linux/kernel/cgroup.c
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   1/*
   2 *  Generic process-grouping system.
   3 *
   4 *  Based originally on the cpuset system, extracted by Paul Menage
   5 *  Copyright (C) 2006 Google, Inc
   6 *
   7 *  Notifications support
   8 *  Copyright (C) 2009 Nokia Corporation
   9 *  Author: Kirill A. Shutemov
  10 *
  11 *  Copyright notices from the original cpuset code:
  12 *  --------------------------------------------------
  13 *  Copyright (C) 2003 BULL SA.
  14 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
  15 *
  16 *  Portions derived from Patrick Mochel's sysfs code.
  17 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
  18 *
  19 *  2003-10-10 Written by Simon Derr.
  20 *  2003-10-22 Updates by Stephen Hemminger.
  21 *  2004 May-July Rework by Paul Jackson.
  22 *  ---------------------------------------------------
  23 *
  24 *  This file is subject to the terms and conditions of the GNU General Public
  25 *  License.  See the file COPYING in the main directory of the Linux
  26 *  distribution for more details.
  27 */
  28
  29#include <linux/cgroup.h>
  30#include <linux/ctype.h>
  31#include <linux/errno.h>
  32#include <linux/fs.h>
  33#include <linux/kernel.h>
  34#include <linux/list.h>
  35#include <linux/mm.h>
  36#include <linux/mutex.h>
  37#include <linux/mount.h>
  38#include <linux/pagemap.h>
  39#include <linux/proc_fs.h>
  40#include <linux/rcupdate.h>
  41#include <linux/sched.h>
  42#include <linux/backing-dev.h>
  43#include <linux/seq_file.h>
  44#include <linux/slab.h>
  45#include <linux/magic.h>
  46#include <linux/spinlock.h>
  47#include <linux/string.h>
  48#include <linux/sort.h>
  49#include <linux/kmod.h>
  50#include <linux/module.h>
  51#include <linux/delayacct.h>
  52#include <linux/cgroupstats.h>
  53#include <linux/hash.h>
  54#include <linux/namei.h>
  55#include <linux/smp_lock.h>
  56#include <linux/pid_namespace.h>
  57#include <linux/idr.h>
  58#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
  59#include <linux/eventfd.h>
  60#include <linux/poll.h>
  61
  62#include <asm/atomic.h>
  63
  64static DEFINE_MUTEX(cgroup_mutex);
  65
  66/*
  67 * Generate an array of cgroup subsystem pointers. At boot time, this is
  68 * populated up to CGROUP_BUILTIN_SUBSYS_COUNT, and modular subsystems are
  69 * registered after that. The mutable section of this array is protected by
  70 * cgroup_mutex.
  71 */
  72#define SUBSYS(_x) &_x ## _subsys,
  73static struct cgroup_subsys *subsys[CGROUP_SUBSYS_COUNT] = {
  74#include <linux/cgroup_subsys.h>
  75};
  76
  77#define MAX_CGROUP_ROOT_NAMELEN 64
  78
  79/*
  80 * A cgroupfs_root represents the root of a cgroup hierarchy,
  81 * and may be associated with a superblock to form an active
  82 * hierarchy
  83 */
  84struct cgroupfs_root {
  85        struct super_block *sb;
  86
  87        /*
  88         * The bitmask of subsystems intended to be attached to this
  89         * hierarchy
  90         */
  91        unsigned long subsys_bits;
  92
  93        /* Unique id for this hierarchy. */
  94        int hierarchy_id;
  95
  96        /* The bitmask of subsystems currently attached to this hierarchy */
  97        unsigned long actual_subsys_bits;
  98
  99        /* A list running through the attached subsystems */
 100        struct list_head subsys_list;
 101
 102        /* The root cgroup for this hierarchy */
 103        struct cgroup top_cgroup;
 104
 105        /* Tracks how many cgroups are currently defined in hierarchy.*/
 106        int number_of_cgroups;
 107
 108        /* A list running through the active hierarchies */
 109        struct list_head root_list;
 110
 111        /* Hierarchy-specific flags */
 112        unsigned long flags;
 113
 114        /* The path to use for release notifications. */
 115        char release_agent_path[PATH_MAX];
 116
 117        /* The name for this hierarchy - may be empty */
 118        char name[MAX_CGROUP_ROOT_NAMELEN];
 119};
 120
 121/*
 122 * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
 123 * subsystems that are otherwise unattached - it never has more than a
 124 * single cgroup, and all tasks are part of that cgroup.
 125 */
 126static struct cgroupfs_root rootnode;
 127
 128/*
 129 * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
 130 * cgroup_subsys->use_id != 0.
 131 */
 132#define CSS_ID_MAX      (65535)
 133struct css_id {
 134        /*
 135         * The css to which this ID points. This pointer is set to valid value
 136         * after cgroup is populated. If cgroup is removed, this will be NULL.
 137         * This pointer is expected to be RCU-safe because destroy()
 138         * is called after synchronize_rcu(). But for safe use, css_is_removed()
 139         * css_tryget() should be used for avoiding race.
 140         */
 141        struct cgroup_subsys_state *css;
 142        /*
 143         * ID of this css.
 144         */
 145        unsigned short id;
 146        /*
 147         * Depth in hierarchy which this ID belongs to.
 148         */
 149        unsigned short depth;
 150        /*
 151         * ID is freed by RCU. (and lookup routine is RCU safe.)
 152         */
 153        struct rcu_head rcu_head;
 154        /*
 155         * Hierarchy of CSS ID belongs to.
 156         */
 157        unsigned short stack[0]; /* Array of Length (depth+1) */
 158};
 159
 160/*
 161 * cgroup_event represents events which userspace want to recieve.
 162 */
 163struct cgroup_event {
 164        /*
 165         * Cgroup which the event belongs to.
 166         */
 167        struct cgroup *cgrp;
 168        /*
 169         * Control file which the event associated.
 170         */
 171        struct cftype *cft;
 172        /*
 173         * eventfd to signal userspace about the event.
 174         */
 175        struct eventfd_ctx *eventfd;
 176        /*
 177         * Each of these stored in a list by the cgroup.
 178         */
 179        struct list_head list;
 180        /*
 181         * All fields below needed to unregister event when
 182         * userspace closes eventfd.
 183         */
 184        poll_table pt;
 185        wait_queue_head_t *wqh;
 186        wait_queue_t wait;
 187        struct work_struct remove;
 188};
 189
 190/* The list of hierarchy roots */
 191
 192static LIST_HEAD(roots);
 193static int root_count;
 194
 195static DEFINE_IDA(hierarchy_ida);
 196static int next_hierarchy_id;
 197static DEFINE_SPINLOCK(hierarchy_id_lock);
 198
 199/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
 200#define dummytop (&rootnode.top_cgroup)
 201
 202/* This flag indicates whether tasks in the fork and exit paths should
 203 * check for fork/exit handlers to call. This avoids us having to do
 204 * extra work in the fork/exit path if none of the subsystems need to
 205 * be called.
 206 */
 207static int need_forkexit_callback __read_mostly;
 208
 209#ifdef CONFIG_PROVE_LOCKING
 210int cgroup_lock_is_held(void)
 211{
 212        return lockdep_is_held(&cgroup_mutex);
 213}
 214#else /* #ifdef CONFIG_PROVE_LOCKING */
 215int cgroup_lock_is_held(void)
 216{
 217        return mutex_is_locked(&cgroup_mutex);
 218}
 219#endif /* #else #ifdef CONFIG_PROVE_LOCKING */
 220
 221EXPORT_SYMBOL_GPL(cgroup_lock_is_held);
 222
 223/* convenient tests for these bits */
 224inline int cgroup_is_removed(const struct cgroup *cgrp)
 225{
 226        return test_bit(CGRP_REMOVED, &cgrp->flags);
 227}
 228
 229/* bits in struct cgroupfs_root flags field */
 230enum {
 231        ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
 232};
 233
 234static int cgroup_is_releasable(const struct cgroup *cgrp)
 235{
 236        const int bits =
 237                (1 << CGRP_RELEASABLE) |
 238                (1 << CGRP_NOTIFY_ON_RELEASE);
 239        return (cgrp->flags & bits) == bits;
 240}
 241
 242static int notify_on_release(const struct cgroup *cgrp)
 243{
 244        return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
 245}
 246
 247/*
 248 * for_each_subsys() allows you to iterate on each subsystem attached to
 249 * an active hierarchy
 250 */
 251#define for_each_subsys(_root, _ss) \
 252list_for_each_entry(_ss, &_root->subsys_list, sibling)
 253
 254/* for_each_active_root() allows you to iterate across the active hierarchies */
 255#define for_each_active_root(_root) \
 256list_for_each_entry(_root, &roots, root_list)
 257
 258/* the list of cgroups eligible for automatic release. Protected by
 259 * release_list_lock */
 260static LIST_HEAD(release_list);
 261static DEFINE_SPINLOCK(release_list_lock);
 262static void cgroup_release_agent(struct work_struct *work);
 263static DECLARE_WORK(release_agent_work, cgroup_release_agent);
 264static void check_for_release(struct cgroup *cgrp);
 265
 266/* Link structure for associating css_set objects with cgroups */
 267struct cg_cgroup_link {
 268        /*
 269         * List running through cg_cgroup_links associated with a
 270         * cgroup, anchored on cgroup->css_sets
 271         */
 272        struct list_head cgrp_link_list;
 273        struct cgroup *cgrp;
 274        /*
 275         * List running through cg_cgroup_links pointing at a
 276         * single css_set object, anchored on css_set->cg_links
 277         */
 278        struct list_head cg_link_list;
 279        struct css_set *cg;
 280};
 281
 282/* The default css_set - used by init and its children prior to any
 283 * hierarchies being mounted. It contains a pointer to the root state
 284 * for each subsystem. Also used to anchor the list of css_sets. Not
 285 * reference-counted, to improve performance when child cgroups
 286 * haven't been created.
 287 */
 288
 289static struct css_set init_css_set;
 290static struct cg_cgroup_link init_css_set_link;
 291
 292static int cgroup_init_idr(struct cgroup_subsys *ss,
 293                           struct cgroup_subsys_state *css);
 294
 295/* css_set_lock protects the list of css_set objects, and the
 296 * chain of tasks off each css_set.  Nests outside task->alloc_lock
 297 * due to cgroup_iter_start() */
 298static DEFINE_RWLOCK(css_set_lock);
 299static int css_set_count;
 300
 301/*
 302 * hash table for cgroup groups. This improves the performance to find
 303 * an existing css_set. This hash doesn't (currently) take into
 304 * account cgroups in empty hierarchies.
 305 */
 306#define CSS_SET_HASH_BITS       7
 307#define CSS_SET_TABLE_SIZE      (1 << CSS_SET_HASH_BITS)
 308static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];
 309
 310static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
 311{
 312        int i;
 313        int index;
 314        unsigned long tmp = 0UL;
 315
 316        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
 317                tmp += (unsigned long)css[i];
 318        tmp = (tmp >> 16) ^ tmp;
 319
 320        index = hash_long(tmp, CSS_SET_HASH_BITS);
 321
 322        return &css_set_table[index];
 323}
 324
 325static void free_css_set_rcu(struct rcu_head *obj)
 326{
 327        struct css_set *cg = container_of(obj, struct css_set, rcu_head);
 328        kfree(cg);
 329}
 330
 331/* We don't maintain the lists running through each css_set to its
 332 * task until after the first call to cgroup_iter_start(). This
 333 * reduces the fork()/exit() overhead for people who have cgroups
 334 * compiled into their kernel but not actually in use */
 335static int use_task_css_set_links __read_mostly;
 336
 337static void __put_css_set(struct css_set *cg, int taskexit)
 338{
 339        struct cg_cgroup_link *link;
 340        struct cg_cgroup_link *saved_link;
 341        /*
 342         * Ensure that the refcount doesn't hit zero while any readers
 343         * can see it. Similar to atomic_dec_and_lock(), but for an
 344         * rwlock
 345         */
 346        if (atomic_add_unless(&cg->refcount, -1, 1))
 347                return;
 348        write_lock(&css_set_lock);
 349        if (!atomic_dec_and_test(&cg->refcount)) {
 350                write_unlock(&css_set_lock);
 351                return;
 352        }
 353
 354        /* This css_set is dead. unlink it and release cgroup refcounts */
 355        hlist_del(&cg->hlist);
 356        css_set_count--;
 357
 358        list_for_each_entry_safe(link, saved_link, &cg->cg_links,
 359                                 cg_link_list) {
 360                struct cgroup *cgrp = link->cgrp;
 361                list_del(&link->cg_link_list);
 362                list_del(&link->cgrp_link_list);
 363                if (atomic_dec_and_test(&cgrp->count) &&
 364                    notify_on_release(cgrp)) {
 365                        if (taskexit)
 366                                set_bit(CGRP_RELEASABLE, &cgrp->flags);
 367                        check_for_release(cgrp);
 368                }
 369
 370                kfree(link);
 371        }
 372
 373        write_unlock(&css_set_lock);
 374        call_rcu(&cg->rcu_head, free_css_set_rcu);
 375}
 376
 377/*
 378 * refcounted get/put for css_set objects
 379 */
 380static inline void get_css_set(struct css_set *cg)
 381{
 382        atomic_inc(&cg->refcount);
 383}
 384
 385static inline void put_css_set(struct css_set *cg)
 386{
 387        __put_css_set(cg, 0);
 388}
 389
 390static inline void put_css_set_taskexit(struct css_set *cg)
 391{
 392        __put_css_set(cg, 1);
 393}
 394
 395/*
 396 * compare_css_sets - helper function for find_existing_css_set().
 397 * @cg: candidate css_set being tested
 398 * @old_cg: existing css_set for a task
 399 * @new_cgrp: cgroup that's being entered by the task
 400 * @template: desired set of css pointers in css_set (pre-calculated)
 401 *
 402 * Returns true if "cg" matches "old_cg" except for the hierarchy
 403 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 404 */
 405static bool compare_css_sets(struct css_set *cg,
 406                             struct css_set *old_cg,
 407                             struct cgroup *new_cgrp,
 408                             struct cgroup_subsys_state *template[])
 409{
 410        struct list_head *l1, *l2;
 411
 412        if (memcmp(template, cg->subsys, sizeof(cg->subsys))) {
 413                /* Not all subsystems matched */
 414                return false;
 415        }
 416
 417        /*
 418         * Compare cgroup pointers in order to distinguish between
 419         * different cgroups in heirarchies with no subsystems. We
 420         * could get by with just this check alone (and skip the
 421         * memcmp above) but on most setups the memcmp check will
 422         * avoid the need for this more expensive check on almost all
 423         * candidates.
 424         */
 425
 426        l1 = &cg->cg_links;
 427        l2 = &old_cg->cg_links;
 428        while (1) {
 429                struct cg_cgroup_link *cgl1, *cgl2;
 430                struct cgroup *cg1, *cg2;
 431
 432                l1 = l1->next;
 433                l2 = l2->next;
 434                /* See if we reached the end - both lists are equal length. */
 435                if (l1 == &cg->cg_links) {
 436                        BUG_ON(l2 != &old_cg->cg_links);
 437                        break;
 438                } else {
 439                        BUG_ON(l2 == &old_cg->cg_links);
 440                }
 441                /* Locate the cgroups associated with these links. */
 442                cgl1 = list_entry(l1, struct cg_cgroup_link, cg_link_list);
 443                cgl2 = list_entry(l2, struct cg_cgroup_link, cg_link_list);
 444                cg1 = cgl1->cgrp;
 445                cg2 = cgl2->cgrp;
 446                /* Hierarchies should be linked in the same order. */
 447                BUG_ON(cg1->root != cg2->root);
 448
 449                /*
 450                 * If this hierarchy is the hierarchy of the cgroup
 451                 * that's changing, then we need to check that this
 452                 * css_set points to the new cgroup; if it's any other
 453                 * hierarchy, then this css_set should point to the
 454                 * same cgroup as the old css_set.
 455                 */
 456                if (cg1->root == new_cgrp->root) {
 457                        if (cg1 != new_cgrp)
 458                                return false;
 459                } else {
 460                        if (cg1 != cg2)
 461                                return false;
 462                }
 463        }
 464        return true;
 465}
 466
 467/*
 468 * find_existing_css_set() is a helper for
 469 * find_css_set(), and checks to see whether an existing
 470 * css_set is suitable.
 471 *
 472 * oldcg: the cgroup group that we're using before the cgroup
 473 * transition
 474 *
 475 * cgrp: the cgroup that we're moving into
 476 *
 477 * template: location in which to build the desired set of subsystem
 478 * state objects for the new cgroup group
 479 */
 480static struct css_set *find_existing_css_set(
 481        struct css_set *oldcg,
 482        struct cgroup *cgrp,
 483        struct cgroup_subsys_state *template[])
 484{
 485        int i;
 486        struct cgroupfs_root *root = cgrp->root;
 487        struct hlist_head *hhead;
 488        struct hlist_node *node;
 489        struct css_set *cg;
 490
 491        /*
 492         * Build the set of subsystem state objects that we want to see in the
 493         * new css_set. while subsystems can change globally, the entries here
 494         * won't change, so no need for locking.
 495         */
 496        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 497                if (root->subsys_bits & (1UL << i)) {
 498                        /* Subsystem is in this hierarchy. So we want
 499                         * the subsystem state from the new
 500                         * cgroup */
 501                        template[i] = cgrp->subsys[i];
 502                } else {
 503                        /* Subsystem is not in this hierarchy, so we
 504                         * don't want to change the subsystem state */
 505                        template[i] = oldcg->subsys[i];
 506                }
 507        }
 508
 509        hhead = css_set_hash(template);
 510        hlist_for_each_entry(cg, node, hhead, hlist) {
 511                if (!compare_css_sets(cg, oldcg, cgrp, template))
 512                        continue;
 513
 514                /* This css_set matches what we need */
 515                return cg;
 516        }
 517
 518        /* No existing cgroup group matched */
 519        return NULL;
 520}
 521
 522static void free_cg_links(struct list_head *tmp)
 523{
 524        struct cg_cgroup_link *link;
 525        struct cg_cgroup_link *saved_link;
 526
 527        list_for_each_entry_safe(link, saved_link, tmp, cgrp_link_list) {
 528                list_del(&link->cgrp_link_list);
 529                kfree(link);
 530        }
 531}
 532
 533/*
 534 * allocate_cg_links() allocates "count" cg_cgroup_link structures
 535 * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
 536 * success or a negative error
 537 */
 538static int allocate_cg_links(int count, struct list_head *tmp)
 539{
 540        struct cg_cgroup_link *link;
 541        int i;
 542        INIT_LIST_HEAD(tmp);
 543        for (i = 0; i < count; i++) {
 544                link = kmalloc(sizeof(*link), GFP_KERNEL);
 545                if (!link) {
 546                        free_cg_links(tmp);
 547                        return -ENOMEM;
 548                }
 549                list_add(&link->cgrp_link_list, tmp);
 550        }
 551        return 0;
 552}
 553
 554/**
 555 * link_css_set - a helper function to link a css_set to a cgroup
 556 * @tmp_cg_links: cg_cgroup_link objects allocated by allocate_cg_links()
 557 * @cg: the css_set to be linked
 558 * @cgrp: the destination cgroup
 559 */
 560static void link_css_set(struct list_head *tmp_cg_links,
 561                         struct css_set *cg, struct cgroup *cgrp)
 562{
 563        struct cg_cgroup_link *link;
 564
 565        BUG_ON(list_empty(tmp_cg_links));
 566        link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
 567                                cgrp_link_list);
 568        link->cg = cg;
 569        link->cgrp = cgrp;
 570        atomic_inc(&cgrp->count);
 571        list_move(&link->cgrp_link_list, &cgrp->css_sets);
 572        /*
 573         * Always add links to the tail of the list so that the list
 574         * is sorted by order of hierarchy creation
 575         */
 576        list_add_tail(&link->cg_link_list, &cg->cg_links);
 577}
 578
 579/*
 580 * find_css_set() takes an existing cgroup group and a
 581 * cgroup object, and returns a css_set object that's
 582 * equivalent to the old group, but with the given cgroup
 583 * substituted into the appropriate hierarchy. Must be called with
 584 * cgroup_mutex held
 585 */
 586static struct css_set *find_css_set(
 587        struct css_set *oldcg, struct cgroup *cgrp)
 588{
 589        struct css_set *res;
 590        struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
 591
 592        struct list_head tmp_cg_links;
 593
 594        struct hlist_head *hhead;
 595        struct cg_cgroup_link *link;
 596
 597        /* First see if we already have a cgroup group that matches
 598         * the desired set */
 599        read_lock(&css_set_lock);
 600        res = find_existing_css_set(oldcg, cgrp, template);
 601        if (res)
 602                get_css_set(res);
 603        read_unlock(&css_set_lock);
 604
 605        if (res)
 606                return res;
 607
 608        res = kmalloc(sizeof(*res), GFP_KERNEL);
 609        if (!res)
 610                return NULL;
 611
 612        /* Allocate all the cg_cgroup_link objects that we'll need */
 613        if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
 614                kfree(res);
 615                return NULL;
 616        }
 617
 618        atomic_set(&res->refcount, 1);
 619        INIT_LIST_HEAD(&res->cg_links);
 620        INIT_LIST_HEAD(&res->tasks);
 621        INIT_HLIST_NODE(&res->hlist);
 622
 623        /* Copy the set of subsystem state objects generated in
 624         * find_existing_css_set() */
 625        memcpy(res->subsys, template, sizeof(res->subsys));
 626
 627        write_lock(&css_set_lock);
 628        /* Add reference counts and links from the new css_set. */
 629        list_for_each_entry(link, &oldcg->cg_links, cg_link_list) {
 630                struct cgroup *c = link->cgrp;
 631                if (c->root == cgrp->root)
 632                        c = cgrp;
 633                link_css_set(&tmp_cg_links, res, c);
 634        }
 635
 636        BUG_ON(!list_empty(&tmp_cg_links));
 637
 638        css_set_count++;
 639
 640        /* Add this cgroup group to the hash table */
 641        hhead = css_set_hash(res->subsys);
 642        hlist_add_head(&res->hlist, hhead);
 643
 644        write_unlock(&css_set_lock);
 645
 646        return res;
 647}
 648
 649/*
 650 * Return the cgroup for "task" from the given hierarchy. Must be
 651 * called with cgroup_mutex held.
