
1498{
1499    if (!root)
1500        return;
1501
1502    BUG_ON(!root->hierarchy_id);
1503    spin_lock(&hierarchy_id_lock);
1504    ida_remove(&hierarchy_ida, root->hierarchy_id);
1505    spin_unlock(&hierarchy_id_lock);
1506    kfree(root);
1507}
1508
1509static int cgroup_set_super(struct super_block *sb, void *data)
1510{
1511    int ret;
1512    struct cgroup_sb_opts *opts = data;
1513
1514    /* If we don't have a new root, we can't set up a new sb */
1515    if (!opts->new_root)
1516        return -EINVAL;
1517
1518    BUG_ON(!opts->subsys_bits && !opts->none);
1519
1520    ret = set_anon_super(sb, NULL);
1521    if (ret)
1522        return ret;
1523
1524    sb->s_fs_info = opts->new_root;
1525    opts->new_root->sb = sb;
1526
1527    sb->s_blocksize = PAGE_CACHE_SIZE;
1528    sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
1529    sb->s_magic = CGROUP_SUPER_MAGIC;
1530    sb->s_op = &cgroup_ops;
1531
1532    return 0;
1533}
1534
1535static int cgroup_get_rootdir(struct super_block *sb)
1536{
1537    static const struct dentry_operations cgroup_dops = {
1538        .d_iput = cgroup_diput,
1539        .d_delete = cgroup_delete,
1540    };
1541
1542    struct inode *inode =
1543        cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
1544
1545    if (!inode)
1546        return -ENOMEM;
1547
1548    inode->i_fop = &simple_dir_operations;
1549    inode->i_op = &cgroup_dir_inode_operations;
1550    /* directories start off with i_nlink == 2 (for "." entry) */
1551    inc_nlink(inode);
1552    sb->s_root = d_make_root(inode);
1553    if (!sb->s_root)
1554        return -ENOMEM;
1555    /* for everything else we want ->d_op set */
1556    sb->s_d_op = &cgroup_dops;
1557    return 0;
1558}
1559
1560static struct dentry *cgroup_mount(struct file_system_type *fs_type,
1561             int flags, const char *unused_dev_name,
1562             void *data)
1563{
1564    struct cgroup_sb_opts opts;
1565    struct cgroupfs_root *root;
1566    int ret = 0;
1567    struct super_block *sb;
1568    struct cgroupfs_root *new_root;
1569    struct inode *inode;
1570
1571    /* First find the desired set of subsystems */
1572    mutex_lock(&cgroup_mutex);
1573    ret = parse_cgroupfs_options(data, &opts);
1574    mutex_unlock(&cgroup_mutex);
1575    if (ret)
1576        goto out_err;
1577
1578    /*
1579     * Allocate a new cgroup root. We may not need it if we're
1580     * reusing an existing hierarchy.
1581     */
1582    new_root = cgroup_root_from_opts(&opts);
1583    if (IS_ERR(new_root)) {
1584        ret = PTR_ERR(new_root);
1585        goto drop_modules;
1586    }
1587    opts.new_root = new_root;
1588
1589    /* Locate an existing or new sb for this hierarchy */
1590    sb = sget(fs_type, cgroup_test_super, cgroup_set_super, &opts);
1591    if (IS_ERR(sb)) {
1592        ret = PTR_ERR(sb);
1593        cgroup_drop_root(opts.new_root);
1594        goto drop_modules;
1595    }
1596
1597    root = sb->s_fs_info;
1598    BUG_ON(!root);
1599    if (root == opts.new_root) {
1600        /* We used the new root structure, so this is a new hierarchy */
1601        struct list_head tmp_cg_links;
1602        struct cgroup *root_cgrp = &root->top_cgroup;
1603        struct cgroupfs_root *existing_root;
1604        const struct cred *cred;
1605        int i;
1606
1607        BUG_ON(sb->s_root != NULL);
1608
1609        ret = cgroup_get_rootdir(sb);
1610        if (ret)
1611            goto drop_new_super;
1612        inode = sb->s_root->d_inode;
1613
1614        mutex_lock(&inode->i_mutex);
1615        mutex_lock(&cgroup_mutex);
1616        mutex_lock(&cgroup_root_mutex);
1617
1618        /* Check for name clashes with existing mounts */
1619        ret = -EBUSY;
1620        if (strlen(root->name))
1621            for_each_active_root(existing_root)
1622                if (!strcmp(existing_root->name, root->name))
1623                    goto unlock_drop;
1624
1625        /*
1626         * We're accessing css_set_count without locking
1627         * css_set_lock here, but that's OK - it can only be
1628         * increased by someone holding cgroup_lock, and
1629         * that's us. The worst that can happen is that we
1630         * have some link structures left over
1631         */
1632        ret = allocate_cg_links(css_set_count, &tmp_cg_links);
1633        if (ret)
1634            goto unlock_drop;
1635
1636        ret = rebind_subsystems(root, root->subsys_bits);
1637        if (ret == -EBUSY) {
1638            free_cg_links(&tmp_cg_links);
1639            goto unlock_drop;
1640        }
1641        /*
1642         * There must be no failure case after here, since rebinding
1643         * takes care of subsystems' refcounts, which are explicitly
1644         * dropped in the failure exit path.
1645         */
1646
1647        /* EBUSY should be the only error here */
1648        BUG_ON(ret);
1649
1650        list_add(&root->root_list, &roots);
1651        root_count++;
1652
1653        sb->s_root->d_fsdata = root_cgrp;
1654        root->top_cgroup.dentry = sb->s_root;
1655
1656        /* Link the top cgroup in this hierarchy into all
1657         * the css_set objects */
1658        write_lock(&css_set_lock);
1659        for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
1660            struct hlist_head *hhead = &css_set_table[i];
1661            struct hlist_node *node;
1662            struct css_set *cg;
1663
1664            hlist_for_each_entry(cg, node, hhead, hlist)
1665                link_css_set(&tmp_cg_links, cg, root_cgrp);
1666        }
1667        write_unlock(&css_set_lock);
1668
1669        free_cg_links(&tmp_cg_links);
1670
1671        BUG_ON(!list_empty(&root_cgrp->sibling));
1672        BUG_ON(!list_empty(&root_cgrp->children));
1673        BUG_ON(root->number_of_cgroups != 1);
1674
1675        cred = override_creds(&init_cred);
1676        cgroup_populate_dir(root_cgrp);
1677        revert_creds(cred);
1678        mutex_unlock(&cgroup_root_mutex);
1679        mutex_unlock(&cgroup_mutex);
1680        mutex_unlock(&inode->i_mutex);
1681    } else {
1682        /*
1683         * We re-used an existing hierarchy - the new root (if
1684         * any) is not needed
1685         */
1686        cgroup_drop_root(opts.new_root);
1687        /* no subsys rebinding, so refcounts don't change */
1688        drop_parsed_module_refcounts(opts.subsys_bits);
1689    }
1690
1691    kfree(opts.release_agent);
1692    kfree(opts.name);
1693    return dget(sb->s_root);
1694
1695 unlock_drop:
1696    mutex_unlock(&cgroup_root_mutex);
1697    mutex_unlock(&cgroup_mutex);
1698    mutex_unlock(&inode->i_mutex);
1699 drop_new_super:
1700    deactivate_locked_super(sb);
1701 drop_modules:
1702    drop_parsed_module_refcounts(opts.subsys_bits);
1703 out_err:
1704    kfree(opts.release_agent);
1705    kfree(opts.name);
1706    return ERR_PTR(ret);
1707}
1708
1709static void cgroup_kill_sb(struct super_block *sb) {
1710    struct cgroupfs_root *root = sb->s_fs_info;
1711    struct cgroup *cgrp = &root->top_cgroup;
1712    int ret;
1713    struct cg_cgroup_link *link;
1714    struct cg_cgroup_link *saved_link;
1715
1716    BUG_ON(!root);
1717
1718    BUG_ON(root->number_of_cgroups != 1);
1719    BUG_ON(!list_empty(&cgrp->children));
1720    BUG_ON(!list_empty(&cgrp->sibling));
1721
1722    mutex_lock(&cgroup_mutex);
1723    mutex_lock(&cgroup_root_mutex);
1724
1725    /* Rebind all subsystems back to the default hierarchy */
1726    ret = rebind_subsystems(root, 0);
1727    /* Shouldn't be able to fail ... */
1728    BUG_ON(ret);
1729
1730    /*
1731     * Release all the links from css_sets to this hierarchy's
1732     * root cgroup
1733     */
1734    write_lock(&css_set_lock);
1735
1736    list_for_each_entry_safe(link, saved_link, &cgrp->css_sets,
1737                 cgrp_link_list) {
1738        list_del(&link->cg_link_list);
1739        list_del(&link->cgrp_link_list);
1740        kfree(link);
1741    }
1742    write_unlock(&css_set_lock);
1743
1744    if (!list_empty(&root->root_list)) {
1745        list_del(&root->root_list);
1746        root_count--;
1747    }
1748
1749    mutex_unlock(&cgroup_root_mutex);
1750    mutex_unlock(&cgroup_mutex);
1751
1752    kill_litter_super(sb);
1753    cgroup_drop_root(root);
1754}
1755
1756static struct file_system_type cgroup_fs_type = {
1757    .name = "cgroup",
1758    .mount = cgroup_mount,
1759    .kill_sb = cgroup_kill_sb,
1760};
1761
1762static struct kobject *cgroup_kobj;
1763
1764/**
1765 * cgroup_path - generate the path of a cgroup
1766 * @cgrp: the cgroup in question
1767 * @buf: the buffer to write the path into
1768 * @buflen: the length of the buffer
1769 *
1770 * Called with cgroup_mutex held or else with an RCU-protected cgroup
1771 * reference. Writes path of cgroup into buf. Returns 0 on success,
1772 * -errno on error.
1773 */
1774int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
1775{
1776    char *start;
1777    struct dentry *dentry = rcu_dereference_check(cgrp->dentry,
1778                              cgroup_lock_is_held());
1779
1780    if (!dentry || cgrp == dummytop) {
1781        /*
1782         * Inactive subsystems have no dentry for their root
1783         * cgroup
1784         */
1785        strcpy(buf, "/");
1786        return 0;
1787    }
1788
1789    start = buf + buflen;
1790
1791    *--start = '\0';
1792    for (;;) {
1793        int len = dentry->d_name.len;
1794
1795        if ((start -= len) < buf)
1796            return -ENAMETOOLONG;
1797        memcpy(start, dentry->d_name.name, len);
1798        cgrp = cgrp->parent;
1799        if (!cgrp)
1800            break;
1801
1802        dentry = rcu_dereference_check(cgrp->dentry,
1803                           cgroup_lock_is_held());
1804        if (!cgrp->parent)
1805            continue;
1806        if (--start < buf)
1807            return -ENAMETOOLONG;
1808        *start = '/';
1809    }
1810    memmove(buf, start, buf + buflen - start);
1811    return 0;
1812}
1813EXPORT_SYMBOL_GPL(cgroup_path);
1814
1815/*
1816 * Control Group taskset
1817 */
1818struct task_and_cgroup {
1819    struct task_struct *task;
1820    struct cgroup *cgrp;
1821    struct css_set *cg;
1822};
1823
1824struct cgroup_taskset {
1825    struct task_and_cgroup single;
1826    struct flex_array *tc_array;
1827    int tc_array_len;
1828    int idx;
1829    struct cgroup *cur_cgrp;
1830};
1831
1832/**
1833 * cgroup_taskset_first - reset taskset and return the first task
1834 * @tset: taskset of interest
1835 *
1836 * @tset iteration is initialized and the first task is returned.
1837 */
1838struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset)
1839{
1840    if (tset->tc_array) {
1841        tset->idx = 0;
1842        return cgroup_taskset_next(tset);
1843    } else {
1844        tset->cur_cgrp = tset->single.cgrp;
1845        return tset->single.task;
1846    }
1847}
1848EXPORT_SYMBOL_GPL(cgroup_taskset_first);
1849
1850/**
1851 * cgroup_taskset_next - iterate to the next task in taskset
1852 * @tset: taskset of interest
1853 *
1854 * Return the next task in @tset. Iteration must have been initialized
1855 * with cgroup_taskset_first().
1856 */
1857struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
1858{
1859    struct task_and_cgroup *tc;
1860
1861    if (!tset->tc_array || tset->idx >= tset->tc_array_len)
1862        return NULL;
1863
1864    tc = flex_array_get(tset->tc_array, tset->idx++);
1865    tset->cur_cgrp = tc->cgrp;
1866    return tc->task;
1867}
1868EXPORT_SYMBOL_GPL(cgroup_taskset_next);
1869
1870/**
1871 * cgroup_taskset_cur_cgroup - return the matching cgroup for the current task
1872 * @tset: taskset of interest
1873 *
1874 * Return the cgroup for the current (last returned) task of @tset. This
1875 * function must be preceded by either cgroup_taskset_first() or
1876 * cgroup_taskset_next().
1877 */
1878struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset)
1879{
1880    return tset->cur_cgrp;
1881}
1882EXPORT_SYMBOL_GPL(cgroup_taskset_cur_cgroup);
1883
1884/**
1885 * cgroup_taskset_size - return the number of tasks in taskset
1886 * @tset: taskset of interest
1887 */
1888int cgroup_taskset_size(struct cgroup_taskset *tset)
1889{
1890    return tset->tc_array ? tset->tc_array_len : 1;
1891}
1892EXPORT_SYMBOL_GPL(cgroup_taskset_size);
1893
1894
1895/*
1896 * cgroup_task_migrate - move a task from one cgroup to another.
1897 *
1898 * 'guarantee' is set if the caller promises that a new css_set for the task
1899 * will already exist. If not set, this function might sleep, and can fail with
1900 * -ENOMEM. Must be called with cgroup_mutex and threadgroup locked.
1901 */
1902static void cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
1903                struct task_struct *tsk, struct css_set *newcg)
1904{
1905    struct css_set *oldcg;
1906
1907    /*
1908     * We are synchronized through threadgroup_lock() against PF_EXITING
1909     * setting such that we can't race against cgroup_exit() changing the
1910     * css_set to init_css_set and dropping the old one.
1911     */
1912    WARN_ON_ONCE(tsk->flags & PF_EXITING);
1913    oldcg = tsk->cgroups;
1914
1915    task_lock(tsk);
1916    rcu_assign_pointer(tsk->cgroups, newcg);
1917    task_unlock(tsk);
1918
1919    /* Update the css_set linked lists if we're using them */
1920    write_lock(&css_set_lock);
1921    if (!list_empty(&tsk->cg_list))
1922        list_move(&tsk->cg_list, &newcg->tasks);
1923    write_unlock(&css_set_lock);
1924
1925    /*
1926     * We just gained a reference on oldcg by taking it from the task. As
1927     * trading it for newcg is protected by cgroup_mutex, we're safe to drop
1928     * it here; it will be freed under RCU.
1929     */
1930    put_css_set(oldcg);
1931
1932    set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
1933}
1934
1935/**
1936 * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
1937 * @cgrp: the cgroup the task is attaching to
1938 * @tsk: the task to be attached
1939 *
1940 * Call with cgroup_mutex and threadgroup locked. May take task_lock of
1941 * @tsk during call.
1942 */
1943int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
1944{
1945    int retval = 0;
1946    struct cgroup_subsys *ss, *failed_ss = NULL;
1947    struct cgroup *oldcgrp;
1948    struct cgroupfs_root *root = cgrp->root;
1949    struct cgroup_taskset tset = { };
1950    struct css_set *newcg;
1951
1952    /* @tsk either already exited or can't exit until the end */
1953    if (tsk->flags & PF_EXITING)
1954        return -ESRCH;
1955
1956    /* Nothing to do if the task is already in that cgroup */
1957    oldcgrp = task_cgroup_from_root(tsk, root);
1958    if (cgrp == oldcgrp)
1959        return 0;
1960
1961    tset.single.task = tsk;
1962    tset.single.cgrp = oldcgrp;
1963
1964    for_each_subsys(root, ss) {
1965        if (ss->can_attach) {
1966            retval = ss->can_attach(cgrp, &tset);
1967            if (retval) {
1968                /*
1969                 * Remember on which subsystem the can_attach()
1970                 * failed, so that we only call cancel_attach()
1971                 * against the subsystems whose can_attach()
1972                 * succeeded. (See below)
1973                 */
1974                failed_ss = ss;
1975                goto out;
1976            }
1977        }
1978    }
1979
1980    newcg = find_css_set(tsk->cgroups, cgrp);
1981    if (!newcg) {
1982        retval = -ENOMEM;
1983        goto out;
1984    }
1985
1986    cgroup_task_migrate(cgrp, oldcgrp, tsk, newcg);
1987
1988    for_each_subsys(root, ss) {
1989        if (ss->attach)
1990            ss->attach(cgrp, &tset);
1991    }
1992
1993    synchronize_rcu();
1994
1995    /*
1996     * wake up rmdir() waiter. the rmdir should fail since the cgroup
1997     * is no longer empty.
