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/cred.h>
  31#include <linux/ctype.h>
  32#include <linux/errno.h>
  33#include <linux/fs.h>
  34#include <linux/init_task.h>
  35#include <linux/kernel.h>
  36#include <linux/list.h>
  37#include <linux/mm.h>
  38#include <linux/mutex.h>
  39#include <linux/mount.h>
  40#include <linux/pagemap.h>
  41#include <linux/proc_fs.h>
  42#include <linux/rcupdate.h>
  43#include <linux/sched.h>
  44#include <linux/backing-dev.h>
  45#include <linux/seq_file.h>
  46#include <linux/slab.h>
  47#include <linux/magic.h>
  48#include <linux/spinlock.h>
  49#include <linux/string.h>
  50#include <linux/sort.h>
  51#include <linux/kmod.h>
  52#include <linux/module.h>
  53#include <linux/delayacct.h>
  54#include <linux/cgroupstats.h>
  55#include <linux/hash.h>
  56#include <linux/namei.h>
  57#include <linux/pid_namespace.h>
  58#include <linux/idr.h>
  59#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
  60#include <linux/eventfd.h>
  61#include <linux/poll.h>
  62#include <linux/flex_array.h> /* used in cgroup_attach_proc */
  63#include <linux/kthread.h>
  64
  65#include <linux/atomic.h>
  66
  67/* css deactivation bias, makes css->refcnt negative to deny new trygets */
  68#define CSS_DEACT_BIAS          INT_MIN
  69
  70/*
  71 * cgroup_mutex is the master lock.  Any modification to cgroup or its
  72 * hierarchy must be performed while holding it.
  73 *
  74 * cgroup_root_mutex nests inside cgroup_mutex and should be held to modify
  75 * cgroupfs_root of any cgroup hierarchy - subsys list, flags,
  76 * release_agent_path and so on.  Modifying requires both cgroup_mutex and
  77 * cgroup_root_mutex.  Readers can acquire either of the two.  This is to
  78 * break the following locking order cycle.
  79 *
  80 *  A. cgroup_mutex -> cred_guard_mutex -> s_type->i_mutex_key -> namespace_sem
  81 *  B. namespace_sem -> cgroup_mutex
  82 *
  83 * B happens only through cgroup_show_options() and using cgroup_root_mutex
  84 * breaks it.
  85 */
  86static DEFINE_MUTEX(cgroup_mutex);
  87static DEFINE_MUTEX(cgroup_root_mutex);
  88
  89/*
  90 * Generate an array of cgroup subsystem pointers. At boot time, this is
  91 * populated with the built in subsystems, and modular subsystems are
  92 * registered after that. The mutable section of this array is protected by
  93 * cgroup_mutex.
  94 */
  95#define SUBSYS(_x) [_x ## _subsys_id] = &_x ## _subsys,
  96#define IS_SUBSYS_ENABLED(option) IS_BUILTIN(option)
  97static struct cgroup_subsys *subsys[CGROUP_SUBSYS_COUNT] = {
  98#include <linux/cgroup_subsys.h>
  99};
 100
 101#define MAX_CGROUP_ROOT_NAMELEN 64
 102
 103/*
 104 * A cgroupfs_root represents the root of a cgroup hierarchy,
 105 * and may be associated with a superblock to form an active
 106 * hierarchy
 107 */
 108struct cgroupfs_root {
 109        struct super_block *sb;
 110
 111        /*
 112         * The bitmask of subsystems intended to be attached to this
 113         * hierarchy
 114         */
 115        unsigned long subsys_mask;
 116
 117        /* Unique id for this hierarchy. */
 118        int hierarchy_id;
 119
 120        /* The bitmask of subsystems currently attached to this hierarchy */
 121        unsigned long actual_subsys_mask;
 122
 123        /* A list running through the attached subsystems */
 124        struct list_head subsys_list;
 125
 126        /* The root cgroup for this hierarchy */
 127        struct cgroup top_cgroup;
 128
 129        /* Tracks how many cgroups are currently defined in hierarchy.*/
 130        int number_of_cgroups;
 131
 132        /* A list running through the active hierarchies */
 133        struct list_head root_list;
 134
 135        /* All cgroups on this root, cgroup_mutex protected */
 136        struct list_head allcg_list;
 137
 138        /* Hierarchy-specific flags */
 139        unsigned long flags;
 140
 141        /* The path to use for release notifications. */
 142        char release_agent_path[PATH_MAX];
 143
 144        /* The name for this hierarchy - may be empty */
 145        char name[MAX_CGROUP_ROOT_NAMELEN];
 146};
 147
 148/*
 149 * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
 150 * subsystems that are otherwise unattached - it never has more than a
 151 * single cgroup, and all tasks are part of that cgroup.
 152 */
 153static struct cgroupfs_root rootnode;
 154
 155/*
 156 * cgroupfs file entry, pointed to from leaf dentry->d_fsdata.
 157 */
 158struct cfent {
 159        struct list_head                node;
 160        struct dentry                   *dentry;
 161        struct cftype                   *type;
 162};
 163
 164/*
 165 * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
 166 * cgroup_subsys->use_id != 0.
 167 */
 168#define CSS_ID_MAX      (65535)
 169struct css_id {
 170        /*
 171         * The css to which this ID points. This pointer is set to valid value
 172         * after cgroup is populated. If cgroup is removed, this will be NULL.
 173         * This pointer is expected to be RCU-safe because destroy()
 174         * is called after synchronize_rcu(). But for safe use, css_is_removed()
 175         * css_tryget() should be used for avoiding race.
 176         */
 177        struct cgroup_subsys_state __rcu *css;
 178        /*
 179         * ID of this css.
 180         */
 181        unsigned short id;
 182        /*
 183         * Depth in hierarchy which this ID belongs to.
 184         */
 185        unsigned short depth;
 186        /*
 187         * ID is freed by RCU. (and lookup routine is RCU safe.)
 188         */
 189        struct rcu_head rcu_head;
 190        /*
 191         * Hierarchy of CSS ID belongs to.
 192         */
 193        unsigned short stack[0]; /* Array of Length (depth+1) */
 194};
 195
 196/*
 197 * cgroup_event represents events which userspace want to receive.
 198 */
 199struct cgroup_event {
 200        /*
 201         * Cgroup which the event belongs to.
 202         */
 203        struct cgroup *cgrp;
 204        /*
 205         * Control file which the event associated.
 206         */
 207        struct cftype *cft;
 208        /*
 209         * eventfd to signal userspace about the event.
 210         */
 211        struct eventfd_ctx *eventfd;
 212        /*
 213         * Each of these stored in a list by the cgroup.
 214         */
 215        struct list_head list;
 216        /*
 217         * All fields below needed to unregister event when
 218         * userspace closes eventfd.
 219         */
 220        poll_table pt;
 221        wait_queue_head_t *wqh;
 222        wait_queue_t wait;
 223        struct work_struct remove;
 224};
 225
 226/* The list of hierarchy roots */
 227
 228static LIST_HEAD(roots);
 229static int root_count;
 230
 231static DEFINE_IDA(hierarchy_ida);
 232static int next_hierarchy_id;
 233static DEFINE_SPINLOCK(hierarchy_id_lock);
 234
 235/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
 236#define dummytop (&rootnode.top_cgroup)
 237
 238/* This flag indicates whether tasks in the fork and exit paths should
 239 * check for fork/exit handlers to call. This avoids us having to do
 240 * extra work in the fork/exit path if none of the subsystems need to
 241 * be called.
 242 */
 243static int need_forkexit_callback __read_mostly;
 244
 245#ifdef CONFIG_PROVE_LOCKING
 246int cgroup_lock_is_held(void)
 247{
 248        return lockdep_is_held(&cgroup_mutex);
 249}
 250#else /* #ifdef CONFIG_PROVE_LOCKING */
 251int cgroup_lock_is_held(void)
 252{
 253        return mutex_is_locked(&cgroup_mutex);
 254}
 255#endif /* #else #ifdef CONFIG_PROVE_LOCKING */
 256
 257EXPORT_SYMBOL_GPL(cgroup_lock_is_held);
 258
 259static int css_unbias_refcnt(int refcnt)
 260{
 261        return refcnt >= 0 ? refcnt : refcnt - CSS_DEACT_BIAS;
 262}
 263
 264/* the current nr of refs, always >= 0 whether @css is deactivated or not */
 265static int css_refcnt(struct cgroup_subsys_state *css)
 266{
 267        int v = atomic_read(&css->refcnt);
 268
 269        return css_unbias_refcnt(v);
 270}
 271
 272/* convenient tests for these bits */
 273inline int cgroup_is_removed(const struct cgroup *cgrp)
 274{
 275        return test_bit(CGRP_REMOVED, &cgrp->flags);
 276}
 277
 278/* bits in struct cgroupfs_root flags field */
 279enum {
 280        ROOT_NOPREFIX,  /* mounted subsystems have no named prefix */
 281        ROOT_XATTR,     /* supports extended attributes */
 282};
 283
 284static int cgroup_is_releasable(const struct cgroup *cgrp)
 285{
 286        const int bits =
 287                (1 << CGRP_RELEASABLE) |
 288                (1 << CGRP_NOTIFY_ON_RELEASE);
 289        return (cgrp->flags & bits) == bits;
 290}
 291
 292static int notify_on_release(const struct cgroup *cgrp)
 293{
 294        return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
 295}
 296
 297static int clone_children(const struct cgroup *cgrp)
 298{
 299        return test_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
 300}
 301
 302/*
 303 * for_each_subsys() allows you to iterate on each subsystem attached to
 304 * an active hierarchy
 305 */
 306#define for_each_subsys(_root, _ss) \
 307list_for_each_entry(_ss, &_root->subsys_list, sibling)
 308
 309/* for_each_active_root() allows you to iterate across the active hierarchies */
 310#define for_each_active_root(_root) \
 311list_for_each_entry(_root, &roots, root_list)
 312
 313static inline struct cgroup *__d_cgrp(struct dentry *dentry)
 314{
 315        return dentry->d_fsdata;
 316}
 317
 318static inline struct cfent *__d_cfe(struct dentry *dentry)
 319{
 320        return dentry->d_fsdata;
 321}
 322
 323static inline struct cftype *__d_cft(struct dentry *dentry)
 324{
 325        return __d_cfe(dentry)->type;
 326}
 327
 328/* the list of cgroups eligible for automatic release. Protected by
 329 * release_list_lock */
 330static LIST_HEAD(release_list);
 331static DEFINE_RAW_SPINLOCK(release_list_lock);
 332static void cgroup_release_agent(struct work_struct *work);
 333static DECLARE_WORK(release_agent_work, cgroup_release_agent);
 334static void check_for_release(struct cgroup *cgrp);
 335
 336/* Link structure for associating css_set objects with cgroups */
 337struct cg_cgroup_link {
 338        /*
 339         * List running through cg_cgroup_links associated with a
 340         * cgroup, anchored on cgroup->css_sets
 341         */
 342        struct list_head cgrp_link_list;
 343        struct cgroup *cgrp;
 344        /*
 345         * List running through cg_cgroup_links pointing at a
 346         * single css_set object, anchored on css_set->cg_links
 347         */
 348        struct list_head cg_link_list;
 349        struct css_set *cg;
 350};
 351
 352/* The default css_set - used by init and its children prior to any
 353 * hierarchies being mounted. It contains a pointer to the root state
 354 * for each subsystem. Also used to anchor the list of css_sets. Not
 355 * reference-counted, to improve performance when child cgroups
 356 * haven't been created.
 357 */
 358
 359static struct css_set init_css_set;
 360static struct cg_cgroup_link init_css_set_link;
 361
 362static int cgroup_init_idr(struct cgroup_subsys *ss,
 363                           struct cgroup_subsys_state *css);
 364
 365/* css_set_lock protects the list of css_set objects, and the
 366 * chain of tasks off each css_set.  Nests outside task->alloc_lock
 367 * due to cgroup_iter_start() */
 368static DEFINE_RWLOCK(css_set_lock);
 369static int css_set_count;
 370
 371/*
 372 * hash table for cgroup groups. This improves the performance to find
 373 * an existing css_set. This hash doesn't (currently) take into
 374 * account cgroups in empty hierarchies.
 375 */
 376#define CSS_SET_HASH_BITS       7
 377#define CSS_SET_TABLE_SIZE      (1 << CSS_SET_HASH_BITS)
 378static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];
 379
 380static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
 381{
 382        int i;
 383        int index;
 384        unsigned long tmp = 0UL;
 385
 386        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
 387                tmp += (unsigned long)css[i];
 388        tmp = (tmp >> 16) ^ tmp;
 389
 390        index = hash_long(tmp, CSS_SET_HASH_BITS);
 391
 392        return &css_set_table[index];
 393}
 394
 395/* We don't maintain the lists running through each css_set to its
 396 * task until after the first call to cgroup_iter_start(). This
 397 * reduces the fork()/exit() overhead for people who have cgroups
 398 * compiled into their kernel but not actually in use */
 399static int use_task_css_set_links __read_mostly;
 400
 401static void __put_css_set(struct css_set *cg, int taskexit)
 402{
 403        struct cg_cgroup_link *link;
 404        struct cg_cgroup_link *saved_link;
 405        /*
 406         * Ensure that the refcount doesn't hit zero while any readers
 407         * can see it. Similar to atomic_dec_and_lock(), but for an
 408         * rwlock
 409         */
 410        if (atomic_add_unless(&cg->refcount, -1, 1))
 411                return;
 412        write_lock(&css_set_lock);
 413        if (!atomic_dec_and_test(&cg->refcount)) {
 414                write_unlock(&css_set_lock);
 415                return;
 416        }
 417
 418        /* This css_set is dead. unlink it and release cgroup refcounts */
 419        hlist_del(&cg->hlist);
 420        css_set_count--;
 421
 422        list_for_each_entry_safe(link, saved_link, &cg->cg_links,
 423                                 cg_link_list) {
 424                struct cgroup *cgrp = link->cgrp;
 425                list_del(&link->cg_link_list);
 426                list_del(&link->cgrp_link_list);
 427                if (atomic_dec_and_test(&cgrp->count) &&
 428                    notify_on_release(cgrp)) {
 429                        if (taskexit)
 430                                set_bit(CGRP_RELEASABLE, &cgrp->flags);
 431                        check_for_release(cgrp);
 432                }
 433
 434                kfree(link);
 435        }
 436
 437        write_unlock(&css_set_lock);
 438        kfree_rcu(cg, rcu_head);
 439}
 440
 441/*
 442 * refcounted get/put for css_set objects
 443 */
 444static inline void get_css_set(struct css_set *cg)
 445{
 446        atomic_inc(&cg->refcount);
 447}
 448
 449static inline void put_css_set(struct css_set *cg)
 450{
 451        __put_css_set(cg, 0);
 452}
 453
 454static inline void put_css_set_taskexit(struct css_set *cg)
 455{
 456        __put_css_set(cg, 1);
 457}
 458
 459/*
 460 * compare_css_sets - helper function for find_existing_css_set().