 652 */
 653static struct cgroup *task_cgroup_from_root(struct task_struct *task,
 654                                            struct cgroupfs_root *root)
 655{
 656        struct css_set *css;
 657        struct cgroup *res = NULL;
 658
 659        BUG_ON(!mutex_is_locked(&cgroup_mutex));
 660        read_lock(&css_set_lock);
 661        /*
 662         * No need to lock the task - since we hold cgroup_mutex the
 663         * task can't change groups, so the only thing that can happen
 664         * is that it exits and its css is set back to init_css_set.
 665         */
 666        css = task->cgroups;
 667        if (css == &init_css_set) {
 668                res = &root->top_cgroup;
 669        } else {
 670                struct cg_cgroup_link *link;
 671                list_for_each_entry(link, &css->cg_links, cg_link_list) {
 672                        struct cgroup *c = link->cgrp;
 673                        if (c->root == root) {
 674                                res = c;
 675                                break;
 676                        }
 677                }
 678        }
 679        read_unlock(&css_set_lock);
 680        BUG_ON(!res);
 681        return res;
 682}
 683
 684/*
 685 * There is one global cgroup mutex. We also require taking
 686 * task_lock() when dereferencing a task's cgroup subsys pointers.
 687 * See "The task_lock() exception", at the end of this comment.
 688 *
 689 * A task must hold cgroup_mutex to modify cgroups.
 690 *
 691 * Any task can increment and decrement the count field without lock.
 692 * So in general, code holding cgroup_mutex can't rely on the count
 693 * field not changing.  However, if the count goes to zero, then only
 694 * cgroup_attach_task() can increment it again.  Because a count of zero
 695 * means that no tasks are currently attached, therefore there is no
 696 * way a task attached to that cgroup can fork (the other way to
 697 * increment the count).  So code holding cgroup_mutex can safely
 698 * assume that if the count is zero, it will stay zero. Similarly, if
 699 * a task holds cgroup_mutex on a cgroup with zero count, it
 700 * knows that the cgroup won't be removed, as cgroup_rmdir()
 701 * needs that mutex.
 702 *
 703 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
 704 * (usually) take cgroup_mutex.  These are the two most performance
 705 * critical pieces of code here.  The exception occurs on cgroup_exit(),
 706 * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
 707 * is taken, and if the cgroup count is zero, a usermode call made
 708 * to the release agent with the name of the cgroup (path relative to
 709 * the root of cgroup file system) as the argument.
 710 *
 711 * A cgroup can only be deleted if both its 'count' of using tasks
 712 * is zero, and its list of 'children' cgroups is empty.  Since all
 713 * tasks in the system use _some_ cgroup, and since there is always at
 714 * least one task in the system (init, pid == 1), therefore, top_cgroup
 715 * always has either children cgroups and/or using tasks.  So we don't
 716 * need a special hack to ensure that top_cgroup cannot be deleted.
 717 *
 718 *      The task_lock() exception
 719 *
 720 * The need for this exception arises from the action of
 721 * cgroup_attach_task(), which overwrites one tasks cgroup pointer with
 722 * another.  It does so using cgroup_mutex, however there are
 723 * several performance critical places that need to reference
 724 * task->cgroup without the expense of grabbing a system global
 725 * mutex.  Therefore except as noted below, when dereferencing or, as
 726 * in cgroup_attach_task(), modifying a task'ss cgroup pointer we use
 727 * task_lock(), which acts on a spinlock (task->alloc_lock) already in
 728 * the task_struct routinely used for such matters.
 729 *
 730 * P.S.  One more locking exception.  RCU is used to guard the
 731 * update of a tasks cgroup pointer by cgroup_attach_task()
 732 */
 733
 734/**
 735 * cgroup_lock - lock out any changes to cgroup structures
 736 *
 737 */
 738void cgroup_lock(void)
 739{
 740        mutex_lock(&cgroup_mutex);
 741}
 742EXPORT_SYMBOL_GPL(cgroup_lock);
 743
 744/**
 745 * cgroup_unlock - release lock on cgroup changes
 746 *
 747 * Undo the lock taken in a previous cgroup_lock() call.
 748 */
 749void cgroup_unlock(void)
 750{
 751        mutex_unlock(&cgroup_mutex);
 752}
 753EXPORT_SYMBOL_GPL(cgroup_unlock);
 754
 755/*
 756 * A couple of forward declarations required, due to cyclic reference loop:
 757 * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
 758 * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
 759 * -> cgroup_mkdir.
 760 */
 761
 762static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);
 763static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
 764static int cgroup_populate_dir(struct cgroup *cgrp);
 765static const struct inode_operations cgroup_dir_inode_operations;
 766static const struct file_operations proc_cgroupstats_operations;
 767
 768static struct backing_dev_info cgroup_backing_dev_info = {
 769        .name           = "cgroup",
 770        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
 771};
 772
 773static int alloc_css_id(struct cgroup_subsys *ss,
 774                        struct cgroup *parent, struct cgroup *child);
 775
 776static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
 777{
 778        struct inode *inode = new_inode(sb);
 779
 780        if (inode) {
 781                inode->i_mode = mode;
 782                inode->i_uid = current_fsuid();
 783                inode->i_gid = current_fsgid();
 784                inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 785                inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
 786        }
 787        return inode;
 788}
 789
 790/*
 791 * Call subsys's pre_destroy handler.
 792 * This is called before css refcnt check.
 793 */
 794static int cgroup_call_pre_destroy(struct cgroup *cgrp)
 795{
 796        struct cgroup_subsys *ss;
 797        int ret = 0;
 798
 799        for_each_subsys(cgrp->root, ss)
 800                if (ss->pre_destroy) {
 801                        ret = ss->pre_destroy(ss, cgrp);
 802                        if (ret)
 803                                break;
 804                }
 805
 806        return ret;
 807}
 808
 809static void free_cgroup_rcu(struct rcu_head *obj)
 810{
 811        struct cgroup *cgrp = container_of(obj, struct cgroup, rcu_head);
 812
 813        kfree(cgrp);
 814}
 815
 816static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 817{
 818        /* is dentry a directory ? if so, kfree() associated cgroup */
 819        if (S_ISDIR(inode->i_mode)) {
 820                struct cgroup *cgrp = dentry->d_fsdata;
 821                struct cgroup_subsys *ss;
 822                BUG_ON(!(cgroup_is_removed(cgrp)));
 823                /* It's possible for external users to be holding css
 824                 * reference counts on a cgroup; css_put() needs to
 825                 * be able to access the cgroup after decrementing
 826                 * the reference count in order to know if it needs to
 827                 * queue the cgroup to be handled by the release
 828                 * agent */
 829                synchronize_rcu();
 830
 831                mutex_lock(&cgroup_mutex);
 832                /*
 833                 * Release the subsystem state objects.
 834                 */
 835                for_each_subsys(cgrp->root, ss)
 836                        ss->destroy(ss, cgrp);
 837
 838                cgrp->root->number_of_cgroups--;
 839                mutex_unlock(&cgroup_mutex);
 840
 841                /*
 842                 * Drop the active superblock reference that we took when we
 843                 * created the cgroup
 844                 */
 845                deactivate_super(cgrp->root->sb);
 846
 847                /*
 848                 * if we're getting rid of the cgroup, refcount should ensure
 849                 * that there are no pidlists left.
 850                 */
 851                BUG_ON(!list_empty(&cgrp->pidlists));
 852
 853                call_rcu(&cgrp->rcu_head, free_cgroup_rcu);
 854        }
 855        iput(inode);
 856}
 857
 858static void remove_dir(struct dentry *d)
 859{
 860        struct dentry *parent = dget(d->d_parent);
 861
 862        d_delete(d);
 863        simple_rmdir(parent->d_inode, d);
 864        dput(parent);
 865}
 866
 867static void cgroup_clear_directory(struct dentry *dentry)
 868{
 869        struct list_head *node;
 870
 871        BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
 872        spin_lock(&dcache_lock);
 873        node = dentry->d_subdirs.next;
 874        while (node != &dentry->d_subdirs) {
 875                struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
 876                list_del_init(node);
 877                if (d->d_inode) {
 878                        /* This should never be called on a cgroup
 879                         * directory with child cgroups */
 880                        BUG_ON(d->d_inode->i_mode & S_IFDIR);
 881                        d = dget_locked(d);
 882                        spin_unlock(&dcache_lock);
 883                        d_delete(d);
 884                        simple_unlink(dentry->d_inode, d);
 885                        dput(d);
 886                        spin_lock(&dcache_lock);
 887                }
 888                node = dentry->d_subdirs.next;
 889        }
 890        spin_unlock(&dcache_lock);
 891}
 892
 893/*
 894 * NOTE : the dentry must have been dget()'ed
 895 */
 896static void cgroup_d_remove_dir(struct dentry *dentry)
 897{
 898        cgroup_clear_directory(dentry);
 899
 900        spin_lock(&dcache_lock);
 901        list_del_init(&dentry->d_u.d_child);
 902        spin_unlock(&dcache_lock);
 903        remove_dir(dentry);
 904}
 905
 906/*
 907 * A queue for waiters to do rmdir() cgroup. A tasks will sleep when
 908 * cgroup->count == 0 && list_empty(&cgroup->children) && subsys has some
 909 * reference to css->refcnt. In general, this refcnt is expected to goes down
 910 * to zero, soon.
 911 *
 912 * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
 913 */
 914DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
 915
 916static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
 917{
 918        if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
 919                wake_up_all(&cgroup_rmdir_waitq);
 920}
 921
 922void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
 923{
 924        css_get(css);
 925}
 926
 927void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
 928{
 929        cgroup_wakeup_rmdir_waiter(css->cgroup);
 930        css_put(css);
 931}
 932
 933/*
 934 * Call with cgroup_mutex held. Drops reference counts on modules, including
 935 * any duplicate ones that parse_cgroupfs_options took. If this function
 936 * returns an error, no reference counts are touched.
 937 */
 938static int rebind_subsystems(struct cgroupfs_root *root,
 939                              unsigned long final_bits)
 940{
 941        unsigned long added_bits, removed_bits;
 942        struct cgroup *cgrp = &root->top_cgroup;
 943        int i;
 944
 945        BUG_ON(!mutex_is_locked(&cgroup_mutex));
 946
 947        removed_bits = root->actual_subsys_bits & ~final_bits;
 948        added_bits = final_bits & ~root->actual_subsys_bits;
 949        /* Check that any added subsystems are currently free */
 950        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 951                unsigned long bit = 1UL << i;
 952                struct cgroup_subsys *ss = subsys[i];
 953                if (!(bit & added_bits))
 954                        continue;
 955                /*
 956                 * Nobody should tell us to do a subsys that doesn't exist:
 957                 * parse_cgroupfs_options should catch that case and refcounts
 958                 * ensure that subsystems won't disappear once selected.
 959                 */
 960                BUG_ON(ss == NULL);
 961                if (ss->root != &rootnode) {
 962                        /* Subsystem isn't free */
 963                        return -EBUSY;
 964                }
 965        }
 966
 967        /* Currently we don't handle adding/removing subsystems when
 968         * any child cgroups exist. This is theoretically supportable
 969         * but involves complex error handling, so it's being left until
 970         * later */
 971        if (root->number_of_cgroups > 1)
 972                return -EBUSY;
 973
 974        /* Process each subsystem */
 975        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 976                struct cgroup_subsys *ss = subsys[i];
 977                unsigned long bit = 1UL << i;
 978                if (bit & added_bits) {
 979                        /* We're binding this subsystem to this hierarchy */
 980                        BUG_ON(ss == NULL);
 981                        BUG_ON(cgrp->subsys[i]);
 982                        BUG_ON(!dummytop->subsys[i]);
 983                        BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
 984                        mutex_lock(&ss->hierarchy_mutex);
 985                        cgrp->subsys[i] = dummytop->subsys[i];
 986                        cgrp->subsys[i]->cgroup = cgrp;
 987                        list_move(&ss->sibling, &root->subsys_list);
 988                        ss->root = root;
 989                        if (ss->bind)
 990                                ss->bind(ss, cgrp);
 991                        mutex_unlock(&ss->hierarchy_mutex);
 992                        /* refcount was already taken, and we're keeping it */
 993                } else if (bit & removed_bits) {
 994                        /* We're removing this subsystem */
 995                        BUG_ON(ss == NULL);
 996                        BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
 997                        BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
 998                        mutex_lock(&ss->hierarchy_mutex);
 999                        if (ss->bind)
1000                                ss->bind(ss, dummytop);
1001                        dummytop->subsys[i]->cgroup = dummytop;
1002                        cgrp->subsys[i] = NULL;
1003                        subsys[i]->root = &rootnode;
1004                        list_move(&ss->sibling, &rootnode.subsys_list);
1005                        mutex_unlock(&ss->hierarchy_mutex);
1006                        /* subsystem is now free - drop reference on module */
1007                        module_put(ss->module);
1008                } else if (bit & final_bits) {
1009                        /* Subsystem state should already exist */
1010                        BUG_ON(ss == NULL);
1011                        BUG_ON(!cgrp->subsys[i]);
1012                        /*
1013                         * a refcount was taken, but we already had one, so
1014                         * drop the extra reference.
1015                         */
1016                        module_put(ss->module);
1017#ifdef CONFIG_MODULE_UNLOAD
1018                        BUG_ON(ss->module && !module_refcount(ss->module));
1019#endif
1020                } else {
1021                        /* Subsystem state shouldn't exist */
1022                        BUG_ON(cgrp->subsys[i]);
1023                }
1024        }
1025        root->subsys_bits = root->actual_subsys_bits = final_bits;
1026        synchronize_rcu();
1027
1028        return 0;
1029}
1030
1031static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
1032{
1033        struct cgroupfs_root *root = vfs->mnt_sb->s_fs_info;
1034        struct cgroup_subsys *ss;
1035
1036        mutex_lock(&cgroup_mutex);
1037        for_each_subsys(root, ss)
1038                seq_printf(seq, ",%s", ss->name);
1039        if (test_bit(ROOT_NOPREFIX, &root->flags))
1040                seq_puts(seq, ",noprefix");
1041        if (strlen(root->release_agent_path))
1042                seq_printf(seq, ",release_agent=%s", root->release_agent_path);
1043        if (strlen(root->name))
1044                seq_printf(seq, ",name=%s", root->name);
1045        mutex_unlock(&cgroup_mutex);
1046        return 0;
1047}
1048
1049struct cgroup_sb_opts {
1050        unsigned long subsys_bits;
1051        unsigned long flags;
1052        char *release_agent;
1053        char *name;
1054        /* User explicitly requested empty subsystem */
1055        bool none;
1056
1057        struct cgroupfs_root *new_root;
1058
1059};
1060
1061/*
1062 * Convert a hierarchy specifier into a bitmask of subsystems and flags. Call
1063 * with cgroup_mutex held to protect the subsys[] array. This function takes
1064 * refcounts on subsystems to be used, unless it returns error, in which case
1065 * no refcounts are taken.
1066 */
1067static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1068{
1069        char *token, *o = data ?: "all";
1070        unsigned long mask = (unsigned long)-1;
1071        int i;
1072        bool module_pin_failed = false;
1073
1074        BUG_ON(!mutex_is_locked(&cgroup_mutex));
1075
1076#ifdef CONFIG_CPUSETS
1077        mask = ~(1UL << cpuset_subsys_id);
1078#endif
1079
1080        memset(opts, 0, sizeof(*opts));
1081
1082        while ((token = strsep(&o, ",")) != NULL) {
1083                if (!*token)
1084                        return -EINVAL;
1085                if (!strcmp(token, "all")) {
1086                        /* Add all non-disabled subsystems */
1087                        opts->subsys_bits = 0;
1088                        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1089                                struct cgroup_subsys *ss = subsys[i];
1090                                if (ss == NULL)
1091                                        continue;
1092                                if (!ss->disabled)
1093                                        opts->subsys_bits |= 1ul << i;
1094                        }
1095                } else if (!strcmp(token, "none")) {
1096                        /* Explicitly have no subsystems */
1097                        opts->none = true;
1098                } else if (!strcmp(token, "noprefix")) {
1099                        set_bit(ROOT_NOPREFIX, &opts->flags);
1100                } else if (!strncmp(token, "release_agent=", 14)) {
1101                        /* Specifying two release agents is forbidden */
1102                        if (opts->release_agent)
1103                                return -EINVAL;
1104                        opts->release_agent =
1105                                kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1106                        if (!opts->release_agent)
1107                                return -ENOMEM;
1108                } else if (!strncmp(token, "name=", 5)) {
1109                        const char *name = token + 5;
1110                        /* Can't specify an empty name */
1111                        if (!strlen(name))
1112                                return -EINVAL;
1113                        /* Must match [\w.-]+ */
1114                        for (i = 0; i < strlen(name); i++) {
1115                                char c = name[i];
1116                                if (isalnum(c))
1117                                        continue;
1118                                if ((c == '.') || (c == '-') || (c == '_'))
1119                                        continue;
1120                                return -EINVAL;
1121                        }
1122                        /* Specifying two names is forbidden */
1123                        if (opts->name)
1124                                return -EINVAL;
1125                        opts->name = kstrndup(name,
1126                                              MAX_CGROUP_ROOT_NAMELEN - 1,
1127                                              GFP_KERNEL);
1128                        if (!opts->name)
1129                                return -ENOMEM;
1130                } else {
1131                        struct cgroup_subsys *ss;
1132                        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1133                                ss = subsys[i];
1134                                if (ss == NULL)
1135                                        continue;
1136                                if (!strcmp(token, ss->name)) {
1137                                        if (!ss->disabled)
1138                                                set_bit(i, &opts->subsys_bits);
1139                                        break;
1140                                }
1141                        }
1142                        if (i == CGROUP_SUBSYS_COUNT)
1143                                return -ENOENT;
1144                }
1145        }
1146
1147        /* Consistency checks */
1148
1149        /*
1150         * Option noprefix was introduced just for backward compatibility
1151         * with the old cpuset, so we allow noprefix only if mounting just
1152         * the cpuset subsystem.