1998     */
1999    cgroup_wakeup_rmdir_waiter(cgrp);
2000out:
2001    if (retval) {
2002        for_each_subsys(root, ss) {
2003            if (ss == failed_ss)
2004                /*
2005                 * This subsystem was the one that failed the
2006                 * can_attach() check earlier, so we don't need
2007                 * to call cancel_attach() against it or any
2008                 * remaining subsystems.
2009                 */
2010                break;
2011            if (ss->cancel_attach)
2012                ss->cancel_attach(cgrp, &tset);
2013        }
2014    }
2015    return retval;
2016}
2017
2018/**
2019 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2020 * @from: attach to all cgroups of a given task
2021 * @tsk: the task to be attached
2022 */
2023int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2024{
2025    struct cgroupfs_root *root;
2026    int retval = 0;
2027
2028    cgroup_lock();
2029    for_each_active_root(root) {
2030        struct cgroup *from_cg = task_cgroup_from_root(from, root);
2031
2032        retval = cgroup_attach_task(from_cg, tsk);
2033        if (retval)
2034            break;
2035    }
2036    cgroup_unlock();
2037
2038    return retval;
2039}
2040EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2041
2042/**
2043 * cgroup_attach_proc - attach all threads in a threadgroup to a cgroup
2044 * @cgrp: the cgroup to attach to
2045 * @leader: the threadgroup leader task_struct of the group to be attached
2046 *
2047 * Call holding cgroup_mutex and the group_rwsem of the leader. Will take
2048 * task_lock of each thread in leader's threadgroup individually in turn.
2049 */
2050static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
2051{
2052    int retval, i, group_size;
2053    struct cgroup_subsys *ss, *failed_ss = NULL;
2054    /* guaranteed to be initialized later, but the compiler needs this */
2055    struct cgroupfs_root *root = cgrp->root;
2056    /* threadgroup list cursor and array */
2057    struct task_struct *tsk;
2058    struct task_and_cgroup *tc;
2059    struct flex_array *group;
2060    struct cgroup_taskset tset = { };
2061
2062    /*
2063     * step 0: in order to do expensive, possibly blocking operations for
2064     * every thread, we cannot iterate the thread group list, since it needs
2065     * rcu or tasklist locked. instead, build an array of all threads in the
2066     * group - group_rwsem prevents new threads from appearing, and if
2067     * threads exit, this will just be an over-estimate.
2068     */
2069    group_size = get_nr_threads(leader);
2070    /* flex_array supports very large thread-groups better than kmalloc. */
2071    group = flex_array_alloc(sizeof(*tc), group_size, GFP_KERNEL);
2072    if (!group)
2073        return -ENOMEM;
2074    /* pre-allocate to guarantee space while iterating in rcu read-side. */
2075    retval = flex_array_prealloc(group, 0, group_size - 1, GFP_KERNEL);
2076    if (retval)
2077        goto out_free_group_list;
2078
2079    tsk = leader;
2080    i = 0;
2081    /*
2082     * Prevent freeing of tasks while we take a snapshot. Tasks that are
2083     * already PF_EXITING could be freed from underneath us unless we
2084     * take an rcu_read_lock.
2085     */
2086    rcu_read_lock();
2087    do {
2088        struct task_and_cgroup ent;
2089
2090        /* @tsk either already exited or can't exit until the end */
2091        if (tsk->flags & PF_EXITING)
2092            continue;
2093
2094        /* as per above, nr_threads may decrease, but not increase. */
2095        BUG_ON(i >= group_size);
2096        ent.task = tsk;
2097        ent.cgrp = task_cgroup_from_root(tsk, root);
2098        /* nothing to do if this task is already in the cgroup */
2099        if (ent.cgrp == cgrp)
2100            continue;
2101        /*
2102         * saying GFP_ATOMIC has no effect here because we did prealloc
2103         * earlier, but it's good form to communicate our expectations.
2104         */
2105        retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
2106        BUG_ON(retval != 0);
2107        i++;
2108    } while_each_thread(leader, tsk);
2109    rcu_read_unlock();
2110    /* remember the number of threads in the array for later. */
2111    group_size = i;
2112    tset.tc_array = group;
2113    tset.tc_array_len = group_size;
2114
2115    /* methods shouldn't be called if no task is actually migrating */
2116    retval = 0;
2117    if (!group_size)
2118        goto out_free_group_list;
2119
2120    /*
2121     * step 1: check that we can legitimately attach to the cgroup.
2122     */
2123    for_each_subsys(root, ss) {
2124        if (ss->can_attach) {
2125            retval = ss->can_attach(cgrp, &tset);
2126            if (retval) {
2127                failed_ss = ss;
2128                goto out_cancel_attach;
2129            }
2130        }
2131    }
2132
2133    /*
2134     * step 2: make sure css_sets exist for all threads to be migrated.
2135     * we use find_css_set, which allocates a new one if necessary.
2136     */
2137    for (i = 0; i < group_size; i++) {
2138        tc = flex_array_get(group, i);
2139        tc->cg = find_css_set(tc->task->cgroups, cgrp);
2140        if (!tc->cg) {
2141            retval = -ENOMEM;
2142            goto out_put_css_set_refs;
2143        }
2144    }
2145
2146    /*
2147     * step 3: now that we're guaranteed success wrt the css_sets,
2148     * proceed to move all tasks to the new cgroup. There are no
2149     * failure cases after here, so this is the commit point.
2150     */
2151    for (i = 0; i < group_size; i++) {
2152        tc = flex_array_get(group, i);
2153        cgroup_task_migrate(cgrp, tc->cgrp, tc->task, tc->cg);
2154    }
2155    /* nothing is sensitive to fork() after this point. */
2156
2157    /*
2158     * step 4: do subsystem attach callbacks.
2159     */
2160    for_each_subsys(root, ss) {
2161        if (ss->attach)
2162            ss->attach(cgrp, &tset);
2163    }
2164
2165    /*
2166     * step 5: success! and cleanup
2167     */
2168    synchronize_rcu();
2169    cgroup_wakeup_rmdir_waiter(cgrp);
2170    retval = 0;
2171out_put_css_set_refs:
2172    if (retval) {
2173        for (i = 0; i < group_size; i++) {
2174            tc = flex_array_get(group, i);
2175            if (!tc->cg)
2176                break;
2177            put_css_set(tc->cg);
2178        }
2179    }
2180out_cancel_attach:
2181    if (retval) {
2182        for_each_subsys(root, ss) {
2183            if (ss == failed_ss)
2184                break;
2185            if (ss->cancel_attach)
2186                ss->cancel_attach(cgrp, &tset);
2187        }
2188    }
2189out_free_group_list:
2190    flex_array_free(group);
2191    return retval;
2192}
2193
2194/*
2195 * Find the task_struct of the task to attach by vpid and pass it along to the
2196 * function to attach either it or all tasks in its threadgroup. Will lock
2197 * cgroup_mutex and threadgroup; may take task_lock of task.
2198 */
2199static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
2200{
2201    struct task_struct *tsk;
2202    const struct cred *cred = current_cred(), *tcred;
2203    int ret;
2204
2205    if (!cgroup_lock_live_group(cgrp))
2206        return -ENODEV;
2207
2208retry_find_task:
2209    rcu_read_lock();
2210    if (pid) {
2211        tsk = find_task_by_vpid(pid);
2212        if (!tsk) {
2213            rcu_read_unlock();
2214            ret= -ESRCH;
2215            goto out_unlock_cgroup;
2216        }
2217        /*
2218         * even if we're attaching all tasks in the thread group, we
2219         * only need to check permissions on one of them.
2220         */
2221        tcred = __task_cred(tsk);
2222        if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2223            !uid_eq(cred->euid, tcred->uid) &&
2224            !uid_eq(cred->euid, tcred->suid)) {
2225            rcu_read_unlock();
2226            ret = -EACCES;
2227            goto out_unlock_cgroup;
2228        }
2229    } else
2230        tsk = current;
2231
2232    if (threadgroup)
2233        tsk = tsk->group_leader;
2234
2235    /*
2236     * Workqueue threads may acquire PF_THREAD_BOUND and become
2237     * trapped in a cpuset, or RT worker may be born in a cgroup
2238     * with no rt_runtime allocated. Just say no.
2239     */
2240    if (tsk == kthreadd_task || (tsk->flags & PF_THREAD_BOUND)) {
2241        ret = -EINVAL;
2242        rcu_read_unlock();
2243        goto out_unlock_cgroup;
2244    }
2245
2246    get_task_struct(tsk);
2247    rcu_read_unlock();
2248
2249    threadgroup_lock(tsk);
2250    if (threadgroup) {
2251        if (!thread_group_leader(tsk)) {
2252            /*
2253             * a race with de_thread from another thread's exec()
2254             * may strip us of our leadership, if this happens,
2255             * there is no choice but to throw this task away and
2256             * try again; this is
2257             * "double-double-toil-and-trouble-check locking".
2258             */
2259            threadgroup_unlock(tsk);
2260            put_task_struct(tsk);
2261            goto retry_find_task;
2262        }
2263        ret = cgroup_attach_proc(cgrp, tsk);
2264    } else
2265        ret = cgroup_attach_task(cgrp, tsk);
2266    threadgroup_unlock(tsk);
2267
2268    put_task_struct(tsk);
2269out_unlock_cgroup:
2270    cgroup_unlock();
2271    return ret;
2272}
2273
2274static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
2275{
2276    return attach_task_by_pid(cgrp, pid, false);
2277}
2278
2279static int cgroup_procs_write(struct cgroup *cgrp, struct cftype *cft, u64 tgid)
2280{
2281    return attach_task_by_pid(cgrp, tgid, true);
2282}
2283
2284/**
2285 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
2286 * @cgrp: the cgroup to be checked for liveness
2287 *
2288 * On success, returns true; the lock should be later released with
2289 * cgroup_unlock(). On failure returns false with no lock held.
2290 */
2291bool cgroup_lock_live_group(struct cgroup *cgrp)
2292{
2293    mutex_lock(&cgroup_mutex);
2294    if (cgroup_is_removed(cgrp)) {
2295        mutex_unlock(&cgroup_mutex);
2296        return false;
2297    }
2298    return true;
2299}
2300EXPORT_SYMBOL_GPL(cgroup_lock_live_group);
2301
2302static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
2303                      const char *buffer)
2304{
2305    BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
2306    if (strlen(buffer) >= PATH_MAX)
2307        return -EINVAL;
2308    if (!cgroup_lock_live_group(cgrp))
2309        return -ENODEV;
2310    mutex_lock(&cgroup_root_mutex);
2311    strcpy(cgrp->root->release_agent_path, buffer);
2312    mutex_unlock(&cgroup_root_mutex);
2313    cgroup_unlock();
2314    return 0;
2315}
2316
2317static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
2318                     struct seq_file *seq)
2319{
2320    if (!cgroup_lock_live_group(cgrp))
2321        return -ENODEV;
2322    seq_puts(seq, cgrp->root->release_agent_path);
2323    seq_putc(seq, '\n');
2324    cgroup_unlock();
2325    return 0;
2326}
2327
2328/* A buffer size big enough for numbers or short strings */
2329#define CGROUP_LOCAL_BUFFER_SIZE 64
2330
2331static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
2332                struct file *file,
2333                const char __user *userbuf,
2334                size_t nbytes, loff_t *unused_ppos)
2335{
2336    char buffer[CGROUP_LOCAL_BUFFER_SIZE];
2337    int retval = 0;
2338    char *end;
2339
2340    if (!nbytes)
2341        return -EINVAL;
2342    if (nbytes >= sizeof(buffer))
2343        return -E2BIG;
2344    if (copy_from_user(buffer, userbuf, nbytes))
2345        return -EFAULT;
2346
2347    buffer[nbytes] = 0; /* nul-terminate */
2348    if (cft->write_u64) {
2349        u64 val = simple_strtoull(strstrip(buffer), &end, 0);
2350        if (*end)
2351            return -EINVAL;
2352        retval = cft->write_u64(cgrp, cft, val);
2353    } else {
2354        s64 val = simple_strtoll(strstrip(buffer), &end, 0);
2355        if (*end)
2356            return -EINVAL;
2357        retval = cft->write_s64(cgrp, cft, val);
2358    }
2359    if (!retval)
2360        retval = nbytes;
2361    return retval;
2362}
2363
2364static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
2365                   struct file *file,
2366                   const char __user *userbuf,
2367                   size_t nbytes, loff_t *unused_ppos)
2368{
2369    char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
2370    int retval = 0;
2371    size_t max_bytes = cft->max_write_len;
2372    char *buffer = local_buffer;
2373
2374    if (!max_bytes)
2375        max_bytes = sizeof(local_buffer) - 1;
2376    if (nbytes >= max_bytes)
2377        return -E2BIG;
2378    /* Allocate a dynamic buffer if we need one */
2379    if (nbytes >= sizeof(local_buffer)) {
2380        buffer = kmalloc(nbytes + 1, GFP_KERNEL);
2381        if (buffer == NULL)
2382            return -ENOMEM;
2383    }
2384    if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
2385        retval = -EFAULT;
2386        goto out;
2387    }
2388
2389    buffer[nbytes] = 0; /* nul-terminate */
2390    retval = cft->write_string(cgrp, cft, strstrip(buffer));
2391    if (!retval)
2392        retval = nbytes;
2393out:
2394    if (buffer != local_buffer)
2395        kfree(buffer);
2396    return retval;
2397}
2398
2399static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
2400                        size_t nbytes, loff_t *ppos)
2401{
2402    struct cftype *cft = __d_cft(file->f_dentry);
2403    struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2404
2405    if (cgroup_is_removed(cgrp))
2406        return -ENODEV;
2407    if (cft->write)
2408        return cft->write(cgrp, cft, file, buf, nbytes, ppos);
2409    if (cft->write_u64 || cft->write_s64)
2410        return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
2411    if (cft->write_string)
2412        return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
2413    if (cft->trigger) {
2414        int ret = cft->trigger(cgrp, (unsigned int)cft->private);
2415        return ret ? ret : nbytes;
2416    }
2417    return -EINVAL;
2418}
2419
2420static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
2421                   struct file *file,
2422                   char __user *buf, size_t nbytes,
2423                   loff_t *ppos)
2424{
2425    char tmp[CGROUP_LOCAL_BUFFER_SIZE];
2426    u64 val = cft->read_u64(cgrp, cft);
2427    int len = sprintf(tmp, "%llu\n", (unsigned long long) val);
2428
2429    return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
2430}
2431
2432static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
2433                   struct file *file,
2434                   char __user *buf, size_t nbytes,
2435                   loff_t *ppos)
2436{
2437    char tmp[CGROUP_LOCAL_BUFFER_SIZE];
2438    s64 val = cft->read_s64(cgrp, cft);
2439    int len = sprintf(tmp, "%lld\n", (long long) val);
2440
2441    return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
2442}
2443
2444static ssize_t cgroup_file_read(struct file *file, char __user *buf,
2445                   size_t nbytes, loff_t *ppos)
2446{
2447    struct cftype *cft = __d_cft(file->f_dentry);
2448    struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2449
2450    if (cgroup_is_removed(cgrp))
2451        return -ENODEV;
2452
2453    if (cft->read)
2454        return cft->read(cgrp, cft, file, buf, nbytes, ppos);
2455    if (cft->read_u64)
2456        return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
2457    if (cft->read_s64)
2458        return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
2459    return -EINVAL;
2460}
2461
2462/*
2463 * seqfile ops/methods for returning structured data. Currently just
2464 * supports string->u64 maps, but can be extended in future.
2465 */
2466
2467struct cgroup_seqfile_state {
2468    struct cftype *cft;
2469    struct cgroup *cgroup;
2470};
2471
2472static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
2473{
2474    struct seq_file *sf = cb->state;
2475    return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
2476}
2477
2478static int cgroup_seqfile_show(struct seq_file *m, void *arg)
2479{
2480    struct cgroup_seqfile_state *state = m->private;
2481    struct cftype *cft = state->cft;
2482    if (cft->read_map) {
2483        struct cgroup_map_cb cb = {
2484            .fill = cgroup_map_add,
2485            .state = m,
2486        };
2487        return cft->read_map(state->cgroup, cft, &cb);
2488    }
2489    return cft->read_seq_string(state->cgroup, cft, m);
2490}
2491
2492static int cgroup_seqfile_release(struct inode *inode, struct file *file)
2493{
2494    struct seq_file *seq = file->private_data;
2495    kfree(seq->private);
2496    return single_release(inode, file);
2497}
2498
2499static const struct file_operations cgroup_seqfile_operations = {
2500    .read = seq_read,
2501    .write = cgroup_file_write,
2502    .llseek = seq_lseek,
2503    .release = cgroup_seqfile_release,
2504};
2505
2506static int cgroup_file_open(struct inode *inode, struct file *file)
2507{
2508    int err;
2509    struct cftype *cft;
2510
2511    err = generic_file_open(inode, file);
2512    if (err)
2513        return err;
2514    cft = __d_cft(file->f_dentry);
2515
2516    if (cft->read_map || cft->read_seq_string) {
2517        struct cgroup_seqfile_state *state =
2518            kzalloc(sizeof(*state), GFP_USER);
2519        if (!state)
2520            return -ENOMEM;
2521        state->cft = cft;
2522        state->cgroup = __d_cgrp(file->f_dentry->d_parent);
2523        file->f_op = &cgroup_seqfile_operations;
2524        err = single_open(file, cgroup_seqfile_show, state);
2525        if (err < 0)
2526            kfree(state);
2527    } else if (cft->open)
2528        err = cft->open(inode, file);
2529    else
2530        err = 0;
2531
2532    return err;
2533}
2534
2535static int cgroup_file_release(struct inode *inode, struct file *file)
2536{
2537    struct cftype *cft = __d_cft(file->f_dentry);
2538    if (cft->release)
2539        return cft->release(inode, file);
2540    return 0;
2541}
2542
2543/*
2544 * cgroup_rename - Only allow simple rename of directories in place.