 461 * @cg: candidate css_set being tested
 462 * @old_cg: existing css_set for a task
 463 * @new_cgrp: cgroup that's being entered by the task
 464 * @template: desired set of css pointers in css_set (pre-calculated)
 465 *
 466 * Returns true if "cg" matches "old_cg" except for the hierarchy
 467 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 468 */
 469static bool compare_css_sets(struct css_set *cg,
 470                             struct css_set *old_cg,
 471                             struct cgroup *new_cgrp,
 472                             struct cgroup_subsys_state *template[])
 473{
 474        struct list_head *l1, *l2;
 475
 476        if (memcmp(template, cg->subsys, sizeof(cg->subsys))) {
 477                /* Not all subsystems matched */
 478                return false;
 479        }
 480
 481        /*
 482         * Compare cgroup pointers in order to distinguish between
 483         * different cgroups in heirarchies with no subsystems. We
 484         * could get by with just this check alone (and skip the
 485         * memcmp above) but on most setups the memcmp check will
 486         * avoid the need for this more expensive check on almost all
 487         * candidates.
 488         */
 489
 490        l1 = &cg->cg_links;
 491        l2 = &old_cg->cg_links;
 492        while (1) {
 493                struct cg_cgroup_link *cgl1, *cgl2;
 494                struct cgroup *cg1, *cg2;
 495
 496                l1 = l1->next;
 497                l2 = l2->next;
 498                /* See if we reached the end - both lists are equal length. */
 499                if (l1 == &cg->cg_links) {
 500                        BUG_ON(l2 != &old_cg->cg_links);
 501                        break;
 502                } else {
 503                        BUG_ON(l2 == &old_cg->cg_links);
 504                }
 505                /* Locate the cgroups associated with these links. */
 506                cgl1 = list_entry(l1, struct cg_cgroup_link, cg_link_list);
 507                cgl2 = list_entry(l2, struct cg_cgroup_link, cg_link_list);
 508                cg1 = cgl1->cgrp;
 509                cg2 = cgl2->cgrp;
 510                /* Hierarchies should be linked in the same order. */
 511                BUG_ON(cg1->root != cg2->root);
 512
 513                /*
 514                 * If this hierarchy is the hierarchy of the cgroup
 515                 * that's changing, then we need to check that this
 516                 * css_set points to the new cgroup; if it's any other
 517                 * hierarchy, then this css_set should point to the
 518                 * same cgroup as the old css_set.
 519                 */
 520                if (cg1->root == new_cgrp->root) {
 521                        if (cg1 != new_cgrp)
 522                                return false;
 523                } else {
 524                        if (cg1 != cg2)
 525                                return false;
 526                }
 527        }
 528        return true;
 529}
 530
 531/*
 532 * find_existing_css_set() is a helper for
 533 * find_css_set(), and checks to see whether an existing
 534 * css_set is suitable.
 535 *
 536 * oldcg: the cgroup group that we're using before the cgroup
 537 * transition
 538 *
 539 * cgrp: the cgroup that we're moving into
 540 *
 541 * template: location in which to build the desired set of subsystem
 542 * state objects for the new cgroup group
 543 */
 544static struct css_set *find_existing_css_set(
 545        struct css_set *oldcg,
 546        struct cgroup *cgrp,
 547        struct cgroup_subsys_state *template[])
 548{
 549        int i;
 550        struct cgroupfs_root *root = cgrp->root;
 551        struct hlist_head *hhead;
 552        struct hlist_node *node;
 553        struct css_set *cg;
 554
 555        /*
 556         * Build the set of subsystem state objects that we want to see in the
 557         * new css_set. while subsystems can change globally, the entries here
 558         * won't change, so no need for locking.
 559         */
 560        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 561                if (root->subsys_mask & (1UL << i)) {
 562                        /* Subsystem is in this hierarchy. So we want
 563                         * the subsystem state from the new
 564                         * cgroup */
 565                        template[i] = cgrp->subsys[i];
 566                } else {
 567                        /* Subsystem is not in this hierarchy, so we
 568                         * don't want to change the subsystem state */
 569                        template[i] = oldcg->subsys[i];
 570                }
 571        }
 572
 573        hhead = css_set_hash(template);
 574        hlist_for_each_entry(cg, node, hhead, hlist) {
 575                if (!compare_css_sets(cg, oldcg, cgrp, template))
 576                        continue;
 577
 578                /* This css_set matches what we need */
 579                return cg;
 580        }
 581
 582        /* No existing cgroup group matched */
 583        return NULL;
 584}
 585
 586static void free_cg_links(struct list_head *tmp)
 587{
 588        struct cg_cgroup_link *link;
 589        struct cg_cgroup_link *saved_link;
 590
 591        list_for_each_entry_safe(link, saved_link, tmp, cgrp_link_list) {
 592                list_del(&link->cgrp_link_list);
 593                kfree(link);
 594        }
 595}
 596
 597/*
 598 * allocate_cg_links() allocates "count" cg_cgroup_link structures
 599 * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
 600 * success or a negative error
 601 */
 602static int allocate_cg_links(int count, struct list_head *tmp)
 603{
 604        struct cg_cgroup_link *link;
 605        int i;
 606        INIT_LIST_HEAD(tmp);
 607        for (i = 0; i < count; i++) {
 608                link = kmalloc(sizeof(*link), GFP_KERNEL);
 609                if (!link) {
 610                        free_cg_links(tmp);
 611                        return -ENOMEM;
 612                }
 613                list_add(&link->cgrp_link_list, tmp);
 614        }
 615        return 0;
 616}
 617
 618/**
 619 * link_css_set - a helper function to link a css_set to a cgroup
 620 * @tmp_cg_links: cg_cgroup_link objects allocated by allocate_cg_links()
 621 * @cg: the css_set to be linked
 622 * @cgrp: the destination cgroup
 623 */
 624static void link_css_set(struct list_head *tmp_cg_links,
 625                         struct css_set *cg, struct cgroup *cgrp)
 626{
 627        struct cg_cgroup_link *link;
 628
 629        BUG_ON(list_empty(tmp_cg_links));
 630        link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
 631                                cgrp_link_list);
 632        link->cg = cg;
 633        link->cgrp = cgrp;
 634        atomic_inc(&cgrp->count);
 635        list_move(&link->cgrp_link_list, &cgrp->css_sets);
 636        /*
 637         * Always add links to the tail of the list so that the list
 638         * is sorted by order of hierarchy creation
 639         */
 640        list_add_tail(&link->cg_link_list, &cg->cg_links);
 641}
 642
 643/*
 644 * find_css_set() takes an existing cgroup group and a
 645 * cgroup object, and returns a css_set object that's
 646 * equivalent to the old group, but with the given cgroup
 647 * substituted into the appropriate hierarchy. Must be called with
 648 * cgroup_mutex held
 649 */
 650static struct css_set *find_css_set(
 651        struct css_set *oldcg, struct cgroup *cgrp)
 652{
 653        struct css_set *res;
 654        struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
 655
 656        struct list_head tmp_cg_links;
 657
 658        struct hlist_head *hhead;
 659        struct cg_cgroup_link *link;
 660
 661        /* First see if we already have a cgroup group that matches
 662         * the desired set */
 663        read_lock(&css_set_lock);
 664        res = find_existing_css_set(oldcg, cgrp, template);
 665        if (res)
 666                get_css_set(res);
 667        read_unlock(&css_set_lock);
 668
 669        if (res)
 670                return res;
 671
 672        res = kmalloc(sizeof(*res), GFP_KERNEL);
 673        if (!res)
 674                return NULL;
 675
 676        /* Allocate all the cg_cgroup_link objects that we'll need */
 677        if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
 678                kfree(res);
 679                return NULL;
 680        }
 681
 682        atomic_set(&res->refcount, 1);
 683        INIT_LIST_HEAD(&res->cg_links);
 684        INIT_LIST_HEAD(&res->tasks);
 685        INIT_HLIST_NODE(&res->hlist);
 686
 687        /* Copy the set of subsystem state objects generated in
 688         * find_existing_css_set() */
 689        memcpy(res->subsys, template, sizeof(res->subsys));
 690
 691        write_lock(&css_set_lock);
 692        /* Add reference counts and links from the new css_set. */
 693        list_for_each_entry(link, &oldcg->cg_links, cg_link_list) {
 694                struct cgroup *c = link->cgrp;
 695                if (c->root == cgrp->root)
 696                        c = cgrp;
 697                link_css_set(&tmp_cg_links, res, c);
 698        }
 699
 700        BUG_ON(!list_empty(&tmp_cg_links));
 701
 702        css_set_count++;
 703
 704        /* Add this cgroup group to the hash table */
 705        hhead = css_set_hash(res->subsys);
 706        hlist_add_head(&res->hlist, hhead);
 707
 708        write_unlock(&css_set_lock);
 709
 710        return res;
 711}
 712
 713/*
 714 * Return the cgroup for "task" from the given hierarchy. Must be
 715 * called with cgroup_mutex held.
 716 */
 717static struct cgroup *task_cgroup_from_root(struct task_struct *task,
 718                                            struct cgroupfs_root *root)
 719{
 720        struct css_set *css;
 721        struct cgroup *res = NULL;
 722
 723        BUG_ON(!mutex_is_locked(&cgroup_mutex));
 724        read_lock(&css_set_lock);
 725        /*
 726         * No need to lock the task - since we hold cgroup_mutex the
 727         * task can't change groups, so the only thing that can happen
 728         * is that it exits and its css is set back to init_css_set.
 729         */
 730        css = task->cgroups;
 731        if (css == &init_css_set) {
 732                res = &root->top_cgroup;
 733        } else {
 734                struct cg_cgroup_link *link;
 735                list_for_each_entry(link, &css->cg_links, cg_link_list) {
 736                        struct cgroup *c = link->cgrp;
 737                        if (c->root == root) {
 738                                res = c;
 739                                break;
 740                        }
 741                }
 742        }
 743        read_unlock(&css_set_lock);
 744        BUG_ON(!res);
 745        return res;
 746}
 747
 748/*
 749 * There is one global cgroup mutex. We also require taking
 750 * task_lock() when dereferencing a task's cgroup subsys pointers.
 751 * See "The task_lock() exception", at the end of this comment.
 752 *
 753 * A task must hold cgroup_mutex to modify cgroups.
 754 *
 755 * Any task can increment and decrement the count field without lock.
 756 * So in general, code holding cgroup_mutex can't rely on the count
 757 * field not changing.  However, if the count goes to zero, then only
 758 * cgroup_attach_task() can increment it again.  Because a count of zero
 759 * means that no tasks are currently attached, therefore there is no
 760 * way a task attached to that cgroup can fork (the other way to
 761 * increment the count).  So code holding cgroup_mutex can safely
 762 * assume that if the count is zero, it will stay zero. Similarly, if
 763 * a task holds cgroup_mutex on a cgroup with zero count, it
 764 * knows that the cgroup won't be removed, as cgroup_rmdir()
 765 * needs that mutex.
 766 *
 767 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
 768 * (usually) take cgroup_mutex.  These are the two most performance
 769 * critical pieces of code here.  The exception occurs on cgroup_exit(),
 770 * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
 771 * is taken, and if the cgroup count is zero, a usermode call made
 772 * to the release agent with the name of the cgroup (path relative to
 773 * the root of cgroup file system) as the argument.
 774 *
 775 * A cgroup can only be deleted if both its 'count' of using tasks
 776 * is zero, and its list of 'children' cgroups is empty.  Since all
 777 * tasks in the system use _some_ cgroup, and since there is always at
 778 * least one task in the system (init, pid == 1), therefore, top_cgroup
 779 * always has either children cgroups and/or using tasks.  So we don't
 780 * need a special hack to ensure that top_cgroup cannot be deleted.
 781 *
 782 *      The task_lock() exception
 783 *
 784 * The need for this exception arises from the action of
 785 * cgroup_attach_task(), which overwrites one tasks cgroup pointer with
 786 * another.  It does so using cgroup_mutex, however there are
 787 * several performance critical places that need to reference
 788 * task->cgroup without the expense of grabbing a system global
 789 * mutex.  Therefore except as noted below, when dereferencing or, as
 790 * in cgroup_attach_task(), modifying a task'ss cgroup pointer we use
 791 * task_lock(), which acts on a spinlock (task->alloc_lock) already in
 792 * the task_struct routinely used for such matters.