1153         */
1154        if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
1155            (opts->subsys_bits & mask))
1156                return -EINVAL;
1157
1158
1159        /* Can't specify "none" and some subsystems */
1160        if (opts->subsys_bits && opts->none)
1161                return -EINVAL;
1162
1163        /*
1164         * We either have to specify by name or by subsystems. (So all
1165         * empty hierarchies must have a name).
1166         */
1167        if (!opts->subsys_bits && !opts->name)
1168                return -EINVAL;
1169
1170        /*
1171         * Grab references on all the modules we'll need, so the subsystems
1172         * don't dance around before rebind_subsystems attaches them. This may
1173         * take duplicate reference counts on a subsystem that's already used,
1174         * but rebind_subsystems handles this case.
1175         */
1176        for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
1177                unsigned long bit = 1UL << i;
1178
1179                if (!(bit & opts->subsys_bits))
1180                        continue;
1181                if (!try_module_get(subsys[i]->module)) {
1182                        module_pin_failed = true;
1183                        break;
1184                }
1185        }
1186        if (module_pin_failed) {
1187                /*
1188                 * oops, one of the modules was going away. this means that we
1189                 * raced with a module_delete call, and to the user this is
1190                 * essentially a "subsystem doesn't exist" case.
1191                 */
1192                for (i--; i >= CGROUP_BUILTIN_SUBSYS_COUNT; i--) {
1193                        /* drop refcounts only on the ones we took */
1194                        unsigned long bit = 1UL << i;
1195
1196                        if (!(bit & opts->subsys_bits))
1197                                continue;
1198                        module_put(subsys[i]->module);
1199                }
1200                return -ENOENT;
1201        }
1202
1203        return 0;
1204}
1205
1206static void drop_parsed_module_refcounts(unsigned long subsys_bits)
1207{
1208        int i;
1209        for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
1210                unsigned long bit = 1UL << i;
1211
1212                if (!(bit & subsys_bits))
1213                        continue;
1214                module_put(subsys[i]->module);
1215        }
1216}
1217
1218static int cgroup_remount(struct super_block *sb, int *flags, char *data)
1219{
1220        int ret = 0;
1221        struct cgroupfs_root *root = sb->s_fs_info;
1222        struct cgroup *cgrp = &root->top_cgroup;
1223        struct cgroup_sb_opts opts;
1224
1225        lock_kernel();
1226        mutex_lock(&cgrp->dentry->d_inode->i_mutex);
1227        mutex_lock(&cgroup_mutex);
1228
1229        /* See what subsystems are wanted */
1230        ret = parse_cgroupfs_options(data, &opts);
1231        if (ret)
1232                goto out_unlock;
1233
1234        /* Don't allow flags or name to change at remount */
1235        if (opts.flags != root->flags ||
1236            (opts.name && strcmp(opts.name, root->name))) {
1237                ret = -EINVAL;
1238                drop_parsed_module_refcounts(opts.subsys_bits);
1239                goto out_unlock;
1240        }
1241
1242        ret = rebind_subsystems(root, opts.subsys_bits);
1243        if (ret) {
1244                drop_parsed_module_refcounts(opts.subsys_bits);
1245                goto out_unlock;
1246        }
1247
1248        /* (re)populate subsystem files */
1249        cgroup_populate_dir(cgrp);
1250
1251        if (opts.release_agent)
1252                strcpy(root->release_agent_path, opts.release_agent);
1253 out_unlock:
1254        kfree(opts.release_agent);
1255        kfree(opts.name);
1256        mutex_unlock(&cgroup_mutex);
1257        mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
1258        unlock_kernel();
1259        return ret;
1260}
1261
1262static const struct super_operations cgroup_ops = {
1263        .statfs = simple_statfs,
1264        .drop_inode = generic_delete_inode,
1265        .show_options = cgroup_show_options,
1266        .remount_fs = cgroup_remount,
1267};
1268
1269static void init_cgroup_housekeeping(struct cgroup *cgrp)
1270{
1271        INIT_LIST_HEAD(&cgrp->sibling);
1272        INIT_LIST_HEAD(&cgrp->children);
1273        INIT_LIST_HEAD(&cgrp->css_sets);
1274        INIT_LIST_HEAD(&cgrp->release_list);
1275        INIT_LIST_HEAD(&cgrp->pidlists);
1276        mutex_init(&cgrp->pidlist_mutex);
1277        INIT_LIST_HEAD(&cgrp->event_list);
1278        spin_lock_init(&cgrp->event_list_lock);
1279}
1280
1281static void init_cgroup_root(struct cgroupfs_root *root)
1282{
1283        struct cgroup *cgrp = &root->top_cgroup;
1284        INIT_LIST_HEAD(&root->subsys_list);
1285        INIT_LIST_HEAD(&root->root_list);
1286        root->number_of_cgroups = 1;
1287        cgrp->root = root;
1288        cgrp->top_cgroup = cgrp;
1289        init_cgroup_housekeeping(cgrp);
1290}
1291
1292static bool init_root_id(struct cgroupfs_root *root)
1293{
1294        int ret = 0;
1295
1296        do {
1297                if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))
1298                        return false;
1299                spin_lock(&hierarchy_id_lock);
1300                /* Try to allocate the next unused ID */
1301                ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
1302                                        &root->hierarchy_id);
1303                if (ret == -ENOSPC)
1304                        /* Try again starting from 0 */
1305                        ret = ida_get_new(&hierarchy_ida, &root->hierarchy_id);
1306                if (!ret) {
1307                        next_hierarchy_id = root->hierarchy_id + 1;
1308                } else if (ret != -EAGAIN) {
1309                        /* Can only get here if the 31-bit IDR is full ... */
1310                        BUG_ON(ret);
1311                }
1312                spin_unlock(&hierarchy_id_lock);
1313        } while (ret);
1314        return true;
1315}
1316
1317static int cgroup_test_super(struct super_block *sb, void *data)
1318{
1319        struct cgroup_sb_opts *opts = data;
1320        struct cgroupfs_root *root = sb->s_fs_info;
1321
1322        /* If we asked for a name then it must match */
1323        if (opts->name && strcmp(opts->name, root->name))
1324                return 0;
1325
1326        /*
1327         * If we asked for subsystems (or explicitly for no
1328         * subsystems) then they must match
1329         */
1330        if ((opts->subsys_bits || opts->none)
1331            && (opts->subsys_bits != root->subsys_bits))
1332                return 0;
1333
1334        return 1;
1335}
1336
1337static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
1338{
1339        struct cgroupfs_root *root;
1340
1341        if (!opts->subsys_bits && !opts->none)
1342                return NULL;
1343
1344        root = kzalloc(sizeof(*root), GFP_KERNEL);
1345        if (!root)
1346                return ERR_PTR(-ENOMEM);
1347
1348        if (!init_root_id(root)) {
1349                kfree(root);
1350                return ERR_PTR(-ENOMEM);
1351        }
1352        init_cgroup_root(root);
1353
1354        root->subsys_bits = opts->subsys_bits;
1355        root->flags = opts->flags;
1356        if (opts->release_agent)
1357                strcpy(root->release_agent_path, opts->release_agent);
1358        if (opts->name)
1359                strcpy(root->name, opts->name);
1360        return root;
1361}
1362
1363static void cgroup_drop_root(struct cgroupfs_root *root)
1364{
1365        if (!root)
1366                return;
1367
1368        BUG_ON(!root->hierarchy_id);
1369        spin_lock(&hierarchy_id_lock);
1370        ida_remove(&hierarchy_ida, root->hierarchy_id);
1371        spin_unlock(&hierarchy_id_lock);
1372        kfree(root);
1373}
1374
1375static int cgroup_set_super(struct super_block *sb, void *data)
1376{
1377        int ret;
1378        struct cgroup_sb_opts *opts = data;
1379
1380        /* If we don't have a new root, we can't set up a new sb */
1381        if (!opts->new_root)
1382                return -EINVAL;
1383
1384        BUG_ON(!opts->subsys_bits && !opts->none);
1385
1386        ret = set_anon_super(sb, NULL);
1387        if (ret)
1388                return ret;
1389
1390        sb->s_fs_info = opts->new_root;
1391        opts->new_root->sb = sb;
1392
1393        sb->s_blocksize = PAGE_CACHE_SIZE;
1394        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
1395        sb->s_magic = CGROUP_SUPER_MAGIC;
1396        sb->s_op = &cgroup_ops;
1397
1398        return 0;
1399}
1400
1401static int cgroup_get_rootdir(struct super_block *sb)
1402{
1403        struct inode *inode =
1404                cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
1405        struct dentry *dentry;
1406
1407        if (!inode)
1408                return -ENOMEM;
1409
1410        inode->i_fop = &simple_dir_operations;
1411        inode->i_op = &cgroup_dir_inode_operations;
1412        /* directories start off with i_nlink == 2 (for "." entry) */
1413        inc_nlink(inode);
1414        dentry = d_alloc_root(inode);
1415        if (!dentry) {
1416                iput(inode);
1417                return -ENOMEM;
1418        }
1419        sb->s_root = dentry;
1420        return 0;
1421}
1422
1423static int cgroup_get_sb(struct file_system_type *fs_type,
1424                         int flags, const char *unused_dev_name,
1425                         void *data, struct vfsmount *mnt)
1426{
1427        struct cgroup_sb_opts opts;
1428        struct cgroupfs_root *root;
1429        int ret = 0;
1430        struct super_block *sb;
1431        struct cgroupfs_root *new_root;
1432
1433        /* First find the desired set of subsystems */
1434        mutex_lock(&cgroup_mutex);
1435        ret = parse_cgroupfs_options(data, &opts);
1436        mutex_unlock(&cgroup_mutex);
1437        if (ret)
1438                goto out_err;
1439
1440        /*
1441         * Allocate a new cgroup root. We may not need it if we're
1442         * reusing an existing hierarchy.
1443         */
1444        new_root = cgroup_root_from_opts(&opts);
1445        if (IS_ERR(new_root)) {
1446                ret = PTR_ERR(new_root);
1447                goto drop_modules;
1448        }
1449        opts.new_root = new_root;
1450
1451        /* Locate an existing or new sb for this hierarchy */
1452        sb = sget(fs_type, cgroup_test_super, cgroup_set_super, &opts);
1453        if (IS_ERR(sb)) {
1454                ret = PTR_ERR(sb);
1455                cgroup_drop_root(opts.new_root);
1456                goto drop_modules;
1457        }
1458
1459        root = sb->s_fs_info;
1460        BUG_ON(!root);
1461        if (root == opts.new_root) {
1462                /* We used the new root structure, so this is a new hierarchy */
1463                struct list_head tmp_cg_links;
1464                struct cgroup *root_cgrp = &root->top_cgroup;
1465                struct inode *inode;
1466                struct cgroupfs_root *existing_root;
1467                int i;
1468
1469                BUG_ON(sb->s_root != NULL);
1470
1471                ret = cgroup_get_rootdir(sb);
1472                if (ret)
1473                        goto drop_new_super;
1474                inode = sb->s_root->d_inode;
1475
1476                mutex_lock(&inode->i_mutex);
1477                mutex_lock(&cgroup_mutex);
1478
1479                if (strlen(root->name)) {
1480                        /* Check for name clashes with existing mounts */
1481                        for_each_active_root(existing_root) {
1482                                if (!strcmp(existing_root->name, root->name)) {
1483                                        ret = -EBUSY;
1484                                        mutex_unlock(&cgroup_mutex);
1485                                        mutex_unlock(&inode->i_mutex);
1486                                        goto drop_new_super;
1487                                }
1488                        }
1489                }
1490
1491                /*
1492                 * We're accessing css_set_count without locking
1493                 * css_set_lock here, but that's OK - it can only be
1494                 * increased by someone holding cgroup_lock, and
1495                 * that's us. The worst that can happen is that we
1496                 * have some link structures left over
1497                 */
1498                ret = allocate_cg_links(css_set_count, &tmp_cg_links);
1499                if (ret) {
1500                        mutex_unlock(&cgroup_mutex);
1501                        mutex_unlock(&inode->i_mutex);
1502                        goto drop_new_super;
1503                }
1504
1505                ret = rebind_subsystems(root, root->subsys_bits);
1506                if (ret == -EBUSY) {
1507                        mutex_unlock(&cgroup_mutex);
1508                        mutex_unlock(&inode->i_mutex);
1509                        free_cg_links(&tmp_cg_links);
1510                        goto drop_new_super;
1511                }
1512                /*
1513                 * There must be no failure case after here, since rebinding
1514                 * takes care of subsystems' refcounts, which are explicitly
1515                 * dropped in the failure exit path.
1516                 */
1517
1518                /* EBUSY should be the only error here */
1519                BUG_ON(ret);
1520
1521                list_add(&root->root_list, &roots);
1522                root_count++;
1523
1524                sb->s_root->d_fsdata = root_cgrp;
1525                root->top_cgroup.dentry = sb->s_root;
1526
1527                /* Link the top cgroup in this hierarchy into all
1528                 * the css_set objects */
1529                write_lock(&css_set_lock);
1530                for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
1531                        struct hlist_head *hhead = &css_set_table[i];
1532                        struct hlist_node *node;
1533                        struct css_set *cg;
1534
1535                        hlist_for_each_entry(cg, node, hhead, hlist)
1536                                link_css_set(&tmp_cg_links, cg, root_cgrp);
1537                }
1538                write_unlock(&css_set_lock);
1539
1540                free_cg_links(&tmp_cg_links);
1541
1542                BUG_ON(!list_empty(&root_cgrp->sibling));
1543                BUG_ON(!list_empty(&root_cgrp->children));
1544                BUG_ON(root->number_of_cgroups != 1);
1545
1546                cgroup_populate_dir(root_cgrp);
1547                mutex_unlock(&cgroup_mutex);
1548                mutex_unlock(&inode->i_mutex);
1549        } else {
1550                /*
1551                 * We re-used an existing hierarchy - the new root (if
1552                 * any) is not needed
1553                 */
1554                cgroup_drop_root(opts.new_root);
1555                /* no subsys rebinding, so refcounts don't change */
1556                drop_parsed_module_refcounts(opts.subsys_bits);
1557        }
1558
1559        simple_set_mnt(mnt, sb);
1560        kfree(opts.release_agent);
1561        kfree(opts.name);
1562        return 0;
1563
1564 drop_new_super:
1565        deactivate_locked_super(sb);
1566 drop_modules:
1567        drop_parsed_module_refcounts(opts.subsys_bits);
1568 out_err:
1569        kfree(opts.release_agent);
1570        kfree(opts.name);
1571
1572        return ret;
1573}
1574
1575static void cgroup_kill_sb(struct super_block *sb) {
1576        struct cgroupfs_root *root = sb->s_fs_info;
1577        struct cgroup *cgrp = &root->top_cgroup;
1578        int ret;
1579        struct cg_cgroup_link *link;
1580        struct cg_cgroup_link *saved_link;
1581
1582        BUG_ON(!root);
1583
1584        BUG_ON(root->number_of_cgroups != 1);
1585        BUG_ON(!list_empty(&cgrp->children));
1586        BUG_ON(!list_empty(&cgrp->sibling));
1587
1588        mutex_lock(&cgroup_mutex);
1589
1590        /* Rebind all subsystems back to the default hierarchy */
1591        ret = rebind_subsystems(root, 0);
1592        /* Shouldn't be able to fail ... */
1593        BUG_ON(ret);
1594
1595        /*
1596         * Release all the links from css_sets to this hierarchy's
1597         * root cgroup
1598         */
1599        write_lock(&css_set_lock);
1600
1601        list_for_each_entry_safe(link, saved_link, &cgrp->css_sets,
1602                                 cgrp_link_list) {
1603                list_del(&link->cg_link_list);
1604                list_del(&link->cgrp_link_list);
1605                kfree(link);
1606        }
1607        write_unlock(&css_set_lock);
1608
1609        if (!list_empty(&root->root_list)) {
1610                list_del(&root->root_list);
1611                root_count--;
1612        }
1613
1614        mutex_unlock(&cgroup_mutex);
1615
1616        kill_litter_super(sb);
1617        cgroup_drop_root(root);
1618}
1619
1620static struct file_system_type cgroup_fs_type = {
1621        .name = "cgroup",
1622        .get_sb = cgroup_get_sb,
1623        .kill_sb = cgroup_kill_sb,
1624};
1625
1626static struct kobject *cgroup_kobj;
1627
1628static inline struct cgroup *__d_cgrp(struct dentry *dentry)
1629{
1630        return dentry->d_fsdata;
1631}
1632
1633static inline struct cftype *__d_cft(struct dentry *dentry)
1634{
1635        return dentry->d_fsdata;
1636}
1637
1638/**
1639 * cgroup_path - generate the path of a cgroup
1640 * @cgrp: the cgroup in question
1641 * @buf: the buffer to write the path into
1642 * @buflen: the length of the buffer
1643 *
1644 * Called with cgroup_mutex held or else with an RCU-protected cgroup
1645 * reference.  Writes path of cgroup into buf.  Returns 0 on success,
1646 * -errno on error.
1647 */
1648int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
1649{
1650        char *start;
1651        struct dentry *dentry = rcu_dereference_check(cgrp->dentry,
1652                                                      rcu_read_lock_held() ||
1653                                                      cgroup_lock_is_held());
1654
1655        if (!dentry || cgrp == dummytop) {
1656                /*
1657                 * Inactive subsystems have no dentry for their root
1658                 * cgroup
1659                 */
1660                strcpy(buf, "/");
1661                return 0;
1662        }
1663
1664        start = buf + buflen;
1665
1666        *--start = '\0';
1667        for (;;) {
1668                int len = dentry->d_name.len;
1669
1670                if ((start -= len) < buf)
1671                        return -ENAMETOOLONG;
1672                memcpy(start, dentry->d_name.name, len);
1673                cgrp = cgrp->parent;
1674                if (!cgrp)
1675                        break;
1676
1677                dentry = rcu_dereference_check(cgrp->dentry,
1678                                               rcu_read_lock_held() ||
1679                                               cgroup_lock_is_held());
1680                if (!cgrp->parent)
1681                        continue;
1682                if (--start < buf)
1683                        return -ENAMETOOLONG;
1684                *start = '/';
1685        }
1686        memmove(buf, start, buf + buflen - start);
1687        return 0;
1688}
1689EXPORT_SYMBOL_GPL(cgroup_path);
1690
1691/**
1692 * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
1693 * @cgrp: the cgroup the task is attaching to
1694 * @tsk: the task to be attached
1695 *
1696 * Call holding cgroup_mutex. May take task_lock of
1697 * the task 'tsk' during call.