2545 */
2546static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
2547                struct inode *new_dir, struct dentry *new_dentry)
2548{
2549    if (!S_ISDIR(old_dentry->d_inode->i_mode))
2550        return -ENOTDIR;
2551    if (new_dentry->d_inode)
2552        return -EEXIST;
2553    if (old_dir != new_dir)
2554        return -EIO;
2555    return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
2556}
2557
2558static const struct file_operations cgroup_file_operations = {
2559    .read = cgroup_file_read,
2560    .write = cgroup_file_write,
2561    .llseek = generic_file_llseek,
2562    .open = cgroup_file_open,
2563    .release = cgroup_file_release,
2564};
2565
2566static const struct inode_operations cgroup_dir_inode_operations = {
2567    .lookup = cgroup_lookup,
2568    .mkdir = cgroup_mkdir,
2569    .rmdir = cgroup_rmdir,
2570    .rename = cgroup_rename,
2571};
2572
2573static struct dentry *cgroup_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
2574{
2575    if (dentry->d_name.len > NAME_MAX)
2576        return ERR_PTR(-ENAMETOOLONG);
2577    d_add(dentry, NULL);
2578    return NULL;
2579}
2580
2581/*
2582 * Check if a file is a control file
2583 */
2584static inline struct cftype *__file_cft(struct file *file)
2585{
2586    if (file->f_dentry->d_inode->i_fop != &cgroup_file_operations)
2587        return ERR_PTR(-EINVAL);
2588    return __d_cft(file->f_dentry);
2589}
2590
2591static int cgroup_create_file(struct dentry *dentry, umode_t mode,
2592                struct super_block *sb)
2593{
2594    struct inode *inode;
2595
2596    if (!dentry)
2597        return -ENOENT;
2598    if (dentry->d_inode)
2599        return -EEXIST;
2600
2601    inode = cgroup_new_inode(mode, sb);
2602    if (!inode)
2603        return -ENOMEM;
2604
2605    if (S_ISDIR(mode)) {
2606        inode->i_op = &cgroup_dir_inode_operations;
2607        inode->i_fop = &simple_dir_operations;
2608
2609        /* start off with i_nlink == 2 (for "." entry) */
2610        inc_nlink(inode);
2611
2612        /* start with the directory inode held, so that we can
2613         * populate it without racing with another mkdir */
2614        mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
2615    } else if (S_ISREG(mode)) {
2616        inode->i_size = 0;
2617        inode->i_fop = &cgroup_file_operations;
2618    }
2619    d_instantiate(dentry, inode);
2620    dget(dentry); /* Extra count - pin the dentry in core */
2621    return 0;
2622}
2623
2624/*
2625 * cgroup_create_dir - create a directory for an object.
2626 * @cgrp: the cgroup we create the directory for. It must have a valid
2627 * ->parent field. And we are going to fill its ->dentry field.
2628 * @dentry: dentry of the new cgroup
2629 * @mode: mode to set on new directory.
2630 */
2631static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
2632                umode_t mode)
2633{
2634    struct dentry *parent;
2635    int error = 0;
2636
2637    parent = cgrp->parent->dentry;
2638    error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb);
2639    if (!error) {
2640        dentry->d_fsdata = cgrp;
2641        inc_nlink(parent->d_inode);
2642        rcu_assign_pointer(cgrp->dentry, dentry);
2643        dget(dentry);
2644    }
2645    dput(dentry);
2646
2647    return error;
2648}
2649
2650/**
2651 * cgroup_file_mode - deduce file mode of a control file
2652 * @cft: the control file in question
2653 *
2654 * returns cft->mode if ->mode is not 0
2655 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
2656 * returns S_IRUGO if it has only a read handler
2657 * returns S_IWUSR if it has only a write hander
2658 */
2659static umode_t cgroup_file_mode(const struct cftype *cft)
2660{
2661    umode_t mode = 0;
2662
2663    if (cft->mode)
2664        return cft->mode;
2665
2666    if (cft->read || cft->read_u64 || cft->read_s64 ||
2667        cft->read_map || cft->read_seq_string)
2668        mode |= S_IRUGO;
2669
2670    if (cft->write || cft->write_u64 || cft->write_s64 ||
2671        cft->write_string || cft->trigger)
2672        mode |= S_IWUSR;
2673
2674    return mode;
2675}
2676
2677static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
2678               const struct cftype *cft)
2679{
2680    struct dentry *dir = cgrp->dentry;
2681    struct cgroup *parent = __d_cgrp(dir);
2682    struct dentry *dentry;
2683    struct cfent *cfe;
2684    int error;
2685    umode_t mode;
2686    char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
2687
2688    /* does @cft->flags tell us to skip creation on @cgrp? */
2689    if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
2690        return 0;
2691    if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgrp->parent)
2692        return 0;
2693
2694    if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
2695        strcpy(name, subsys->name);
2696        strcat(name, ".");
2697    }
2698    strcat(name, cft->name);
2699
2700    BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
2701
2702    cfe = kzalloc(sizeof(*cfe), GFP_KERNEL);
2703    if (!cfe)
2704        return -ENOMEM;
2705
2706    dentry = lookup_one_len(name, dir, strlen(name));
2707    if (IS_ERR(dentry)) {
2708        error = PTR_ERR(dentry);
2709        goto out;
2710    }
2711
2712    mode = cgroup_file_mode(cft);
2713    error = cgroup_create_file(dentry, mode | S_IFREG, cgrp->root->sb);
2714    if (!error) {
2715        cfe->type = (void *)cft;
2716        cfe->dentry = dentry;
2717        dentry->d_fsdata = cfe;
2718        list_add_tail(&cfe->node, &parent->files);
2719        cfe = NULL;
2720    }
2721    dput(dentry);
2722out:
2723    kfree(cfe);
2724    return error;
2725}
2726
2727static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
2728                  const struct cftype cfts[], bool is_add)
2729{
2730    const struct cftype *cft;
2731    int err, ret = 0;
2732
2733    for (cft = cfts; cft->name[0] != '\0'; cft++) {
2734        if (is_add)
2735            err = cgroup_add_file(cgrp, subsys, cft);
2736        else
2737            err = cgroup_rm_file(cgrp, cft);
2738        if (err) {
2739            pr_warning("cgroup_addrm_files: failed to %s %s, err=%d\n",
2740                   is_add ? "add" : "remove", cft->name, err);
2741            ret = err;
2742        }
2743    }
2744    return ret;
2745}
2746
2747static DEFINE_MUTEX(cgroup_cft_mutex);
2748
2749static void cgroup_cfts_prepare(void)
2750    __acquires(&cgroup_cft_mutex) __acquires(&cgroup_mutex)
2751{
2752    /*
2753     * Thanks to the entanglement with vfs inode locking, we can't walk
2754     * the existing cgroups under cgroup_mutex and create files.
2755     * Instead, we increment reference on all cgroups and build list of
2756     * them using @cgrp->cft_q_node. Grab cgroup_cft_mutex to ensure
2757     * exclusive access to the field.
2758     */
2759    mutex_lock(&cgroup_cft_mutex);
2760    mutex_lock(&cgroup_mutex);
2761}
2762
2763static void cgroup_cfts_commit(struct cgroup_subsys *ss,
2764                   const struct cftype *cfts, bool is_add)
2765    __releases(&cgroup_mutex) __releases(&cgroup_cft_mutex)
2766{
2767    LIST_HEAD(pending);
2768    struct cgroup *cgrp, *n;
2769
2770    /* %NULL @cfts indicates abort and don't bother if @ss isn't attached */
2771    if (cfts && ss->root != &rootnode) {
2772        list_for_each_entry(cgrp, &ss->root->allcg_list, allcg_node) {
2773            dget(cgrp->dentry);
2774            list_add_tail(&cgrp->cft_q_node, &pending);
2775        }
2776    }
2777
2778    mutex_unlock(&cgroup_mutex);
2779
2780    /*
2781     * All new cgroups will see @cfts update on @ss->cftsets. Add/rm
2782     * files for all cgroups which were created before.
2783     */
2784    list_for_each_entry_safe(cgrp, n, &pending, cft_q_node) {
2785        struct inode *inode = cgrp->dentry->d_inode;
2786
2787        mutex_lock(&inode->i_mutex);
2788        mutex_lock(&cgroup_mutex);
2789        if (!cgroup_is_removed(cgrp))
2790            cgroup_addrm_files(cgrp, ss, cfts, is_add);
2791        mutex_unlock(&cgroup_mutex);
2792        mutex_unlock(&inode->i_mutex);
2793
2794        list_del_init(&cgrp->cft_q_node);
2795        dput(cgrp->dentry);
2796    }
2797
2798    mutex_unlock(&cgroup_cft_mutex);
2799}
2800
2801/**
2802 * cgroup_add_cftypes - add an array of cftypes to a subsystem
2803 * @ss: target cgroup subsystem
2804 * @cfts: zero-length name terminated array of cftypes
2805 *
2806 * Register @cfts to @ss. Files described by @cfts are created for all
2807 * existing cgroups to which @ss is attached and all future cgroups will
2808 * have them too. This function can be called anytime whether @ss is
2809 * attached or not.
2810 *
2811 * Returns 0 on successful registration, -errno on failure. Note that this
2812 * function currently returns 0 as long as @cfts registration is successful
2813 * even if some file creation attempts on existing cgroups fail.
2814 */
2815int cgroup_add_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts)
2816{
2817    struct cftype_set *set;
2818
2819    set = kzalloc(sizeof(*set), GFP_KERNEL);
2820    if (!set)
2821        return -ENOMEM;
2822
2823    cgroup_cfts_prepare();
2824    set->cfts = cfts;
2825    list_add_tail(&set->node, &ss->cftsets);
2826    cgroup_cfts_commit(ss, cfts, true);
2827
2828    return 0;
2829}
2830EXPORT_SYMBOL_GPL(cgroup_add_cftypes);
2831
2832/**
2833 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
2834 * @ss: target cgroup subsystem
2835 * @cfts: zero-length name terminated array of cftypes
2836 *
2837 * Unregister @cfts from @ss. Files described by @cfts are removed from
2838 * all existing cgroups to which @ss is attached and all future cgroups
2839 * won't have them either. This function can be called anytime whether @ss
2840 * is attached or not.
2841 *
2842 * Returns 0 on successful unregistration, -ENOENT if @cfts is not
2843 * registered with @ss.
2844 */
2845int cgroup_rm_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts)
2846{
2847    struct cftype_set *set;
2848
2849    cgroup_cfts_prepare();
2850
2851    list_for_each_entry(set, &ss->cftsets, node) {
2852        if (set->cfts == cfts) {
2853            list_del_init(&set->node);
2854            cgroup_cfts_commit(ss, cfts, false);
2855            return 0;
2856        }
2857    }
2858
2859    cgroup_cfts_commit(ss, NULL, false);
2860    return -ENOENT;
2861}
2862
2863/**
2864 * cgroup_task_count - count the number of tasks in a cgroup.
2865 * @cgrp: the cgroup in question
2866 *
2867 * Return the number of tasks in the cgroup.
2868 */
2869int cgroup_task_count(const struct cgroup *cgrp)
2870{
2871    int count = 0;
2872    struct cg_cgroup_link *link;
2873
2874    read_lock(&css_set_lock);
2875    list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
2876        count += atomic_read(&link->cg->refcount);
2877    }
2878    read_unlock(&css_set_lock);
2879    return count;
2880}
2881
2882/*
2883 * Advance a list_head iterator. The iterator should be positioned at
2884 * the start of a css_set
2885 */
2886static void cgroup_advance_iter(struct cgroup *cgrp,
2887                struct cgroup_iter *it)
2888{
2889    struct list_head *l = it->cg_link;
2890    struct cg_cgroup_link *link;
2891    struct css_set *cg;
2892
2893    /* Advance to the next non-empty css_set */
2894    do {
2895        l = l->next;
2896        if (l == &cgrp->css_sets) {
2897            it->cg_link = NULL;
2898            return;
2899        }
2900        link = list_entry(l, struct cg_cgroup_link, cgrp_link_list);
2901        cg = link->cg;
2902    } while (list_empty(&cg->tasks));
2903    it->cg_link = l;
2904    it->task = cg->tasks.next;
2905}
2906
2907/*
2908 * To reduce the fork() overhead for systems that are not actually
2909 * using their cgroups capability, we don't maintain the lists running
2910 * through each css_set to its tasks until we see the list actually
2911 * used - in other words after the first call to cgroup_iter_start().
2912 */
2913static void cgroup_enable_task_cg_lists(void)
2914{
2915    struct task_struct *p, *g;
2916    write_lock(&css_set_lock);
2917    use_task_css_set_links = 1;
2918    /*
2919     * We need tasklist_lock because RCU is not safe against
2920     * while_each_thread(). Besides, a forking task that has passed
2921     * cgroup_post_fork() without seeing use_task_css_set_links = 1
2922     * is not guaranteed to have its child immediately visible in the
2923     * tasklist if we walk through it with RCU.
2924     */
2925    read_lock(&tasklist_lock);
2926    do_each_thread(g, p) {
2927        task_lock(p);
2928        /*
2929         * We should check if the process is exiting, otherwise
2930         * it will race with cgroup_exit() in that the list
2931         * entry won't be deleted though the process has exited.
2932         */
2933        if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
2934            list_add(&p->cg_list, &p->cgroups->tasks);
2935        task_unlock(p);
2936    } while_each_thread(g, p);
2937    read_unlock(&tasklist_lock);
2938    write_unlock(&css_set_lock);
2939}
2940
2941void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
2942    __acquires(css_set_lock)
2943{
2944    /*
2945     * The first time anyone tries to iterate across a cgroup,
2946     * we need to enable the list linking each css_set to its
2947     * tasks, and fix up all existing tasks.
2948     */
2949    if (!use_task_css_set_links)
2950        cgroup_enable_task_cg_lists();
2951
2952    read_lock(&css_set_lock);
2953    it->cg_link = &cgrp->css_sets;
2954    cgroup_advance_iter(cgrp, it);
2955}
2956
2957struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
2958                    struct cgroup_iter *it)
2959{
2960    struct task_struct *res;
2961    struct list_head *l = it->task;
2962    struct cg_cgroup_link *link;
2963
2964    /* If the iterator cg is NULL, we have no tasks */
2965    if (!it->cg_link)
2966        return NULL;
2967    res = list_entry(l, struct task_struct, cg_list);
2968    /* Advance iterator to find next entry */
2969    l = l->next;
2970    link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list);
2971    if (l == &link->cg->tasks) {
2972        /* We reached the end of this task list - move on to
2973         * the next cg_cgroup_link */
2974        cgroup_advance_iter(cgrp, it);
2975    } else {
2976        it->task = l;
2977    }
2978    return res;
2979}
2980
2981void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
2982    __releases(css_set_lock)
2983{
2984    read_unlock(&css_set_lock);
2985}
2986
2987static inline int started_after_time(struct task_struct *t1,
2988                     struct timespec *time,
2989                     struct task_struct *t2)
2990{
2991    int start_diff = timespec_compare(&t1->start_time, time);
2992    if (start_diff > 0) {
2993        return 1;
2994    } else if (start_diff < 0) {
2995        return 0;
2996    } else {
2997        /*
2998         * Arbitrarily, if two processes started at the same
2999         * time, we'll say that the lower pointer value
3000         * started first. Note that t2 may have exited by now
3001         * so this may not be a valid pointer any longer, but
3002         * that's fine - it still serves to distinguish
3003         * between two tasks started (effectively) simultaneously.
3004         */
3005        return t1 > t2;
3006    }
3007}
3008
3009/*
3010 * This function is a callback from heap_insert() and is used to order
3011 * the heap.
3012 * In this case we order the heap in descending task start time.
3013 */
3014static inline int started_after(void *p1, void *p2)
3015{
3016    struct task_struct *t1 = p1;
3017    struct task_struct *t2 = p2;
3018    return started_after_time(t1, &t2->start_time, t2);
3019}
3020
3021/**
3022 * cgroup_scan_tasks - iterate though all the tasks in a cgroup
3023 * @scan: struct cgroup_scanner containing arguments for the scan
3024 *
3025 * Arguments include pointers to callback functions test_task() and
3026 * process_task().
3027 * Iterate through all the tasks in a cgroup, calling test_task() for each,
3028 * and if it returns true, call process_task() for it also.