 793 *
 794 * P.S.  One more locking exception.  RCU is used to guard the
 795 * update of a tasks cgroup pointer by cgroup_attach_task()
 796 */
 797
 798/**
 799 * cgroup_lock - lock out any changes to cgroup structures
 800 *
 801 */
 802void cgroup_lock(void)
 803{
 804        mutex_lock(&cgroup_mutex);
 805}
 806EXPORT_SYMBOL_GPL(cgroup_lock);
 807
 808/**
 809 * cgroup_unlock - release lock on cgroup changes
 810 *
 811 * Undo the lock taken in a previous cgroup_lock() call.
 812 */
 813void cgroup_unlock(void)
 814{
 815        mutex_unlock(&cgroup_mutex);
 816}
 817EXPORT_SYMBOL_GPL(cgroup_unlock);
 818
 819/*
 820 * A couple of forward declarations required, due to cyclic reference loop:
 821 * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
 822 * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
 823 * -> cgroup_mkdir.
 824 */
 825
 826static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode);
 827static struct dentry *cgroup_lookup(struct inode *, struct dentry *, unsigned int);
 828static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
 829static int cgroup_populate_dir(struct cgroup *cgrp, bool base_files,
 830                               unsigned long subsys_mask);
 831static const struct inode_operations cgroup_dir_inode_operations;
 832static const struct file_operations proc_cgroupstats_operations;
 833
 834static struct backing_dev_info cgroup_backing_dev_info = {
 835        .name           = "cgroup",
 836        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
 837};
 838
 839static int alloc_css_id(struct cgroup_subsys *ss,
 840                        struct cgroup *parent, struct cgroup *child);
 841
 842static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
 843{
 844        struct inode *inode = new_inode(sb);
 845
 846        if (inode) {
 847                inode->i_ino = get_next_ino();
 848                inode->i_mode = mode;
 849                inode->i_uid = current_fsuid();
 850                inode->i_gid = current_fsgid();
 851                inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 852                inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
 853        }
 854        return inode;
 855}
 856
 857/*
 858 * Call subsys's pre_destroy handler.
 859 * This is called before css refcnt check.
 860 */
 861static int cgroup_call_pre_destroy(struct cgroup *cgrp)
 862{
 863        struct cgroup_subsys *ss;
 864        int ret = 0;
 865
 866        for_each_subsys(cgrp->root, ss) {
 867                if (!ss->pre_destroy)
 868                        continue;
 869
 870                ret = ss->pre_destroy(cgrp);
 871                if (ret) {
 872                        /* ->pre_destroy() failure is being deprecated */
 873                        WARN_ON_ONCE(!ss->__DEPRECATED_clear_css_refs);
 874                        break;
 875                }
 876        }
 877
 878        return ret;
 879}
 880
 881static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 882{
 883        /* is dentry a directory ? if so, kfree() associated cgroup */
 884        if (S_ISDIR(inode->i_mode)) {
 885                struct cgroup *cgrp = dentry->d_fsdata;
 886                struct cgroup_subsys *ss;
 887                BUG_ON(!(cgroup_is_removed(cgrp)));
 888                /* It's possible for external users to be holding css
 889                 * reference counts on a cgroup; css_put() needs to
 890                 * be able to access the cgroup after decrementing
 891                 * the reference count in order to know if it needs to
 892                 * queue the cgroup to be handled by the release
 893                 * agent */
 894                synchronize_rcu();
 895
 896                mutex_lock(&cgroup_mutex);
 897                /*
 898                 * Release the subsystem state objects.
 899                 */
 900                for_each_subsys(cgrp->root, ss)
 901                        ss->destroy(cgrp);
 902
 903                cgrp->root->number_of_cgroups--;
 904                mutex_unlock(&cgroup_mutex);
 905
 906                /*
 907                 * Drop the active superblock reference that we took when we
 908                 * created the cgroup
 909                 */
 910                deactivate_super(cgrp->root->sb);
 911
 912                /*
 913                 * if we're getting rid of the cgroup, refcount should ensure
 914                 * that there are no pidlists left.
 915                 */
 916                BUG_ON(!list_empty(&cgrp->pidlists));
 917
 918                simple_xattrs_free(&cgrp->xattrs);
 919
 920                kfree_rcu(cgrp, rcu_head);
 921        } else {
 922                struct cfent *cfe = __d_cfe(dentry);
 923                struct cgroup *cgrp = dentry->d_parent->d_fsdata;
 924                struct cftype *cft = cfe->type;
 925
 926                WARN_ONCE(!list_empty(&cfe->node) &&
 927                          cgrp != &cgrp->root->top_cgroup,
 928                          "cfe still linked for %s\n", cfe->type->name);
 929                kfree(cfe);
 930                simple_xattrs_free(&cft->xattrs);
 931        }
 932        iput(inode);
 933}
 934
 935static int cgroup_delete(const struct dentry *d)
 936{
 937        return 1;
 938}
 939
 940static void remove_dir(struct dentry *d)
 941{
 942        struct dentry *parent = dget(d->d_parent);
 943
 944        d_delete(d);
 945        simple_rmdir(parent->d_inode, d);
 946        dput(parent);
 947}
 948
 949static int cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
 950{
 951        struct cfent *cfe;
 952
 953        lockdep_assert_held(&cgrp->dentry->d_inode->i_mutex);
 954        lockdep_assert_held(&cgroup_mutex);
 955
 956        list_for_each_entry(cfe, &cgrp->files, node) {
 957                struct dentry *d = cfe->dentry;
 958
 959                if (cft && cfe->type != cft)
 960                        continue;
 961
 962                dget(d);
 963                d_delete(d);
 964                simple_unlink(cgrp->dentry->d_inode, d);
 965                list_del_init(&cfe->node);
 966                dput(d);
 967
 968                return 0;
 969        }
 970        return -ENOENT;
 971}
 972
 973/**
 974 * cgroup_clear_directory - selective removal of base and subsystem files
 975 * @dir: directory containing the files
 976 * @base_files: true if the base files should be removed
 977 * @subsys_mask: mask of the subsystem ids whose files should be removed
 978 */
 979static void cgroup_clear_directory(struct dentry *dir, bool base_files,
 980                                   unsigned long subsys_mask)
 981{
 982        struct cgroup *cgrp = __d_cgrp(dir);
 983        struct cgroup_subsys *ss;
 984
 985        for_each_subsys(cgrp->root, ss) {
 986                struct cftype_set *set;
 987                if (!test_bit(ss->subsys_id, &subsys_mask))
 988                        continue;
 989                list_for_each_entry(set, &ss->cftsets, node)
 990                        cgroup_rm_file(cgrp, set->cfts);
 991        }
 992        if (base_files) {
 993                while (!list_empty(&cgrp->files))
 994                        cgroup_rm_file(cgrp, NULL);
 995        }
 996}
 997
 998/*
 999 * NOTE : the dentry must have been dget()'ed
1000 */
1001static void cgroup_d_remove_dir(struct dentry *dentry)
1002{
1003        struct dentry *parent;
1004        struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
1005
1006        cgroup_clear_directory(dentry, true, root->subsys_mask);
1007
1008        parent = dentry->d_parent;
1009        spin_lock(&parent->d_lock);
1010        spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1011        list_del_init(&dentry->d_u.d_child);
1012        spin_unlock(&dentry->d_lock);
1013        spin_unlock(&parent->d_lock);
1014        remove_dir(dentry);
1015}
1016
1017/*
1018 * A queue for waiters to do rmdir() cgroup. A tasks will sleep when
1019 * cgroup->count == 0 && list_empty(&cgroup->children) && subsys has some
1020 * reference to css->refcnt. In general, this refcnt is expected to goes down
1021 * to zero, soon.
1022 *
1023 * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
1024 */
1025static DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
1026
1027static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
1028{
1029        if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
1030                wake_up_all(&cgroup_rmdir_waitq);
1031}
1032
1033void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
1034{
1035        css_get(css);
1036}
1037
1038void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
1039{
1040        cgroup_wakeup_rmdir_waiter(css->cgroup);
1041        css_put(css);
1042}
1043
1044/*
1045 * Call with cgroup_mutex held. Drops reference counts on modules, including
1046 * any duplicate ones that parse_cgroupfs_options took. If this function
1047 * returns an error, no reference counts are touched.
1048 */
1049static int rebind_subsystems(struct cgroupfs_root *root,
1050                              unsigned long final_subsys_mask)
1051{
1052        unsigned long added_mask, removed_mask;
1053        struct cgroup *cgrp = &root->top_cgroup;
1054        int i;
1055
1056        BUG_ON(!mutex_is_locked(&cgroup_mutex));
1057        BUG_ON(!mutex_is_locked(&cgroup_root_mutex));
1058
1059        removed_mask = root->actual_subsys_mask & ~final_subsys_mask;
1060        added_mask = final_subsys_mask & ~root->actual_subsys_mask;
1061        /* Check that any added subsystems are currently free */
1062        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1063                unsigned long bit = 1UL << i;
1064                struct cgroup_subsys *ss = subsys[i];
1065                if (!(bit & added_mask))
1066                        continue;
1067                /*
1068                 * Nobody should tell us to do a subsys that doesn't exist:
1069                 * parse_cgroupfs_options should catch that case and refcounts
1070                 * ensure that subsystems won't disappear once selected.
1071                 */
1072                BUG_ON(ss == NULL);
1073                if (ss->root != &rootnode) {
1074                        /* Subsystem isn't free */
1075                        return -EBUSY;
1076                }
1077        }
1078
1079        /* Currently we don't handle adding/removing subsystems when
1080         * any child cgroups exist. This is theoretically supportable
1081         * but involves complex error handling, so it's being left until
1082         * later */
1083        if (root->number_of_cgroups > 1)
1084                return -EBUSY;
1085
1086        /* Process each subsystem */
1087        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1088                struct cgroup_subsys *ss = subsys[i];
1089                unsigned long bit = 1UL << i;
1090                if (bit & added_mask) {
1091                        /* We're binding this subsystem to this hierarchy */
1092                        BUG_ON(ss == NULL);
1093                        BUG_ON(cgrp->subsys[i]);
1094                        BUG_ON(!dummytop->subsys[i]);
1095                        BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
1096                        cgrp->subsys[i] = dummytop->subsys[i];
1097                        cgrp->subsys[i]->cgroup = cgrp;
1098                        list_move(&ss->sibling, &root->subsys_list);
1099                        ss->root = root;
1100                        if (ss->bind)
1101                                ss->bind(cgrp);
1102                        /* refcount was already taken, and we're keeping it */
1103                } else if (bit & removed_mask) {
1104                        /* We're removing this subsystem */
1105                        BUG_ON(ss == NULL);
1106                        BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
1107                        BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
1108                        if (ss->bind)
1109                                ss->bind(dummytop);
1110                        dummytop->subsys[i]->cgroup = dummytop;
1111                        cgrp->subsys[i] = NULL;
1112                        subsys[i]->root = &rootnode;
1113                        list_move(&ss->sibling, &rootnode.subsys_list);
1114                        /* subsystem is now free - drop reference on module */
1115                        module_put(ss->module);
1116                } else if (bit & final_subsys_mask) {
1117                        /* Subsystem state should already exist */
1118                        BUG_ON(ss == NULL);
1119                        BUG_ON(!cgrp->subsys[i]);
1120                        /*
1121                         * a refcount was taken, but we already had one, so
1122                         * drop the extra reference.
1123                         */
1124                        module_put(ss->module);
1125#ifdef CONFIG_MODULE_UNLOAD
1126                        BUG_ON(ss->module && !module_refcount(ss->module));
1127#endif
1128                } else {
1129                        /* Subsystem state shouldn't exist */
1130                        BUG_ON(cgrp->subsys[i]);
1131                }
1132        }
1133        root->subsys_mask = root->actual_subsys_mask = final_subsys_mask;
1134        synchronize_rcu();
1135
1136        return 0;
1137}
1138
1139static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
1140{
1141        struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
1142        struct cgroup_subsys *ss;
1143
1144        mutex_lock(&cgroup_root_mutex);
1145        for_each_subsys(root, ss)
1146                seq_printf(seq, ",%s", ss->name);
1147        if (test_bit(ROOT_NOPREFIX, &root->flags))
1148                seq_puts(seq, ",noprefix");
1149        if (test_bit(ROOT_XATTR, &root->flags))
1150                seq_puts(seq, ",xattr");
1151        if (strlen(root->release_agent_path))
1152                seq_printf(seq, ",release_agent=%s", root->release_agent_path);
1153        if (clone_children(&root->top_cgroup))
1154                seq_puts(seq, ",clone_children");
1155        if (strlen(root->name))
1156                seq_printf(seq, ",name=%s", root->name);
1157        mutex_unlock(&cgroup_root_mutex);
1158        return 0;
1159}
1160
1161struct cgroup_sb_opts {
1162        unsigned long subsys_mask;
1163        unsigned long flags;
1164        char *release_agent;
1165        bool clone_children;
1166        char *name;
1167        /* User explicitly requested empty subsystem */
1168        bool none;
1169
1170        struct cgroupfs_root *new_root;
1171
1172};
1173
1174/*
1175 * Convert a hierarchy specifier into a bitmask of subsystems and flags. Call
1176 * with cgroup_mutex held to protect the subsys[] array. This function takes
1177 * refcounts on subsystems to be used, unless it returns error, in which case
1178 * no refcounts are taken.