1698 */
1699int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
1700{
1701        int retval = 0;
1702        struct cgroup_subsys *ss, *failed_ss = NULL;
1703        struct cgroup *oldcgrp;
1704        struct css_set *cg;
1705        struct css_set *newcg;
1706        struct cgroupfs_root *root = cgrp->root;
1707
1708        /* Nothing to do if the task is already in that cgroup */
1709        oldcgrp = task_cgroup_from_root(tsk, root);
1710        if (cgrp == oldcgrp)
1711                return 0;
1712
1713        for_each_subsys(root, ss) {
1714                if (ss->can_attach) {
1715                        retval = ss->can_attach(ss, cgrp, tsk, false);
1716                        if (retval) {
1717                                /*
1718                                 * Remember on which subsystem the can_attach()
1719                                 * failed, so that we only call cancel_attach()
1720                                 * against the subsystems whose can_attach()
1721                                 * succeeded. (See below)
1722                                 */
1723                                failed_ss = ss;
1724                                goto out;
1725                        }
1726                }
1727        }
1728
1729        task_lock(tsk);
1730        cg = tsk->cgroups;
1731        get_css_set(cg);
1732        task_unlock(tsk);
1733        /*
1734         * Locate or allocate a new css_set for this task,
1735         * based on its final set of cgroups
1736         */
1737        newcg = find_css_set(cg, cgrp);
1738        put_css_set(cg);
1739        if (!newcg) {
1740                retval = -ENOMEM;
1741                goto out;
1742        }
1743
1744        task_lock(tsk);
1745        if (tsk->flags & PF_EXITING) {
1746                task_unlock(tsk);
1747                put_css_set(newcg);
1748                retval = -ESRCH;
1749                goto out;
1750        }
1751        rcu_assign_pointer(tsk->cgroups, newcg);
1752        task_unlock(tsk);
1753
1754        /* Update the css_set linked lists if we're using them */
1755        write_lock(&css_set_lock);
1756        if (!list_empty(&tsk->cg_list)) {
1757                list_del(&tsk->cg_list);
1758                list_add(&tsk->cg_list, &newcg->tasks);
1759        }
1760        write_unlock(&css_set_lock);
1761
1762        for_each_subsys(root, ss) {
1763                if (ss->attach)
1764                        ss->attach(ss, cgrp, oldcgrp, tsk, false);
1765        }
1766        set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
1767        synchronize_rcu();
1768        put_css_set(cg);
1769
1770        /*
1771         * wake up rmdir() waiter. the rmdir should fail since the cgroup
1772         * is no longer empty.
1773         */
1774        cgroup_wakeup_rmdir_waiter(cgrp);
1775out:
1776        if (retval) {
1777                for_each_subsys(root, ss) {
1778                        if (ss == failed_ss)
1779                                /*
1780                                 * This subsystem was the one that failed the
1781                                 * can_attach() check earlier, so we don't need
1782                                 * to call cancel_attach() against it or any
1783                                 * remaining subsystems.
1784                                 */
1785                                break;
1786                        if (ss->cancel_attach)
1787                                ss->cancel_attach(ss, cgrp, tsk, false);
1788                }
1789        }
1790        return retval;
1791}
1792
1793/**
1794 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
1795 * @from: attach to all cgroups of a given task
1796 * @tsk: the task to be attached
1797 */
1798int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
1799{
1800        struct cgroupfs_root *root;
1801        int retval = 0;
1802
1803        cgroup_lock();
1804        for_each_active_root(root) {
1805                struct cgroup *from_cg = task_cgroup_from_root(from, root);
1806
1807                retval = cgroup_attach_task(from_cg, tsk);
1808                if (retval)
1809                        break;
1810        }
1811        cgroup_unlock();
1812
1813        return retval;
1814}
1815EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
1816
1817/*
1818 * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
1819 * held. May take task_lock of task
1820 */
1821static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
1822{
1823        struct task_struct *tsk;
1824        const struct cred *cred = current_cred(), *tcred;
1825        int ret;
1826
1827        if (pid) {
1828                rcu_read_lock();
1829                tsk = find_task_by_vpid(pid);
1830                if (!tsk || tsk->flags & PF_EXITING) {
1831                        rcu_read_unlock();
1832                        return -ESRCH;
1833                }
1834
1835                tcred = __task_cred(tsk);
1836                if (cred->euid &&
1837                    cred->euid != tcred->uid &&
1838                    cred->euid != tcred->suid) {
1839                        rcu_read_unlock();
1840                        return -EACCES;
1841                }
1842                get_task_struct(tsk);
1843                rcu_read_unlock();
1844        } else {
1845                tsk = current;
1846                get_task_struct(tsk);
1847        }
1848
1849        ret = cgroup_attach_task(cgrp, tsk);
1850        put_task_struct(tsk);
1851        return ret;
1852}
1853
1854static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
1855{
1856        int ret;
1857        if (!cgroup_lock_live_group(cgrp))
1858                return -ENODEV;
1859        ret = attach_task_by_pid(cgrp, pid);
1860        cgroup_unlock();
1861        return ret;
1862}
1863
1864/**
1865 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
1866 * @cgrp: the cgroup to be checked for liveness
1867 *
1868 * On success, returns true; the lock should be later released with
1869 * cgroup_unlock(). On failure returns false with no lock held.
1870 */
1871bool cgroup_lock_live_group(struct cgroup *cgrp)
1872{
1873        mutex_lock(&cgroup_mutex);
1874        if (cgroup_is_removed(cgrp)) {
1875                mutex_unlock(&cgroup_mutex);
1876                return false;
1877        }
1878        return true;
1879}
1880EXPORT_SYMBOL_GPL(cgroup_lock_live_group);
1881
1882static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
1883                                      const char *buffer)
1884{
1885        BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
1886        if (!cgroup_lock_live_group(cgrp))
1887                return -ENODEV;
1888        strcpy(cgrp->root->release_agent_path, buffer);
1889        cgroup_unlock();
1890        return 0;
1891}
1892
1893static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
1894                                     struct seq_file *seq)
1895{
1896        if (!cgroup_lock_live_group(cgrp))
1897                return -ENODEV;
1898        seq_puts(seq, cgrp->root->release_agent_path);
1899        seq_putc(seq, '\n');
1900        cgroup_unlock();
1901        return 0;
1902}
1903
1904/* A buffer size big enough for numbers or short strings */
1905#define CGROUP_LOCAL_BUFFER_SIZE 64
1906
1907static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
1908                                struct file *file,
1909                                const char __user *userbuf,
1910                                size_t nbytes, loff_t *unused_ppos)
1911{
1912        char buffer[CGROUP_LOCAL_BUFFER_SIZE];
1913        int retval = 0;
1914        char *end;
1915
1916        if (!nbytes)
1917                return -EINVAL;
1918        if (nbytes >= sizeof(buffer))
1919                return -E2BIG;
1920        if (copy_from_user(buffer, userbuf, nbytes))
1921                return -EFAULT;
1922
1923        buffer[nbytes] = 0;     /* nul-terminate */
1924        if (cft->write_u64) {
1925                u64 val = simple_strtoull(strstrip(buffer), &end, 0);
1926                if (*end)
1927                        return -EINVAL;
1928                retval = cft->write_u64(cgrp, cft, val);
1929        } else {
1930                s64 val = simple_strtoll(strstrip(buffer), &end, 0);
1931                if (*end)
1932                        return -EINVAL;
1933                retval = cft->write_s64(cgrp, cft, val);
1934        }
1935        if (!retval)
1936                retval = nbytes;
1937        return retval;
1938}
1939
1940static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
1941                                   struct file *file,
1942                                   const char __user *userbuf,
1943                                   size_t nbytes, loff_t *unused_ppos)
1944{
1945        char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
1946        int retval = 0;
1947        size_t max_bytes = cft->max_write_len;
1948        char *buffer = local_buffer;
1949
1950        if (!max_bytes)
1951                max_bytes = sizeof(local_buffer) - 1;
1952        if (nbytes >= max_bytes)
1953                return -E2BIG;
1954        /* Allocate a dynamic buffer if we need one */
1955        if (nbytes >= sizeof(local_buffer)) {
1956                buffer = kmalloc(nbytes + 1, GFP_KERNEL);
1957                if (buffer == NULL)
1958                        return -ENOMEM;
1959        }
1960        if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
1961                retval = -EFAULT;
1962                goto out;
1963        }
1964
1965        buffer[nbytes] = 0;     /* nul-terminate */
1966        retval = cft->write_string(cgrp, cft, strstrip(buffer));
1967        if (!retval)
1968                retval = nbytes;
1969out:
1970        if (buffer != local_buffer)
1971                kfree(buffer);
1972        return retval;
1973}
1974
1975static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
1976                                                size_t nbytes, loff_t *ppos)
1977{
1978        struct cftype *cft = __d_cft(file->f_dentry);
1979        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
1980
1981        if (cgroup_is_removed(cgrp))
1982                return -ENODEV;
1983        if (cft->write)
1984                return cft->write(cgrp, cft, file, buf, nbytes, ppos);
1985        if (cft->write_u64 || cft->write_s64)
1986                return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
1987        if (cft->write_string)
1988                return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
1989        if (cft->trigger) {
1990                int ret = cft->trigger(cgrp, (unsigned int)cft->private);
1991                return ret ? ret : nbytes;
1992        }
1993        return -EINVAL;
1994}
1995
1996static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
1997                               struct file *file,
1998                               char __user *buf, size_t nbytes,
1999                               loff_t *ppos)
2000{
2001        char tmp[CGROUP_LOCAL_BUFFER_SIZE];
2002        u64 val = cft->read_u64(cgrp, cft);
2003        int len = sprintf(tmp, "%llu\n", (unsigned long long) val);
2004
2005        return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
2006}
2007
2008static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
2009                               struct file *file,
2010                               char __user *buf, size_t nbytes,
2011                               loff_t *ppos)
2012{
2013        char tmp[CGROUP_LOCAL_BUFFER_SIZE];
2014        s64 val = cft->read_s64(cgrp, cft);
2015        int len = sprintf(tmp, "%lld\n", (long long) val);
2016
2017        return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
2018}
2019
2020static ssize_t cgroup_file_read(struct file *file, char __user *buf,
2021                                   size_t nbytes, loff_t *ppos)
2022{
2023        struct cftype *cft = __d_cft(file->f_dentry);
2024        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2025
2026        if (cgroup_is_removed(cgrp))
2027                return -ENODEV;
2028
2029        if (cft->read)
2030                return cft->read(cgrp, cft, file, buf, nbytes, ppos);
2031        if (cft->read_u64)
2032                return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
2033        if (cft->read_s64)
2034                return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
2035        return -EINVAL;
2036}
2037
2038/*
2039 * seqfile ops/methods for returning structured data. Currently just
2040 * supports string->u64 maps, but can be extended in future.
2041 */
2042
2043struct cgroup_seqfile_state {
2044        struct cftype *cft;
2045        struct cgroup *cgroup;
2046};
2047
2048static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
2049{
2050        struct seq_file *sf = cb->state;
2051        return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
2052}
2053
2054static int cgroup_seqfile_show(struct seq_file *m, void *arg)
2055{
2056        struct cgroup_seqfile_state *state = m->private;
2057        struct cftype *cft = state->cft;
2058        if (cft->read_map) {
2059                struct cgroup_map_cb cb = {
2060                        .fill = cgroup_map_add,
2061                        .state = m,
2062                };
2063                return cft->read_map(state->cgroup, cft, &cb);
2064        }
2065        return cft->read_seq_string(state->cgroup, cft, m);
2066}
2067
2068static int cgroup_seqfile_release(struct inode *inode, struct file *file)
2069{
2070        struct seq_file *seq = file->private_data;
2071        kfree(seq->private);
2072        return single_release(inode, file);
2073}
2074
2075static const struct file_operations cgroup_seqfile_operations = {
2076        .read = seq_read,
2077        .write = cgroup_file_write,
2078        .llseek = seq_lseek,
2079        .release = cgroup_seqfile_release,
2080};
2081
2082static int cgroup_file_open(struct inode *inode, struct file *file)
2083{
2084        int err;
2085        struct cftype *cft;
2086
2087        err = generic_file_open(inode, file);
2088        if (err)
2089                return err;
2090        cft = __d_cft(file->f_dentry);
2091
2092        if (cft->read_map || cft->read_seq_string) {
2093                struct cgroup_seqfile_state *state =
2094                        kzalloc(sizeof(*state), GFP_USER);
2095                if (!state)
2096                        return -ENOMEM;
2097                state->cft = cft;
2098                state->cgroup = __d_cgrp(file->f_dentry->d_parent);
2099                file->f_op = &cgroup_seqfile_operations;
2100                err = single_open(file, cgroup_seqfile_show, state);
2101                if (err < 0)
2102                        kfree(state);
2103        } else if (cft->open)
2104                err = cft->open(inode, file);
2105        else
2106                err = 0;
2107
2108        return err;
2109}
2110
2111static int cgroup_file_release(struct inode *inode, struct file *file)
2112{
2113        struct cftype *cft = __d_cft(file->f_dentry);
2114        if (cft->release)
2115                return cft->release(inode, file);
2116        return 0;
2117}
2118
2119/*
2120 * cgroup_rename - Only allow simple rename of directories in place.
2121 */
2122static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
2123                            struct inode *new_dir, struct dentry *new_dentry)
2124{
2125        if (!S_ISDIR(old_dentry->d_inode->i_mode))
2126                return -ENOTDIR;
2127        if (new_dentry->d_inode)
2128                return -EEXIST;
2129        if (old_dir != new_dir)
2130                return -EIO;
2131        return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
2132}
2133
2134static const struct file_operations cgroup_file_operations = {
2135        .read = cgroup_file_read,
2136        .write = cgroup_file_write,
2137        .llseek = generic_file_llseek,
2138        .open = cgroup_file_open,
2139        .release = cgroup_file_release,
2140};
2141
2142static const struct inode_operations cgroup_dir_inode_operations = {
2143        .lookup = simple_lookup,
2144        .mkdir = cgroup_mkdir,
2145        .rmdir = cgroup_rmdir,
2146        .rename = cgroup_rename,
2147};
2148
2149/*
2150 * Check if a file is a control file
2151 */
2152static inline struct cftype *__file_cft(struct file *file)
2153{
2154        if (file->f_dentry->d_inode->i_fop != &cgroup_file_operations)
2155                return ERR_PTR(-EINVAL);
2156        return __d_cft(file->f_dentry);
2157}
2158
2159static int cgroup_create_file(struct dentry *dentry, mode_t mode,
2160                                struct super_block *sb)
2161{
2162        static const struct dentry_operations cgroup_dops = {
2163                .d_iput = cgroup_diput,
2164        };
2165
2166        struct inode *inode;
2167
2168        if (!dentry)
2169                return -ENOENT;
2170        if (dentry->d_inode)
2171                return -EEXIST;
2172
2173        inode = cgroup_new_inode(mode, sb);
2174        if (!inode)
2175                return -ENOMEM;
2176
2177        if (S_ISDIR(mode)) {
2178                inode->i_op = &cgroup_dir_inode_operations;
2179                inode->i_fop = &simple_dir_operations;
2180
2181                /* start off with i_nlink == 2 (for "." entry) */
2182                inc_nlink(inode);
2183
2184                /* start with the directory inode held, so that we can
2185                 * populate it without racing with another mkdir */
2186                mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
2187        } else if (S_ISREG(mode)) {
2188                inode->i_size = 0;
2189                inode->i_fop = &cgroup_file_operations;
2190        }
2191        dentry->d_op = &cgroup_dops;
2192        d_instantiate(dentry, inode);
2193        dget(dentry);   /* Extra count - pin the dentry in core */
2194        return 0;
2195}
2196
2197/*
2198 * cgroup_create_dir - create a directory for an object.
2199 * @cgrp: the cgroup we create the directory for. It must have a valid
2200 *        ->parent field. And we are going to fill its ->dentry field.
2201 * @dentry: dentry of the new cgroup
2202 * @mode: mode to set on new directory.
2203 */
2204static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
2205                                mode_t mode)
2206{
2207        struct dentry *parent;
2208        int error = 0;
2209
2210        parent = cgrp->parent->dentry;
2211        error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb);
2212        if (!error) {
2213                dentry->d_fsdata = cgrp;
2214                inc_nlink(parent->d_inode);
2215                rcu_assign_pointer(cgrp->dentry, dentry);
2216                dget(dentry);
2217        }
2218        dput(dentry);
2219
2220        return error;
2221}
2222
2223/**
2224 * cgroup_file_mode - deduce file mode of a control file
2225 * @cft: the control file in question
2226 *
2227 * returns cft->mode if ->mode is not 0
2228 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
2229 * returns S_IRUGO if it has only a read handler
2230 * returns S_IWUSR if it has only a write hander
2231 */
2232static mode_t cgroup_file_mode(const struct cftype *cft)
2233{
2234        mode_t mode = 0;
2235
2236        if (cft->mode)
2237                return cft->mode;
2238
2239        if (cft->read || cft->read_u64 || cft->read_s64 ||
2240            cft->read_map || cft->read_seq_string)
2241                mode |= S_IRUGO;
2242
2243        if (cft->write || cft->write_u64 || cft->write_s64 ||
2244            cft->write_string || cft->trigger)
2245                mode |= S_IWUSR;
2246
2247        return mode;
2248}
2249
2250int cgroup_add_file(struct cgroup *cgrp,
2251                       struct cgroup_subsys *subsys,
2252                       const struct cftype *cft)
2253{
2254        struct dentry *dir = cgrp->dentry;
2255        struct dentry *dentry;
2256        int error;
2257        mode_t mode;
2258
2259        char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
2260        if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
2261                strcpy(name, subsys->name);
2262                strcat(name, ".");
2263        }
2264        strcat(name, cft->name);
2265        BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
2266        dentry = lookup_one_len(name, dir, strlen(name));
2267        if (!IS_ERR(dentry)) {
2268                mode = cgroup_file_mode(cft);
2269                error = cgroup_create_file(dentry, mode | S_IFREG,
2270                                                cgrp->root->sb);
2271                if (!error)
2272                        dentry->d_fsdata = (void *)cft;
2273                dput(dentry);
2274        } else
2275                error = PTR_ERR(dentry);
2276        return error;
2277}
2278EXPORT_SYMBOL_GPL(cgroup_add_file);
2279
2280int cgroup_add_files(struct cgroup *cgrp,
2281                        struct cgroup_subsys *subsys,
2282                        const struct cftype cft[],
2283                        int count)
2284{
2285        int i, err;
2286        for (i = 0; i < count; i++) {
2287                err = cgroup_add_file(cgrp, subsys, &cft[i]);
2288                if (err)
2289                        return err;
2290        }
2291        return 0;
2292}
2293EXPORT_SYMBOL_GPL(cgroup_add_files);
2294
2295/**
2296 * cgroup_task_count - count the number of tasks in a cgroup.
2297 * @cgrp: the cgroup in question
2298 *
2299 * Return the number of tasks in the cgroup.
2300 */
2301int cgroup_task_count(const struct cgroup *cgrp)
2302{
2303        int count = 0;
2304        struct cg_cgroup_link *link;
2305
2306        read_lock(&css_set_lock);
2307        list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
2308                count += atomic_read(&link->cg->refcount);
2309        }
2310        read_unlock(&css_set_lock);
2311        return count;
2312}
2313
2314/*
2315 * Advance a list_head iterator.  The iterator should be positioned at
2316 * the start of a css_set
2317 */
2318static void cgroup_advance_iter(struct cgroup *cgrp,
2319                                struct cgroup_iter *it)
2320{
2321        struct list_head *l = it->cg_link;
2322        struct cg_cgroup_link *link;
2323        struct css_set *cg;
2324
2325        /* Advance to the next non-empty css_set */
2326        do {
2327                l = l->next;
2328                if (l == &cgrp->css_sets) {
2329                        it->cg_link = NULL;
2330                        return;
2331                }
2332                link = list_entry(l, struct cg_cgroup_link, cgrp_link_list);
2333                cg = link->cg;
2334        } while (list_empty(&cg->tasks));
2335        it->cg_link = l;
2336        it->task = cg->tasks.next;
2337}
2338
2339/*
2340 * To reduce the fork() overhead for systems that are not actually
2341 * using their cgroups capability, we don't maintain the lists running
2342 * through each css_set to its tasks until we see the list actually
2343 * used - in other words after the first call to cgroup_iter_start().