3029 * The test_task pointer may be NULL, meaning always true (select all tasks).
3030 * Effectively duplicates cgroup_iter_{start,next,end}()
3031 * but does not lock css_set_lock for the call to process_task().
3032 * The struct cgroup_scanner may be embedded in any structure of the caller's
3033 * creation.
3034 * It is guaranteed that process_task() will act on every task that
3035 * is a member of the cgroup for the duration of this call. This
3036 * function may or may not call process_task() for tasks that exit
3037 * or move to a different cgroup during the call, or are forked or
3038 * move into the cgroup during the call.
3039 *
3040 * Note that test_task() may be called with locks held, and may in some
3041 * situations be called multiple times for the same task, so it should
3042 * be cheap.
3043 * If the heap pointer in the struct cgroup_scanner is non-NULL, a heap has been
3044 * pre-allocated and will be used for heap operations (and its "gt" member will
3045 * be overwritten), else a temporary heap will be used (allocation of which
3046 * may cause this function to fail).
3047 */
3048int cgroup_scan_tasks(struct cgroup_scanner *scan)
3049{
3050    int retval, i;
3051    struct cgroup_iter it;
3052    struct task_struct *p, *dropped;
3053    /* Never dereference latest_task, since it's not refcounted */
3054    struct task_struct *latest_task = NULL;
3055    struct ptr_heap tmp_heap;
3056    struct ptr_heap *heap;
3057    struct timespec latest_time = { 0, 0 };
3058
3059    if (scan->heap) {
3060        /* The caller supplied our heap and pre-allocated its memory */
3061        heap = scan->heap;
3062        heap->gt = &started_after;
3063    } else {
3064        /* We need to allocate our own heap memory */
3065        heap = &tmp_heap;
3066        retval = heap_init(heap, PAGE_SIZE, GFP_KERNEL, &started_after);
3067        if (retval)
3068            /* cannot allocate the heap */
3069            return retval;
3070    }
3071
3072 again:
3073    /*
3074     * Scan tasks in the cgroup, using the scanner's "test_task" callback
3075     * to determine which are of interest, and using the scanner's
3076     * "process_task" callback to process any of them that need an update.
3077     * Since we don't want to hold any locks during the task updates,
3078     * gather tasks to be processed in a heap structure.
3079     * The heap is sorted by descending task start time.
3080     * If the statically-sized heap fills up, we overflow tasks that
3081     * started later, and in future iterations only consider tasks that
3082     * started after the latest task in the previous pass. This
3083     * guarantees forward progress and that we don't miss any tasks.
3084     */
3085    heap->size = 0;
3086    cgroup_iter_start(scan->cg, &it);
3087    while ((p = cgroup_iter_next(scan->cg, &it))) {
3088        /*
3089         * Only affect tasks that qualify per the caller's callback,
3090         * if he provided one
3091         */
3092        if (scan->test_task && !scan->test_task(p, scan))
3093            continue;
3094        /*
3095         * Only process tasks that started after the last task
3096         * we processed
3097         */
3098        if (!started_after_time(p, &latest_time, latest_task))
3099            continue;
3100        dropped = heap_insert(heap, p);
3101        if (dropped == NULL) {
3102            /*
3103             * The new task was inserted; the heap wasn't
3104             * previously full
3105             */
3106            get_task_struct(p);
3107        } else if (dropped != p) {
3108            /*
3109             * The new task was inserted, and pushed out a
3110             * different task
3111             */
3112            get_task_struct(p);
3113            put_task_struct(dropped);
3114        }
3115        /*
3116         * Else the new task was newer than anything already in
3117         * the heap and wasn't inserted
3118         */
3119    }
3120    cgroup_iter_end(scan->cg, &it);
3121
3122    if (heap->size) {
3123        for (i = 0; i < heap->size; i++) {
3124            struct task_struct *q = heap->ptrs[i];
3125            if (i == 0) {
3126                latest_time = q->start_time;
3127                latest_task = q;
3128            }
3129            /* Process the task per the caller's callback */
3130            scan->process_task(q, scan);
3131            put_task_struct(q);
3132        }
3133        /*
3134         * If we had to process any tasks at all, scan again
3135         * in case some of them were in the middle of forking
3136         * children that didn't get processed.
3137         * Not the most efficient way to do it, but it avoids
3138         * having to take callback_mutex in the fork path
3139         */
3140        goto again;
3141    }
3142    if (heap == &tmp_heap)
3143        heap_free(&tmp_heap);
3144    return 0;
3145}
3146
3147/*
3148 * Stuff for reading the 'tasks'/'procs' files.
3149 *
3150 * Reading this file can return large amounts of data if a cgroup has
3151 * *lots* of attached tasks. So it may need several calls to read(),
3152 * but we cannot guarantee that the information we produce is correct
3153 * unless we produce it entirely atomically.
3154 *
3155 */
3156
3157/* which pidlist file are we talking about? */
3158enum cgroup_filetype {
3159    CGROUP_FILE_PROCS,
3160    CGROUP_FILE_TASKS,
3161};
3162
3163/*
3164 * A pidlist is a list of pids that virtually represents the contents of one
3165 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
3166 * a pair (one each for procs, tasks) for each pid namespace that's relevant
3167 * to the cgroup.
3168 */
3169struct cgroup_pidlist {
3170    /*
3171     * used to find which pidlist is wanted. doesn't change as long as
3172     * this particular list stays in the list.
3173    */
3174    struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
3175    /* array of xids */
3176    pid_t *list;
3177    /* how many elements the above list has */
3178    int length;
3179    /* how many files are using the current array */
3180    int use_count;
3181    /* each of these stored in a list by its cgroup */
3182    struct list_head links;
3183    /* pointer to the cgroup we belong to, for list removal purposes */
3184    struct cgroup *owner;
3185    /* protects the other fields */
3186    struct rw_semaphore mutex;
3187};
3188
3189/*
3190 * The following two functions "fix" the issue where there are more pids
3191 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
3192 * TODO: replace with a kernel-wide solution to this problem
3193 */
3194#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
3195static void *pidlist_allocate(int count)
3196{
3197    if (PIDLIST_TOO_LARGE(count))
3198        return vmalloc(count * sizeof(pid_t));
3199    else
3200        return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
3201}
3202static void pidlist_free(void *p)
3203{
3204    if (is_vmalloc_addr(p))
3205        vfree(p);
3206    else
3207        kfree(p);
3208}
3209static void *pidlist_resize(void *p, int newcount)
3210{
3211    void *newlist;
3212    /* note: if new alloc fails, old p will still be valid either way */
3213    if (is_vmalloc_addr(p)) {
3214        newlist = vmalloc(newcount * sizeof(pid_t));
3215        if (!newlist)
3216            return NULL;
3217        memcpy(newlist, p, newcount * sizeof(pid_t));
3218        vfree(p);
3219    } else {
3220        newlist = krealloc(p, newcount * sizeof(pid_t), GFP_KERNEL);
3221    }
3222    return newlist;
3223}
3224
3225/*
3226 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
3227 * If the new stripped list is sufficiently smaller and there's enough memory
3228 * to allocate a new buffer, will let go of the unneeded memory. Returns the
3229 * number of unique elements.
3230 */
3231/* is the size difference enough that we should re-allocate the array? */
3232#define PIDLIST_REALLOC_DIFFERENCE(old, new) ((old) - PAGE_SIZE >= (new))
3233static int pidlist_uniq(pid_t **p, int length)
3234{
3235    int src, dest = 1;
3236    pid_t *list = *p;
3237    pid_t *newlist;
3238
3239    /*
3240     * we presume the 0th element is unique, so i starts at 1. trivial
3241     * edge cases first; no work needs to be done for either
3242     */
3243    if (length == 0 || length == 1)
3244        return length;
3245    /* src and dest walk down the list; dest counts unique elements */
3246    for (src = 1; src < length; src++) {
3247        /* find next unique element */
3248        while (list[src] == list[src-1]) {
3249            src++;
3250            if (src == length)
3251                goto after;
3252        }
3253        /* dest always points to where the next unique element goes */
3254        list[dest] = list[src];
3255        dest++;
3256    }
3257after:
3258    /*
3259     * if the length difference is large enough, we want to allocate a
3260     * smaller buffer to save memory. if this fails due to out of memory,
3261     * we'll just stay with what we've got.
3262     */
3263    if (PIDLIST_REALLOC_DIFFERENCE(length, dest)) {
3264        newlist = pidlist_resize(list, dest);
3265        if (newlist)
3266            *p = newlist;
3267    }
3268    return dest;
3269}
3270
3271static int cmppid(const void *a, const void *b)
3272{
3273    return *(pid_t *)a - *(pid_t *)b;
3274}
3275
3276/*
3277 * find the appropriate pidlist for our purpose (given procs vs tasks)
3278 * returns with the lock on that pidlist already held, and takes care
3279 * of the use count, or returns NULL with no locks held if we're out of
3280 * memory.
3281 */
3282static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
3283                          enum cgroup_filetype type)
3284{
3285    struct cgroup_pidlist *l;
3286    /* don't need task_nsproxy() if we're looking at ourself */
3287    struct pid_namespace *ns = current->nsproxy->pid_ns;
3288
3289    /*
3290     * We can't drop the pidlist_mutex before taking the l->mutex in case
3291     * the last ref-holder is trying to remove l from the list at the same
3292     * time. Holding the pidlist_mutex precludes somebody taking whichever
3293     * list we find out from under us - compare release_pid_array().
3294     */
3295    mutex_lock(&cgrp->pidlist_mutex);
3296    list_for_each_entry(l, &cgrp->pidlists, links) {
3297        if (l->key.type == type && l->key.ns == ns) {
3298            /* make sure l doesn't vanish out from under us */
3299            down_write(&l->mutex);
3300            mutex_unlock(&cgrp->pidlist_mutex);
3301            return l;
3302        }
3303    }
3304    /* entry not found; create a new one */
3305    l = kmalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
3306    if (!l) {
3307        mutex_unlock(&cgrp->pidlist_mutex);
3308        return l;
3309    }
3310    init_rwsem(&l->mutex);
3311    down_write(&l->mutex);
3312    l->key.type = type;
3313    l->key.ns = get_pid_ns(ns);
3314    l->use_count = 0; /* don't increment here */
3315    l->list = NULL;
3316    l->owner = cgrp;
3317    list_add(&l->links, &cgrp->pidlists);
3318    mutex_unlock(&cgrp->pidlist_mutex);
3319    return l;
3320}
3321
3322/*
3323 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
3324 */
3325static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
3326                  struct cgroup_pidlist **lp)
3327{
3328    pid_t *array;
3329    int length;
3330    int pid, n = 0; /* used for populating the array */
3331    struct cgroup_iter it;
3332    struct task_struct *tsk;
3333    struct cgroup_pidlist *l;
3334
3335    /*
3336     * If cgroup gets more users after we read count, we won't have
3337     * enough space - tough. This race is indistinguishable to the
3338     * caller from the case that the additional cgroup users didn't
3339     * show up until sometime later on.
3340     */
3341    length = cgroup_task_count(cgrp);
3342    array = pidlist_allocate(length);
3343    if (!array)
3344        return -ENOMEM;
3345    /* now, populate the array */
3346    cgroup_iter_start(cgrp, &it);
3347    while ((tsk = cgroup_iter_next(cgrp, &it))) {
3348        if (unlikely(n == length))
3349            break;
3350        /* get tgid or pid for procs or tasks file respectively */
3351        if (type == CGROUP_FILE_PROCS)
3352            pid = task_tgid_vnr(tsk);
3353        else
3354            pid = task_pid_vnr(tsk);
3355        if (pid > 0) /* make sure to only use valid results */
3356            array[n++] = pid;
3357    }
3358    cgroup_iter_end(cgrp, &it);
3359    length = n;
3360    /* now sort & (if procs) strip out duplicates */
3361    sort(array, length, sizeof(pid_t), cmppid, NULL);
3362    if (type == CGROUP_FILE_PROCS)
3363        length = pidlist_uniq(&array, length);
3364    l = cgroup_pidlist_find(cgrp, type);
3365    if (!l) {
3366        pidlist_free(array);
3367        return -ENOMEM;
3368    }
3369    /* store array, freeing old if necessary - lock already held */
3370    pidlist_free(l->list);
3371    l->list = array;
3372    l->length = length;
3373    l->use_count++;
3374    up_write(&l->mutex);
3375    *lp = l;
3376    return 0;
3377}
3378
3379/**
3380 * cgroupstats_build - build and fill cgroupstats
3381 * @stats: cgroupstats to fill information into
3382 * @dentry: A dentry entry belonging to the cgroup for which stats have
3383 * been requested.
3384 *
3385 * Build and fill cgroupstats so that taskstats can export it to user
3386 * space.
3387 */
3388int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
3389{
3390    int ret = -EINVAL;
3391    struct cgroup *cgrp;
3392    struct cgroup_iter it;
3393    struct task_struct *tsk;
3394
3395    /*
3396     * Validate dentry by checking the superblock operations,
3397     * and make sure it's a directory.
3398     */
3399    if (dentry->d_sb->s_op != &cgroup_ops ||
3400        !S_ISDIR(dentry->d_inode->i_mode))
3401         goto err;
3402
3403    ret = 0;
3404    cgrp = dentry->d_fsdata;
3405
3406    cgroup_iter_start(cgrp, &it);
3407    while ((tsk = cgroup_iter_next(cgrp, &it))) {
3408        switch (tsk->state) {
3409        case TASK_RUNNING:
3410            stats->nr_running++;
3411            break;
3412        case TASK_INTERRUPTIBLE:
3413            stats->nr_sleeping++;
3414            break;
3415        case TASK_UNINTERRUPTIBLE:
3416            stats->nr_uninterruptible++;
3417            break;
3418        case TASK_STOPPED:
3419            stats->nr_stopped++;
3420            break;
3421        default:
3422            if (delayacct_is_task_waiting_on_io(tsk))
3423                stats->nr_io_wait++;
3424            break;
3425        }
3426    }
3427    cgroup_iter_end(cgrp, &it);
3428
3429err:
3430    return ret;
3431}
3432
3433
3434/*
3435 * seq_file methods for the tasks/procs files. The seq_file position is the
3436 * next pid to display; the seq_file iterator is a pointer to the pid
3437 * in the cgroup->l->list array.
3438 */
3439
3440static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
3441{
3442    /*
3443     * Initially we receive a position value that corresponds to
3444     * one more than the last pid shown (or 0 on the first call or
3445     * after a seek to the start). Use a binary-search to find the
3446     * next pid to display, if any
3447     */
3448    struct cgroup_pidlist *l = s->private;
3449    int index = 0, pid = *pos;
3450    int *iter;
3451
3452    down_read(&l->mutex);
3453    if (pid) {
3454        int end = l->length;
3455
3456        while (index < end) {
3457            int mid = (index + end) / 2;
3458            if (l->list[mid] == pid) {
3459                index = mid;
3460                break;
3461            } else if (l->list[mid] <= pid)
3462                index = mid + 1;
3463            else
3464                end = mid;
3465        }
3466    }
3467    /* If we're off the end of the array, we're done */
3468    if (index >= l->length)
3469        return NULL;
3470    /* Update the abstract position to be the actual pid that we found */
3471    iter = l->list + index;
3472    *pos = *iter;
3473    return iter;
3474}
3475
3476static void cgroup_pidlist_stop(struct seq_file *s, void *v)
3477{
3478    struct cgroup_pidlist *l = s->private;
3479    up_read(&l->mutex);
3480}
3481
3482static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
3483{
3484    struct cgroup_pidlist *l = s->private;
3485    pid_t *p = v;
3486    pid_t *end = l->list + l->length;
3487    /*
3488     * Advance to the next pid in the array. If this goes off the
3489     * end, we're done
3490     */
3491    p++;
3492    if (p >= end) {
3493        return NULL;
3494    } else {
3495        *pos = *p;
3496        return p;
3497    }
3498}
3499
3500static int cgroup_pidlist_show(struct seq_file *s, void *v)
3501{
3502    return seq_printf(s, "%d\n", *(int *)v);
3503}
3504
3505/*
3506 * seq_operations functions for iterating on pidlists through seq_file -
3507 * independent of whether it's tasks or procs
3508 */
3509static const struct seq_operations cgroup_pidlist_seq_operations = {
3510    .start = cgroup_pidlist_start,
3511    .stop = cgroup_pidlist_stop,
3512    .next = cgroup_pidlist_next,
3513    .show = cgroup_pidlist_show,
3514};
3515
3516static void cgroup_release_pid_array(struct cgroup_pidlist *l)
3517{
3518    /*
3519     * the case where we're the last user of this particular pidlist will
3520     * have us remove it from the cgroup's list, which entails taking the
3521     * mutex. since in pidlist_find the pidlist->lock depends on cgroup->
3522     * pidlist_mutex, we have to take pidlist_mutex first.