1179 */
1180static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1181{
1182        char *token, *o = data;
1183        bool all_ss = false, one_ss = false;
1184        unsigned long mask = (unsigned long)-1;
1185        int i;
1186        bool module_pin_failed = false;
1187
1188        BUG_ON(!mutex_is_locked(&cgroup_mutex));
1189
1190#ifdef CONFIG_CPUSETS
1191        mask = ~(1UL << cpuset_subsys_id);
1192#endif
1193
1194        memset(opts, 0, sizeof(*opts));
1195
1196        while ((token = strsep(&o, ",")) != NULL) {
1197                if (!*token)
1198                        return -EINVAL;
1199                if (!strcmp(token, "none")) {
1200                        /* Explicitly have no subsystems */
1201                        opts->none = true;
1202                        continue;
1203                }
1204                if (!strcmp(token, "all")) {
1205                        /* Mutually exclusive option 'all' + subsystem name */
1206                        if (one_ss)
1207                                return -EINVAL;
1208                        all_ss = true;
1209                        continue;
1210                }
1211                if (!strcmp(token, "noprefix")) {
1212                        set_bit(ROOT_NOPREFIX, &opts->flags);
1213                        continue;
1214                }
1215                if (!strcmp(token, "clone_children")) {
1216                        opts->clone_children = true;
1217                        continue;
1218                }
1219                if (!strcmp(token, "xattr")) {
1220                        set_bit(ROOT_XATTR, &opts->flags);
1221                        continue;
1222                }
1223                if (!strncmp(token, "release_agent=", 14)) {
1224                        /* Specifying two release agents is forbidden */
1225                        if (opts->release_agent)
1226                                return -EINVAL;
1227                        opts->release_agent =
1228                                kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1229                        if (!opts->release_agent)
1230                                return -ENOMEM;
1231                        continue;
1232                }
1233                if (!strncmp(token, "name=", 5)) {
1234                        const char *name = token + 5;
1235                        /* Can't specify an empty name */
1236                        if (!strlen(name))
1237                                return -EINVAL;
1238                        /* Must match [\w.-]+ */
1239                        for (i = 0; i < strlen(name); i++) {
1240                                char c = name[i];
1241                                if (isalnum(c))
1242                                        continue;
1243                                if ((c == '.') || (c == '-') || (c == '_'))
1244                                        continue;
1245                                return -EINVAL;
1246                        }
1247                        /* Specifying two names is forbidden */
1248                        if (opts->name)
1249                                return -EINVAL;
1250                        opts->name = kstrndup(name,
1251                                              MAX_CGROUP_ROOT_NAMELEN - 1,
1252                                              GFP_KERNEL);
1253                        if (!opts->name)
1254                                return -ENOMEM;
1255
1256                        continue;
1257                }
1258
1259                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1260                        struct cgroup_subsys *ss = subsys[i];
1261                        if (ss == NULL)
1262                                continue;
1263                        if (strcmp(token, ss->name))
1264                                continue;
1265                        if (ss->disabled)
1266                                continue;
1267
1268                        /* Mutually exclusive option 'all' + subsystem name */
1269                        if (all_ss)
1270                                return -EINVAL;
1271                        set_bit(i, &opts->subsys_mask);
1272                        one_ss = true;
1273
1274                        break;
1275                }
1276                if (i == CGROUP_SUBSYS_COUNT)
1277                        return -ENOENT;
1278        }
1279
1280        /*
1281         * If the 'all' option was specified select all the subsystems,
1282         * otherwise if 'none', 'name=' and a subsystem name options
1283         * were not specified, let's default to 'all'
1284         */
1285        if (all_ss || (!one_ss && !opts->none && !opts->name)) {
1286                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1287                        struct cgroup_subsys *ss = subsys[i];
1288                        if (ss == NULL)
1289                                continue;
1290                        if (ss->disabled)
1291                                continue;
1292                        set_bit(i, &opts->subsys_mask);
1293                }
1294        }
1295
1296        /* Consistency checks */
1297
1298        /*
1299         * Option noprefix was introduced just for backward compatibility
1300         * with the old cpuset, so we allow noprefix only if mounting just
1301         * the cpuset subsystem.
1302         */
1303        if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
1304            (opts->subsys_mask & mask))
1305                return -EINVAL;
1306
1307
1308        /* Can't specify "none" and some subsystems */
1309        if (opts->subsys_mask && opts->none)
1310                return -EINVAL;
1311
1312        /*
1313         * We either have to specify by name or by subsystems. (So all
1314         * empty hierarchies must have a name).
1315         */
1316        if (!opts->subsys_mask && !opts->name)
1317                return -EINVAL;
1318
1319        /*
1320         * Grab references on all the modules we'll need, so the subsystems
1321         * don't dance around before rebind_subsystems attaches them. This may
1322         * take duplicate reference counts on a subsystem that's already used,
1323         * but rebind_subsystems handles this case.
1324         */
1325        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1326                unsigned long bit = 1UL << i;
1327
1328                if (!(bit & opts->subsys_mask))
1329                        continue;
1330                if (!try_module_get(subsys[i]->module)) {
1331                        module_pin_failed = true;
1332                        break;
1333                }
1334        }
1335        if (module_pin_failed) {
1336                /*
1337                 * oops, one of the modules was going away. this means that we
1338                 * raced with a module_delete call, and to the user this is
1339                 * essentially a "subsystem doesn't exist" case.
1340                 */
1341                for (i--; i >= 0; i--) {
1342                        /* drop refcounts only on the ones we took */
1343                        unsigned long bit = 1UL << i;
1344
1345                        if (!(bit & opts->subsys_mask))
1346                                continue;
1347                        module_put(subsys[i]->module);
1348                }
1349                return -ENOENT;
1350        }
1351
1352        return 0;
1353}
1354
1355static void drop_parsed_module_refcounts(unsigned long subsys_mask)
1356{
1357        int i;
1358        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
1359                unsigned long bit = 1UL << i;
1360
1361                if (!(bit & subsys_mask))
1362                        continue;
1363                module_put(subsys[i]->module);
1364        }
1365}
1366
1367static int cgroup_remount(struct super_block *sb, int *flags, char *data)
1368{
1369        int ret = 0;
1370        struct cgroupfs_root *root = sb->s_fs_info;
1371        struct cgroup *cgrp = &root->top_cgroup;
1372        struct cgroup_sb_opts opts;
1373        unsigned long added_mask, removed_mask;
1374
1375        mutex_lock(&cgrp->dentry->d_inode->i_mutex);
1376        mutex_lock(&cgroup_mutex);
1377        mutex_lock(&cgroup_root_mutex);
1378
1379        /* See what subsystems are wanted */
1380        ret = parse_cgroupfs_options(data, &opts);
1381        if (ret)
1382                goto out_unlock;
1383
1384        /* See feature-removal-schedule.txt */
1385        if (opts.subsys_mask != root->actual_subsys_mask || opts.release_agent)
1386                pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
1387                           task_tgid_nr(current), current->comm);
1388
1389        added_mask = opts.subsys_mask & ~root->subsys_mask;
1390        removed_mask = root->subsys_mask & ~opts.subsys_mask;
1391
1392        /* Don't allow flags or name to change at remount */
1393        if (opts.flags != root->flags ||
1394            (opts.name && strcmp(opts.name, root->name))) {
1395                ret = -EINVAL;
1396                drop_parsed_module_refcounts(opts.subsys_mask);
1397                goto out_unlock;
1398        }
1399
1400        ret = rebind_subsystems(root, opts.subsys_mask);
1401        if (ret) {
1402                drop_parsed_module_refcounts(opts.subsys_mask);
1403                goto out_unlock;
1404        }
1405
1406        /* clear out any existing files and repopulate subsystem files */
1407        cgroup_clear_directory(cgrp->dentry, false, removed_mask);
1408        /* re-populate subsystem files */
1409        cgroup_populate_dir(cgrp, false, added_mask);
1410
1411        if (opts.release_agent)
1412                strcpy(root->release_agent_path, opts.release_agent);
1413 out_unlock:
1414        kfree(opts.release_agent);
1415        kfree(opts.name);
1416        mutex_unlock(&cgroup_root_mutex);
1417        mutex_unlock(&cgroup_mutex);
1418        mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
1419        return ret;
1420}
1421
1422static const struct super_operations cgroup_ops = {
1423        .statfs = simple_statfs,
1424        .drop_inode = generic_delete_inode,
1425        .show_options = cgroup_show_options,
1426        .remount_fs = cgroup_remount,
1427};
1428
1429static void init_cgroup_housekeeping(struct cgroup *cgrp)
1430{
1431        INIT_LIST_HEAD(&cgrp->sibling);
1432        INIT_LIST_HEAD(&cgrp->children);
1433        INIT_LIST_HEAD(&cgrp->files);
1434        INIT_LIST_HEAD(&cgrp->css_sets);
1435        INIT_LIST_HEAD(&cgrp->release_list);
1436        INIT_LIST_HEAD(&cgrp->pidlists);
1437        mutex_init(&cgrp->pidlist_mutex);
1438        INIT_LIST_HEAD(&cgrp->event_list);
1439        spin_lock_init(&cgrp->event_list_lock);
1440        simple_xattrs_init(&cgrp->xattrs);
1441}
1442
1443static void init_cgroup_root(struct cgroupfs_root *root)
1444{
1445        struct cgroup *cgrp = &root->top_cgroup;
1446
1447        INIT_LIST_HEAD(&root->subsys_list);
1448        INIT_LIST_HEAD(&root->root_list);
1449        INIT_LIST_HEAD(&root->allcg_list);
1450        root->number_of_cgroups = 1;
1451        cgrp->root = root;
1452        cgrp->top_cgroup = cgrp;
1453        list_add_tail(&cgrp->allcg_node, &root->allcg_list);
1454        init_cgroup_housekeeping(cgrp);
1455}
1456
1457static bool init_root_id(struct cgroupfs_root *root)
1458{
1459        int ret = 0;
1460
1461        do {
1462                if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))
1463                        return false;
1464                spin_lock(&hierarchy_id_lock);
1465                /* Try to allocate the next unused ID */
1466                ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
1467                                        &root->hierarchy_id);
1468                if (ret == -ENOSPC)
1469                        /* Try again starting from 0 */
1470                        ret = ida_get_new(&hierarchy_ida, &root->hierarchy_id);
1471                if (!ret) {
1472                        next_hierarchy_id = root->hierarchy_id + 1;
1473                } else if (ret != -EAGAIN) {
1474                        /* Can only get here if the 31-bit IDR is full ... */
1475                        BUG_ON(ret);
1476                }
1477                spin_unlock(&hierarchy_id_lock);
1478        } while (ret);
1479        return true;
1480}
1481
1482static int cgroup_test_super(struct super_block *sb, void *data)
1483{
1484        struct cgroup_sb_opts *opts = data;
1485        struct cgroupfs_root *root = sb->s_fs_info;
1486
1487        /* If we asked for a name then it must match */
1488        if (opts->name && strcmp(opts->name, root->name))
1489                return 0;
1490
1491        /*
1492         * If we asked for subsystems (or explicitly for no
1493         * subsystems) then they must match
1494         */
1495        if ((opts->subsys_mask || opts->none)
1496            && (opts->subsys_mask != root->subsys_mask))
1497                return 0;
1498
1499        return 1;
1500}
1501
1502static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
1503{
1504        struct cgroupfs_root *root;
1505
1506        if (!opts->subsys_mask && !opts->none)
1507                return NULL;
1508
1509        root = kzalloc(sizeof(*root), GFP_KERNEL);
1510        if (!root)
1511                return ERR_PTR(-ENOMEM);
1512
1513        if (!init_root_id(root)) {
1514                kfree(root);
1515                return ERR_PTR(-ENOMEM);
1516        }
1517        init_cgroup_root(root);
1518
1519        root->subsys_mask = opts->subsys_mask;
1520        root->flags = opts->flags;
1521        if (opts->release_agent)
1522                strcpy(root->release_agent_path, opts->release_agent);
1523        if (opts->name)
1524                strcpy(root->name, opts->name);
1525        if (opts->clone_children)
1526                set_bit(CGRP_CLONE_CHILDREN, &root->top_cgroup.flags);
1527        return root;
1528}
1529
1530static void cgroup_drop_root(struct cgroupfs_root *root)
1531{
1532        if (!root)
1533                return;
1534
1535        BUG_ON(!root->hierarchy_id);
1536        spin_lock(&hierarchy_id_lock);
1537        ida_remove(&hierarchy_ida, root->hierarchy_id);
1538        spin_unlock(&hierarchy_id_lock);
1539        kfree(root);
1540}
1541
1542static int cgroup_set_super(struct super_block *sb, void *data)
1543{
1544        int ret;
1545        struct cgroup_sb_opts *opts = data;
1546
1547        /* If we don't have a new root, we can't set up a new sb */
1548        if (!opts->new_root)
1549                return -EINVAL;
1550
1551        BUG_ON(!opts->subsys_mask && !opts->none);
1552
1553        ret = set_anon_super(sb, NULL);
1554        if (ret)
1555                return ret;
1556
1557        sb->s_fs_info = opts->new_root;
1558        opts->new_root->sb = sb;
1559
1560        sb->s_blocksize = PAGE_CACHE_SIZE;
1561        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
1562        sb->s_magic = CGROUP_SUPER_MAGIC;
1563        sb->s_op = &cgroup_ops;
1564
1565        return 0;
1566}
1567
1568static int cgroup_get_rootdir(struct super_block *sb)
1569{
1570        static const struct dentry_operations cgroup_dops = {
1571                .d_iput = cgroup_diput,
1572                .d_delete = cgroup_delete,
1573        };
1574
1575        struct inode *inode =
1576                cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
1577
1578        if (!inode)
1579                return -ENOMEM;
1580
1581        inode->i_fop = &simple_dir_operations;
1582        inode->i_op = &cgroup_dir_inode_operations;
1583        /* directories start off with i_nlink == 2 (for "." entry) */
1584        inc_nlink(inode);
1585        sb->s_root = d_make_root(inode);
1586        if (!sb->s_root)
1587                return -ENOMEM;
1588        /* for everything else we want ->d_op set */
1589        sb->s_d_op = &cgroup_dops;
1590        return 0;
1591}
1592
1593static struct dentry *cgroup_mount(struct file_system_type *fs_type,
1594                         int flags, const char *unused_dev_name,
1595                         void *data)
1596{
1597        struct cgroup_sb_opts opts;
1598        struct cgroupfs_root *root;
1599        int ret = 0;
1600        struct super_block *sb;
1601        struct cgroupfs_root *new_root;
1602        struct inode *inode;
1603
1604        /* First find the desired set of subsystems */
1605        mutex_lock(&cgroup_mutex);
1606        ret = parse_cgroupfs_options(data, &opts);
1607        mutex_unlock(&cgroup_mutex);
1608        if (ret)
1609                goto out_err;
1610
1611        /*
1612         * Allocate a new cgroup root. We may not need it if we're
1613         * reusing an existing hierarchy.