2344 *
2345 * The tasklist_lock is not held here, as do_each_thread() and
2346 * while_each_thread() are protected by RCU.
2347 */
2348static void cgroup_enable_task_cg_lists(void)
2349{
2350        struct task_struct *p, *g;
2351        write_lock(&css_set_lock);
2352        use_task_css_set_links = 1;
2353        do_each_thread(g, p) {
2354                task_lock(p);
2355                /*
2356                 * We should check if the process is exiting, otherwise
2357                 * it will race with cgroup_exit() in that the list
2358                 * entry won't be deleted though the process has exited.
2359                 */
2360                if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
2361                        list_add(&p->cg_list, &p->cgroups->tasks);
2362                task_unlock(p);
2363        } while_each_thread(g, p);
2364        write_unlock(&css_set_lock);
2365}
2366
2367void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
2368{
2369        /*
2370         * The first time anyone tries to iterate across a cgroup,
2371         * we need to enable the list linking each css_set to its
2372         * tasks, and fix up all existing tasks.
2373         */
2374        if (!use_task_css_set_links)
2375                cgroup_enable_task_cg_lists();
2376
2377        read_lock(&css_set_lock);
2378        it->cg_link = &cgrp->css_sets;
2379        cgroup_advance_iter(cgrp, it);
2380}
2381
2382struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
2383                                        struct cgroup_iter *it)
2384{
2385        struct task_struct *res;
2386        struct list_head *l = it->task;
2387        struct cg_cgroup_link *link;
2388
2389        /* If the iterator cg is NULL, we have no tasks */
2390        if (!it->cg_link)
2391                return NULL;
2392        res = list_entry(l, struct task_struct, cg_list);
2393        /* Advance iterator to find next entry */
2394        l = l->next;
2395        link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list);
2396        if (l == &link->cg->tasks) {
2397                /* We reached the end of this task list - move on to
2398                 * the next cg_cgroup_link */
2399                cgroup_advance_iter(cgrp, it);
2400        } else {
2401                it->task = l;
2402        }
2403        return res;
2404}
2405
2406void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
2407{
2408        read_unlock(&css_set_lock);
2409}
2410
2411static inline int started_after_time(struct task_struct *t1,
2412                                     struct timespec *time,
2413                                     struct task_struct *t2)
2414{
2415        int start_diff = timespec_compare(&t1->start_time, time);
2416        if (start_diff > 0) {
2417                return 1;
2418        } else if (start_diff < 0) {
2419                return 0;
2420        } else {
2421                /*
2422                 * Arbitrarily, if two processes started at the same
2423                 * time, we'll say that the lower pointer value
2424                 * started first. Note that t2 may have exited by now
2425                 * so this may not be a valid pointer any longer, but
2426                 * that's fine - it still serves to distinguish
2427                 * between two tasks started (effectively) simultaneously.
2428                 */
2429                return t1 > t2;
2430        }
2431}
2432
2433/*
2434 * This function is a callback from heap_insert() and is used to order
2435 * the heap.
2436 * In this case we order the heap in descending task start time.
2437 */
2438static inline int started_after(void *p1, void *p2)
2439{
2440        struct task_struct *t1 = p1;
2441        struct task_struct *t2 = p2;
2442        return started_after_time(t1, &t2->start_time, t2);
2443}
2444
2445/**
2446 * cgroup_scan_tasks - iterate though all the tasks in a cgroup
2447 * @scan: struct cgroup_scanner containing arguments for the scan
2448 *
2449 * Arguments include pointers to callback functions test_task() and
2450 * process_task().
2451 * Iterate through all the tasks in a cgroup, calling test_task() for each,
2452 * and if it returns true, call process_task() for it also.
2453 * The test_task pointer may be NULL, meaning always true (select all tasks).
2454 * Effectively duplicates cgroup_iter_{start,next,end}()
2455 * but does not lock css_set_lock for the call to process_task().
2456 * The struct cgroup_scanner may be embedded in any structure of the caller's
2457 * creation.
2458 * It is guaranteed that process_task() will act on every task that
2459 * is a member of the cgroup for the duration of this call. This
2460 * function may or may not call process_task() for tasks that exit
2461 * or move to a different cgroup during the call, or are forked or
2462 * move into the cgroup during the call.
2463 *
2464 * Note that test_task() may be called with locks held, and may in some
2465 * situations be called multiple times for the same task, so it should
2466 * be cheap.
2467 * If the heap pointer in the struct cgroup_scanner is non-NULL, a heap has been
2468 * pre-allocated and will be used for heap operations (and its "gt" member will
2469 * be overwritten), else a temporary heap will be used (allocation of which
2470 * may cause this function to fail).
2471 */
2472int cgroup_scan_tasks(struct cgroup_scanner *scan)
2473{
2474        int retval, i;
2475        struct cgroup_iter it;
2476        struct task_struct *p, *dropped;
2477        /* Never dereference latest_task, since it's not refcounted */
2478        struct task_struct *latest_task = NULL;
2479        struct ptr_heap tmp_heap;
2480        struct ptr_heap *heap;
2481        struct timespec latest_time = { 0, 0 };
2482
2483        if (scan->heap) {
2484                /* The caller supplied our heap and pre-allocated its memory */
2485                heap = scan->heap;
2486                heap->gt = &started_after;
2487        } else {
2488                /* We need to allocate our own heap memory */
2489                heap = &tmp_heap;
2490                retval = heap_init(heap, PAGE_SIZE, GFP_KERNEL, &started_after);
2491                if (retval)
2492                        /* cannot allocate the heap */
2493                        return retval;
2494        }
2495
2496 again:
2497        /*
2498         * Scan tasks in the cgroup, using the scanner's "test_task" callback
2499         * to determine which are of interest, and using the scanner's
2500         * "process_task" callback to process any of them that need an update.
2501         * Since we don't want to hold any locks during the task updates,
2502         * gather tasks to be processed in a heap structure.
2503         * The heap is sorted by descending task start time.
2504         * If the statically-sized heap fills up, we overflow tasks that
2505         * started later, and in future iterations only consider tasks that
2506         * started after the latest task in the previous pass. This
2507         * guarantees forward progress and that we don't miss any tasks.
2508         */
2509        heap->size = 0;
2510        cgroup_iter_start(scan->cg, &it);
2511        while ((p = cgroup_iter_next(scan->cg, &it))) {
2512                /*
2513                 * Only affect tasks that qualify per the caller's callback,
2514                 * if he provided one
2515                 */
2516                if (scan->test_task && !scan->test_task(p, scan))
2517                        continue;
2518                /*
2519                 * Only process tasks that started after the last task
2520                 * we processed
2521                 */
2522                if (!started_after_time(p, &latest_time, latest_task))
2523                        continue;
2524                dropped = heap_insert(heap, p);
2525                if (dropped == NULL) {
2526                        /*
2527                         * The new task was inserted; the heap wasn't
2528                         * previously full
2529                         */
2530                        get_task_struct(p);
2531                } else if (dropped != p) {
2532                        /*
2533                         * The new task was inserted, and pushed out a
2534                         * different task
2535                         */
2536                        get_task_struct(p);
2537                        put_task_struct(dropped);
2538                }
2539                /*
2540                 * Else the new task was newer than anything already in
2541                 * the heap and wasn't inserted
2542                 */
2543        }
2544        cgroup_iter_end(scan->cg, &it);
2545
2546        if (heap->size) {
2547                for (i = 0; i < heap->size; i++) {
2548                        struct task_struct *q = heap->ptrs[i];
2549                        if (i == 0) {
2550                                latest_time = q->start_time;
2551                                latest_task = q;
2552                        }
2553                        /* Process the task per the caller's callback */
2554                        scan->process_task(q, scan);
2555                        put_task_struct(q);
2556                }
2557                /*
2558                 * If we had to process any tasks at all, scan again
2559                 * in case some of them were in the middle of forking
2560                 * children that didn't get processed.
2561                 * Not the most efficient way to do it, but it avoids
2562                 * having to take callback_mutex in the fork path
2563                 */
2564                goto again;
2565        }
2566        if (heap == &tmp_heap)
2567                heap_free(&tmp_heap);
2568        return 0;
2569}
2570
2571/*
2572 * Stuff for reading the 'tasks'/'procs' files.
2573 *
2574 * Reading this file can return large amounts of data if a cgroup has
2575 * *lots* of attached tasks. So it may need several calls to read(),
2576 * but we cannot guarantee that the information we produce is correct
2577 * unless we produce it entirely atomically.
2578 *
2579 */
2580
2581/*
2582 * The following two functions "fix" the issue where there are more pids
2583 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
2584 * TODO: replace with a kernel-wide solution to this problem
2585 */
2586#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
2587static void *pidlist_allocate(int count)
2588{
2589        if (PIDLIST_TOO_LARGE(count))
2590                return vmalloc(count * sizeof(pid_t));
2591        else
2592                return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
2593}
2594static void pidlist_free(void *p)
2595{
2596        if (is_vmalloc_addr(p))
2597                vfree(p);
2598        else
2599                kfree(p);
2600}
2601static void *pidlist_resize(void *p, int newcount)
2602{
2603        void *newlist;
2604        /* note: if new alloc fails, old p will still be valid either way */
2605        if (is_vmalloc_addr(p)) {
2606                newlist = vmalloc(newcount * sizeof(pid_t));
2607                if (!newlist)
2608                        return NULL;
2609                memcpy(newlist, p, newcount * sizeof(pid_t));
2610                vfree(p);
2611        } else {
2612                newlist = krealloc(p, newcount * sizeof(pid_t), GFP_KERNEL);
2613        }
2614        return newlist;
2615}
2616
2617/*
2618 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
2619 * If the new stripped list is sufficiently smaller and there's enough memory
2620 * to allocate a new buffer, will let go of the unneeded memory. Returns the
2621 * number of unique elements.
2622 */
2623/* is the size difference enough that we should re-allocate the array? */
2624#define PIDLIST_REALLOC_DIFFERENCE(old, new) ((old) - PAGE_SIZE >= (new))
2625static int pidlist_uniq(pid_t **p, int length)
2626{
2627        int src, dest = 1;
2628        pid_t *list = *p;
2629        pid_t *newlist;
2630
2631        /*
2632         * we presume the 0th element is unique, so i starts at 1. trivial
2633         * edge cases first; no work needs to be done for either
2634         */
2635        if (length == 0 || length == 1)
2636                return length;
2637        /* src and dest walk down the list; dest counts unique elements */
2638        for (src = 1; src < length; src++) {
2639                /* find next unique element */
2640                while (list[src] == list[src-1]) {
2641                        src++;
2642                        if (src == length)
2643                                goto after;
2644                }
2645                /* dest always points to where the next unique element goes */
2646                list[dest] = list[src];
2647                dest++;
2648        }
2649after:
2650        /*
2651         * if the length difference is large enough, we want to allocate a
2652         * smaller buffer to save memory. if this fails due to out of memory,
2653         * we'll just stay with what we've got.
2654         */
2655        if (PIDLIST_REALLOC_DIFFERENCE(length, dest)) {
2656                newlist = pidlist_resize(list, dest);
2657                if (newlist)
2658                        *p = newlist;
2659        }
2660        return dest;
2661}
2662
2663static int cmppid(const void *a, const void *b)
2664{
2665        return *(pid_t *)a - *(pid_t *)b;
2666}
2667
2668/*
2669 * find the appropriate pidlist for our purpose (given procs vs tasks)
2670 * returns with the lock on that pidlist already held, and takes care
2671 * of the use count, or returns NULL with no locks held if we're out of
2672 * memory.
2673 */
2674static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
2675                                                  enum cgroup_filetype type)
2676{
2677        struct cgroup_pidlist *l;
2678        /* don't need task_nsproxy() if we're looking at ourself */
2679        struct pid_namespace *ns = current->nsproxy->pid_ns;
2680
2681        /*
2682         * We can't drop the pidlist_mutex before taking the l->mutex in case
2683         * the last ref-holder is trying to remove l from the list at the same
2684         * time. Holding the pidlist_mutex precludes somebody taking whichever
2685         * list we find out from under us - compare release_pid_array().
2686         */
2687        mutex_lock(&cgrp->pidlist_mutex);
2688        list_for_each_entry(l, &cgrp->pidlists, links) {
2689                if (l->key.type == type && l->key.ns == ns) {
2690                        /* make sure l doesn't vanish out from under us */
2691                        down_write(&l->mutex);
2692                        mutex_unlock(&cgrp->pidlist_mutex);
2693                        return l;
2694                }
2695        }
2696        /* entry not found; create a new one */
2697        l = kmalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
2698        if (!l) {
2699                mutex_unlock(&cgrp->pidlist_mutex);
2700                return l;
2701        }
2702        init_rwsem(&l->mutex);
2703        down_write(&l->mutex);
2704        l->key.type = type;
2705        l->key.ns = get_pid_ns(ns);
2706        l->use_count = 0; /* don't increment here */
2707        l->list = NULL;
2708        l->owner = cgrp;
2709        list_add(&l->links, &cgrp->pidlists);
2710        mutex_unlock(&cgrp->pidlist_mutex);
2711        return l;
2712}
2713
2714/*
2715 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
2716 */
2717static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
2718                              struct cgroup_pidlist **lp)
2719{
2720        pid_t *array;
2721        int length;
2722        int pid, n = 0; /* used for populating the array */
2723        struct cgroup_iter it;
2724        struct task_struct *tsk;
2725        struct cgroup_pidlist *l;
2726
2727        /*
2728         * If cgroup gets more users after we read count, we won't have
2729         * enough space - tough.  This race is indistinguishable to the
2730         * caller from the case that the additional cgroup users didn't
2731         * show up until sometime later on.
2732         */
2733        length = cgroup_task_count(cgrp);
2734        array = pidlist_allocate(length);
2735        if (!array)
2736                return -ENOMEM;
2737        /* now, populate the array */
2738        cgroup_iter_start(cgrp, &it);
2739        while ((tsk = cgroup_iter_next(cgrp, &it))) {
2740                if (unlikely(n == length))
2741                        break;
2742                /* get tgid or pid for procs or tasks file respectively */
2743                if (type == CGROUP_FILE_PROCS)
2744                        pid = task_tgid_vnr(tsk);
2745                else
2746                        pid = task_pid_vnr(tsk);
2747                if (pid > 0) /* make sure to only use valid results */
2748                        array[n++] = pid;
2749        }
2750        cgroup_iter_end(cgrp, &it);
2751        length = n;
2752        /* now sort & (if procs) strip out duplicates */
2753        sort(array, length, sizeof(pid_t), cmppid, NULL);
2754        if (type == CGROUP_FILE_PROCS)
2755                length = pidlist_uniq(&array, length);
2756        l = cgroup_pidlist_find(cgrp, type);
2757        if (!l) {
2758                pidlist_free(array);
2759                return -ENOMEM;
2760        }
2761        /* store array, freeing old if necessary - lock already held */
2762        pidlist_free(l->list);
2763        l->list = array;
2764        l->length = length;
2765        l->use_count++;
2766        up_write(&l->mutex);
2767        *lp = l;
2768        return 0;
2769}
2770
2771/**
2772 * cgroupstats_build - build and fill cgroupstats
2773 * @stats: cgroupstats to fill information into
2774 * @dentry: A dentry entry belonging to the cgroup for which stats have
2775 * been requested.
2776 *
2777 * Build and fill cgroupstats so that taskstats can export it to user
2778 * space.
2779 */
2780int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
2781{
2782        int ret = -EINVAL;
2783        struct cgroup *cgrp;
2784        struct cgroup_iter it;
2785        struct task_struct *tsk;
2786
2787        /*
2788         * Validate dentry by checking the superblock operations,
2789         * and make sure it's a directory.
2790         */
2791        if (dentry->d_sb->s_op != &cgroup_ops ||
2792            !S_ISDIR(dentry->d_inode->i_mode))
2793                 goto err;
2794
2795        ret = 0;
2796        cgrp = dentry->d_fsdata;
2797
2798        cgroup_iter_start(cgrp, &it);
2799        while ((tsk = cgroup_iter_next(cgrp, &it))) {
2800                switch (tsk->state) {
2801                case TASK_RUNNING:
2802                        stats->nr_running++;
2803                        break;
2804                case TASK_INTERRUPTIBLE:
2805                        stats->nr_sleeping++;
2806                        break;
2807                case TASK_UNINTERRUPTIBLE:
2808                        stats->nr_uninterruptible++;
2809                        break;
2810                case TASK_STOPPED:
2811                        stats->nr_stopped++;
2812                        break;
2813                default:
2814                        if (delayacct_is_task_waiting_on_io(tsk))
2815                                stats->nr_io_wait++;
2816                        break;
2817                }
2818        }
2819        cgroup_iter_end(cgrp, &it);
2820
2821err:
2822        return ret;
2823}
2824
2825
2826/*
2827 * seq_file methods for the tasks/procs files. The seq_file position is the
2828 * next pid to display; the seq_file iterator is a pointer to the pid
2829 * in the cgroup->l->list array.
2830 */
2831
2832static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
2833{
2834        /*
2835         * Initially we receive a position value that corresponds to
2836         * one more than the last pid shown (or 0 on the first call or
2837         * after a seek to the start). Use a binary-search to find the
2838         * next pid to display, if any
2839         */
2840        struct cgroup_pidlist *l = s->private;
2841        int index = 0, pid = *pos;
2842        int *iter;
2843
2844        down_read(&l->mutex);
2845        if (pid) {
2846                int end = l->length;
2847
2848                while (index < end) {
2849                        int mid = (index + end) / 2;
2850                        if (l->list[mid] == pid) {
2851                                index = mid;
2852                                break;
2853                        } else if (l->list[mid] <= pid)
2854                                index = mid + 1;
2855                        else
2856                                end = mid;
2857                }
2858        }
2859        /* If we're off the end of the array, we're done */
2860        if (index >= l->length)
2861                return NULL;
2862        /* Update the abstract position to be the actual pid that we found */
2863        iter = l->list + index;
2864        *pos = *iter;
2865        return iter;
2866}
2867
2868static void cgroup_pidlist_stop(struct seq_file *s, void *v)
2869{
2870        struct cgroup_pidlist *l = s->private;
2871        up_read(&l->mutex);
2872}
2873
2874static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
2875{
2876        struct cgroup_pidlist *l = s->private;
2877        pid_t *p = v;
2878        pid_t *end = l->list + l->length;
2879        /*
2880         * Advance to the next pid in the array. If this goes off the
2881         * end, we're done
2882         */
2883        p++;
2884        if (p >= end) {
2885                return NULL;
2886        } else {
2887                *pos = *p;
2888                return p;
2889        }
2890}
2891
2892static int cgroup_pidlist_show(struct seq_file *s, void *v)
2893{
2894        return seq_printf(s, "%d\n", *(int *)v);
2895}
2896
2897/*
2898 * seq_operations functions for iterating on pidlists through seq_file -
2899 * independent of whether it's tasks or procs
2900 */
2901static const struct seq_operations cgroup_pidlist_seq_operations = {
2902        .start = cgroup_pidlist_start,
2903        .stop = cgroup_pidlist_stop,
2904        .next = cgroup_pidlist_next,
2905        .show = cgroup_pidlist_show,
2906};
2907
2908static void cgroup_release_pid_array(struct cgroup_pidlist *l)
2909{
2910        /*
2911         * the case where we're the last user of this particular pidlist will
2912         * have us remove it from the cgroup's list, which entails taking the
2913         * mutex. since in pidlist_find the pidlist->lock depends on cgroup->
2914         * pidlist_mutex, we have to take pidlist_mutex first.