3523     */
3524    mutex_lock(&l->owner->pidlist_mutex);
3525    down_write(&l->mutex);
3526    BUG_ON(!l->use_count);
3527    if (!--l->use_count) {
3528        /* we're the last user if refcount is 0; remove and free */
3529        list_del(&l->links);
3530        mutex_unlock(&l->owner->pidlist_mutex);
3531        pidlist_free(l->list);
3532        put_pid_ns(l->key.ns);
3533        up_write(&l->mutex);
3534        kfree(l);
3535        return;
3536    }
3537    mutex_unlock(&l->owner->pidlist_mutex);
3538    up_write(&l->mutex);
3539}
3540
3541static int cgroup_pidlist_release(struct inode *inode, struct file *file)
3542{
3543    struct cgroup_pidlist *l;
3544    if (!(file->f_mode & FMODE_READ))
3545        return 0;
3546    /*
3547     * the seq_file will only be initialized if the file was opened for
3548     * reading; hence we check if it's not null only in that case.
3549     */
3550    l = ((struct seq_file *)file->private_data)->private;
3551    cgroup_release_pid_array(l);
3552    return seq_release(inode, file);
3553}
3554
3555static const struct file_operations cgroup_pidlist_operations = {
3556    .read = seq_read,
3557    .llseek = seq_lseek,
3558    .write = cgroup_file_write,
3559    .release = cgroup_pidlist_release,
3560};
3561
3562/*
3563 * The following functions handle opens on a file that displays a pidlist
3564 * (tasks or procs). Prepare an array of the process/thread IDs of whoever's
3565 * in the cgroup.
3566 */
3567/* helper function for the two below it */
3568static int cgroup_pidlist_open(struct file *file, enum cgroup_filetype type)
3569{
3570    struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
3571    struct cgroup_pidlist *l;
3572    int retval;
3573
3574    /* Nothing to do for write-only files */
3575    if (!(file->f_mode & FMODE_READ))
3576        return 0;
3577
3578    /* have the array populated */
3579    retval = pidlist_array_load(cgrp, type, &l);
3580    if (retval)
3581        return retval;
3582    /* configure file information */
3583    file->f_op = &cgroup_pidlist_operations;
3584
3585    retval = seq_open(file, &cgroup_pidlist_seq_operations);
3586    if (retval) {
3587        cgroup_release_pid_array(l);
3588        return retval;
3589    }
3590    ((struct seq_file *)file->private_data)->private = l;
3591    return 0;
3592}
3593static int cgroup_tasks_open(struct inode *unused, struct file *file)
3594{
3595    return cgroup_pidlist_open(file, CGROUP_FILE_TASKS);
3596}
3597static int cgroup_procs_open(struct inode *unused, struct file *file)
3598{
3599    return cgroup_pidlist_open(file, CGROUP_FILE_PROCS);
3600}
3601
3602static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
3603                        struct cftype *cft)
3604{
3605    return notify_on_release(cgrp);
3606}
3607
3608static int cgroup_write_notify_on_release(struct cgroup *cgrp,
3609                      struct cftype *cft,
3610                      u64 val)
3611{
3612    clear_bit(CGRP_RELEASABLE, &cgrp->flags);
3613    if (val)
3614        set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3615    else
3616        clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3617    return 0;
3618}
3619
3620/*
3621 * Unregister event and free resources.
3622 *
3623 * Gets called from workqueue.
3624 */
3625static void cgroup_event_remove(struct work_struct *work)
3626{
3627    struct cgroup_event *event = container_of(work, struct cgroup_event,
3628            remove);
3629    struct cgroup *cgrp = event->cgrp;
3630
3631    event->cft->unregister_event(cgrp, event->cft, event->eventfd);
3632
3633    eventfd_ctx_put(event->eventfd);
3634    kfree(event);
3635    dput(cgrp->dentry);
3636}
3637
3638/*
3639 * Gets called on POLLHUP on eventfd when user closes it.
3640 *
3641 * Called with wqh->lock held and interrupts disabled.
3642 */
3643static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
3644        int sync, void *key)
3645{
3646    struct cgroup_event *event = container_of(wait,
3647            struct cgroup_event, wait);
3648    struct cgroup *cgrp = event->cgrp;
3649    unsigned long flags = (unsigned long)key;
3650
3651    if (flags & POLLHUP) {
3652        __remove_wait_queue(event->wqh, &event->wait);
3653        spin_lock(&cgrp->event_list_lock);
3654        list_del(&event->list);
3655        spin_unlock(&cgrp->event_list_lock);
3656        /*
3657         * We are in atomic context, but cgroup_event_remove() may
3658         * sleep, so we have to call it in workqueue.
3659         */
3660        schedule_work(&event->remove);
3661    }
3662
3663    return 0;
3664}
3665
3666static void cgroup_event_ptable_queue_proc(struct file *file,
3667        wait_queue_head_t *wqh, poll_table *pt)
3668{
3669    struct cgroup_event *event = container_of(pt,
3670            struct cgroup_event, pt);
3671
3672    event->wqh = wqh;
3673    add_wait_queue(wqh, &event->wait);
3674}
3675
3676/*
3677 * Parse input and register new cgroup event handler.
3678 *
3679 * Input must be in format '<event_fd> <control_fd> <args>'.
3680 * Interpretation of args is defined by control file implementation.
3681 */
3682static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
3683                      const char *buffer)
3684{
3685    struct cgroup_event *event = NULL;
3686    unsigned int efd, cfd;
3687    struct file *efile = NULL;
3688    struct file *cfile = NULL;
3689    char *endp;
3690    int ret;
3691
3692    efd = simple_strtoul(buffer, &endp, 10);
3693    if (*endp != ' ')
3694        return -EINVAL;
3695    buffer = endp + 1;
3696
3697    cfd = simple_strtoul(buffer, &endp, 10);
3698    if ((*endp != ' ') && (*endp != '\0'))
3699        return -EINVAL;
3700    buffer = endp + 1;
3701
3702    event = kzalloc(sizeof(*event), GFP_KERNEL);
3703    if (!event)
3704        return -ENOMEM;
3705    event->cgrp = cgrp;
3706    INIT_LIST_HEAD(&event->list);
3707    init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
3708    init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
3709    INIT_WORK(&event->remove, cgroup_event_remove);
3710
3711    efile = eventfd_fget(efd);
3712    if (IS_ERR(efile)) {
3713        ret = PTR_ERR(efile);
3714        goto fail;
3715    }
3716
3717    event->eventfd = eventfd_ctx_fileget(efile);
3718    if (IS_ERR(event->eventfd)) {
3719        ret = PTR_ERR(event->eventfd);
3720        goto fail;
3721    }
3722
3723    cfile = fget(cfd);
3724    if (!cfile) {
3725        ret = -EBADF;
3726        goto fail;
3727    }
3728
3729    /* the process need read permission on control file */
3730    /* AV: shouldn't we check that it's been opened for read instead? */
3731    ret = inode_permission(cfile->f_path.dentry->d_inode, MAY_READ);
3732    if (ret < 0)
3733        goto fail;
3734
3735    event->cft = __file_cft(cfile);
3736    if (IS_ERR(event->cft)) {
3737        ret = PTR_ERR(event->cft);
3738        goto fail;
3739    }
3740
3741    if (!event->cft->register_event || !event->cft->unregister_event) {
3742        ret = -EINVAL;
3743        goto fail;
3744    }
3745
3746    ret = event->cft->register_event(cgrp, event->cft,
3747            event->eventfd, buffer);
3748    if (ret)
3749        goto fail;
3750
3751    if (efile->f_op->poll(efile, &event->pt) & POLLHUP) {
3752        event->cft->unregister_event(cgrp, event->cft, event->eventfd);
3753        ret = 0;
3754        goto fail;
3755    }
3756
3757    /*
3758     * Events should be removed after rmdir of cgroup directory, but before
3759     * destroying subsystem state objects. Let's take reference to cgroup
3760     * directory dentry to do that.
3761     */
3762    dget(cgrp->dentry);
3763
3764    spin_lock(&cgrp->event_list_lock);
3765    list_add(&event->list, &cgrp->event_list);
3766    spin_unlock(&cgrp->event_list_lock);
3767
3768    fput(cfile);
3769    fput(efile);
3770
3771    return 0;
3772
3773fail:
3774    if (cfile)
3775        fput(cfile);
3776
3777    if (event && event->eventfd && !IS_ERR(event->eventfd))
3778        eventfd_ctx_put(event->eventfd);
3779
3780    if (!IS_ERR_OR_NULL(efile))
3781        fput(efile);
3782
3783    kfree(event);
3784
3785    return ret;
3786}
3787
3788static u64 cgroup_clone_children_read(struct cgroup *cgrp,
3789                    struct cftype *cft)
3790{
3791    return clone_children(cgrp);
3792}
3793
3794static int cgroup_clone_children_write(struct cgroup *cgrp,
3795                     struct cftype *cft,
3796                     u64 val)
3797{
3798    if (val)
3799        set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
3800    else
3801        clear_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
3802    return 0;
3803}
3804
3805/*
3806 * for the common functions, 'private' gives the type of file
3807 */
3808/* for hysterical raisins, we can't put this on the older files */
3809#define CGROUP_FILE_GENERIC_PREFIX "cgroup."
3810static struct cftype files[] = {
3811    {
3812        .name = "tasks",
3813        .open = cgroup_tasks_open,
3814        .write_u64 = cgroup_tasks_write,
3815        .release = cgroup_pidlist_release,
3816        .mode = S_IRUGO | S_IWUSR,
3817    },
3818    {
3819        .name = CGROUP_FILE_GENERIC_PREFIX "procs",
3820        .open = cgroup_procs_open,
3821        .write_u64 = cgroup_procs_write,
3822        .release = cgroup_pidlist_release,
3823        .mode = S_IRUGO | S_IWUSR,
3824    },
3825    {
3826        .name = "notify_on_release",
3827        .read_u64 = cgroup_read_notify_on_release,
3828        .write_u64 = cgroup_write_notify_on_release,
3829    },
3830    {
3831        .name = CGROUP_FILE_GENERIC_PREFIX "event_control",
3832        .write_string = cgroup_write_event_control,
3833        .mode = S_IWUGO,
3834    },
3835    {
3836        .name = "cgroup.clone_children",
3837        .read_u64 = cgroup_clone_children_read,
3838        .write_u64 = cgroup_clone_children_write,
3839    },
3840    {
3841        .name = "release_agent",
3842        .flags = CFTYPE_ONLY_ON_ROOT,
3843        .read_seq_string = cgroup_release_agent_show,
3844        .write_string = cgroup_release_agent_write,
3845        .max_write_len = PATH_MAX,
3846    },
3847    { } /* terminate */
3848};
3849
3850static int cgroup_populate_dir(struct cgroup *cgrp)
3851{
3852    int err;
3853    struct cgroup_subsys *ss;
3854
3855    err = cgroup_addrm_files(cgrp, NULL, files, true);
3856    if (err < 0)
3857        return err;
3858
3859    /* process cftsets of each subsystem */
3860    for_each_subsys(cgrp->root, ss) {
3861        struct cftype_set *set;
3862
3863        list_for_each_entry(set, &ss->cftsets, node)
3864            cgroup_addrm_files(cgrp, ss, set->cfts, true);
3865    }
3866
3867    /* This cgroup is ready now */
3868    for_each_subsys(cgrp->root, ss) {
3869        struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
3870        /*
3871         * Update id->css pointer and make this css visible from
3872         * CSS ID functions. This pointer will be dereferened
3873         * from RCU-read-side without locks.
3874         */
3875        if (css->id)
3876            rcu_assign_pointer(css->id->css, css);
3877    }
3878
3879    return 0;
3880}
3881
3882static void css_dput_fn(struct work_struct *work)
3883{
3884    struct cgroup_subsys_state *css =
3885        container_of(work, struct cgroup_subsys_state, dput_work);
3886    struct dentry *dentry = css->cgroup->dentry;
3887    struct super_block *sb = dentry->d_sb;
3888
3889    atomic_inc(&sb->s_active);
3890    dput(dentry);
3891    deactivate_super(sb);
3892}
3893
3894static void init_cgroup_css(struct cgroup_subsys_state *css,
3895                   struct cgroup_subsys *ss,
3896                   struct cgroup *cgrp)
3897{
3898    css->cgroup = cgrp;
3899    atomic_set(&css->refcnt, 1);
3900    css->flags = 0;
3901    css->id = NULL;
3902    if (cgrp == dummytop)
3903        set_bit(CSS_ROOT, &css->flags);
3904    BUG_ON(cgrp->subsys[ss->subsys_id]);
3905    cgrp->subsys[ss->subsys_id] = css;
3906
3907    /*
3908     * If !clear_css_refs, css holds an extra ref to @cgrp->dentry
3909     * which is put on the last css_put(). dput() requires process
3910     * context, which css_put() may be called without. @css->dput_work
3911     * will be used to invoke dput() asynchronously from css_put().
3912     */
3913    INIT_WORK(&css->dput_work, css_dput_fn);
3914    if (ss->__DEPRECATED_clear_css_refs)
3915        set_bit(CSS_CLEAR_CSS_REFS, &css->flags);
3916}
3917
3918static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
3919{
3920    /* We need to take each hierarchy_mutex in a consistent order */
3921    int i;
3922
3923    /*
3924     * No worry about a race with rebind_subsystems that might mess up the
3925     * locking order, since both parties are under cgroup_mutex.
3926     */
3927    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3928        struct cgroup_subsys *ss = subsys[i];
3929        if (ss == NULL)
3930            continue;
3931        if (ss->root == root)
3932            mutex_lock(&ss->hierarchy_mutex);
3933    }
3934}
3935
3936static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
3937{
3938    int i;
3939
3940    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3941        struct cgroup_subsys *ss = subsys[i];
3942        if (ss == NULL)
3943            continue;
3944        if (ss->root == root)
3945            mutex_unlock(&ss->hierarchy_mutex);
3946    }
3947}
3948
3949/*
3950 * cgroup_create - create a cgroup
3951 * @parent: cgroup that will be parent of the new cgroup
3952 * @dentry: dentry of the new cgroup
3953 * @mode: mode to set on new inode
3954 *
3955 * Must be called with the mutex on the parent inode held
3956 */
3957static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
3958                 umode_t mode)
3959{
3960    struct cgroup *cgrp;
3961    struct cgroupfs_root *root = parent->root;
3962    int err = 0;
3963    struct cgroup_subsys *ss;
3964    struct super_block *sb = root->sb;
3965
3966    cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
3967    if (!cgrp)
3968        return -ENOMEM;
3969
3970    /* Grab a reference on the superblock so the hierarchy doesn't
3971     * get deleted on unmount if there are child cgroups. This
3972     * can be done outside cgroup_mutex, since the sb can't
3973     * disappear while someone has an open control file on the
3974     * fs */
3975    atomic_inc(&sb->s_active);
3976
3977    mutex_lock(&cgroup_mutex);
3978
3979    init_cgroup_housekeeping(cgrp);
3980
3981    cgrp->parent = parent;
3982    cgrp->root = parent->root;
3983    cgrp->top_cgroup = parent->top_cgroup;
3984
3985    if (notify_on_release(parent))
3986        set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3987
3988    if (clone_children(parent))
3989        set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
3990
3991    for_each_subsys(root, ss) {
3992        struct cgroup_subsys_state *css = ss->create(cgrp);
3993
3994        if (IS_ERR(css)) {
3995            err = PTR_ERR(css);
3996            goto err_destroy;
3997        }
3998        init_cgroup_css(css, ss, cgrp);
3999        if (ss->use_id) {
4000            err = alloc_css_id(ss, parent, cgrp);
4001            if (err)
4002                goto err_destroy;
4003        }
4004        /* At error, ->destroy() callback has to free assigned ID. */
4005        if (clone_children(parent) && ss->post_clone)
4006            ss->post_clone(cgrp);
4007    }
4008
4009    cgroup_lock_hierarchy(root);
4010    list_add(&cgrp->sibling, &cgrp->parent->children);
4011    cgroup_unlock_hierarchy(root);
4012    root->number_of_cgroups++;
4013
4014    err = cgroup_create_dir(cgrp, dentry, mode);
4015    if (err < 0)
4016        goto err_remove;
4017
4018    /* If !clear_css_refs, each css holds a ref to the cgroup's dentry */
4019    for_each_subsys(root, ss)
4020        if (!ss->__DEPRECATED_clear_css_refs)
4021            dget(dentry);
4022
4023    /* The cgroup directory was pre-locked for us */
4024    BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
4025
4026    list_add_tail(&cgrp->allcg_node, &root->allcg_list);
4027
4028    err = cgroup_populate_dir(cgrp);
4029    /* If err < 0, we have a half-filled directory - oh well ;) */
4030
4031    mutex_unlock(&cgroup_mutex);
4032    mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
4033
4034    return 0;
4035
4036 err_remove:
4037
4038    cgroup_lock_hierarchy(root);
4039    list_del(&cgrp->sibling);
4040    cgroup_unlock_hierarchy(root);
4041    root->number_of_cgroups--;
4042
4043 err_destroy:
4044
4045    for_each_subsys(root, ss) {
4046        if (cgrp->subsys[ss->subsys_id])
4047            ss->destroy(cgrp);
4048    }
4049
4050    mutex_unlock(&cgroup_mutex);
4051
4052    /* Release the reference count that we took on the superblock */
4053    deactivate_super(sb);
4054
4055    kfree(cgrp);
4056    return err;
4057}
4058
4059static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
4060{
4061    struct cgroup *c_parent = dentry->d_parent->d_fsdata;
4062
4063    /* the vfs holds inode->i_mutex already */
4064    return cgroup_create(c_parent, dentry, mode | S_IFDIR);
4065}
4066
4067/*
4068 * Check the reference count on each subsystem. Since we already
4069 * established that there are no tasks in the cgroup, if the css refcount
4070 * is also 1, then there should be no outstanding references, so the
4071 * subsystem is safe to destroy. We scan across all subsystems rather than
4072 * using the per-hierarchy linked list of mounted subsystems since we can
4073 * be called via check_for_release() with no synchronization other than
4074 * RCU, and the subsystem linked list isn't RCU-safe.