1614         */
1615        new_root = cgroup_root_from_opts(&opts);
1616        if (IS_ERR(new_root)) {
1617                ret = PTR_ERR(new_root);
1618                goto drop_modules;
1619        }
1620        opts.new_root = new_root;
1621
1622        /* Locate an existing or new sb for this hierarchy */
1623        sb = sget(fs_type, cgroup_test_super, cgroup_set_super, 0, &opts);
1624        if (IS_ERR(sb)) {
1625                ret = PTR_ERR(sb);
1626                cgroup_drop_root(opts.new_root);
1627                goto drop_modules;
1628        }
1629
1630        root = sb->s_fs_info;
1631        BUG_ON(!root);
1632        if (root == opts.new_root) {
1633                /* We used the new root structure, so this is a new hierarchy */
1634                struct list_head tmp_cg_links;
1635                struct cgroup *root_cgrp = &root->top_cgroup;
1636                struct cgroupfs_root *existing_root;
1637                const struct cred *cred;
1638                int i;
1639
1640                BUG_ON(sb->s_root != NULL);
1641
1642                ret = cgroup_get_rootdir(sb);
1643                if (ret)
1644                        goto drop_new_super;
1645                inode = sb->s_root->d_inode;
1646
1647                mutex_lock(&inode->i_mutex);
1648                mutex_lock(&cgroup_mutex);
1649                mutex_lock(&cgroup_root_mutex);
1650
1651                /* Check for name clashes with existing mounts */
1652                ret = -EBUSY;
1653                if (strlen(root->name))
1654                        for_each_active_root(existing_root)
1655                                if (!strcmp(existing_root->name, root->name))
1656                                        goto unlock_drop;
1657
1658                /*
1659                 * We're accessing css_set_count without locking
1660                 * css_set_lock here, but that's OK - it can only be
1661                 * increased by someone holding cgroup_lock, and
1662                 * that's us. The worst that can happen is that we
1663                 * have some link structures left over
1664                 */
1665                ret = allocate_cg_links(css_set_count, &tmp_cg_links);
1666                if (ret)
1667                        goto unlock_drop;
1668
1669                ret = rebind_subsystems(root, root->subsys_mask);
1670                if (ret == -EBUSY) {
1671                        free_cg_links(&tmp_cg_links);
1672                        goto unlock_drop;
1673                }
1674                /*
1675                 * There must be no failure case after here, since rebinding
1676                 * takes care of subsystems' refcounts, which are explicitly
1677                 * dropped in the failure exit path.
1678                 */
1679
1680                /* EBUSY should be the only error here */
1681                BUG_ON(ret);
1682
1683                list_add(&root->root_list, &roots);
1684                root_count++;
1685
1686                sb->s_root->d_fsdata = root_cgrp;
1687                root->top_cgroup.dentry = sb->s_root;
1688
1689                /* Link the top cgroup in this hierarchy into all
1690                 * the css_set objects */
1691                write_lock(&css_set_lock);
1692                for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
1693                        struct hlist_head *hhead = &css_set_table[i];
1694                        struct hlist_node *node;
1695                        struct css_set *cg;
1696
1697                        hlist_for_each_entry(cg, node, hhead, hlist)
1698                                link_css_set(&tmp_cg_links, cg, root_cgrp);
1699                }
1700                write_unlock(&css_set_lock);
1701
1702                free_cg_links(&tmp_cg_links);
1703
1704                BUG_ON(!list_empty(&root_cgrp->sibling));
1705                BUG_ON(!list_empty(&root_cgrp->children));
1706                BUG_ON(root->number_of_cgroups != 1);
1707
1708                cred = override_creds(&init_cred);
1709                cgroup_populate_dir(root_cgrp, true, root->subsys_mask);
1710                revert_creds(cred);
1711                mutex_unlock(&cgroup_root_mutex);
1712                mutex_unlock(&cgroup_mutex);
1713                mutex_unlock(&inode->i_mutex);
1714        } else {
1715                /*
1716                 * We re-used an existing hierarchy - the new root (if
1717                 * any) is not needed
1718                 */
1719                cgroup_drop_root(opts.new_root);
1720                /* no subsys rebinding, so refcounts don't change */
1721                drop_parsed_module_refcounts(opts.subsys_mask);
1722        }
1723
1724        kfree(opts.release_agent);
1725        kfree(opts.name);
1726        return dget(sb->s_root);
1727
1728 unlock_drop:
1729        mutex_unlock(&cgroup_root_mutex);
1730        mutex_unlock(&cgroup_mutex);
1731        mutex_unlock(&inode->i_mutex);
1732 drop_new_super:
1733        deactivate_locked_super(sb);
1734 drop_modules:
1735        drop_parsed_module_refcounts(opts.subsys_mask);
1736 out_err:
1737        kfree(opts.release_agent);
1738        kfree(opts.name);
1739        return ERR_PTR(ret);
1740}
1741
1742static void cgroup_kill_sb(struct super_block *sb) {
1743        struct cgroupfs_root *root = sb->s_fs_info;
1744        struct cgroup *cgrp = &root->top_cgroup;
1745        int ret;
1746        struct cg_cgroup_link *link;
1747        struct cg_cgroup_link *saved_link;
1748
1749        BUG_ON(!root);
1750
1751        BUG_ON(root->number_of_cgroups != 1);
1752        BUG_ON(!list_empty(&cgrp->children));
1753        BUG_ON(!list_empty(&cgrp->sibling));
1754
1755        mutex_lock(&cgroup_mutex);
1756        mutex_lock(&cgroup_root_mutex);
1757
1758        /* Rebind all subsystems back to the default hierarchy */
1759        ret = rebind_subsystems(root, 0);
1760        /* Shouldn't be able to fail ... */
1761        BUG_ON(ret);
1762
1763        /*
1764         * Release all the links from css_sets to this hierarchy's
1765         * root cgroup
1766         */
1767        write_lock(&css_set_lock);
1768
1769        list_for_each_entry_safe(link, saved_link, &cgrp->css_sets,
1770                                 cgrp_link_list) {
1771                list_del(&link->cg_link_list);
1772                list_del(&link->cgrp_link_list);
1773                kfree(link);
1774        }
1775        write_unlock(&css_set_lock);
1776
1777        if (!list_empty(&root->root_list)) {
1778                list_del(&root->root_list);
1779                root_count--;
1780        }
1781
1782        mutex_unlock(&cgroup_root_mutex);
1783        mutex_unlock(&cgroup_mutex);
1784
1785        simple_xattrs_free(&cgrp->xattrs);
1786
1787        kill_litter_super(sb);
1788        cgroup_drop_root(root);
1789}
1790
1791static struct file_system_type cgroup_fs_type = {
1792        .name = "cgroup",
1793        .mount = cgroup_mount,
1794        .kill_sb = cgroup_kill_sb,
1795};
1796
1797static struct kobject *cgroup_kobj;
1798
1799/**
1800 * cgroup_path - generate the path of a cgroup
1801 * @cgrp: the cgroup in question
1802 * @buf: the buffer to write the path into
1803 * @buflen: the length of the buffer
1804 *
1805 * Called with cgroup_mutex held or else with an RCU-protected cgroup
1806 * reference.  Writes path of cgroup into buf.  Returns 0 on success,
1807 * -errno on error.
1808 */
1809int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
1810{
1811        char *start;
1812        struct dentry *dentry = rcu_dereference_check(cgrp->dentry,
1813                                                      cgroup_lock_is_held());
1814
1815        if (!dentry || cgrp == dummytop) {
1816                /*
1817                 * Inactive subsystems have no dentry for their root
1818                 * cgroup
1819                 */
1820                strcpy(buf, "/");
1821                return 0;
1822        }
1823
1824        start = buf + buflen;
1825
1826        *--start = '\0';
1827        for (;;) {
1828                int len = dentry->d_name.len;
1829
1830                if ((start -= len) < buf)
1831                        return -ENAMETOOLONG;
1832                memcpy(start, dentry->d_name.name, len);
1833                cgrp = cgrp->parent;
1834                if (!cgrp)
1835                        break;
1836
1837                dentry = rcu_dereference_check(cgrp->dentry,
1838                                               cgroup_lock_is_held());
1839                if (!cgrp->parent)
1840                        continue;
1841                if (--start < buf)
1842                        return -ENAMETOOLONG;
1843                *start = '/';
1844        }
1845        memmove(buf, start, buf + buflen - start);
1846        return 0;
1847}
1848EXPORT_SYMBOL_GPL(cgroup_path);
1849
1850/*
1851 * Control Group taskset
1852 */
1853struct task_and_cgroup {
1854        struct task_struct      *task;
1855        struct cgroup           *cgrp;
1856        struct css_set          *cg;
1857};
1858
1859struct cgroup_taskset {
1860        struct task_and_cgroup  single;
1861        struct flex_array       *tc_array;
1862        int                     tc_array_len;
1863        int                     idx;
1864        struct cgroup           *cur_cgrp;
1865};
1866
1867/**
1868 * cgroup_taskset_first - reset taskset and return the first task
1869 * @tset: taskset of interest
1870 *
1871 * @tset iteration is initialized and the first task is returned.
1872 */
1873struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset)
1874{
1875        if (tset->tc_array) {
1876                tset->idx = 0;
1877                return cgroup_taskset_next(tset);
1878        } else {
1879                tset->cur_cgrp = tset->single.cgrp;
1880                return tset->single.task;
1881        }
1882}
1883EXPORT_SYMBOL_GPL(cgroup_taskset_first);
1884
1885/**
1886 * cgroup_taskset_next - iterate to the next task in taskset
1887 * @tset: taskset of interest
1888 *
1889 * Return the next task in @tset.  Iteration must have been initialized
1890 * with cgroup_taskset_first().
1891 */
1892struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
1893{
1894        struct task_and_cgroup *tc;
1895
1896        if (!tset->tc_array || tset->idx >= tset->tc_array_len)
1897                return NULL;
1898
1899        tc = flex_array_get(tset->tc_array, tset->idx++);
1900        tset->cur_cgrp = tc->cgrp;
1901        return tc->task;
1902}
1903EXPORT_SYMBOL_GPL(cgroup_taskset_next);
1904
1905/**
1906 * cgroup_taskset_cur_cgroup - return the matching cgroup for the current task
1907 * @tset: taskset of interest
1908 *
1909 * Return the cgroup for the current (last returned) task of @tset.  This
1910 * function must be preceded by either cgroup_taskset_first() or
1911 * cgroup_taskset_next().
1912 */
1913struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset)
1914{
1915        return tset->cur_cgrp;
1916}
1917EXPORT_SYMBOL_GPL(cgroup_taskset_cur_cgroup);
1918
1919/**
1920 * cgroup_taskset_size - return the number of tasks in taskset
1921 * @tset: taskset of interest
1922 */
1923int cgroup_taskset_size(struct cgroup_taskset *tset)
1924{
1925        return tset->tc_array ? tset->tc_array_len : 1;
1926}
1927EXPORT_SYMBOL_GPL(cgroup_taskset_size);
1928
1929
1930/*
1931 * cgroup_task_migrate - move a task from one cgroup to another.
1932 *
1933 * 'guarantee' is set if the caller promises that a new css_set for the task
1934 * will already exist. If not set, this function might sleep, and can fail with
1935 * -ENOMEM. Must be called with cgroup_mutex and threadgroup locked.
1936 */
1937static void cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
1938                                struct task_struct *tsk, struct css_set *newcg)
1939{
1940        struct css_set *oldcg;
1941
1942        /*
1943         * We are synchronized through threadgroup_lock() against PF_EXITING
1944         * setting such that we can't race against cgroup_exit() changing the
1945         * css_set to init_css_set and dropping the old one.
1946         */
1947        WARN_ON_ONCE(tsk->flags & PF_EXITING);
1948        oldcg = tsk->cgroups;
1949
1950        task_lock(tsk);
1951        rcu_assign_pointer(tsk->cgroups, newcg);
1952        task_unlock(tsk);
1953
1954        /* Update the css_set linked lists if we're using them */
1955        write_lock(&css_set_lock);
1956        if (!list_empty(&tsk->cg_list))
1957                list_move(&tsk->cg_list, &newcg->tasks);
1958        write_unlock(&css_set_lock);
1959
1960        /*
1961         * We just gained a reference on oldcg by taking it from the task. As
1962         * trading it for newcg is protected by cgroup_mutex, we're safe to drop
1963         * it here; it will be freed under RCU.
1964         */
1965        set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
1966        put_css_set(oldcg);
1967}
1968
1969/**
1970 * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
1971 * @cgrp: the cgroup the task is attaching to
1972 * @tsk: the task to be attached
1973 *
1974 * Call with cgroup_mutex and threadgroup locked. May take task_lock of
1975 * @tsk during call.