2915         */
2916        mutex_lock(&l->owner->pidlist_mutex);
2917        down_write(&l->mutex);
2918        BUG_ON(!l->use_count);
2919        if (!--l->use_count) {
2920                /* we're the last user if refcount is 0; remove and free */
2921                list_del(&l->links);
2922                mutex_unlock(&l->owner->pidlist_mutex);
2923                pidlist_free(l->list);
2924                put_pid_ns(l->key.ns);
2925                up_write(&l->mutex);
2926                kfree(l);
2927                return;
2928        }
2929        mutex_unlock(&l->owner->pidlist_mutex);
2930        up_write(&l->mutex);
2931}
2932
2933static int cgroup_pidlist_release(struct inode *inode, struct file *file)
2934{
2935        struct cgroup_pidlist *l;
2936        if (!(file->f_mode & FMODE_READ))
2937                return 0;
2938        /*
2939         * the seq_file will only be initialized if the file was opened for
2940         * reading; hence we check if it's not null only in that case.
2941         */
2942        l = ((struct seq_file *)file->private_data)->private;
2943        cgroup_release_pid_array(l);
2944        return seq_release(inode, file);
2945}
2946
2947static const struct file_operations cgroup_pidlist_operations = {
2948        .read = seq_read,
2949        .llseek = seq_lseek,
2950        .write = cgroup_file_write,
2951        .release = cgroup_pidlist_release,
2952};
2953
2954/*
2955 * The following functions handle opens on a file that displays a pidlist
2956 * (tasks or procs). Prepare an array of the process/thread IDs of whoever's
2957 * in the cgroup.
2958 */
2959/* helper function for the two below it */
2960static int cgroup_pidlist_open(struct file *file, enum cgroup_filetype type)
2961{
2962        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2963        struct cgroup_pidlist *l;
2964        int retval;
2965
2966        /* Nothing to do for write-only files */
2967        if (!(file->f_mode & FMODE_READ))
2968                return 0;
2969
2970        /* have the array populated */
2971        retval = pidlist_array_load(cgrp, type, &l);
2972        if (retval)
2973                return retval;
2974        /* configure file information */
2975        file->f_op = &cgroup_pidlist_operations;
2976
2977        retval = seq_open(file, &cgroup_pidlist_seq_operations);
2978        if (retval) {
2979                cgroup_release_pid_array(l);
2980                return retval;
2981        }
2982        ((struct seq_file *)file->private_data)->private = l;
2983        return 0;
2984}
2985static int cgroup_tasks_open(struct inode *unused, struct file *file)
2986{
2987        return cgroup_pidlist_open(file, CGROUP_FILE_TASKS);
2988}
2989static int cgroup_procs_open(struct inode *unused, struct file *file)
2990{
2991        return cgroup_pidlist_open(file, CGROUP_FILE_PROCS);
2992}
2993
2994static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
2995                                            struct cftype *cft)
2996{
2997        return notify_on_release(cgrp);
2998}
2999
3000static int cgroup_write_notify_on_release(struct cgroup *cgrp,
3001                                          struct cftype *cft,
3002                                          u64 val)
3003{
3004        clear_bit(CGRP_RELEASABLE, &cgrp->flags);
3005        if (val)
3006                set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3007        else
3008                clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3009        return 0;
3010}
3011
3012/*
3013 * Unregister event and free resources.
3014 *
3015 * Gets called from workqueue.
3016 */
3017static void cgroup_event_remove(struct work_struct *work)
3018{
3019        struct cgroup_event *event = container_of(work, struct cgroup_event,
3020                        remove);
3021        struct cgroup *cgrp = event->cgrp;
3022
3023        event->cft->unregister_event(cgrp, event->cft, event->eventfd);
3024
3025        eventfd_ctx_put(event->eventfd);
3026        kfree(event);
3027        dput(cgrp->dentry);
3028}
3029
3030/*
3031 * Gets called on POLLHUP on eventfd when user closes it.
3032 *
3033 * Called with wqh->lock held and interrupts disabled.
3034 */
3035static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
3036                int sync, void *key)
3037{
3038        struct cgroup_event *event = container_of(wait,
3039                        struct cgroup_event, wait);
3040        struct cgroup *cgrp = event->cgrp;
3041        unsigned long flags = (unsigned long)key;
3042
3043        if (flags & POLLHUP) {
3044                __remove_wait_queue(event->wqh, &event->wait);
3045                spin_lock(&cgrp->event_list_lock);
3046                list_del(&event->list);
3047                spin_unlock(&cgrp->event_list_lock);
3048                /*
3049                 * We are in atomic context, but cgroup_event_remove() may
3050                 * sleep, so we have to call it in workqueue.
3051                 */
3052                schedule_work(&event->remove);
3053        }
3054
3055        return 0;
3056}
3057
3058static void cgroup_event_ptable_queue_proc(struct file *file,
3059                wait_queue_head_t *wqh, poll_table *pt)
3060{
3061        struct cgroup_event *event = container_of(pt,
3062                        struct cgroup_event, pt);
3063
3064        event->wqh = wqh;
3065        add_wait_queue(wqh, &event->wait);
3066}
3067
3068/*
3069 * Parse input and register new cgroup event handler.
3070 *
3071 * Input must be in format '<event_fd> <control_fd> <args>'.
3072 * Interpretation of args is defined by control file implementation.
3073 */
3074static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
3075                                      const char *buffer)
3076{
3077        struct cgroup_event *event = NULL;
3078        unsigned int efd, cfd;
3079        struct file *efile = NULL;
3080        struct file *cfile = NULL;
3081        char *endp;
3082        int ret;
3083
3084        efd = simple_strtoul(buffer, &endp, 10);
3085        if (*endp != ' ')
3086                return -EINVAL;
3087        buffer = endp + 1;
3088
3089        cfd = simple_strtoul(buffer, &endp, 10);
3090        if ((*endp != ' ') && (*endp != '\0'))
3091                return -EINVAL;
3092        buffer = endp + 1;
3093
3094        event = kzalloc(sizeof(*event), GFP_KERNEL);
3095        if (!event)
3096                return -ENOMEM;
3097        event->cgrp = cgrp;
3098        INIT_LIST_HEAD(&event->list);
3099        init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
3100        init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
3101        INIT_WORK(&event->remove, cgroup_event_remove);
3102
3103        efile = eventfd_fget(efd);
3104        if (IS_ERR(efile)) {
3105                ret = PTR_ERR(efile);
3106                goto fail;
3107        }
3108
3109        event->eventfd = eventfd_ctx_fileget(efile);
3110        if (IS_ERR(event->eventfd)) {
3111                ret = PTR_ERR(event->eventfd);
3112                goto fail;
3113        }
3114
3115        cfile = fget(cfd);
3116        if (!cfile) {
3117                ret = -EBADF;
3118                goto fail;
3119        }
3120
3121        /* the process need read permission on control file */
3122        ret = file_permission(cfile, MAY_READ);
3123        if (ret < 0)
3124                goto fail;
3125
3126        event->cft = __file_cft(cfile);
3127        if (IS_ERR(event->cft)) {
3128                ret = PTR_ERR(event->cft);
3129                goto fail;
3130        }
3131
3132        if (!event->cft->register_event || !event->cft->unregister_event) {
3133                ret = -EINVAL;
3134                goto fail;
3135        }
3136
3137        ret = event->cft->register_event(cgrp, event->cft,
3138                        event->eventfd, buffer);
3139        if (ret)
3140                goto fail;
3141
3142        if (efile->f_op->poll(efile, &event->pt) & POLLHUP) {
3143                event->cft->unregister_event(cgrp, event->cft, event->eventfd);
3144                ret = 0;
3145                goto fail;
3146        }
3147
3148        /*
3149         * Events should be removed after rmdir of cgroup directory, but before
3150         * destroying subsystem state objects. Let's take reference to cgroup
3151         * directory dentry to do that.
3152         */
3153        dget(cgrp->dentry);
3154
3155        spin_lock(&cgrp->event_list_lock);
3156        list_add(&event->list, &cgrp->event_list);
3157        spin_unlock(&cgrp->event_list_lock);
3158
3159        fput(cfile);
3160        fput(efile);
3161
3162        return 0;
3163
3164fail:
3165        if (cfile)
3166                fput(cfile);
3167
3168        if (event && event->eventfd && !IS_ERR(event->eventfd))
3169                eventfd_ctx_put(event->eventfd);
3170
3171        if (!IS_ERR_OR_NULL(efile))
3172                fput(efile);
3173
3174        kfree(event);
3175
3176        return ret;
3177}
3178
3179/*
3180 * for the common functions, 'private' gives the type of file
3181 */
3182/* for hysterical raisins, we can't put this on the older files */
3183#define CGROUP_FILE_GENERIC_PREFIX "cgroup."
3184static struct cftype files[] = {
3185        {
3186                .name = "tasks",
3187                .open = cgroup_tasks_open,
3188                .write_u64 = cgroup_tasks_write,
3189                .release = cgroup_pidlist_release,
3190                .mode = S_IRUGO | S_IWUSR,
3191        },
3192        {
3193                .name = CGROUP_FILE_GENERIC_PREFIX "procs",
3194                .open = cgroup_procs_open,
3195                /* .write_u64 = cgroup_procs_write, TODO */
3196                .release = cgroup_pidlist_release,
3197                .mode = S_IRUGO,
3198        },
3199        {
3200                .name = "notify_on_release",
3201                .read_u64 = cgroup_read_notify_on_release,
3202                .write_u64 = cgroup_write_notify_on_release,
3203        },
3204        {
3205                .name = CGROUP_FILE_GENERIC_PREFIX "event_control",
3206                .write_string = cgroup_write_event_control,
3207                .mode = S_IWUGO,
3208        },
3209};
3210
3211static struct cftype cft_release_agent = {
3212        .name = "release_agent",
3213        .read_seq_string = cgroup_release_agent_show,
3214        .write_string = cgroup_release_agent_write,
3215        .max_write_len = PATH_MAX,
3216};
3217
3218static int cgroup_populate_dir(struct cgroup *cgrp)
3219{
3220        int err;
3221        struct cgroup_subsys *ss;
3222
3223        /* First clear out any existing files */
3224        cgroup_clear_directory(cgrp->dentry);
3225
3226        err = cgroup_add_files(cgrp, NULL, files, ARRAY_SIZE(files));
3227        if (err < 0)
3228                return err;
3229
3230        if (cgrp == cgrp->top_cgroup) {
3231                if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0)
3232                        return err;
3233        }
3234
3235        for_each_subsys(cgrp->root, ss) {
3236                if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
3237                        return err;
3238        }
3239        /* This cgroup is ready now */
3240        for_each_subsys(cgrp->root, ss) {
3241                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
3242                /*
3243                 * Update id->css pointer and make this css visible from
3244                 * CSS ID functions. This pointer will be dereferened
3245                 * from RCU-read-side without locks.
3246                 */
3247                if (css->id)
3248                        rcu_assign_pointer(css->id->css, css);
3249        }
3250
3251        return 0;
3252}
3253
3254static void init_cgroup_css(struct cgroup_subsys_state *css,
3255                               struct cgroup_subsys *ss,
3256                               struct cgroup *cgrp)
3257{
3258        css->cgroup = cgrp;
3259        atomic_set(&css->refcnt, 1);
3260        css->flags = 0;
3261        css->id = NULL;
3262        if (cgrp == dummytop)
3263                set_bit(CSS_ROOT, &css->flags);
3264        BUG_ON(cgrp->subsys[ss->subsys_id]);
3265        cgrp->subsys[ss->subsys_id] = css;
3266}
3267
3268static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
3269{
3270        /* We need to take each hierarchy_mutex in a consistent order */
3271        int i;
3272
3273        /*
3274         * No worry about a race with rebind_subsystems that might mess up the
3275         * locking order, since both parties are under cgroup_mutex.
3276         */
3277        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3278                struct cgroup_subsys *ss = subsys[i];
3279                if (ss == NULL)
3280                        continue;
3281                if (ss->root == root)
3282                        mutex_lock(&ss->hierarchy_mutex);
3283        }
3284}
3285
3286static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
3287{
3288        int i;
3289
3290        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3291                struct cgroup_subsys *ss = subsys[i];
3292                if (ss == NULL)
3293                        continue;
3294                if (ss->root == root)
3295                        mutex_unlock(&ss->hierarchy_mutex);
3296        }
3297}
3298
3299/*
3300 * cgroup_create - create a cgroup
3301 * @parent: cgroup that will be parent of the new cgroup
3302 * @dentry: dentry of the new cgroup
3303 * @mode: mode to set on new inode
3304 *
3305 * Must be called with the mutex on the parent inode held
3306 */
3307static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
3308                             mode_t mode)
3309{
3310        struct cgroup *cgrp;
3311        struct cgroupfs_root *root = parent->root;
3312        int err = 0;
3313        struct cgroup_subsys *ss;
3314        struct super_block *sb = root->sb;
3315
3316        cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
3317        if (!cgrp)
3318                return -ENOMEM;
3319
3320        /* Grab a reference on the superblock so the hierarchy doesn't
3321         * get deleted on unmount if there are child cgroups.  This
3322         * can be done outside cgroup_mutex, since the sb can't
3323         * disappear while someone has an open control file on the
3324         * fs */
3325        atomic_inc(&sb->s_active);
3326
3327        mutex_lock(&cgroup_mutex);
3328
3329        init_cgroup_housekeeping(cgrp);
3330
3331        cgrp->parent = parent;
3332        cgrp->root = parent->root;
3333        cgrp->top_cgroup = parent->top_cgroup;
3334
3335        if (notify_on_release(parent))
3336                set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3337
3338        for_each_subsys(root, ss) {
3339                struct cgroup_subsys_state *css = ss->create(ss, cgrp);
3340
3341                if (IS_ERR(css)) {
3342                        err = PTR_ERR(css);
3343                        goto err_destroy;
3344                }
3345                init_cgroup_css(css, ss, cgrp);
3346                if (ss->use_id) {
3347                        err = alloc_css_id(ss, parent, cgrp);
3348                        if (err)
3349                                goto err_destroy;
3350                }
3351                /* At error, ->destroy() callback has to free assigned ID. */
3352        }
3353
3354        cgroup_lock_hierarchy(root);
3355        list_add(&cgrp->sibling, &cgrp->parent->children);
3356        cgroup_unlock_hierarchy(root);
3357        root->number_of_cgroups++;
3358
3359        err = cgroup_create_dir(cgrp, dentry, mode);
3360        if (err < 0)
3361                goto err_remove;
3362
3363        /* The cgroup directory was pre-locked for us */
3364        BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
3365
3366        err = cgroup_populate_dir(cgrp);
3367        /* If err < 0, we have a half-filled directory - oh well ;) */
3368
3369        mutex_unlock(&cgroup_mutex);
3370        mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
3371
3372        return 0;
3373
3374 err_remove:
3375
3376        cgroup_lock_hierarchy(root);
3377        list_del(&cgrp->sibling);
3378        cgroup_unlock_hierarchy(root);
3379        root->number_of_cgroups--;
3380
3381 err_destroy:
3382
3383        for_each_subsys(root, ss) {
3384                if (cgrp->subsys[ss->subsys_id])
3385                        ss->destroy(ss, cgrp);
3386        }
3387
3388        mutex_unlock(&cgroup_mutex);
3389
3390        /* Release the reference count that we took on the superblock */
3391        deactivate_super(sb);
3392
3393        kfree(cgrp);
3394        return err;
3395}
3396
3397static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)
3398{
3399        struct cgroup *c_parent = dentry->d_parent->d_fsdata;
3400
3401        /* the vfs holds inode->i_mutex already */
3402        return cgroup_create(c_parent, dentry, mode | S_IFDIR);
3403}
3404
3405static int cgroup_has_css_refs(struct cgroup *cgrp)
3406{
3407        /* Check the reference count on each subsystem. Since we
3408         * already established that there are no tasks in the
3409         * cgroup, if the css refcount is also 1, then there should
3410         * be no outstanding references, so the subsystem is safe to
3411         * destroy. We scan across all subsystems rather than using
3412         * the per-hierarchy linked list of mounted subsystems since
3413         * we can be called via check_for_release() with no
3414         * synchronization other than RCU, and the subsystem linked
3415         * list isn't RCU-safe */
3416        int i;
3417        /*
3418         * We won't need to lock the subsys array, because the subsystems
3419         * we're concerned about aren't going anywhere since our cgroup root
3420         * has a reference on them.
3421         */
3422        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3423                struct cgroup_subsys *ss = subsys[i];
3424                struct cgroup_subsys_state *css;
3425                /* Skip subsystems not present or not in this hierarchy */
3426                if (ss == NULL || ss->root != cgrp->root)
3427                        continue;
3428                css = cgrp->subsys[ss->subsys_id];
3429                /* When called from check_for_release() it's possible
3430                 * that by this point the cgroup has been removed
3431                 * and the css deleted. But a false-positive doesn't
3432                 * matter, since it can only happen if the cgroup
3433                 * has been deleted and hence no longer needs the
3434                 * release agent to be called anyway. */
3435                if (css && (atomic_read(&css->refcnt) > 1))
3436                        return 1;
3437        }
3438        return 0;
3439}
3440
3441/*
3442 * Atomically mark all (or else none) of the cgroup's CSS objects as
3443 * CSS_REMOVED. Return true on success, or false if the cgroup has
3444 * busy subsystems. Call with cgroup_mutex held
3445 */
3446
3447static int cgroup_clear_css_refs(struct cgroup *cgrp)
3448{
3449        struct cgroup_subsys *ss;
3450        unsigned long flags;
3451        bool failed = false;
3452        local_irq_save(flags);
3453        for_each_subsys(cgrp->root, ss) {
3454                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
3455                int refcnt;
3456                while (1) {
3457                        /* We can only remove a CSS with a refcnt==1 */
3458                        refcnt = atomic_read(&css->refcnt);
3459                        if (refcnt > 1) {
3460                                failed = true;
3461                                goto done;
3462                        }
3463                        BUG_ON(!refcnt);
3464                        /*
3465                         * Drop the refcnt to 0 while we check other
3466                         * subsystems. This will cause any racing
3467                         * css_tryget() to spin until we set the
3468                         * CSS_REMOVED bits or abort
3469                         */
3470                        if (atomic_cmpxchg(&css->refcnt, refcnt, 0) == refcnt)
3471                                break;
3472                        cpu_relax();
3473                }
3474        }
3475 done:
3476        for_each_subsys(cgrp->root, ss) {
3477                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
3478                if (failed) {
3479                        /*
3480                         * Restore old refcnt if we previously managed
3481                         * to clear it from 1 to 0
3482                         */
3483                        if (!atomic_read(&css->refcnt))
3484                                atomic_set(&css->refcnt, 1);
3485                } else {
3486                        /* Commit the fact that the CSS is removed */
3487                        set_bit(CSS_REMOVED, &css->flags);
3488                }
3489        }
3490        local_irq_restore(flags);
3491        return !failed;
3492}
3493
3494static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
3495{
3496        struct cgroup *cgrp = dentry->d_fsdata;
3497        struct dentry *d;
3498        struct cgroup *parent;
3499        DEFINE_WAIT(wait);
3500        struct cgroup_event *event, *tmp;
3501        int ret;
3502
3503        /* the vfs holds both inode->i_mutex already */
3504again:
3505        mutex_lock(&cgroup_mutex);
3506        if (atomic_read(&cgrp->count) != 0) {
3507                mutex_unlock(&cgroup_mutex);
3508                return -EBUSY;
3509        }
3510        if (!list_empty(&cgrp->children)) {
3511                mutex_unlock(&cgroup_mutex);
3512                return -EBUSY;
3513        }
3514        mutex_unlock(&cgroup_mutex);
3515
3516        /*
3517         * In general, subsystem has no css->refcnt after pre_destroy(). But
3518         * in racy cases, subsystem may have to get css->refcnt after
3519         * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
3520         * make rmdir return -EBUSY too often. To avoid that, we use waitqueue
3521         * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
3522         * and subsystem's reference count handling. Please see css_get/put
3523         * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
3524         */
3525        set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3526
3527        /*
3528         * Call pre_destroy handlers of subsys. Notify subsystems
3529         * that rmdir() request comes.