4075 */
4076static int cgroup_has_css_refs(struct cgroup *cgrp)
4077{
4078    int i;
4079
4080    /*
4081     * We won't need to lock the subsys array, because the subsystems
4082     * we're concerned about aren't going anywhere since our cgroup root
4083     * has a reference on them.
4084     */
4085    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4086        struct cgroup_subsys *ss = subsys[i];
4087        struct cgroup_subsys_state *css;
4088
4089        /* Skip subsystems not present or not in this hierarchy */
4090        if (ss == NULL || ss->root != cgrp->root)
4091            continue;
4092
4093        css = cgrp->subsys[ss->subsys_id];
4094        /*
4095         * When called from check_for_release() it's possible
4096         * that by this point the cgroup has been removed
4097         * and the css deleted. But a false-positive doesn't
4098         * matter, since it can only happen if the cgroup
4099         * has been deleted and hence no longer needs the
4100         * release agent to be called anyway.
4101         */
4102        if (css && css_refcnt(css) > 1)
4103            return 1;
4104    }
4105    return 0;
4106}
4107
4108/*
4109 * Atomically mark all (or else none) of the cgroup's CSS objects as
4110 * CSS_REMOVED. Return true on success, or false if the cgroup has
4111 * busy subsystems. Call with cgroup_mutex held
4112 *
4113 * Depending on whether a subsys has __DEPRECATED_clear_css_refs set or
4114 * not, cgroup removal behaves differently.
4115 *
4116 * If clear is set, css refcnt for the subsystem should be zero before
4117 * cgroup removal can be committed. This is implemented by
4118 * CGRP_WAIT_ON_RMDIR and retry logic around ->pre_destroy(), which may be
4119 * called multiple times until all css refcnts reach zero and is allowed to
4120 * veto removal on any invocation. This behavior is deprecated and will be
4121 * removed as soon as the existing user (memcg) is updated.
4122 *
4123 * If clear is not set, each css holds an extra reference to the cgroup's
4124 * dentry and cgroup removal proceeds regardless of css refs.
4125 * ->pre_destroy() will be called at least once and is not allowed to fail.
4126 * On the last put of each css, whenever that may be, the extra dentry ref
4127 * is put so that dentry destruction happens only after all css's are
4128 * released.
4129 */
4130static int cgroup_clear_css_refs(struct cgroup *cgrp)
4131{
4132    struct cgroup_subsys *ss;
4133    unsigned long flags;
4134    bool failed = false;
4135
4136    local_irq_save(flags);
4137
4138    /*
4139     * Block new css_tryget() by deactivating refcnt. If all refcnts
4140     * for subsystems w/ clear_css_refs set were 1 at the moment of
4141     * deactivation, we succeeded.
4142     */
4143    for_each_subsys(cgrp->root, ss) {
4144        struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
4145
4146        WARN_ON(atomic_read(&css->refcnt) < 0);
4147        atomic_add(CSS_DEACT_BIAS, &css->refcnt);
4148
4149        if (ss->__DEPRECATED_clear_css_refs)
4150            failed |= css_refcnt(css) != 1;
4151    }
4152
4153    /*
4154     * If succeeded, set REMOVED and put all the base refs; otherwise,
4155     * restore refcnts to positive values. Either way, all in-progress
4156     * css_tryget() will be released.
4157     */
4158    for_each_subsys(cgrp->root, ss) {
4159        struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
4160
4161        if (!failed) {
4162            set_bit(CSS_REMOVED, &css->flags);
4163            css_put(css);
4164        } else {
4165            atomic_sub(CSS_DEACT_BIAS, &css->refcnt);
4166        }
4167    }
4168
4169    local_irq_restore(flags);
4170    return !failed;
4171}
4172
4173static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
4174{
4175    struct cgroup *cgrp = dentry->d_fsdata;
4176    struct dentry *d;
4177    struct cgroup *parent;
4178    DEFINE_WAIT(wait);
4179    struct cgroup_event *event, *tmp;
4180    int ret;
4181
4182    /* the vfs holds both inode->i_mutex already */
4183again:
4184    mutex_lock(&cgroup_mutex);
4185    if (atomic_read(&cgrp->count) != 0) {
4186        mutex_unlock(&cgroup_mutex);
4187        return -EBUSY;
4188    }
4189    if (!list_empty(&cgrp->children)) {
4190        mutex_unlock(&cgroup_mutex);
4191        return -EBUSY;
4192    }
4193    mutex_unlock(&cgroup_mutex);
4194
4195    /*
4196     * In general, subsystem has no css->refcnt after pre_destroy(). But
4197     * in racy cases, subsystem may have to get css->refcnt after
4198     * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
4199     * make rmdir return -EBUSY too often. To avoid that, we use waitqueue
4200     * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
4201     * and subsystem's reference count handling. Please see css_get/put
4202     * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
4203     */
4204    set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4205
4206    /*
4207     * Call pre_destroy handlers of subsys. Notify subsystems
4208     * that rmdir() request comes.
4209     */
4210    ret = cgroup_call_pre_destroy(cgrp);
4211    if (ret) {
4212        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4213        return ret;
4214    }
4215
4216    mutex_lock(&cgroup_mutex);
4217    parent = cgrp->parent;
4218    if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
4219        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4220        mutex_unlock(&cgroup_mutex);
4221        return -EBUSY;
4222    }
4223    prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
4224    if (!cgroup_clear_css_refs(cgrp)) {
4225        mutex_unlock(&cgroup_mutex);
4226        /*
4227         * Because someone may call cgroup_wakeup_rmdir_waiter() before
4228         * prepare_to_wait(), we need to check this flag.
4229         */
4230        if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
4231            schedule();
4232        finish_wait(&cgroup_rmdir_waitq, &wait);
4233        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4234        if (signal_pending(current))
4235            return -EINTR;
4236        goto again;
4237    }
4238    /* NO css_tryget() can success after here. */
4239    finish_wait(&cgroup_rmdir_waitq, &wait);
4240    clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4241
4242    raw_spin_lock(&release_list_lock);
4243    set_bit(CGRP_REMOVED, &cgrp->flags);
4244    if (!list_empty(&cgrp->release_list))
4245        list_del_init(&cgrp->release_list);
4246    raw_spin_unlock(&release_list_lock);
4247
4248    cgroup_lock_hierarchy(cgrp->root);
4249    /* delete this cgroup from parent->children */
4250    list_del_init(&cgrp->sibling);
4251    cgroup_unlock_hierarchy(cgrp->root);
4252
4253    list_del_init(&cgrp->allcg_node);
4254
4255    d = dget(cgrp->dentry);
4256
4257    cgroup_d_remove_dir(d);
4258    dput(d);
4259
4260    set_bit(CGRP_RELEASABLE, &parent->flags);
4261    check_for_release(parent);
4262
4263    /*
4264     * Unregister events and notify userspace.
4265     * Notify userspace about cgroup removing only after rmdir of cgroup
4266     * directory to avoid race between userspace and kernelspace
4267     */
4268    spin_lock(&cgrp->event_list_lock);
4269    list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
4270        list_del(&event->list);
4271        remove_wait_queue(event->wqh, &event->wait);
4272        eventfd_signal(event->eventfd, 1);
4273        schedule_work(&event->remove);
4274    }
4275    spin_unlock(&cgrp->event_list_lock);
4276
4277    mutex_unlock(&cgroup_mutex);
4278    return 0;
4279}
4280
4281static void __init_or_module cgroup_init_cftsets(struct cgroup_subsys *ss)
4282{
4283    INIT_LIST_HEAD(&ss->cftsets);
4284
4285    /*
4286     * base_cftset is embedded in subsys itself, no need to worry about
4287     * deregistration.
4288     */
4289    if (ss->base_cftypes) {
4290        ss->base_cftset.cfts = ss->base_cftypes;
4291        list_add_tail(&ss->base_cftset.node, &ss->cftsets);
4292    }
4293}
4294
4295static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
4296{
4297    struct cgroup_subsys_state *css;
4298
4299    printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
4300
4301    /* init base cftset */
4302    cgroup_init_cftsets(ss);
4303
4304    /* Create the top cgroup state for this subsystem */
4305    list_add(&ss->sibling, &rootnode.subsys_list);
4306    ss->root = &rootnode;
4307    css = ss->create(dummytop);
4308    /* We don't handle early failures gracefully */
4309    BUG_ON(IS_ERR(css));
4310    init_cgroup_css(css, ss, dummytop);
4311
4312    /* Update the init_css_set to contain a subsys
4313     * pointer to this state - since the subsystem is
4314     * newly registered, all tasks and hence the
4315     * init_css_set is in the subsystem's top cgroup. */
4316    init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
4317
4318    need_forkexit_callback |= ss->fork || ss->exit;
4319
4320    /* At system boot, before all subsystems have been
4321     * registered, no tasks have been forked, so we don't
4322     * need to invoke fork callbacks here. */
4323    BUG_ON(!list_empty(&init_task.tasks));
4324
4325    mutex_init(&ss->hierarchy_mutex);
4326    lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
4327    ss->active = 1;
4328
4329    /* this function shouldn't be used with modular subsystems, since they
4330     * need to register a subsys_id, among other things */
4331    BUG_ON(ss->module);
4332}
4333
4334/**
4335 * cgroup_load_subsys: load and register a modular subsystem at runtime
4336 * @ss: the subsystem to load
4337 *
4338 * This function should be called in a modular subsystem's initcall. If the
4339 * subsystem is built as a module, it will be assigned a new subsys_id and set
4340 * up for use. If the subsystem is built-in anyway, work is delegated to the
4341 * simpler cgroup_init_subsys.
4342 */
4343int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
4344{
4345    int i;
4346    struct cgroup_subsys_state *css;
4347
4348    /* check name and function validity */
4349    if (ss->name == NULL || strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN ||
4350        ss->create == NULL || ss->destroy == NULL)
4351        return -EINVAL;
4352
4353    /*
4354     * we don't support callbacks in modular subsystems. this check is
4355     * before the ss->module check for consistency; a subsystem that could
4356     * be a module should still have no callbacks even if the user isn't
4357     * compiling it as one.
4358     */
4359    if (ss->fork || ss->exit)
4360        return -EINVAL;
4361
4362    /*
4363     * an optionally modular subsystem is built-in: we want to do nothing,
4364     * since cgroup_init_subsys will have already taken care of it.
4365     */
4366    if (ss->module == NULL) {
4367        /* a few sanity checks */
4368        BUG_ON(ss->subsys_id >= CGROUP_BUILTIN_SUBSYS_COUNT);
4369        BUG_ON(subsys[ss->subsys_id] != ss);
4370        return 0;
4371    }
4372
4373    /* init base cftset */
4374    cgroup_init_cftsets(ss);
4375
4376    /*
4377     * need to register a subsys id before anything else - for example,
4378     * init_cgroup_css needs it.
4379     */
4380    mutex_lock(&cgroup_mutex);
4381    /* find the first empty slot in the array */
4382    for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
4383        if (subsys[i] == NULL)
4384            break;
4385    }
4386    if (i == CGROUP_SUBSYS_COUNT) {
4387        /* maximum number of subsystems already registered! */
4388        mutex_unlock(&cgroup_mutex);
4389        return -EBUSY;
4390    }
4391    /* assign ourselves the subsys_id */
4392    ss->subsys_id = i;
4393    subsys[i] = ss;
4394
4395    /*
4396     * no ss->create seems to need anything important in the ss struct, so
4397     * this can happen first (i.e. before the rootnode attachment).
4398     */
4399    css = ss->create(dummytop);
4400    if (IS_ERR(css)) {
4401        /* failure case - need to deassign the subsys[] slot. */
4402        subsys[i] = NULL;
4403        mutex_unlock(&cgroup_mutex);
4404        return PTR_ERR(css);
4405    }
4406
4407    list_add(&ss->sibling, &rootnode.subsys_list);
4408    ss->root = &rootnode;
4409
4410    /* our new subsystem will be attached to the dummy hierarchy. */
4411    init_cgroup_css(css, ss, dummytop);
4412    /* init_idr must be after init_cgroup_css because it sets css->id. */
4413    if (ss->use_id) {
4414        int ret = cgroup_init_idr(ss, css);
4415        if (ret) {
4416            dummytop->subsys[ss->subsys_id] = NULL;
4417            ss->destroy(dummytop);
4418            subsys[i] = NULL;
4419            mutex_unlock(&cgroup_mutex);
4420            return ret;
4421        }
4422    }
4423
4424    /*
4425     * Now we need to entangle the css into the existing css_sets. unlike
4426     * in cgroup_init_subsys, there are now multiple css_sets, so each one
4427     * will need a new pointer to it; done by iterating the css_set_table.
4428     * furthermore, modifying the existing css_sets will corrupt the hash
4429     * table state, so each changed css_set will need its hash recomputed.
4430     * this is all done under the css_set_lock.
4431     */
4432    write_lock(&css_set_lock);
4433    for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
4434        struct css_set *cg;
4435        struct hlist_node *node, *tmp;
4436        struct hlist_head *bucket = &css_set_table[i], *new_bucket;
4437
4438        hlist_for_each_entry_safe(cg, node, tmp, bucket, hlist) {
4439            /* skip entries that we already rehashed */
4440            if (cg->subsys[ss->subsys_id])
4441                continue;
4442            /* remove existing entry */
4443            hlist_del(&cg->hlist);
4444            /* set new value */
4445            cg->subsys[ss->subsys_id] = css;
4446            /* recompute hash and restore entry */
4447            new_bucket = css_set_hash(cg->subsys);
4448            hlist_add_head(&cg->hlist, new_bucket);
4449        }
4450    }
4451    write_unlock(&css_set_lock);
4452
4453    mutex_init(&ss->hierarchy_mutex);
4454    lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
4455    ss->active = 1;
4456
4457    /* success! */
4458    mutex_unlock(&cgroup_mutex);
4459    return 0;
4460}
4461EXPORT_SYMBOL_GPL(cgroup_load_subsys);
4462
4463/**
4464 * cgroup_unload_subsys: unload a modular subsystem
4465 * @ss: the subsystem to unload
4466 *
4467 * This function should be called in a modular subsystem's exitcall. When this
4468 * function is invoked, the refcount on the subsystem's module will be 0, so
4469 * the subsystem will not be attached to any hierarchy.
4470 */
4471void cgroup_unload_subsys(struct cgroup_subsys *ss)
4472{
4473    struct cg_cgroup_link *link;
4474    struct hlist_head *hhead;
4475
4476    BUG_ON(ss->module == NULL);
4477
4478    /*
4479     * we shouldn't be called if the subsystem is in use, and the use of
4480     * try_module_get in parse_cgroupfs_options should ensure that it
4481     * doesn't start being used while we're killing it off.
4482     */
4483    BUG_ON(ss->root != &rootnode);
4484
4485    mutex_lock(&cgroup_mutex);
4486    /* deassign the subsys_id */
4487    BUG_ON(ss->subsys_id < CGROUP_BUILTIN_SUBSYS_COUNT);
4488    subsys[ss->subsys_id] = NULL;
4489
4490    /* remove subsystem from rootnode's list of subsystems */
4491    list_del_init(&ss->sibling);
4492
4493    /*
4494     * disentangle the css from all css_sets attached to the dummytop. as
4495     * in loading, we need to pay our respects to the hashtable gods.
4496     */
4497    write_lock(&css_set_lock);
4498    list_for_each_entry(link, &dummytop->css_sets, cgrp_link_list) {
4499        struct css_set *cg = link->cg;
4500
4501        hlist_del(&cg->hlist);
4502        BUG_ON(!cg->subsys[ss->subsys_id]);
4503        cg->subsys[ss->subsys_id] = NULL;
4504        hhead = css_set_hash(cg->subsys);
4505        hlist_add_head(&cg->hlist, hhead);
4506    }
4507    write_unlock(&css_set_lock);
4508
4509    /*
4510     * remove subsystem's css from the dummytop and free it - need to free
4511     * before marking as null because ss->destroy needs the cgrp->subsys
4512     * pointer to find their state. note that this also takes care of
4513     * freeing the css_id.