1976 */
1977int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
1978{
1979        int retval = 0;
1980        struct cgroup_subsys *ss, *failed_ss = NULL;
1981        struct cgroup *oldcgrp;
1982        struct cgroupfs_root *root = cgrp->root;
1983        struct cgroup_taskset tset = { };
1984        struct css_set *newcg;
1985
1986        /* @tsk either already exited or can't exit until the end */
1987        if (tsk->flags & PF_EXITING)
1988                return -ESRCH;
1989
1990        /* Nothing to do if the task is already in that cgroup */
1991        oldcgrp = task_cgroup_from_root(tsk, root);
1992        if (cgrp == oldcgrp)
1993                return 0;
1994
1995        tset.single.task = tsk;
1996        tset.single.cgrp = oldcgrp;
1997
1998        for_each_subsys(root, ss) {
1999                if (ss->can_attach) {
2000                        retval = ss->can_attach(cgrp, &tset);
2001                        if (retval) {
2002                                /*
2003                                 * Remember on which subsystem the can_attach()
2004                                 * failed, so that we only call cancel_attach()
2005                                 * against the subsystems whose can_attach()
2006                                 * succeeded. (See below)
2007                                 */
2008                                failed_ss = ss;
2009                                goto out;
2010                        }
2011                }
2012        }
2013
2014        newcg = find_css_set(tsk->cgroups, cgrp);
2015        if (!newcg) {
2016                retval = -ENOMEM;
2017                goto out;
2018        }
2019
2020        cgroup_task_migrate(cgrp, oldcgrp, tsk, newcg);
2021
2022        for_each_subsys(root, ss) {
2023                if (ss->attach)
2024                        ss->attach(cgrp, &tset);
2025        }
2026
2027        synchronize_rcu();
2028
2029        /*
2030         * wake up rmdir() waiter. the rmdir should fail since the cgroup
2031         * is no longer empty.
2032         */
2033        cgroup_wakeup_rmdir_waiter(cgrp);
2034out:
2035        if (retval) {
2036                for_each_subsys(root, ss) {
2037                        if (ss == failed_ss)
2038                                /*
2039                                 * This subsystem was the one that failed the
2040                                 * can_attach() check earlier, so we don't need
2041                                 * to call cancel_attach() against it or any
2042                                 * remaining subsystems.
2043                                 */
2044                                break;
2045                        if (ss->cancel_attach)
2046                                ss->cancel_attach(cgrp, &tset);
2047                }
2048        }
2049        return retval;
2050}
2051
2052/**
2053 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2054 * @from: attach to all cgroups of a given task
2055 * @tsk: the task to be attached
2056 */
2057int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2058{
2059        struct cgroupfs_root *root;
2060        int retval = 0;
2061
2062        cgroup_lock();
2063        for_each_active_root(root) {
2064                struct cgroup *from_cg = task_cgroup_from_root(from, root);
2065
2066                retval = cgroup_attach_task(from_cg, tsk);
2067                if (retval)
2068                        break;
2069        }
2070        cgroup_unlock();
2071
2072        return retval;
2073}
2074EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2075
2076/**
2077 * cgroup_attach_proc - attach all threads in a threadgroup to a cgroup
2078 * @cgrp: the cgroup to attach to
2079 * @leader: the threadgroup leader task_struct of the group to be attached
2080 *
2081 * Call holding cgroup_mutex and the group_rwsem of the leader. Will take
2082 * task_lock of each thread in leader's threadgroup individually in turn.
2083 */
2084static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
2085{
2086        int retval, i, group_size;
2087        struct cgroup_subsys *ss, *failed_ss = NULL;
2088        /* guaranteed to be initialized later, but the compiler needs this */
2089        struct cgroupfs_root *root = cgrp->root;
2090        /* threadgroup list cursor and array */
2091        struct task_struct *tsk;
2092        struct task_and_cgroup *tc;
2093        struct flex_array *group;
2094        struct cgroup_taskset tset = { };
2095
2096        /*
2097         * step 0: in order to do expensive, possibly blocking operations for
2098         * every thread, we cannot iterate the thread group list, since it needs
2099         * rcu or tasklist locked. instead, build an array of all threads in the
2100         * group - group_rwsem prevents new threads from appearing, and if
2101         * threads exit, this will just be an over-estimate.
2102         */
2103        group_size = get_nr_threads(leader);
2104        /* flex_array supports very large thread-groups better than kmalloc. */
2105        group = flex_array_alloc(sizeof(*tc), group_size, GFP_KERNEL);
2106        if (!group)
2107                return -ENOMEM;
2108        /* pre-allocate to guarantee space while iterating in rcu read-side. */
2109        retval = flex_array_prealloc(group, 0, group_size - 1, GFP_KERNEL);
2110        if (retval)
2111                goto out_free_group_list;
2112
2113        tsk = leader;
2114        i = 0;
2115        /*
2116         * Prevent freeing of tasks while we take a snapshot. Tasks that are
2117         * already PF_EXITING could be freed from underneath us unless we
2118         * take an rcu_read_lock.
2119         */
2120        rcu_read_lock();
2121        do {
2122                struct task_and_cgroup ent;
2123
2124                /* @tsk either already exited or can't exit until the end */
2125                if (tsk->flags & PF_EXITING)
2126                        continue;
2127
2128                /* as per above, nr_threads may decrease, but not increase. */
2129                BUG_ON(i >= group_size);
2130                ent.task = tsk;
2131                ent.cgrp = task_cgroup_from_root(tsk, root);
2132                /* nothing to do if this task is already in the cgroup */
2133                if (ent.cgrp == cgrp)
2134                        continue;
2135                /*
2136                 * saying GFP_ATOMIC has no effect here because we did prealloc
2137                 * earlier, but it's good form to communicate our expectations.
2138                 */
2139                retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
2140                BUG_ON(retval != 0);
2141                i++;
2142        } while_each_thread(leader, tsk);
2143        rcu_read_unlock();
2144        /* remember the number of threads in the array for later. */
2145        group_size = i;
2146        tset.tc_array = group;
2147        tset.tc_array_len = group_size;
2148
2149        /* methods shouldn't be called if no task is actually migrating */
2150        retval = 0;
2151        if (!group_size)
2152                goto out_free_group_list;
2153
2154        /*
2155         * step 1: check that we can legitimately attach to the cgroup.
2156         */
2157        for_each_subsys(root, ss) {
2158                if (ss->can_attach) {
2159                        retval = ss->can_attach(cgrp, &tset);
2160                        if (retval) {
2161                                failed_ss = ss;
2162                                goto out_cancel_attach;
2163                        }
2164                }
2165        }
2166
2167        /*
2168         * step 2: make sure css_sets exist for all threads to be migrated.
2169         * we use find_css_set, which allocates a new one if necessary.
2170         */
2171        for (i = 0; i < group_size; i++) {
2172                tc = flex_array_get(group, i);
2173                tc->cg = find_css_set(tc->task->cgroups, cgrp);
2174                if (!tc->cg) {
2175                        retval = -ENOMEM;
2176                        goto out_put_css_set_refs;
2177                }
2178        }
2179
2180        /*
2181         * step 3: now that we're guaranteed success wrt the css_sets,
2182         * proceed to move all tasks to the new cgroup.  There are no
2183         * failure cases after here, so this is the commit point.
2184         */
2185        for (i = 0; i < group_size; i++) {
2186                tc = flex_array_get(group, i);
2187                cgroup_task_migrate(cgrp, tc->cgrp, tc->task, tc->cg);
2188        }
2189        /* nothing is sensitive to fork() after this point. */
2190
2191        /*
2192         * step 4: do subsystem attach callbacks.
2193         */
2194        for_each_subsys(root, ss) {
2195                if (ss->attach)
2196                        ss->attach(cgrp, &tset);
2197        }
2198
2199        /*
2200         * step 5: success! and cleanup
2201         */
2202        synchronize_rcu();
2203        cgroup_wakeup_rmdir_waiter(cgrp);
2204        retval = 0;
2205out_put_css_set_refs:
2206        if (retval) {
2207                for (i = 0; i < group_size; i++) {
2208                        tc = flex_array_get(group, i);
2209                        if (!tc->cg)
2210                                break;
2211                        put_css_set(tc->cg);
2212                }
2213        }
2214out_cancel_attach:
2215        if (retval) {
2216                for_each_subsys(root, ss) {
2217                        if (ss == failed_ss)
2218                                break;
2219                        if (ss->cancel_attach)
2220                                ss->cancel_attach(cgrp, &tset);
2221                }
2222        }
2223out_free_group_list:
2224        flex_array_free(group);
2225        return retval;
2226}
2227
2228/*
2229 * Find the task_struct of the task to attach by vpid and pass it along to the
2230 * function to attach either it or all tasks in its threadgroup. Will lock
2231 * cgroup_mutex and threadgroup; may take task_lock of task.
2232 */
2233static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
2234{
2235        struct task_struct *tsk;
2236        const struct cred *cred = current_cred(), *tcred;
2237        int ret;
2238
2239        if (!cgroup_lock_live_group(cgrp))
2240                return -ENODEV;
2241
2242retry_find_task:
2243        rcu_read_lock();
2244        if (pid) {
2245                tsk = find_task_by_vpid(pid);
2246                if (!tsk) {
2247                        rcu_read_unlock();
2248                        ret= -ESRCH;
2249                        goto out_unlock_cgroup;
2250                }
2251                /*
2252                 * even if we're attaching all tasks in the thread group, we
2253                 * only need to check permissions on one of them.
2254                 */
2255                tcred = __task_cred(tsk);
2256                if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2257                    !uid_eq(cred->euid, tcred->uid) &&
2258                    !uid_eq(cred->euid, tcred->suid)) {
2259                        rcu_read_unlock();
2260                        ret = -EACCES;
2261                        goto out_unlock_cgroup;
2262                }
2263        } else
2264                tsk = current;
2265
2266        if (threadgroup)
2267                tsk = tsk->group_leader;
2268
2269        /*
2270         * Workqueue threads may acquire PF_THREAD_BOUND and become
2271         * trapped in a cpuset, or RT worker may be born in a cgroup
2272         * with no rt_runtime allocated.  Just say no.
2273         */
2274        if (tsk == kthreadd_task || (tsk->flags & PF_THREAD_BOUND)) {
2275                ret = -EINVAL;
2276                rcu_read_unlock();
2277                goto out_unlock_cgroup;
2278        }
2279
2280        get_task_struct(tsk);
2281        rcu_read_unlock();
2282
2283        threadgroup_lock(tsk);
2284        if (threadgroup) {
2285                if (!thread_group_leader(tsk)) {
2286                        /*
2287                         * a race with de_thread from another thread's exec()
2288                         * may strip us of our leadership, if this happens,
2289                         * there is no choice but to throw this task away and
2290                         * try again; this is
2291                         * "double-double-toil-and-trouble-check locking".
2292                         */
2293                        threadgroup_unlock(tsk);
2294                        put_task_struct(tsk);
2295                        goto retry_find_task;
2296                }
2297                ret = cgroup_attach_proc(cgrp, tsk);
2298        } else
2299                ret = cgroup_attach_task(cgrp, tsk);
2300        threadgroup_unlock(tsk);
2301
2302        put_task_struct(tsk);
2303out_unlock_cgroup:
2304        cgroup_unlock();
2305        return ret;
2306}
2307
2308static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
2309{
2310        return attach_task_by_pid(cgrp, pid, false);
2311}
2312
2313static int cgroup_procs_write(struct cgroup *cgrp, struct cftype *cft, u64 tgid)
2314{
2315        return attach_task_by_pid(cgrp, tgid, true);
2316}
2317
2318/**
2319 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
2320 * @cgrp: the cgroup to be checked for liveness
2321 *
2322 * On success, returns true; the lock should be later released with
2323 * cgroup_unlock(). On failure returns false with no lock held.