3530         */
3531        ret = cgroup_call_pre_destroy(cgrp);
3532        if (ret) {
3533                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3534                return ret;
3535        }
3536
3537        mutex_lock(&cgroup_mutex);
3538        parent = cgrp->parent;
3539        if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
3540                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3541                mutex_unlock(&cgroup_mutex);
3542                return -EBUSY;
3543        }
3544        prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
3545        if (!cgroup_clear_css_refs(cgrp)) {
3546                mutex_unlock(&cgroup_mutex);
3547                /*
3548                 * Because someone may call cgroup_wakeup_rmdir_waiter() before
3549                 * prepare_to_wait(), we need to check this flag.
3550                 */
3551                if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
3552                        schedule();
3553                finish_wait(&cgroup_rmdir_waitq, &wait);
3554                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3555                if (signal_pending(current))
3556                        return -EINTR;
3557                goto again;
3558        }
3559        /* NO css_tryget() can success after here. */
3560        finish_wait(&cgroup_rmdir_waitq, &wait);
3561        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
3562
3563        spin_lock(&release_list_lock);
3564        set_bit(CGRP_REMOVED, &cgrp->flags);
3565        if (!list_empty(&cgrp->release_list))
3566                list_del(&cgrp->release_list);
3567        spin_unlock(&release_list_lock);
3568
3569        cgroup_lock_hierarchy(cgrp->root);
3570        /* delete this cgroup from parent->children */
3571        list_del(&cgrp->sibling);
3572        cgroup_unlock_hierarchy(cgrp->root);
3573
3574        spin_lock(&cgrp->dentry->d_lock);
3575        d = dget(cgrp->dentry);
3576        spin_unlock(&d->d_lock);
3577
3578        cgroup_d_remove_dir(d);
3579        dput(d);
3580
3581        set_bit(CGRP_RELEASABLE, &parent->flags);
3582        check_for_release(parent);
3583
3584        /*
3585         * Unregister events and notify userspace.
3586         * Notify userspace about cgroup removing only after rmdir of cgroup
3587         * directory to avoid race between userspace and kernelspace
3588         */
3589        spin_lock(&cgrp->event_list_lock);
3590        list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
3591                list_del(&event->list);
3592                remove_wait_queue(event->wqh, &event->wait);
3593                eventfd_signal(event->eventfd, 1);
3594                schedule_work(&event->remove);
3595        }
3596        spin_unlock(&cgrp->event_list_lock);
3597
3598        mutex_unlock(&cgroup_mutex);
3599        return 0;
3600}
3601
3602static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
3603{
3604        struct cgroup_subsys_state *css;
3605
3606        printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
3607
3608        /* Create the top cgroup state for this subsystem */
3609        list_add(&ss->sibling, &rootnode.subsys_list);
3610        ss->root = &rootnode;
3611        css = ss->create(ss, dummytop);
3612        /* We don't handle early failures gracefully */
3613        BUG_ON(IS_ERR(css));
3614        init_cgroup_css(css, ss, dummytop);
3615
3616        /* Update the init_css_set to contain a subsys
3617         * pointer to this state - since the subsystem is
3618         * newly registered, all tasks and hence the
3619         * init_css_set is in the subsystem's top cgroup. */
3620        init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
3621
3622        need_forkexit_callback |= ss->fork || ss->exit;
3623
3624        /* At system boot, before all subsystems have been
3625         * registered, no tasks have been forked, so we don't
3626         * need to invoke fork callbacks here. */
3627        BUG_ON(!list_empty(&init_task.tasks));
3628
3629        mutex_init(&ss->hierarchy_mutex);
3630        lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
3631        ss->active = 1;
3632
3633        /* this function shouldn't be used with modular subsystems, since they
3634         * need to register a subsys_id, among other things */
3635        BUG_ON(ss->module);
3636}
3637
3638/**
3639 * cgroup_load_subsys: load and register a modular subsystem at runtime
3640 * @ss: the subsystem to load
3641 *
3642 * This function should be called in a modular subsystem's initcall. If the
3643 * subsystem is built as a module, it will be assigned a new subsys_id and set
3644 * up for use. If the subsystem is built-in anyway, work is delegated to the
3645 * simpler cgroup_init_subsys.
3646 */
3647int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
3648{
3649        int i;
3650        struct cgroup_subsys_state *css;
3651
3652        /* check name and function validity */
3653        if (ss->name == NULL || strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN ||
3654            ss->create == NULL || ss->destroy == NULL)
3655                return -EINVAL;
3656
3657        /*
3658         * we don't support callbacks in modular subsystems. this check is
3659         * before the ss->module check for consistency; a subsystem that could
3660         * be a module should still have no callbacks even if the user isn't
3661         * compiling it as one.
3662         */
3663        if (ss->fork || ss->exit)
3664                return -EINVAL;
3665
3666        /*
3667         * an optionally modular subsystem is built-in: we want to do nothing,
3668         * since cgroup_init_subsys will have already taken care of it.
3669         */
3670        if (ss->module == NULL) {
3671                /* a few sanity checks */
3672                BUG_ON(ss->subsys_id >= CGROUP_BUILTIN_SUBSYS_COUNT);
3673                BUG_ON(subsys[ss->subsys_id] != ss);
3674                return 0;
3675        }
3676
3677        /*
3678         * need to register a subsys id before anything else - for example,
3679         * init_cgroup_css needs it.
3680         */
3681        mutex_lock(&cgroup_mutex);
3682        /* find the first empty slot in the array */
3683        for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) {
3684                if (subsys[i] == NULL)
3685                        break;
3686        }
3687        if (i == CGROUP_SUBSYS_COUNT) {
3688                /* maximum number of subsystems already registered! */
3689                mutex_unlock(&cgroup_mutex);
3690                return -EBUSY;
3691        }
3692        /* assign ourselves the subsys_id */
3693        ss->subsys_id = i;
3694        subsys[i] = ss;
3695
3696        /*
3697         * no ss->create seems to need anything important in the ss struct, so
3698         * this can happen first (i.e. before the rootnode attachment).
3699         */
3700        css = ss->create(ss, dummytop);
3701        if (IS_ERR(css)) {
3702                /* failure case - need to deassign the subsys[] slot. */
3703                subsys[i] = NULL;
3704                mutex_unlock(&cgroup_mutex);
3705                return PTR_ERR(css);
3706        }
3707
3708        list_add(&ss->sibling, &rootnode.subsys_list);
3709        ss->root = &rootnode;
3710
3711        /* our new subsystem will be attached to the dummy hierarchy. */
3712        init_cgroup_css(css, ss, dummytop);
3713        /* init_idr must be after init_cgroup_css because it sets css->id. */
3714        if (ss->use_id) {
3715                int ret = cgroup_init_idr(ss, css);
3716                if (ret) {
3717                        dummytop->subsys[ss->subsys_id] = NULL;
3718                        ss->destroy(ss, dummytop);
3719                        subsys[i] = NULL;
3720                        mutex_unlock(&cgroup_mutex);
3721                        return ret;
3722                }
3723        }
3724
3725        /*
3726         * Now we need to entangle the css into the existing css_sets. unlike
3727         * in cgroup_init_subsys, there are now multiple css_sets, so each one
3728         * will need a new pointer to it; done by iterating the css_set_table.
3729         * furthermore, modifying the existing css_sets will corrupt the hash
3730         * table state, so each changed css_set will need its hash recomputed.
3731         * this is all done under the css_set_lock.
3732         */
3733        write_lock(&css_set_lock);
3734        for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
3735                struct css_set *cg;
3736                struct hlist_node *node, *tmp;
3737                struct hlist_head *bucket = &css_set_table[i], *new_bucket;
3738
3739                hlist_for_each_entry_safe(cg, node, tmp, bucket, hlist) {
3740                        /* skip entries that we already rehashed */
3741                        if (cg->subsys[ss->subsys_id])
3742                                continue;
3743                        /* remove existing entry */
3744                        hlist_del(&cg->hlist);
3745                        /* set new value */
3746                        cg->subsys[ss->subsys_id] = css;
3747                        /* recompute hash and restore entry */
3748                        new_bucket = css_set_hash(cg->subsys);
3749                        hlist_add_head(&cg->hlist, new_bucket);
3750                }
3751        }
3752        write_unlock(&css_set_lock);
3753
3754        mutex_init(&ss->hierarchy_mutex);
3755        lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
3756        ss->active = 1;
3757
3758        /* success! */
3759        mutex_unlock(&cgroup_mutex);
3760        return 0;
3761}
3762EXPORT_SYMBOL_GPL(cgroup_load_subsys);
3763
3764/**
3765 * cgroup_unload_subsys: unload a modular subsystem
3766 * @ss: the subsystem to unload
3767 *
3768 * This function should be called in a modular subsystem's exitcall. When this
3769 * function is invoked, the refcount on the subsystem's module will be 0, so
3770 * the subsystem will not be attached to any hierarchy.
3771 */
3772void cgroup_unload_subsys(struct cgroup_subsys *ss)
3773{
3774        struct cg_cgroup_link *link;
3775        struct hlist_head *hhead;
3776
3777        BUG_ON(ss->module == NULL);
3778
3779        /*
3780         * we shouldn't be called if the subsystem is in use, and the use of
3781         * try_module_get in parse_cgroupfs_options should ensure that it
3782         * doesn't start being used while we're killing it off.
3783         */
3784        BUG_ON(ss->root != &rootnode);
3785
3786        mutex_lock(&cgroup_mutex);
3787        /* deassign the subsys_id */
3788        BUG_ON(ss->subsys_id < CGROUP_BUILTIN_SUBSYS_COUNT);
3789        subsys[ss->subsys_id] = NULL;
3790
3791        /* remove subsystem from rootnode's list of subsystems */
3792        list_del(&ss->sibling);
3793
3794        /*
3795         * disentangle the css from all css_sets attached to the dummytop. as
3796         * in loading, we need to pay our respects to the hashtable gods.
3797         */
3798        write_lock(&css_set_lock);
3799        list_for_each_entry(link, &dummytop->css_sets, cgrp_link_list) {
3800                struct css_set *cg = link->cg;
3801
3802                hlist_del(&cg->hlist);
3803                BUG_ON(!cg->subsys[ss->subsys_id]);
3804                cg->subsys[ss->subsys_id] = NULL;
3805                hhead = css_set_hash(cg->subsys);
3806                hlist_add_head(&cg->hlist, hhead);
3807        }
3808        write_unlock(&css_set_lock);
3809
3810        /*
3811         * remove subsystem's css from the dummytop and free it - need to free
3812         * before marking as null because ss->destroy needs the cgrp->subsys
3813         * pointer to find their state. note that this also takes care of
3814         * freeing the css_id.
3815         */
3816        ss->destroy(ss, dummytop);
3817        dummytop->subsys[ss->subsys_id] = NULL;
3818
3819        mutex_unlock(&cgroup_mutex);
3820}
3821EXPORT_SYMBOL_GPL(cgroup_unload_subsys);
3822
3823/**
3824 * cgroup_init_early - cgroup initialization at system boot
3825 *
3826 * Initialize cgroups at system boot, and initialize any
3827 * subsystems that request early init.
3828 */
3829int __init cgroup_init_early(void)
3830{
3831        int i;
3832        atomic_set(&init_css_set.refcount, 1);
3833        INIT_LIST_HEAD(&init_css_set.cg_links);
3834        INIT_LIST_HEAD(&init_css_set.tasks);
3835        INIT_HLIST_NODE(&init_css_set.hlist);
3836        css_set_count = 1;
3837        init_cgroup_root(&rootnode);
3838        root_count = 1;
3839        init_task.cgroups = &init_css_set;
3840
3841        init_css_set_link.cg = &init_css_set;
3842        init_css_set_link.cgrp = dummytop;
3843        list_add(&init_css_set_link.cgrp_link_list,
3844                 &rootnode.top_cgroup.css_sets);
3845        list_add(&init_css_set_link.cg_link_list,
3846                 &init_css_set.cg_links);
3847
3848        for (i = 0; i < CSS_SET_TABLE_SIZE; i++)
3849                INIT_HLIST_HEAD(&css_set_table[i]);
3850
3851        /* at bootup time, we don't worry about modular subsystems */
3852        for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
3853                struct cgroup_subsys *ss = subsys[i];
3854
3855                BUG_ON(!ss->name);
3856                BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
3857                BUG_ON(!ss->create);
3858                BUG_ON(!ss->destroy);
3859                if (ss->subsys_id != i) {
3860                        printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
3861                               ss->name, ss->subsys_id);
3862                        BUG();
3863                }
3864
3865                if (ss->early_init)
3866                        cgroup_init_subsys(ss);
3867        }
3868        return 0;
3869}
3870
3871/**
3872 * cgroup_init - cgroup initialization
3873 *
3874 * Register cgroup filesystem and /proc file, and initialize
3875 * any subsystems that didn't request early init.
3876 */
3877int __init cgroup_init(void)
3878{
3879        int err;
3880        int i;
3881        struct hlist_head *hhead;
3882
3883        err = bdi_init(&cgroup_backing_dev_info);
3884        if (err)
3885                return err;
3886
3887        /* at bootup time, we don't worry about modular subsystems */
3888        for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
3889                struct cgroup_subsys *ss = subsys[i];
3890                if (!ss->early_init)
3891                        cgroup_init_subsys(ss);
3892                if (ss->use_id)
3893                        cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
3894        }
3895
3896        /* Add init_css_set to the hash table */
3897        hhead = css_set_hash(init_css_set.subsys);
3898        hlist_add_head(&init_css_set.hlist, hhead);
3899        BUG_ON(!init_root_id(&rootnode));
3900
3901        cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
3902        if (!cgroup_kobj) {
3903                err = -ENOMEM;
3904                goto out;
3905        }
3906
3907        err = register_filesystem(&cgroup_fs_type);
3908        if (err < 0) {
3909                kobject_put(cgroup_kobj);
3910                goto out;
3911        }
3912
3913        proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
3914
3915out:
3916        if (err)
3917                bdi_destroy(&cgroup_backing_dev_info);
3918
3919        return err;
3920}
3921
3922/*
3923 * proc_cgroup_show()
3924 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
3925 *  - Used for /proc/<pid>/cgroup.
3926 *  - No need to task_lock(tsk) on this tsk->cgroup reference, as it
3927 *    doesn't really matter if tsk->cgroup changes after we read it,
3928 *    and we take cgroup_mutex, keeping cgroup_attach_task() from changing it
3929 *    anyway.  No need to check that tsk->cgroup != NULL, thanks to
3930 *    the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
3931 *    cgroup to top_cgroup.
3932 */
3933
3934/* TODO: Use a proper seq_file iterator */
3935static int proc_cgroup_show(struct seq_file *m, void *v)
3936{
3937        struct pid *pid;
3938        struct task_struct *tsk;
3939        char *buf;
3940        int retval;
3941        struct cgroupfs_root *root;
3942
3943        retval = -ENOMEM;
3944        buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
3945        if (!buf)
3946                goto out;
3947
3948        retval = -ESRCH;
3949        pid = m->private;
3950        tsk = get_pid_task(pid, PIDTYPE_PID);
3951        if (!tsk)
3952                goto out_free;
3953
3954        retval = 0;
3955
3956        mutex_lock(&cgroup_mutex);
3957
3958        for_each_active_root(root) {
3959                struct cgroup_subsys *ss;
3960                struct cgroup *cgrp;
3961                int count = 0;
3962
3963                seq_printf(m, "%d:", root->hierarchy_id);
3964                for_each_subsys(root, ss)
3965                        seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
3966                if (strlen(root->name))
3967                        seq_printf(m, "%sname=%s", count ? "," : "",
3968                                   root->name);
3969                seq_putc(m, ':');
3970                cgrp = task_cgroup_from_root(tsk, root);
3971                retval = cgroup_path(cgrp, buf, PAGE_SIZE);
3972                if (retval < 0)
3973                        goto out_unlock;
3974                seq_puts(m, buf);
3975                seq_putc(m, '\n');
3976        }
3977
3978out_unlock:
3979        mutex_unlock(&cgroup_mutex);
3980        put_task_struct(tsk);
3981out_free:
3982        kfree(buf);
3983out:
3984        return retval;
3985}
3986
3987static int cgroup_open(struct inode *inode, struct file *file)
3988{
3989        struct pid *pid = PROC_I(inode)->pid;
3990        return single_open(file, proc_cgroup_show, pid);
3991}
3992
3993const struct file_operations proc_cgroup_operations = {
3994        .open           = cgroup_open,
3995        .read           = seq_read,
3996        .llseek         = seq_lseek,
3997        .release        = single_release,
3998};
3999
4000/* Display information about each subsystem and each hierarchy */
4001static int proc_cgroupstats_show(struct seq_file *m, void *v)
4002{
4003        int i;
4004
4005        seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
4006        /*
4007         * ideally we don't want subsystems moving around while we do this.
4008         * cgroup_mutex is also necessary to guarantee an atomic snapshot of
4009         * subsys/hierarchy state.
4010         */
4011        mutex_lock(&cgroup_mutex);
4012        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4013                struct cgroup_subsys *ss = subsys[i];
4014                if (ss == NULL)
4015                        continue;
4016                seq_printf(m, "%s\t%d\t%d\t%d\n",
4017                           ss->name, ss->root->hierarchy_id,
4018                           ss->root->number_of_cgroups, !ss->disabled);
4019        }
4020        mutex_unlock(&cgroup_mutex);
4021        return 0;
4022}
4023
4024static int cgroupstats_open(struct inode *inode, struct file *file)
4025{
4026        return single_open(file, proc_cgroupstats_show, NULL);
4027}
4028
4029static const struct file_operations proc_cgroupstats_operations = {
4030        .open = cgroupstats_open,
4031        .read = seq_read,
4032        .llseek = seq_lseek,
4033        .release = single_release,
4034};
4035
4036/**
4037 * cgroup_fork - attach newly forked task to its parents cgroup.
4038 * @child: pointer to task_struct of forking parent process.
4039 *
4040 * Description: A task inherits its parent's cgroup at fork().
4041 *
4042 * A pointer to the shared css_set was automatically copied in
4043 * fork.c by dup_task_struct().  However, we ignore that copy, since
4044 * it was not made under the protection of RCU or cgroup_mutex, so
4045 * might no longer be a valid cgroup pointer.  cgroup_attach_task() might
4046 * have already changed current->cgroups, allowing the previously
4047 * referenced cgroup group to be removed and freed.
4048 *
4049 * At the point that cgroup_fork() is called, 'current' is the parent
4050 * task, and the passed argument 'child' points to the child task.
4051 */
4052void cgroup_fork(struct task_struct *child)
4053{
4054        task_lock(current);
4055        child->cgroups = current->cgroups;
4056        get_css_set(child->cgroups);
4057        task_unlock(current);
4058        INIT_LIST_HEAD(&child->cg_list);
4059}
4060
4061/**
4062 * cgroup_fork_callbacks - run fork callbacks
4063 * @child: the new task
4064 *
4065 * Called on a new task very soon before adding it to the
4066 * tasklist. No need to take any locks since no-one can
4067 * be operating on this task.
4068 */
4069void cgroup_fork_callbacks(struct task_struct *child)
4070{
4071        if (need_forkexit_callback) {
4072                int i;
4073                /*
4074                 * forkexit callbacks are only supported for builtin
4075                 * subsystems, and the builtin section of the subsys array is
4076                 * immutable, so we don't need to lock the subsys array here.
4077                 */
4078                for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4079                        struct cgroup_subsys *ss = subsys[i];
4080                        if (ss->fork)
4081                                ss->fork(ss, child);
4082                }
4083        }
4084}
4085
4086/**
4087 * cgroup_post_fork - called on a new task after adding it to the task list
4088 * @child: the task in question
4089 *
4090 * Adds the task to the list running through its css_set if necessary.