4514     */
4515    ss->destroy(dummytop);
4516    dummytop->subsys[ss->subsys_id] = NULL;
4517
4518    mutex_unlock(&cgroup_mutex);
4519}
4520EXPORT_SYMBOL_GPL(cgroup_unload_subsys);
4521
4522/**
4523 * cgroup_init_early - cgroup initialization at system boot
4524 *
4525 * Initialize cgroups at system boot, and initialize any
4526 * subsystems that request early init.
4527 */
4528int __init cgroup_init_early(void)
4529{
4530    int i;
4531    atomic_set(&init_css_set.refcount, 1);
4532    INIT_LIST_HEAD(&init_css_set.cg_links);
4533    INIT_LIST_HEAD(&init_css_set.tasks);
4534    INIT_HLIST_NODE(&init_css_set.hlist);
4535    css_set_count = 1;
4536    init_cgroup_root(&rootnode);
4537    root_count = 1;
4538    init_task.cgroups = &init_css_set;
4539
4540    init_css_set_link.cg = &init_css_set;
4541    init_css_set_link.cgrp = dummytop;
4542    list_add(&init_css_set_link.cgrp_link_list,
4543         &rootnode.top_cgroup.css_sets);
4544    list_add(&init_css_set_link.cg_link_list,
4545         &init_css_set.cg_links);
4546
4547    for (i = 0; i < CSS_SET_TABLE_SIZE; i++)
4548        INIT_HLIST_HEAD(&css_set_table[i]);
4549
4550    /* at bootup time, we don't worry about modular subsystems */
4551    for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4552        struct cgroup_subsys *ss = subsys[i];
4553
4554        BUG_ON(!ss->name);
4555        BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
4556        BUG_ON(!ss->create);
4557        BUG_ON(!ss->destroy);
4558        if (ss->subsys_id != i) {
4559            printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
4560                   ss->name, ss->subsys_id);
4561            BUG();
4562        }
4563
4564        if (ss->early_init)
4565            cgroup_init_subsys(ss);
4566    }
4567    return 0;
4568}
4569
4570/**
4571 * cgroup_init - cgroup initialization
4572 *
4573 * Register cgroup filesystem and /proc file, and initialize
4574 * any subsystems that didn't request early init.
4575 */
4576int __init cgroup_init(void)
4577{
4578    int err;
4579    int i;
4580    struct hlist_head *hhead;
4581
4582    err = bdi_init(&cgroup_backing_dev_info);
4583    if (err)
4584        return err;
4585
4586    /* at bootup time, we don't worry about modular subsystems */
4587    for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4588        struct cgroup_subsys *ss = subsys[i];
4589        if (!ss->early_init)
4590            cgroup_init_subsys(ss);
4591        if (ss->use_id)
4592            cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
4593    }
4594
4595    /* Add init_css_set to the hash table */
4596    hhead = css_set_hash(init_css_set.subsys);
4597    hlist_add_head(&init_css_set.hlist, hhead);
4598    BUG_ON(!init_root_id(&rootnode));
4599
4600    cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
4601    if (!cgroup_kobj) {
4602        err = -ENOMEM;
4603        goto out;
4604    }
4605
4606    err = register_filesystem(&cgroup_fs_type);
4607    if (err < 0) {
4608        kobject_put(cgroup_kobj);
4609        goto out;
4610    }
4611
4612    proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
4613
4614out:
4615    if (err)
4616        bdi_destroy(&cgroup_backing_dev_info);
4617
4618    return err;
4619}
4620
4621/*
4622 * proc_cgroup_show()
4623 * - Print task's cgroup paths into seq_file, one line for each hierarchy
4624 * - Used for /proc/<pid>/cgroup.
4625 * - No need to task_lock(tsk) on this tsk->cgroup reference, as it
4626 * doesn't really matter if tsk->cgroup changes after we read it,
4627 * and we take cgroup_mutex, keeping cgroup_attach_task() from changing it
4628 * anyway. No need to check that tsk->cgroup != NULL, thanks to
4629 * the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
4630 * cgroup to top_cgroup.
4631 */
4632
4633/* TODO: Use a proper seq_file iterator */
4634static int proc_cgroup_show(struct seq_file *m, void *v)
4635{
4636    struct pid *pid;
4637    struct task_struct *tsk;
4638    char *buf;
4639    int retval;
4640    struct cgroupfs_root *root;
4641
4642    retval = -ENOMEM;
4643    buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
4644    if (!buf)
4645        goto out;
4646
4647    retval = -ESRCH;
4648    pid = m->private;
4649    tsk = get_pid_task(pid, PIDTYPE_PID);
4650    if (!tsk)
4651        goto out_free;
4652
4653    retval = 0;
4654
4655    mutex_lock(&cgroup_mutex);
4656
4657    for_each_active_root(root) {
4658        struct cgroup_subsys *ss;
4659        struct cgroup *cgrp;
4660        int count = 0;
4661
4662        seq_printf(m, "%d:", root->hierarchy_id);
4663        for_each_subsys(root, ss)
4664            seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
4665        if (strlen(root->name))
4666            seq_printf(m, "%sname=%s", count ? "," : "",
4667                   root->name);
4668        seq_putc(m, ':');
4669        cgrp = task_cgroup_from_root(tsk, root);
4670        retval = cgroup_path(cgrp, buf, PAGE_SIZE);
4671        if (retval < 0)
4672            goto out_unlock;
4673        seq_puts(m, buf);
4674        seq_putc(m, '\n');
4675    }
4676
4677out_unlock:
4678    mutex_unlock(&cgroup_mutex);
4679    put_task_struct(tsk);
4680out_free:
4681    kfree(buf);
4682out:
4683    return retval;
4684}
4685
4686static int cgroup_open(struct inode *inode, struct file *file)
4687{
4688    struct pid *pid = PROC_I(inode)->pid;
4689    return single_open(file, proc_cgroup_show, pid);
4690}
4691
4692const struct file_operations proc_cgroup_operations = {
4693    .open = cgroup_open,
4694    .read = seq_read,
4695    .llseek = seq_lseek,
4696    .release = single_release,
4697};
4698
4699/* Display information about each subsystem and each hierarchy */
4700static int proc_cgroupstats_show(struct seq_file *m, void *v)
4701{
4702    int i;
4703
4704    seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
4705    /*
4706     * ideally we don't want subsystems moving around while we do this.
4707     * cgroup_mutex is also necessary to guarantee an atomic snapshot of
4708     * subsys/hierarchy state.
4709     */
4710    mutex_lock(&cgroup_mutex);
4711    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4712        struct cgroup_subsys *ss = subsys[i];
4713        if (ss == NULL)
4714            continue;
4715        seq_printf(m, "%s\t%d\t%d\t%d\n",
4716               ss->name, ss->root->hierarchy_id,
4717               ss->root->number_of_cgroups, !ss->disabled);
4718    }
4719    mutex_unlock(&cgroup_mutex);
4720    return 0;
4721}
4722
4723static int cgroupstats_open(struct inode *inode, struct file *file)
4724{
4725    return single_open(file, proc_cgroupstats_show, NULL);
4726}
4727
4728static const struct file_operations proc_cgroupstats_operations = {
4729    .open = cgroupstats_open,
4730    .read = seq_read,
4731    .llseek = seq_lseek,
4732    .release = single_release,
4733};
4734
4735/**
4736 * cgroup_fork - attach newly forked task to its parents cgroup.
4737 * @child: pointer to task_struct of forking parent process.
4738 *
4739 * Description: A task inherits its parent's cgroup at fork().
4740 *
4741 * A pointer to the shared css_set was automatically copied in
4742 * fork.c by dup_task_struct(). However, we ignore that copy, since
4743 * it was not made under the protection of RCU, cgroup_mutex or
4744 * threadgroup_change_begin(), so it might no longer be a valid
4745 * cgroup pointer. cgroup_attach_task() might have already changed
4746 * current->cgroups, allowing the previously referenced cgroup
4747 * group to be removed and freed.
4748 *
4749 * Outside the pointer validity we also need to process the css_set
4750 * inheritance between threadgoup_change_begin() and
4751 * threadgoup_change_end(), this way there is no leak in any process
4752 * wide migration performed by cgroup_attach_proc() that could otherwise
4753 * miss a thread because it is too early or too late in the fork stage.
4754 *
4755 * At the point that cgroup_fork() is called, 'current' is the parent
4756 * task, and the passed argument 'child' points to the child task.
4757 */
4758void cgroup_fork(struct task_struct *child)
4759{
4760    /*
4761     * We don't need to task_lock() current because current->cgroups
4762     * can't be changed concurrently here. The parent obviously hasn't
4763     * exited and called cgroup_exit(), and we are synchronized against
4764     * cgroup migration through threadgroup_change_begin().
4765     */
4766    child->cgroups = current->cgroups;
4767    get_css_set(child->cgroups);
4768    INIT_LIST_HEAD(&child->cg_list);
4769}
4770
4771/**
4772 * cgroup_fork_callbacks - run fork callbacks
4773 * @child: the new task
4774 *
4775 * Called on a new task very soon before adding it to the
4776 * tasklist. No need to take any locks since no-one can
4777 * be operating on this task.
4778 */
4779void cgroup_fork_callbacks(struct task_struct *child)
4780{
4781    if (need_forkexit_callback) {
4782        int i;
4783        /*
4784         * forkexit callbacks are only supported for builtin
4785         * subsystems, and the builtin section of the subsys array is
4786         * immutable, so we don't need to lock the subsys array here.
4787         */
4788        for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4789            struct cgroup_subsys *ss = subsys[i];
4790            if (ss->fork)
4791                ss->fork(child);
4792        }
4793    }
4794}
4795
4796/**
4797 * cgroup_post_fork - called on a new task after adding it to the task list
4798 * @child: the task in question
4799 *
4800 * Adds the task to the list running through its css_set if necessary.
4801 * Has to be after the task is visible on the task list in case we race
4802 * with the first call to cgroup_iter_start() - to guarantee that the
4803 * new task ends up on its list.
4804 */
4805void cgroup_post_fork(struct task_struct *child)
4806{
4807    /*
4808     * use_task_css_set_links is set to 1 before we walk the tasklist
4809     * under the tasklist_lock and we read it here after we added the child
4810     * to the tasklist under the tasklist_lock as well. If the child wasn't
4811     * yet in the tasklist when we walked through it from
4812     * cgroup_enable_task_cg_lists(), then use_task_css_set_links value
4813     * should be visible now due to the paired locking and barriers implied
4814     * by LOCK/UNLOCK: it is written before the tasklist_lock unlock
4815     * in cgroup_enable_task_cg_lists() and read here after the tasklist_lock
4816     * lock on fork.
4817     */
4818    if (use_task_css_set_links) {
4819        write_lock(&css_set_lock);
4820        if (list_empty(&child->cg_list)) {
4821            /*
4822             * It's safe to use child->cgroups without task_lock()
4823             * here because we are protected through
4824             * threadgroup_change_begin() against concurrent
4825             * css_set change in cgroup_task_migrate(). Also
4826             * the task can't exit at that point until
4827             * wake_up_new_task() is called, so we are protected
4828             * against cgroup_exit() setting child->cgroup to
4829             * init_css_set.
4830             */
4831            list_add(&child->cg_list, &child->cgroups->tasks);
4832        }
4833        write_unlock(&css_set_lock);
4834    }
4835}
4836/**
4837 * cgroup_exit - detach cgroup from exiting task
4838 * @tsk: pointer to task_struct of exiting process
4839 * @run_callback: run exit callbacks?
4840 *
4841 * Description: Detach cgroup from @tsk and release it.
4842 *
4843 * Note that cgroups marked notify_on_release force every task in
4844 * them to take the global cgroup_mutex mutex when exiting.
4845 * This could impact scaling on very large systems. Be reluctant to
4846 * use notify_on_release cgroups where very high task exit scaling
4847 * is required on large systems.
4848 *
4849 * the_top_cgroup_hack:
4850 *
4851 * Set the exiting tasks cgroup to the root cgroup (top_cgroup).
4852 *
4853 * We call cgroup_exit() while the task is still competent to
4854 * handle notify_on_release(), then leave the task attached to the
4855 * root cgroup in each hierarchy for the remainder of its exit.
4856 *
4857 * To do this properly, we would increment the reference count on
4858 * top_cgroup, and near the very end of the kernel/exit.c do_exit()
4859 * code we would add a second cgroup function call, to drop that
4860 * reference. This would just create an unnecessary hot spot on
4861 * the top_cgroup reference count, to no avail.
4862 *
4863 * Normally, holding a reference to a cgroup without bumping its
4864 * count is unsafe. The cgroup could go away, or someone could
4865 * attach us to a different cgroup, decrementing the count on
4866 * the first cgroup that we never incremented. But in this case,
4867 * top_cgroup isn't going away, and either task has PF_EXITING set,
4868 * which wards off any cgroup_attach_task() attempts, or task is a failed
4869 * fork, never visible to cgroup_attach_task.
4870 */
4871void cgroup_exit(struct task_struct *tsk, int run_callbacks)
4872{
4873    struct css_set *cg;
4874    int i;
4875
4876    /*
4877     * Unlink from the css_set task list if necessary.
4878     * Optimistically check cg_list before taking
4879     * css_set_lock
4880     */
4881    if (!list_empty(&tsk->cg_list)) {
4882        write_lock(&css_set_lock);
4883        if (!list_empty(&tsk->cg_list))
4884            list_del_init(&tsk->cg_list);
4885        write_unlock(&css_set_lock);
4886    }
4887
4888    /* Reassign the task to the init_css_set. */
4889    task_lock(tsk);
4890    cg = tsk->cgroups;
4891    tsk->cgroups = &init_css_set;
4892
4893    if (run_callbacks && need_forkexit_callback) {
4894        /*
4895         * modular subsystems can't use callbacks, so no need to lock
4896         * the subsys array
4897         */
4898        for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4899            struct cgroup_subsys *ss = subsys[i];
4900            if (ss->exit) {
4901                struct cgroup *old_cgrp =
4902                    rcu_dereference_raw(cg->subsys[i])->cgroup;
4903                struct cgroup *cgrp = task_cgroup(tsk, i);
4904                ss->exit(cgrp, old_cgrp, tsk);
4905            }
4906        }
4907    }
4908    task_unlock(tsk);
4909
4910    if (cg)
4911        put_css_set_taskexit(cg);
4912}
4913
4914/**
4915 * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp
4916 * @cgrp: the cgroup in question
4917 * @task: the task in question
4918 *
4919 * See if @cgrp is a descendant of @task's cgroup in the appropriate
4920 * hierarchy.
4921 *
4922 * If we are sending in dummytop, then presumably we are creating
4923 * the top cgroup in the subsystem.
4924 *
4925 * Called only by the ns (nsproxy) cgroup.
4926 */
4927int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
4928{
4929    int ret;
4930    struct cgroup *target;
4931
4932    if (cgrp == dummytop)
4933        return 1;
4934
4935    target = task_cgroup_from_root(task, cgrp->root);
4936    while (cgrp != target && cgrp!= cgrp->top_cgroup)
4937        cgrp = cgrp->parent;
4938    ret = (cgrp == target);
4939    return ret;
4940}
4941
4942static void check_for_release(struct cgroup *cgrp)
4943{
4944    /* All of these checks rely on RCU to keep the cgroup
4945     * structure alive */
4946    if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count)
4947        && list_empty(&cgrp->children) && !cgroup_has_css_refs(cgrp)) {
4948        /* Control Group is currently removeable. If it's not
4949         * already queued for a userspace notification, queue
4950         * it now */
4951        int need_schedule_work = 0;
4952        raw_spin_lock(&release_list_lock);
4953        if (!cgroup_is_removed(cgrp) &&
4954            list_empty(&cgrp->release_list)) {
4955            list_add(&cgrp->release_list, &release_list);
4956            need_schedule_work = 1;
4957        }
4958        raw_spin_unlock(&release_list_lock);
4959        if (need_schedule_work)
4960            schedule_work(&release_agent_work);
4961    }
4962}
4963
4964/* Caller must verify that the css is not for root cgroup */
4965bool __css_tryget(struct cgroup_subsys_state *css)
4966{
4967    do {
4968        int v = css_refcnt(css);
4969
4970        if (atomic_cmpxchg(&css->refcnt, v, v + 1) == v)
4971            return true;
4972        cpu_relax();
4973    } while (!test_bit(CSS_REMOVED, &css->flags));
4974
4975    return false;
4976}
4977EXPORT_SYMBOL_GPL(__css_tryget);
4978
4979/* Caller must verify that the css is not for root cgroup */
4980void __css_put(struct cgroup_subsys_state *css)
4981{
4982    struct cgroup *cgrp = css->cgroup;
4983    int v;
4984
4985    rcu_read_lock();
4986    v = css_unbias_refcnt(atomic_dec_return(&css->refcnt));
4987
4988    switch (v) {
4989    case 1:
4990        if (notify_on_release(cgrp)) {
4991            set_bit(CGRP_RELEASABLE, &cgrp->flags);
4992            check_for_release(cgrp);
4993        }
4994        cgroup_wakeup_rmdir_waiter(cgrp);
4995        break;
4996    case 0:
4997        if (!test_bit(CSS_CLEAR_CSS_REFS, &css->flags))
4998            schedule_work(&css->dput_work);
4999        break;
5000    }
5001    rcu_read_unlock();
5002}
5003EXPORT_SYMBOL_GPL(__css_put);
5004
5005/*
5006 * Notify userspace when a cgroup is released, by running the
5007 * configured release agent with the name of the cgroup (path
5008 * relative to the root of cgroup file system) as the argument.