2324 */
2325bool cgroup_lock_live_group(struct cgroup *cgrp)
2326{
2327        mutex_lock(&cgroup_mutex);
2328        if (cgroup_is_removed(cgrp)) {
2329                mutex_unlock(&cgroup_mutex);
2330                return false;
2331        }
2332        return true;
2333}
2334EXPORT_SYMBOL_GPL(cgroup_lock_live_group);
2335
2336static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
2337                                      const char *buffer)
2338{
2339        BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
2340        if (strlen(buffer) >= PATH_MAX)
2341                return -EINVAL;
2342        if (!cgroup_lock_live_group(cgrp))
2343                return -ENODEV;
2344        mutex_lock(&cgroup_root_mutex);
2345        strcpy(cgrp->root->release_agent_path, buffer);
2346        mutex_unlock(&cgroup_root_mutex);
2347        cgroup_unlock();
2348        return 0;
2349}
2350
2351static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
2352                                     struct seq_file *seq)
2353{
2354        if (!cgroup_lock_live_group(cgrp))
2355                return -ENODEV;
2356        seq_puts(seq, cgrp->root->release_agent_path);
2357        seq_putc(seq, '\n');
2358        cgroup_unlock();
2359        return 0;
2360}
2361
2362/* A buffer size big enough for numbers or short strings */
2363#define CGROUP_LOCAL_BUFFER_SIZE 64
2364
2365static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
2366                                struct file *file,
2367                                const char __user *userbuf,
2368                                size_t nbytes, loff_t *unused_ppos)
2369{
2370        char buffer[CGROUP_LOCAL_BUFFER_SIZE];
2371        int retval = 0;
2372        char *end;
2373
2374        if (!nbytes)
2375                return -EINVAL;
2376        if (nbytes >= sizeof(buffer))
2377                return -E2BIG;
2378        if (copy_from_user(buffer, userbuf, nbytes))
2379                return -EFAULT;
2380
2381        buffer[nbytes] = 0;     /* nul-terminate */
2382        if (cft->write_u64) {
2383                u64 val = simple_strtoull(strstrip(buffer), &end, 0);
2384                if (*end)
2385                        return -EINVAL;
2386                retval = cft->write_u64(cgrp, cft, val);
2387        } else {
2388                s64 val = simple_strtoll(strstrip(buffer), &end, 0);
2389                if (*end)
2390                        return -EINVAL;
2391                retval = cft->write_s64(cgrp, cft, val);
2392        }
2393        if (!retval)
2394                retval = nbytes;
2395        return retval;
2396}
2397
2398static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
2399                                   struct file *file,
2400                                   const char __user *userbuf,
2401                                   size_t nbytes, loff_t *unused_ppos)
2402{
2403        char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
2404        int retval = 0;
2405        size_t max_bytes = cft->max_write_len;
2406        char *buffer = local_buffer;
2407
2408        if (!max_bytes)
2409                max_bytes = sizeof(local_buffer) - 1;
2410        if (nbytes >= max_bytes)
2411                return -E2BIG;
2412        /* Allocate a dynamic buffer if we need one */
2413        if (nbytes >= sizeof(local_buffer)) {
2414                buffer = kmalloc(nbytes + 1, GFP_KERNEL);
2415                if (buffer == NULL)
2416                        return -ENOMEM;
2417        }
2418        if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
2419                retval = -EFAULT;
2420                goto out;
2421        }
2422
2423        buffer[nbytes] = 0;     /* nul-terminate */
2424        retval = cft->write_string(cgrp, cft, strstrip(buffer));
2425        if (!retval)
2426                retval = nbytes;
2427out:
2428        if (buffer != local_buffer)
2429                kfree(buffer);
2430        return retval;
2431}
2432
2433static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
2434                                                size_t nbytes, loff_t *ppos)
2435{
2436        struct cftype *cft = __d_cft(file->f_dentry);
2437        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2438
2439        if (cgroup_is_removed(cgrp))
2440                return -ENODEV;
2441        if (cft->write)
2442                return cft->write(cgrp, cft, file, buf, nbytes, ppos);
2443        if (cft->write_u64 || cft->write_s64)
2444                return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
2445        if (cft->write_string)
2446                return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
2447        if (cft->trigger) {
2448                int ret = cft->trigger(cgrp, (unsigned int)cft->private);
2449                return ret ? ret : nbytes;
2450        }
2451        return -EINVAL;
2452}
2453
2454static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
2455                               struct file *file,
2456                               char __user *buf, size_t nbytes,
2457                               loff_t *ppos)
2458{
2459        char tmp[CGROUP_LOCAL_BUFFER_SIZE];
2460        u64 val = cft->read_u64(cgrp, cft);
2461        int len = sprintf(tmp, "%llu\n", (unsigned long long) val);
2462
2463        return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
2464}
2465
2466static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
2467                               struct file *file,
2468                               char __user *buf, size_t nbytes,
2469                               loff_t *ppos)
2470{
2471        char tmp[CGROUP_LOCAL_BUFFER_SIZE];
2472        s64 val = cft->read_s64(cgrp, cft);
2473        int len = sprintf(tmp, "%lld\n", (long long) val);
2474
2475        return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
2476}
2477
2478static ssize_t cgroup_file_read(struct file *file, char __user *buf,
2479                                   size_t nbytes, loff_t *ppos)
2480{
2481        struct cftype *cft = __d_cft(file->f_dentry);
2482        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2483
2484        if (cgroup_is_removed(cgrp))
2485                return -ENODEV;
2486
2487        if (cft->read)
2488                return cft->read(cgrp, cft, file, buf, nbytes, ppos);
2489        if (cft->read_u64)
2490                return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
2491        if (cft->read_s64)
2492                return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
2493        return -EINVAL;
2494}
2495
2496/*
2497 * seqfile ops/methods for returning structured data. Currently just
2498 * supports string->u64 maps, but can be extended in future.
2499 */
2500
2501struct cgroup_seqfile_state {
2502        struct cftype *cft;
2503        struct cgroup *cgroup;
2504};
2505
2506static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
2507{
2508        struct seq_file *sf = cb->state;
2509        return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
2510}
2511
2512static int cgroup_seqfile_show(struct seq_file *m, void *arg)
2513{
2514        struct cgroup_seqfile_state *state = m->private;
2515        struct cftype *cft = state->cft;
2516        if (cft->read_map) {
2517                struct cgroup_map_cb cb = {
2518                        .fill = cgroup_map_add,
2519                        .state = m,
2520                };
2521                return cft->read_map(state->cgroup, cft, &cb);
2522        }
2523        return cft->read_seq_string(state->cgroup, cft, m);
2524}
2525
2526static int cgroup_seqfile_release(struct inode *inode, struct file *file)
2527{
2528        struct seq_file *seq = file->private_data;
2529        kfree(seq->private);
2530        return single_release(inode, file);
2531}
2532
2533static const struct file_operations cgroup_seqfile_operations = {
2534        .read = seq_read,
2535        .write = cgroup_file_write,
2536        .llseek = seq_lseek,
2537        .release = cgroup_seqfile_release,
2538};
2539
2540static int cgroup_file_open(struct inode *inode, struct file *file)
2541{
2542        int err;
2543        struct cftype *cft;
2544
2545        err = generic_file_open(inode, file);
2546        if (err)
2547                return err;
2548        cft = __d_cft(file->f_dentry);
2549
2550        if (cft->read_map || cft->read_seq_string) {
2551                struct cgroup_seqfile_state *state =
2552                        kzalloc(sizeof(*state), GFP_USER);
2553                if (!state)
2554                        return -ENOMEM;
2555                state->cft = cft;
2556                state->cgroup = __d_cgrp(file->f_dentry->d_parent);
2557                file->f_op = &cgroup_seqfile_operations;
2558                err = single_open(file, cgroup_seqfile_show, state);
2559                if (err < 0)
2560                        kfree(state);
2561        } else if (cft->open)
2562                err = cft->open(inode, file);
2563        else
2564                err = 0;
2565
2566        return err;
2567}
2568
2569static int cgroup_file_release(struct inode *inode, struct file *file)
2570{
2571        struct cftype *cft = __d_cft(file->f_dentry);
2572        if (cft->release)
2573                return cft->release(inode, file);
2574        return 0;
2575}
2576
2577/*
2578 * cgroup_rename - Only allow simple rename of directories in place.
2579 */
2580static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
2581                            struct inode *new_dir, struct dentry *new_dentry)
2582{
2583        if (!S_ISDIR(old_dentry->d_inode->i_mode))
2584                return -ENOTDIR;
2585        if (new_dentry->d_inode)
2586                return -EEXIST;
2587        if (old_dir != new_dir)
2588                return -EIO;
2589        return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
2590}
2591
2592static struct simple_xattrs *__d_xattrs(struct dentry *dentry)
2593{
2594        if (S_ISDIR(dentry->d_inode->i_mode))
2595                return &__d_cgrp(dentry)->xattrs;
2596        else
2597                return &__d_cft(dentry)->xattrs;
2598}
2599
2600static inline int xattr_enabled(struct dentry *dentry)
2601{
2602        struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
2603        return test_bit(ROOT_XATTR, &root->flags);
2604}
2605
2606static bool is_valid_xattr(const char *name)
2607{
2608        if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) ||
2609            !strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN))
2610                return true;
2611        return false;
2612}
2613
2614static int cgroup_setxattr(struct dentry *dentry, const char *name,
2615                           const void *val, size_t size, int flags)
2616{
2617        if (!xattr_enabled(dentry))
2618                return -EOPNOTSUPP;
2619        if (!is_valid_xattr(name))
2620                return -EINVAL;
2621        return simple_xattr_set(__d_xattrs(dentry), name, val, size, flags);
2622}
2623
2624static int cgroup_removexattr(struct dentry *dentry, const char *name)
2625{
2626        if (!xattr_enabled(dentry))
2627                return -EOPNOTSUPP;
2628        if (!is_valid_xattr(name))
2629                return -EINVAL;
2630        return simple_xattr_remove(__d_xattrs(dentry), name);
2631}
2632
2633static ssize_t cgroup_getxattr(struct dentry *dentry, const char *name,
2634                               void *buf, size_t size)
2635{
2636        if (!xattr_enabled(dentry))
2637                return -EOPNOTSUPP;
2638        if (!is_valid_xattr(name))
2639                return -EINVAL;
2640        return simple_xattr_get(__d_xattrs(dentry), name, buf, size);
2641}
2642
2643static ssize_t cgroup_listxattr(struct dentry *dentry, char *buf, size_t size)
2644{
2645        if (!xattr_enabled(dentry))
2646                return -EOPNOTSUPP;
2647        return simple_xattr_list(__d_xattrs(dentry), buf, size);
2648}
2649
2650static const struct file_operations cgroup_file_operations = {
2651        .read = cgroup_file_read,
2652        .write = cgroup_file_write,
2653        .llseek = generic_file_llseek,
2654        .open = cgroup_file_open,
2655        .release = cgroup_file_release,
2656};
2657
2658static const struct inode_operations cgroup_file_inode_operations = {
2659        .setxattr = cgroup_setxattr,
2660        .getxattr = cgroup_getxattr,
2661        .listxattr = cgroup_listxattr,
2662        .removexattr = cgroup_removexattr,
2663};
2664
2665static const struct inode_operations cgroup_dir_inode_operations = {
2666        .lookup = cgroup_lookup,
2667        .mkdir = cgroup_mkdir,
2668        .rmdir = cgroup_rmdir,
2669        .rename = cgroup_rename,
2670        .setxattr = cgroup_setxattr,
2671        .getxattr = cgroup_getxattr,
2672        .listxattr = cgroup_listxattr,
2673        .removexattr = cgroup_removexattr,
2674};
2675
2676static struct dentry *cgroup_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
2677{
2678        if (dentry->d_name.len > NAME_MAX)
2679                return ERR_PTR(-ENAMETOOLONG);
2680        d_add(dentry, NULL);
2681        return NULL;
2682}
2683
2684/*
2685 * Check if a file is a control file
2686 */
2687static inline struct cftype *__file_cft(struct file *file)
2688{
2689        if (file->f_dentry->d_inode->i_fop != &cgroup_file_operations)
2690                return ERR_PTR(-EINVAL);
2691        return __d_cft(file->f_dentry);
2692}
2693
2694static int cgroup_create_file(struct dentry *dentry, umode_t mode,
2695                                struct super_block *sb)
2696{
2697        struct inode *inode;
2698
2699        if (!dentry)
2700                return -ENOENT;
2701        if (dentry->d_inode)
2702                return -EEXIST;
2703
2704        inode = cgroup_new_inode(mode, sb);
2705        if (!inode)
2706                return -ENOMEM;
2707
2708        if (S_ISDIR(mode)) {
2709                inode->i_op = &cgroup_dir_inode_operations;
2710                inode->i_fop = &simple_dir_operations;
2711
2712                /* start off with i_nlink == 2 (for "." entry) */
2713                inc_nlink(inode);
2714
2715                /* start with the directory inode held, so that we can
2716                 * populate it without racing with another mkdir */
2717                mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
2718        } else if (S_ISREG(mode)) {
2719                inode->i_size = 0;
2720                inode->i_fop = &cgroup_file_operations;
2721                inode->i_op = &cgroup_file_inode_operations;
2722        }
2723        d_instantiate(dentry, inode);
2724        dget(dentry);   /* Extra count - pin the dentry in core */
2725        return 0;
2726}
2727
2728/*
2729 * cgroup_create_dir - create a directory for an object.
2730 * @cgrp: the cgroup we create the directory for. It must have a valid
2731 *        ->parent field. And we are going to fill its ->dentry field.
2732 * @dentry: dentry of the new cgroup
2733 * @mode: mode to set on new directory.