4091 * Has to be after the task is visible on the task list in case we race
4092 * with the first call to cgroup_iter_start() - to guarantee that the
4093 * new task ends up on its list.
4094 */
4095void cgroup_post_fork(struct task_struct *child)
4096{
4097        if (use_task_css_set_links) {
4098                write_lock(&css_set_lock);
4099                task_lock(child);
4100                if (list_empty(&child->cg_list))
4101                        list_add(&child->cg_list, &child->cgroups->tasks);
4102                task_unlock(child);
4103                write_unlock(&css_set_lock);
4104        }
4105}
4106/**
4107 * cgroup_exit - detach cgroup from exiting task
4108 * @tsk: pointer to task_struct of exiting process
4109 * @run_callback: run exit callbacks?
4110 *
4111 * Description: Detach cgroup from @tsk and release it.
4112 *
4113 * Note that cgroups marked notify_on_release force every task in
4114 * them to take the global cgroup_mutex mutex when exiting.
4115 * This could impact scaling on very large systems.  Be reluctant to
4116 * use notify_on_release cgroups where very high task exit scaling
4117 * is required on large systems.
4118 *
4119 * the_top_cgroup_hack:
4120 *
4121 *    Set the exiting tasks cgroup to the root cgroup (top_cgroup).
4122 *
4123 *    We call cgroup_exit() while the task is still competent to
4124 *    handle notify_on_release(), then leave the task attached to the
4125 *    root cgroup in each hierarchy for the remainder of its exit.
4126 *
4127 *    To do this properly, we would increment the reference count on
4128 *    top_cgroup, and near the very end of the kernel/exit.c do_exit()
4129 *    code we would add a second cgroup function call, to drop that
4130 *    reference.  This would just create an unnecessary hot spot on
4131 *    the top_cgroup reference count, to no avail.
4132 *
4133 *    Normally, holding a reference to a cgroup without bumping its
4134 *    count is unsafe.   The cgroup could go away, or someone could
4135 *    attach us to a different cgroup, decrementing the count on
4136 *    the first cgroup that we never incremented.  But in this case,
4137 *    top_cgroup isn't going away, and either task has PF_EXITING set,
4138 *    which wards off any cgroup_attach_task() attempts, or task is a failed
4139 *    fork, never visible to cgroup_attach_task.
4140 */
4141void cgroup_exit(struct task_struct *tsk, int run_callbacks)
4142{
4143        int i;
4144        struct css_set *cg;
4145
4146        if (run_callbacks && need_forkexit_callback) {
4147                /*
4148                 * modular subsystems can't use callbacks, so no need to lock
4149                 * the subsys array
4150                 */
4151                for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4152                        struct cgroup_subsys *ss = subsys[i];
4153                        if (ss->exit)
4154                                ss->exit(ss, tsk);
4155                }
4156        }
4157
4158        /*
4159         * Unlink from the css_set task list if necessary.
4160         * Optimistically check cg_list before taking
4161         * css_set_lock
4162         */
4163        if (!list_empty(&tsk->cg_list)) {
4164                write_lock(&css_set_lock);
4165                if (!list_empty(&tsk->cg_list))
4166                        list_del(&tsk->cg_list);
4167                write_unlock(&css_set_lock);
4168        }
4169
4170        /* Reassign the task to the init_css_set. */
4171        task_lock(tsk);
4172        cg = tsk->cgroups;
4173        tsk->cgroups = &init_css_set;
4174        task_unlock(tsk);
4175        if (cg)
4176                put_css_set_taskexit(cg);
4177}
4178
4179/**
4180 * cgroup_clone - clone the cgroup the given subsystem is attached to
4181 * @tsk: the task to be moved
4182 * @subsys: the given subsystem
4183 * @nodename: the name for the new cgroup
4184 *
4185 * Duplicate the current cgroup in the hierarchy that the given
4186 * subsystem is attached to, and move this task into the new
4187 * child.
4188 */
4189int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
4190                                                        char *nodename)
4191{
4192        struct dentry *dentry;
4193        int ret = 0;
4194        struct cgroup *parent, *child;
4195        struct inode *inode;
4196        struct css_set *cg;
4197        struct cgroupfs_root *root;
4198        struct cgroup_subsys *ss;
4199
4200        /* We shouldn't be called by an unregistered subsystem */
4201        BUG_ON(!subsys->active);
4202
4203        /* First figure out what hierarchy and cgroup we're dealing
4204         * with, and pin them so we can drop cgroup_mutex */
4205        mutex_lock(&cgroup_mutex);
4206 again:
4207        root = subsys->root;
4208        if (root == &rootnode) {
4209                mutex_unlock(&cgroup_mutex);
4210                return 0;
4211        }
4212
4213        /* Pin the hierarchy */
4214        if (!atomic_inc_not_zero(&root->sb->s_active)) {
4215                /* We race with the final deactivate_super() */
4216                mutex_unlock(&cgroup_mutex);
4217                return 0;
4218        }
4219
4220        /* Keep the cgroup alive */
4221        task_lock(tsk);
4222        parent = task_cgroup(tsk, subsys->subsys_id);
4223        cg = tsk->cgroups;
4224        get_css_set(cg);
4225        task_unlock(tsk);
4226
4227        mutex_unlock(&cgroup_mutex);
4228
4229        /* Now do the VFS work to create a cgroup */
4230        inode = parent->dentry->d_inode;
4231
4232        /* Hold the parent directory mutex across this operation to
4233         * stop anyone else deleting the new cgroup */
4234        mutex_lock(&inode->i_mutex);
4235        dentry = lookup_one_len(nodename, parent->dentry, strlen(nodename));
4236        if (IS_ERR(dentry)) {
4237                printk(KERN_INFO
4238                       "cgroup: Couldn't allocate dentry for %s: %ld\n", nodename,
4239                       PTR_ERR(dentry));
4240                ret = PTR_ERR(dentry);
4241                goto out_release;
4242        }
4243
4244        /* Create the cgroup directory, which also creates the cgroup */
4245        ret = vfs_mkdir(inode, dentry, 0755);
4246        child = __d_cgrp(dentry);
4247        dput(dentry);
4248        if (ret) {
4249                printk(KERN_INFO
4250                       "Failed to create cgroup %s: %d\n", nodename,
4251                       ret);
4252                goto out_release;
4253        }
4254
4255        /* The cgroup now exists. Retake cgroup_mutex and check
4256         * that we're still in the same state that we thought we
4257         * were. */
4258        mutex_lock(&cgroup_mutex);
4259        if ((root != subsys->root) ||
4260            (parent != task_cgroup(tsk, subsys->subsys_id))) {
4261                /* Aargh, we raced ... */
4262                mutex_unlock(&inode->i_mutex);
4263                put_css_set(cg);
4264
4265                deactivate_super(root->sb);
4266                /* The cgroup is still accessible in the VFS, but
4267                 * we're not going to try to rmdir() it at this
4268                 * point. */
4269                printk(KERN_INFO
4270                       "Race in cgroup_clone() - leaking cgroup %s\n",
4271                       nodename);
4272                goto again;
4273        }
4274
4275        /* do any required auto-setup */
4276        for_each_subsys(root, ss) {
4277                if (ss->post_clone)
4278                        ss->post_clone(ss, child);
4279        }
4280
4281        /* All seems fine. Finish by moving the task into the new cgroup */
4282        ret = cgroup_attach_task(child, tsk);
4283        mutex_unlock(&cgroup_mutex);
4284
4285 out_release:
4286        mutex_unlock(&inode->i_mutex);
4287
4288        mutex_lock(&cgroup_mutex);
4289        put_css_set(cg);
4290        mutex_unlock(&cgroup_mutex);
4291        deactivate_super(root->sb);
4292        return ret;
4293}
4294
4295/**
4296 * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp
4297 * @cgrp: the cgroup in question
4298 * @task: the task in question
4299 *
4300 * See if @cgrp is a descendant of @task's cgroup in the appropriate
4301 * hierarchy.
4302 *
4303 * If we are sending in dummytop, then presumably we are creating
4304 * the top cgroup in the subsystem.
4305 *
4306 * Called only by the ns (nsproxy) cgroup.
4307 */
4308int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
4309{
4310        int ret;
4311        struct cgroup *target;
4312
4313        if (cgrp == dummytop)
4314                return 1;
4315
4316        target = task_cgroup_from_root(task, cgrp->root);
4317        while (cgrp != target && cgrp!= cgrp->top_cgroup)
4318                cgrp = cgrp->parent;
4319        ret = (cgrp == target);
4320        return ret;
4321}
4322
4323static void check_for_release(struct cgroup *cgrp)
4324{
4325        /* All of these checks rely on RCU to keep the cgroup
4326         * structure alive */
4327        if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count)
4328            && list_empty(&cgrp->children) && !cgroup_has_css_refs(cgrp)) {
4329                /* Control Group is currently removeable. If it's not
4330                 * already queued for a userspace notification, queue
4331                 * it now */
4332                int need_schedule_work = 0;
4333                spin_lock(&release_list_lock);
4334                if (!cgroup_is_removed(cgrp) &&
4335                    list_empty(&cgrp->release_list)) {
4336                        list_add(&cgrp->release_list, &release_list);
4337                        need_schedule_work = 1;
4338                }
4339                spin_unlock(&release_list_lock);
4340                if (need_schedule_work)
4341                        schedule_work(&release_agent_work);
4342        }
4343}
4344
4345/* Caller must verify that the css is not for root cgroup */
4346void __css_put(struct cgroup_subsys_state *css, int count)
4347{
4348        struct cgroup *cgrp = css->cgroup;
4349        int val;
4350        rcu_read_lock();
4351        val = atomic_sub_return(count, &css->refcnt);
4352        if (val == 1) {
4353                if (notify_on_release(cgrp)) {
4354                        set_bit(CGRP_RELEASABLE, &cgrp->flags);
4355                        check_for_release(cgrp);
4356                }
4357                cgroup_wakeup_rmdir_waiter(cgrp);
4358        }
4359        rcu_read_unlock();
4360        WARN_ON_ONCE(val < 1);
4361}
4362EXPORT_SYMBOL_GPL(__css_put);
4363
4364/*
4365 * Notify userspace when a cgroup is released, by running the
4366 * configured release agent with the name of the cgroup (path
4367 * relative to the root of cgroup file system) as the argument.
4368 *
4369 * Most likely, this user command will try to rmdir this cgroup.
4370 *
4371 * This races with the possibility that some other task will be
4372 * attached to this cgroup before it is removed, or that some other
4373 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
4374 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
4375 * unused, and this cgroup will be reprieved from its death sentence,
4376 * to continue to serve a useful existence.  Next time it's released,
4377 * we will get notified again, if it still has 'notify_on_release' set.
4378 *
4379 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
4380 * means only wait until the task is successfully execve()'d.  The
4381 * separate release agent task is forked by call_usermodehelper(),
4382 * then control in this thread returns here, without waiting for the
4383 * release agent task.  We don't bother to wait because the caller of
4384 * this routine has no use for the exit status of the release agent
4385 * task, so no sense holding our caller up for that.
4386 */
4387static void cgroup_release_agent(struct work_struct *work)
4388{
4389        BUG_ON(work != &release_agent_work);
4390        mutex_lock(&cgroup_mutex);
4391        spin_lock(&release_list_lock);
4392        while (!list_empty(&release_list)) {
4393                char *argv[3], *envp[3];
4394                int i;
4395                char *pathbuf = NULL, *agentbuf = NULL;
4396                struct cgroup *cgrp = list_entry(release_list.next,
4397                                                    struct cgroup,
4398                                                    release_list);
4399                list_del_init(&cgrp->release_list);
4400                spin_unlock(&release_list_lock);
4401                pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
4402                if (!pathbuf)
4403                        goto continue_free;
4404                if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
4405                        goto continue_free;
4406                agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
4407                if (!agentbuf)
4408                        goto continue_free;
4409
4410                i = 0;
4411                argv[i++] = agentbuf;
4412                argv[i++] = pathbuf;
4413                argv[i] = NULL;
4414
4415                i = 0;
4416                /* minimal command environment */
4417                envp[i++] = "HOME=/";
4418                envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
4419                envp[i] = NULL;
4420
4421                /* Drop the lock while we invoke the usermode helper,
4422                 * since the exec could involve hitting disk and hence
4423                 * be a slow process */
4424                mutex_unlock(&cgroup_mutex);
4425                call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
4426                mutex_lock(&cgroup_mutex);
4427 continue_free:
4428                kfree(pathbuf);
4429                kfree(agentbuf);
4430                spin_lock(&release_list_lock);
4431        }
4432        spin_unlock(&release_list_lock);
4433        mutex_unlock(&cgroup_mutex);
4434}
4435
4436static int __init cgroup_disable(char *str)
4437{
4438        int i;
4439        char *token;
4440
4441        while ((token = strsep(&str, ",")) != NULL) {
4442                if (!*token)
4443                        continue;
4444                /*
4445                 * cgroup_disable, being at boot time, can't know about module
4446                 * subsystems, so we don't worry about them.
4447                 */
4448                for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
4449                        struct cgroup_subsys *ss = subsys[i];
4450
4451                        if (!strcmp(token, ss->name)) {
4452                                ss->disabled = 1;
4453                                printk(KERN_INFO "Disabling %s control group"
4454                                        " subsystem\n", ss->name);
4455                                break;
4456                        }
4457                }
4458        }
4459        return 1;
4460}
4461__setup("cgroup_disable=", cgroup_disable);
4462
4463/*
4464 * Functons for CSS ID.
4465 */
4466
4467/*
4468 *To get ID other than 0, this should be called when !cgroup_is_removed().
4469 */
4470unsigned short css_id(struct cgroup_subsys_state *css)
4471{
4472        struct css_id *cssid;
4473
4474        /*
4475         * This css_id() can return correct value when somone has refcnt
4476         * on this or this is under rcu_read_lock(). Once css->id is allocated,
4477         * it's unchanged until freed.
4478         */
4479        cssid = rcu_dereference_check(css->id,
4480                        rcu_read_lock_held() || atomic_read(&css->refcnt));
4481
4482        if (cssid)
4483                return cssid->id;
4484        return 0;
4485}
4486EXPORT_SYMBOL_GPL(css_id);
4487
4488unsigned short css_depth(struct cgroup_subsys_state *css)
4489{
4490        struct css_id *cssid;
4491
4492        cssid = rcu_dereference_check(css->id,
4493                        rcu_read_lock_held() || atomic_read(&css->refcnt));
4494
4495        if (cssid)
4496                return cssid->depth;
4497        return 0;
4498}
4499EXPORT_SYMBOL_GPL(css_depth);
4500
4501/**
4502 *  css_is_ancestor - test "root" css is an ancestor of "child"
4503 * @child: the css to be tested.
4504 * @root: the css supporsed to be an ancestor of the child.
4505 *
4506 * Returns true if "root" is an ancestor of "child" in its hierarchy. Because
4507 * this function reads css->id, this use rcu_dereference() and rcu_read_lock().
4508 * But, considering usual usage, the csses should be valid objects after test.
4509 * Assuming that the caller will do some action to the child if this returns
4510 * returns true, the caller must take "child";s reference count.
4511 * If "child" is valid object and this returns true, "root" is valid, too.
4512 */
4513
4514bool css_is_ancestor(struct cgroup_subsys_state *child,
4515                    const struct cgroup_subsys_state *root)
4516{
4517        struct css_id *child_id;
4518        struct css_id *root_id;
4519        bool ret = true;
4520
4521        rcu_read_lock();
4522        child_id  = rcu_dereference(child->id);
4523        root_id = rcu_dereference(root->id);
4524        if (!child_id
4525            || !root_id
4526            || (child_id->depth < root_id->depth)
4527            || (child_id->stack[root_id->depth] != root_id->id))
4528                ret = false;
4529        rcu_read_unlock();
4530        return ret;
4531}
4532
4533static void __free_css_id_cb(struct rcu_head *head)
4534{
4535        struct css_id *id;
4536
4537        id = container_of(head, struct css_id, rcu_head);
4538        kfree(id);
4539}
4540
4541void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
4542{
4543        struct css_id *id = css->id;
4544        /* When this is called before css_id initialization, id can be NULL */
4545        if (!id)
4546                return;
4547
4548        BUG_ON(!ss->use_id);
4549
4550        rcu_assign_pointer(id->css, NULL);
4551        rcu_assign_pointer(css->id, NULL);
4552        spin_lock(&ss->id_lock);
4553        idr_remove(&ss->idr, id->id);
4554        spin_unlock(&ss->id_lock);
4555        call_rcu(&id->rcu_head, __free_css_id_cb);
4556}
4557EXPORT_SYMBOL_GPL(free_css_id);
4558
4559/*
4560 * This is called by init or create(). Then, calls to this function are
4561 * always serialized (By cgroup_mutex() at create()).
4562 */
4563
4564static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
4565{
4566        struct css_id *newid;
4567        int myid, error, size;
4568
4569        BUG_ON(!ss->use_id);
4570
4571        size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
4572        newid = kzalloc(size, GFP_KERNEL);
4573        if (!newid)
4574                return ERR_PTR(-ENOMEM);
4575        /* get id */
4576        if (unlikely(!idr_pre_get(&ss->idr, GFP_KERNEL))) {
4577                error = -ENOMEM;
4578                goto err_out;
4579        }
4580        spin_lock(&ss->id_lock);
4581        /* Don't use 0. allocates an ID of 1-65535 */
4582        error = idr_get_new_above(&ss->idr, newid, 1, &myid);
4583        spin_unlock(&ss->id_lock);
4584
4585        /* Returns error when there are no free spaces for new ID.*/
4586        if (error) {
4587                error = -ENOSPC;
4588                goto err_out;
4589        }
4590        if (myid > CSS_ID_MAX)
4591                goto remove_idr;
4592
4593        newid->id = myid;
4594        newid->depth = depth;
4595        return newid;
4596remove_idr:
4597        error = -ENOSPC;
4598        spin_lock(&ss->id_lock);
4599        idr_remove(&ss->idr, myid);
4600        spin_unlock(&ss->id_lock);
4601err_out:
4602        kfree(newid);
4603        return ERR_PTR(error);
4604
4605}
4606
4607static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
4608                                            struct cgroup_subsys_state *rootcss)
4609{
4610        struct css_id *newid;
4611
4612        spin_lock_init(&ss->id_lock);
4613        idr_init(&ss->idr);
4614
4615        newid = get_new_cssid(ss, 0);
4616        if (IS_ERR(newid))
4617                return PTR_ERR(newid);
4618
4619        newid->stack[0] = newid->id;
4620        newid->css = rootcss;
4621        rootcss->id = newid;
4622        return 0;
4623}
4624
4625static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
4626                        struct cgroup *child)
4627{
4628        int subsys_id, i, depth = 0;
4629        struct cgroup_subsys_state *parent_css, *child_css;
4630        struct css_id *child_id, *parent_id;
4631
4632        subsys_id = ss->subsys_id;
4633        parent_css = parent->subsys[subsys_id];
4634        child_css = child->subsys[subsys_id];
4635        parent_id = parent_css->id;
4636        depth = parent_id->depth + 1;
4637
4638        child_id = get_new_cssid(ss, depth);
4639        if (IS_ERR(child_id))
4640                return PTR_ERR(child_id);
4641
4642        for (i = 0; i < depth; i++)
4643                child_id->stack[i] = parent_id->stack[i];
4644        child_id->stack[depth] = child_id->id;
4645        /*
4646         * child_id->css pointer will be set after this cgroup is available
4647         * see cgroup_populate_dir()
4648         */
4649        rcu_assign_pointer(child_css->id, child_id);
4650
4651        return 0;
4652}
4653
4654/**
4655 * css_lookup - lookup css by id
4656 * @ss: cgroup subsys to be looked into.
4657 * @id: the id
4658 *
4659 * Returns pointer to cgroup_subsys_state if there is valid one with id.
4660</