5009 *
5010 * Most likely, this user command will try to rmdir this cgroup.
5011 *
5012 * This races with the possibility that some other task will be
5013 * attached to this cgroup before it is removed, or that some other
5014 * user task will 'mkdir' a child cgroup of this cgroup. That's ok.
5015 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
5016 * unused, and this cgroup will be reprieved from its death sentence,
5017 * to continue to serve a useful existence. Next time it's released,
5018 * we will get notified again, if it still has 'notify_on_release' set.
5019 *
5020 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
5021 * means only wait until the task is successfully execve()'d. The
5022 * separate release agent task is forked by call_usermodehelper(),
5023 * then control in this thread returns here, without waiting for the
5024 * release agent task. We don't bother to wait because the caller of
5025 * this routine has no use for the exit status of the release agent
5026 * task, so no sense holding our caller up for that.
5027 */
5028static void cgroup_release_agent(struct work_struct *work)
5029{
5030    BUG_ON(work != &release_agent_work);
5031    mutex_lock(&cgroup_mutex);
5032    raw_spin_lock(&release_list_lock);
5033    while (!list_empty(&release_list)) {
5034        char *argv[3], *envp[3];
5035        int i;
5036        char *pathbuf = NULL, *agentbuf = NULL;
5037        struct cgroup *cgrp = list_entry(release_list.next,
5038                            struct cgroup,
5039                            release_list);
5040        list_del_init(&cgrp->release_list);
5041        raw_spin_unlock(&release_list_lock);
5042        pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
5043        if (!pathbuf)
5044            goto continue_free;
5045        if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
5046            goto continue_free;
5047        agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
5048        if (!agentbuf)
5049            goto continue_free;
5050
5051        i = 0;
5052        argv[i++] = agentbuf;
5053        argv[i++] = pathbuf;
5054        argv[i] = NULL;
5055
5056        i = 0;
5057        /* minimal command environment */
5058        envp[i++] = "HOME=/";
5059        envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
5060        envp[i] = NULL;
5061
5062        /* Drop the lock while we invoke the usermode helper,
5063         * since the exec could involve hitting disk and hence
5064         * be a slow process */
5065        mutex_unlock(&cgroup_mutex);
5066        call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
5067        mutex_lock(&cgroup_mutex);
5068 continue_free:
5069        kfree(pathbuf);
5070        kfree(agentbuf);
5071        raw_spin_lock(&release_list_lock);
5072    }
5073    raw_spin_unlock(&release_list_lock);
5074    mutex_unlock(&cgroup_mutex);
5075}
5076
5077static int __init cgroup_disable(char *str)
5078{
5079    int i;
5080    char *token;
5081
5082    while ((token = strsep(&str, ",")) != NULL) {
5083        if (!*token)
5084            continue;
5085        /*
5086         * cgroup_disable, being at boot time, can't know about module
5087         * subsystems, so we don't worry about them.
5088         */
5089        for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
5090            struct cgroup_subsys *ss = subsys[i];
5091
5092            if (!strcmp(token, ss->name)) {
5093                ss->disabled = 1;
5094                printk(KERN_INFO "Disabling %s control group"
5095                    " subsystem\n", ss->name);
5096                break;
5097            }
5098        }
5099    }
5100    return 1;
5101}
5102__setup("cgroup_disable=", cgroup_disable);
5103
5104/*
5105 * Functons for CSS ID.
5106 */
5107
5108/*
5109 *To get ID other than 0, this should be called when !cgroup_is_removed().
5110 */
5111unsigned short css_id(struct cgroup_subsys_state *css)
5112{
5113    struct css_id *cssid;
5114
5115    /*
5116     * This css_id() can return correct value when somone has refcnt
5117     * on this or this is under rcu_read_lock(). Once css->id is allocated,
5118     * it's unchanged until freed.
5119     */
5120    cssid = rcu_dereference_check(css->id, css_refcnt(css));
5121
5122    if (cssid)
5123        return cssid->id;
5124    return 0;
5125}
5126EXPORT_SYMBOL_GPL(css_id);
5127
5128unsigned short css_depth(struct cgroup_subsys_state *css)
5129{
5130    struct css_id *cssid;
5131
5132    cssid = rcu_dereference_check(css->id, css_refcnt(css));
5133
5134    if (cssid)
5135        return cssid->depth;
5136    return 0;
5137}
5138EXPORT_SYMBOL_GPL(css_depth);
5139
5140/**
5141 * css_is_ancestor - test "root" css is an ancestor of "child"
5142 * @child: the css to be tested.
5143 * @root: the css supporsed to be an ancestor of the child.
5144 *
5145 * Returns true if "root" is an ancestor of "child" in its hierarchy. Because
5146 * this function reads css->id, the caller must hold rcu_read_lock().
5147 * But, considering usual usage, the csses should be valid objects after test.
5148 * Assuming that the caller will do some action to the child if this returns
5149 * returns true, the caller must take "child";s reference count.
5150 * If "child" is valid object and this returns true, "root" is valid, too.
5151 */
5152
5153bool css_is_ancestor(struct cgroup_subsys_state *child,
5154            const struct cgroup_subsys_state *root)
5155{
5156    struct css_id *child_id;
5157    struct css_id *root_id;
5158
5159    child_id = rcu_dereference(child->id);
5160    if (!child_id)
5161        return false;
5162    root_id = rcu_dereference(root->id);
5163    if (!root_id)
5164        return false;
5165    if (child_id->depth < root_id->depth)
5166        return false;
5167    if (child_id->stack[root_id->depth] != root_id->id)
5168        return false;
5169    return true;
5170}
5171
5172void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
5173{
5174    struct css_id *id = css->id;
5175    /* When this is called before css_id initialization, id can be NULL */
5176    if (!id)
5177        return;
5178
5179    BUG_ON(!ss->use_id);
5180
5181    rcu_assign_pointer(id->css, NULL);
5182    rcu_assign_pointer(css->id, NULL);
5183    spin_lock(&ss->id_lock);
5184    idr_remove(&ss->idr, id->id);
5185    spin_unlock(&ss->id_lock);
5186    kfree_rcu(id, rcu_head);
5187}
5188EXPORT_SYMBOL_GPL(free_css_id);
5189
5190/*
5191 * This is called by init or create(). Then, calls to this function are
5192 * always serialized (By cgroup_mutex() at create()).
5193 */
5194
5195static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
5196{
5197    struct css_id *newid;
5198    int myid, error, size;
5199
5200    BUG_ON(!ss->use_id);
5201
5202    size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
5203    newid = kzalloc(size, GFP_KERNEL);
5204    if (!newid)
5205        return ERR_PTR(-ENOMEM);
5206    /* get id */
5207    if (unlikely(!idr_pre_get(&ss->idr, GFP_KERNEL))) {
5208        error = -ENOMEM;
5209        goto err_out;
5210    }
5211    spin_lock(&ss->id_lock);
5212    /* Don't use 0. allocates an ID of 1-65535 */
5213    error = idr_get_new_above(&ss->idr, newid, 1, &myid);
5214    spin_unlock(&ss->id_lock);
5215
5216    /* Returns error when there are no free spaces for new ID.*/
5217    if (error) {
5218        error = -ENOSPC;
5219        goto err_out;
5220    }
5221    if (myid > CSS_ID_MAX)
5222        goto remove_idr;
5223
5224    newid->id = myid;
5225    newid->depth = depth;
5226    return newid;
5227remove_idr:
5228    error = -ENOSPC;
5229    spin_lock(&ss->id_lock);
5230    idr_remove(&ss->idr, myid);
5231    spin_unlock(&ss->id_lock);
5232err_out:
5233    kfree(newid);
5234    return ERR_PTR(error);
5235
5236}
5237
5238static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
5239                        struct cgroup_subsys_state *rootcss)
5240{
5241    struct css_id *newid;
5242
5243    spin_lock_init(&ss->id_lock);
5244    idr_init(&ss->idr);
5245
5246    newid = get_new_cssid(ss, 0);
5247    if (IS_ERR(newid))
5248        return PTR_ERR(newid);
5249
5250    newid->stack[0] = newid->id;
5251    newid->css = rootcss;
5252    rootcss->id = newid;
5253    return 0;
5254}
5255
5256static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
5257            struct cgroup *child)
5258{
5259    int subsys_id, i, depth = 0;
5260    struct cgroup_subsys_state *parent_css, *child_css;
5261    struct css_id *child_id, *parent_id;
5262
5263    subsys_id = ss->subsys_id;
5264    parent_css = parent->subsys[subsys_id];
5265    child_css = child->subsys[subsys_id];
5266    parent_id = parent_css->id;
5267    depth = parent_id->depth + 1;
5268
5269    child_id = get_new_cssid(ss, depth);
5270    if (IS_ERR(child_id))
5271        return PTR_ERR(child_id);
5272
5273    for (i = 0; i < depth; i++)
5274        child_id->stack[i] = parent_id->stack[i];
5275    child_id->stack[depth] = child_id->id;
5276    /*
5277     * child_id->css pointer will be set after this cgroup is available
5278     * see cgroup_populate_dir()
5279     */
5280    rcu_assign_pointer(child_css->id, child_id);
5281
5282    return 0;
5283}
5284
5285/**
5286 * css_lookup - lookup css by id
5287 * @ss: cgroup subsys to be looked into.
5288 * @id: the id
5289 *
5290 * Returns pointer to cgroup_subsys_state if there is valid one with id.
5291 * NULL if not. Should be called under rcu_read_lock()
5292 */
5293struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
5294{
5295    struct css_id *cssid = NULL;
5296
5297    BUG_ON(!ss->use_id);
5298    cssid = idr_find(&ss->idr, id);
5299
5300    if (unlikely(!cssid))
5301        return NULL;
5302
5303    return rcu_dereference(cssid->css);
5304}
5305EXPORT_SYMBOL_GPL(css_lookup);
5306
5307/**
5308 * css_get_next - lookup next cgroup under specified hierarchy.
5309 * @ss: pointer to subsystem
5310 * @id: current position of iteration.
5311 * @root: pointer to css. search tree under this.
5312 * @foundid: position of found object.
5313 *
5314 * Search next css under the specified hierarchy of rootid. Calling under
5315 * rcu_read_lock() is necessary. Returns NULL if it reaches the end.
5316 */
5317struct cgroup_subsys_state *
5318css_get_next(struct cgroup_subsys *ss, int id,
5319         struct cgroup_subsys_state *root, int *foundid)
5320{
5321    struct cgroup_subsys_state *ret = NULL;
5322    struct css_id *tmp;
5323    int tmpid;
5324    int rootid = css_id(root);
5325    int depth = css_depth(root);
5326
5327    if (!rootid)
5328        return NULL;
5329
5330    BUG_ON(!ss->use_id);
5331    WARN_ON_ONCE(!rcu_read_lock_held());
5332
5333    /* fill start point for scan */
5334    tmpid = id;
5335    while (1) {
5336        /*
5337         * scan next entry from bitmap(tree), tmpid is updated after
5338         * idr_get_next().
5339         */
5340        tmp = idr_get_next(&ss->idr, &tmpid);
5341        if (!tmp)
5342            break;
5343        if (tmp->depth >= depth && tmp->stack[depth] == rootid) {
5344            ret = rcu_dereference(tmp->css);
5345            if (ret) {
5346                *foundid = tmpid;
5347                break;
5348            }
5349        }
5350        /* continue to scan from next id */
5351        tmpid = tmpid + 1;
5352    }
5353    return ret;
5354}
5355
5356/*
5357 * get corresponding css from file open on cgroupfs directory
5358 */
5359struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
5360{
5361    struct cgroup *cgrp;
5362    struct inode *inode;
5363    struct cgroup_subsys_state *css;
5364
5365    inode = f->f_dentry->d_inode;
5366    /* check in cgroup filesystem dir */
5367    if (inode->i_op != &cgroup_dir_inode_operations)
5368        return ERR_PTR(-EBADF);
5369
5370    if (id < 0 || id >= CGROUP_SUBSYS_COUNT)
5371        return ERR_PTR(-EINVAL);
5372
5373    /* get cgroup */
5374    cgrp = __d_cgrp(f->f_dentry);
5375    css = cgrp->subsys[id];
5376    return css ? css : ERR_PTR(-ENOENT);
5377}
5378
5379#ifdef CONFIG_CGROUP_DEBUG
5380static struct cgroup_subsys_state *debug_create(struct cgroup *cont)
5381{
5382    struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
5383
5384    if (!css)
5385        return ERR_PTR(-ENOMEM);
5386
5387    return css;
5388}
5389
5390static void debug_destroy(struct cgroup *cont)
5391{
5392    kfree(cont->subsys[debug_subsys_id]);
5393}
5394
5395static u64 cgroup_refcount_read(struct cgroup *cont, struct cftype *cft)
5396{
5397    return atomic_read(&cont->count);
5398}
5399
5400static u64 debug_taskcount_read(struct cgroup *cont, struct cftype *cft)
5401{
5402    return cgroup_task_count(cont);
5403}
5404
5405static u64 current_css_set_read(struct cgroup *cont, struct cftype *cft)
5406{
5407    return (u64)(unsigned long)current->cgroups;
5408}
5409
5410static u64 current_css_set_refcount_read(struct cgroup *cont,
5411                       struct cftype *cft)
5412{
5413    u64 count;
5414
5415    rcu_read_lock();
5416    count = atomic_read(&current->cgroups->refcount);
5417    rcu_read_unlock();
5418    return count;
5419}
5420
5421static int current_css_set_cg_links_read(struct cgroup *cont,
5422                     struct cftype *cft,
5423                     struct seq_file *seq)
5424{
5425    struct cg_cgroup_link *link;
5426    struct css_set *cg;
5427
5428    read_lock(&css_set_lock);
5429    rcu_read_lock();
5430    cg = rcu_dereference(current->cgroups);
5431    list_for_each_entry(link, &cg->cg_links, cg_link_list) {
5432        struct cgroup *c = link->cgrp;
5433        const char *name;
5434
5435        if (c->dentry)
5436            name = c->dentry->d_name.name;
5437        else
5438            name = "?";
5439        seq_printf(seq, "Root %d group %s\n",
5440               c->root->hierarchy_id, name);
5441    }
5442    rcu_read_unlock();
5443    read_unlock(&css_set_lock);
5444    return 0;
5445}
5446
5447#define MAX_TASKS_SHOWN_PER_CSS 25
5448static int cgroup_css_links_read(struct cgroup *cont,
5449                 struct cftype *cft,
5450                 struct seq_file *seq)
5451{
5452    struct cg_cgroup_link *link;
5453
5454    read_lock(&css_set_lock);
5455    list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
5456        struct css_set *cg = link->cg;
5457        struct task_struct *task;
5458        int count = 0;
5459        seq_printf(seq, "css_set %p\n", cg);
5460        list_for_each_entry(task, &cg->tasks, cg_list) {
5461            if (count++ > MAX_TASKS_SHOWN_PER_CSS) {
5462                seq_puts(seq, " ...\n");
5463                break;
5464            } else {
5465                seq_printf(seq, " task %d\n",
5466                       task_pid_vnr(task));
5467            }
5468        }
5469    }
5470    read_unlock(&css_set_lock);
5471    return 0;
5472}
5473
5474static u64 releasable_read(struct cgroup *cgrp, struct cftype *cft)
5475{
5476    return test_bit(CGRP_RELEASABLE, &cgrp->flags);
5477}
5478
5479static struct cftype debug_files[] = {
5480    {
5481        .name = "cgroup_refcount",
5482        .read_u64 = cgroup_refcount_read,
5483    },
5484    {
5485        .name = "taskcount",
5486        .read_u64 = debug_taskcount_read,
5487    },
5488
5489    {
5490        .name = "current_css_set",
5491        .read_u64 = current_css_set_read,
5492    },
5493
5494    {
5495        .name = "current_css_set_refcount",
5496        .read_u64 = current_css_set_refcount_read,
5497    },
5498
5499    {
5500        .name = "current_css_set_cg_links",
5501        .read_seq_string = current_css_set_cg_links_read,
5502    },
5503
5504    {
5505        .name = "cgroup_css_links",
5506        .read_seq_string = cgroup_css_links_read,
5507    },
5508
5509    {
5510        .name = "releasable",
5511        .read_u64 = releasable_read,
5512    },
5513
5514    { } /* terminate */
5515};
5516
5517struct cgroup_subsys debug_subsys = {
5518    .name = "debug",
5519    .create = debug_create,
5520    .destroy = debug_destroy,
5521    .subsys_id = debug_subsys_id,
5522    .base_cftypes = debug_files,
5523};
5524#endif /* CONFIG_CGROUP_DEBUG */
5525

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