2734 */
2735static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
2736                                umode_t mode)
2737{
2738        struct dentry *parent;
2739        int error = 0;
2740
2741        parent = cgrp->parent->dentry;
2742        error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb);
2743        if (!error) {
2744                dentry->d_fsdata = cgrp;
2745                inc_nlink(parent->d_inode);
2746                rcu_assign_pointer(cgrp->dentry, dentry);
2747                dget(dentry);
2748        }
2749        dput(dentry);
2750
2751        return error;
2752}
2753
2754/**
2755 * cgroup_file_mode - deduce file mode of a control file
2756 * @cft: the control file in question
2757 *
2758 * returns cft->mode if ->mode is not 0
2759 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
2760 * returns S_IRUGO if it has only a read handler
2761 * returns S_IWUSR if it has only a write hander
2762 */
2763static umode_t cgroup_file_mode(const struct cftype *cft)
2764{
2765        umode_t mode = 0;
2766
2767        if (cft->mode)
2768                return cft->mode;
2769
2770        if (cft->read || cft->read_u64 || cft->read_s64 ||
2771            cft->read_map || cft->read_seq_string)
2772                mode |= S_IRUGO;
2773
2774        if (cft->write || cft->write_u64 || cft->write_s64 ||
2775            cft->write_string || cft->trigger)
2776                mode |= S_IWUSR;
2777
2778        return mode;
2779}
2780
2781static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
2782                           struct cftype *cft)
2783{
2784        struct dentry *dir = cgrp->dentry;
2785        struct cgroup *parent = __d_cgrp(dir);
2786        struct dentry *dentry;
2787        struct cfent *cfe;
2788        int error;
2789        umode_t mode;
2790        char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
2791
2792        simple_xattrs_init(&cft->xattrs);
2793
2794        /* does @cft->flags tell us to skip creation on @cgrp? */
2795        if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent)
2796                return 0;
2797        if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgrp->parent)
2798                return 0;
2799
2800        if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
2801                strcpy(name, subsys->name);
2802                strcat(name, ".");
2803        }
2804        strcat(name, cft->name);
2805
2806        BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
2807
2808        cfe = kzalloc(sizeof(*cfe), GFP_KERNEL);
2809        if (!cfe)
2810                return -ENOMEM;
2811
2812        dentry = lookup_one_len(name, dir, strlen(name));
2813        if (IS_ERR(dentry)) {
2814                error = PTR_ERR(dentry);
2815                goto out;
2816        }
2817
2818        mode = cgroup_file_mode(cft);
2819        error = cgroup_create_file(dentry, mode | S_IFREG, cgrp->root->sb);
2820        if (!error) {
2821                cfe->type = (void *)cft;
2822                cfe->dentry = dentry;
2823                dentry->d_fsdata = cfe;
2824                list_add_tail(&cfe->node, &parent->files);
2825                cfe = NULL;
2826        }
2827        dput(dentry);
2828out:
2829        kfree(cfe);
2830        return error;
2831}
2832
2833static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
2834                              struct cftype cfts[], bool is_add)
2835{
2836        struct cftype *cft;
2837        int err, ret = 0;
2838
2839        for (cft = cfts; cft->name[0] != '\0'; cft++) {
2840                if (is_add)
2841                        err = cgroup_add_file(cgrp, subsys, cft);
2842                else
2843                        err = cgroup_rm_file(cgrp, cft);
2844                if (err) {
2845                        pr_warning("cgroup_addrm_files: failed to %s %s, err=%d\n",
2846                                   is_add ? "add" : "remove", cft->name, err);
2847                        ret = err;
2848                }
2849        }
2850        return ret;
2851}
2852
2853static DEFINE_MUTEX(cgroup_cft_mutex);
2854
2855static void cgroup_cfts_prepare(void)
2856        __acquires(&cgroup_cft_mutex) __acquires(&cgroup_mutex)
2857{
2858        /*
2859         * Thanks to the entanglement with vfs inode locking, we can't walk
2860         * the existing cgroups under cgroup_mutex and create files.
2861         * Instead, we increment reference on all cgroups and build list of
2862         * them using @cgrp->cft_q_node.  Grab cgroup_cft_mutex to ensure
2863         * exclusive access to the field.
2864         */
2865        mutex_lock(&cgroup_cft_mutex);
2866        mutex_lock(&cgroup_mutex);
2867}
2868
2869static void cgroup_cfts_commit(struct cgroup_subsys *ss,
2870                               struct cftype *cfts, bool is_add)
2871        __releases(&cgroup_mutex) __releases(&cgroup_cft_mutex)
2872{
2873        LIST_HEAD(pending);
2874        struct cgroup *cgrp, *n;
2875
2876        /* %NULL @cfts indicates abort and don't bother if @ss isn't attached */
2877        if (cfts && ss->root != &rootnode) {
2878                list_for_each_entry(cgrp, &ss->root->allcg_list, allcg_node) {
2879                        dget(cgrp->dentry);
2880                        list_add_tail(&cgrp->cft_q_node, &pending);
2881                }
2882        }
2883
2884        mutex_unlock(&cgroup_mutex);
2885
2886        /*
2887         * All new cgroups will see @cfts update on @ss->cftsets.  Add/rm
2888         * files for all cgroups which were created before.
2889         */
2890        list_for_each_entry_safe(cgrp, n, &pending, cft_q_node) {
2891                struct inode *inode = cgrp->dentry->d_inode;
2892
2893                mutex_lock(&inode->i_mutex);
2894                mutex_lock(&cgroup_mutex);
2895                if (!cgroup_is_removed(cgrp))
2896                        cgroup_addrm_files(cgrp, ss, cfts, is_add);
2897                mutex_unlock(&cgroup_mutex);
2898                mutex_unlock(&inode->i_mutex);
2899
2900                list_del_init(&cgrp->cft_q_node);
2901                dput(cgrp->dentry);
2902        }
2903
2904        mutex_unlock(&cgroup_cft_mutex);
2905}
2906
2907/**
2908 * cgroup_add_cftypes - add an array of cftypes to a subsystem
2909 * @ss: target cgroup subsystem
2910 * @cfts: zero-length name terminated array of cftypes
2911 *
2912 * Register @cfts to @ss.  Files described by @cfts are created for all
2913 * existing cgroups to which @ss is attached and all future cgroups will
2914 * have them too.  This function can be called anytime whether @ss is
2915 * attached or not.
2916 *
2917 * Returns 0 on successful registration, -errno on failure.  Note that this
2918 * function currently returns 0 as long as @cfts registration is successful
2919 * even if some file creation attempts on existing cgroups fail.
2920 */
2921int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
2922{
2923        struct cftype_set *set;
2924
2925        set = kzalloc(sizeof(*set), GFP_KERNEL);
2926        if (!set)
2927                return -ENOMEM;
2928
2929        cgroup_cfts_prepare();
2930        set->cfts = cfts;
2931        list_add_tail(&set->node, &ss->cftsets);
2932        cgroup_cfts_commit(ss, cfts, true);
2933
2934        return 0;
2935}
2936EXPORT_SYMBOL_GPL(cgroup_add_cftypes);
2937
2938/**
2939 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
2940 * @ss: target cgroup subsystem
2941 * @cfts: zero-length name terminated array of cftypes
2942 *
2943 * Unregister @cfts from @ss.  Files described by @cfts are removed from
2944 * all existing cgroups to which @ss is attached and all future cgroups
2945 * won't have them either.  This function can be called anytime whether @ss
2946 * is attached or not.
2947 *
2948 * Returns 0 on successful unregistration, -ENOENT if @cfts is not
2949 * registered with @ss.
2950 */
2951int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
2952{
2953        struct cftype_set *set;
2954
2955        cgroup_cfts_prepare();
2956
2957        list_for_each_entry(set, &ss->cftsets, node) {
2958                if (set->cfts == cfts) {
2959                        list_del_init(&set->node);
2960                        cgroup_cfts_commit(ss, cfts, false);
2961                        return 0;
2962                }
2963        }
2964
2965        cgroup_cfts_commit(ss, NULL, false);
2966        return -ENOENT;
2967}
2968
2969/**
2970 * cgroup_task_count - count the number of tasks in a cgroup.
2971 * @cgrp: the cgroup in question
2972 *
2973 * Return the number of tasks in the cgroup.
2974 */
2975int cgroup_task_count(const struct cgroup *cgrp)
2976{
2977        int count = 0;
2978        struct cg_cgroup_link *link;
2979
2980        read_lock(&css_set_lock);
2981        list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
2982                count += atomic_read(&link->cg->refcount);
2983        }
2984        read_unlock(&css_set_lock);
2985        return count;
2986}
2987
2988/*
2989 * Advance a list_head iterator.  The iterator should be positioned at
2990 * the start of a css_set
2991 */
2992static void cgroup_advance_iter(struct cgroup *cgrp,
2993                                struct cgroup_iter *it)
2994{
2995        struct list_head *l = it->cg_link;
2996        struct cg_cgroup_link *link;
2997        struct css_set *cg;
2998
2999        /* Advance to the next non-empty css_set */
3000        do {
3001                l = l->next;
3002                if (l == &cgrp->css_sets) {
3003                        it->cg_link = NULL;
3004                        return;
3005                }
3006                link = list_entry(l, struct cg_cgroup_link, cgrp_link_list);
3007                cg = link->cg;
3008        } while (list_empty(&cg->tasks));
3009        it->cg_link = l;
3010        it->task = cg->tasks.next;
3011}
3012
3013/*
3014 * To reduce the fork() overhead for systems that are not actually
3015 * using their cgroups capability, we don't maintain the lists running
3016 * through each css_set to its tasks until we see the list actually
3017 * used - in other words after the first call to cgroup_iter_start().
3018 */
3019static void cgroup_enable_task_cg_lists(void)
3020{
3021        struct task_struct *p, *g;
3022        write_lock(&css_set_lock);
3023        use_task_css_set_links = 1;
3024        /*
3025         * We need tasklist_lock because RCU is not safe against
3026         * while_each_thread(). Besides, a forking task that has passed
3027         * cgroup_post_fork() without seeing use_task_css_set_links = 1
3028         * is not guaranteed to have its child immediately visible in the
3029         * tasklist if we walk through it with RCU.
3030         */
3031        read_lock(&tasklist_lock);
3032        do_each_thread(g, p) {
3033                task_lock(p);
3034                /*
3035                 * We should check if the process is exiting, otherwise
3036                 * it will race with cgroup_exit() in that the list
3037                 * entry won't be deleted though the process has exited.
3038                 */
3039                if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
3040                        list_add(&p->cg_list, &p->cgroups->tasks);
3041                task_unlock(p);
3042        } while_each_thread(g, p);
3043        read_unlock(&tasklist_lock);
3044        write_unlock(&css_set_lock);
3045}
3046
3047void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
3048        __acquires(css_set_lock)
3049{
3050        /*
3051         * The first time anyone tries to iterate across a cgroup,
3052         * we need to enable the list linking each css_set to its
3053         * tasks, and fix up all existing tasks.
3054         */
3055        if (!use_task_css_set_links)
3056                cgroup_enable_task_cg_lists();
3057
3058        read_lock(&css_set_lock);
3059        it->cg_link = &cgrp->css_sets;
3060        cgroup_advance_iter(cgrp, it);
3061}
3062
3063struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
3064                                        struct cgroup_iter *it)
3065{
3066        struct task_struct *res;
3067        struct list_head *l = it->task;
3068        struct cg_cgroup_link *link;
3069
3070        /* If the iterator cg is NULL, we have no tasks */
3071        if (!it->cg_link)
3072                return NULL;
3073        res = list_entry(l, struct task_struct, cg_list);
3074        /* Advance iterator to find next entry */
3075        l = l->next;
3076        link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list);
3077        if (l == &link->cg->tasks) {
3078                /* We reached the end of this task list - move on to
3079                 * the next cg_cgroup_link */
3080                cgroup_advance_iter(cgrp, it);
3081        } else {
3082                it->task = l;
3083        }
3084        return res;
3085}
3086
3087void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
3088        __releases(css_set_lock)
3089{
3090        read_unlock(&css_set_lock);
3091}
3092
3093static inline int started_after_time(struct task_struct *t1,
3094                                     struct timespec *time,
3095                                     struct task_struct *t2)
3096{
3097        int start_diff = timespec_compare(&t1->start_time, time);
3098        if (start_diff > 0) {
3099                return 1;
3100        } else if (start_diff < 0) {
3101                return 0;
3102        } else {
3103                /*
3104                 * Arbitrarily, if two processes started at the same
3105                 * time, we'll say that the lower pointer value
3106                 * started first. Note that t2 may have exited by now
3107                 * so this may not be a valid pointer any longer, but
3108                 * that's fine - it still serves to distinguish
3109                 * between two tasks started (effectively) simultaneously.
3110                 */
3111                return t1 > t2;
3112        }
3113}
3114
3115/*
3116 * This function is a callback from heap_insert() and is used to order
3117 * the heap.
3118 * In this case we order the heap in descending task start time.
3119 */
3120static inline int started_after(void *p1, void *p2)
3121{
3122        struct task_struct *t1 = p1;
3123        struct task_struct *t2 = p2;
3124        return started_after_time(t1, &t2->start_time, t2);
3125}
3126
3127/**
3128 * cgroup_scan_tasks - iterate though all the tasks in a cgroup
3129 * @scan: struct cgroup_scanner containing arguments for the scan
3130 *
3131 * Arguments include pointers to callback functions test_task() and
3132 * process_task().
3133 * Iterate through all the tasks in a cgroup, calling test_task() for each,
3134 * and if it returns true, call process_task() for it also.
3135 * The test_task pointer may be NULL, meaning always true (select all tasks).
3136 * Effectively duplicates cgroup_iter_{start,next,end}()
3137 * but does not lock css_set_lock for the call to process_task().
3138 * The struct cgroup_scanner may be embedded in any structure of the caller's
3139 * creation.
3140 * It is guaranteed that process_task() will act on every task that
3141 * is a member of the cgroup for the duration of this call. This
3142 * function may or may not call process_task() for tasks that exit
3143 * or move to a different cgroup during the call, or are forked or
3144 * move into the cgroup during the call.
3145 *
3146 * Note that test_task() may be called with locks held, and may in some
3147 * situations be called multiple times for the same task, so it should
3148 * be cheap.
3149 * If the heap pointer in the struct cgroup_scanner is non-NULL, a heap has been
3150 * pre-allocated and will be used for heap operations (and its "gt" member will
3151 * be overwritten), else a temporary heap will be used (allocation of which
3152 * may cause this function to fail).
3153 */
3154int cgroup_scan_tasks(struct cgroup_scanner *scan)
3155{
3156        int retval, i;
3157        struct cgroup_iter it;
3158        struct task_struct *p, *dropped;
3159        /* Never dereference latest_task, since it's not refcounted */
3160        struct task_struct *latest_task = NULL;
3161        struct ptr_heap tmp_heap;
3162        struct ptr_heap *heap;
3163        struct timespec latest_time = { 0, 0 };
3164
3165        if (scan->heap) {
3166                /* The caller supplied our heap and pre-allocated its memory */
3167                heap = scan->heap;
3168                heap->gt = &started_after;
3169        } else {
3170                /* We need to allocate our own heap memory */
3171                heap = &tmp_heap;
3172                retval = heap_init(heap, PAGE_SIZE, GFP_KERNEL, &started_after);
3173                if (retval)
3174                        /* cannot allocate the heap */
3175                        return retval;
3176        }
3177
3178 again:
3179        /*
3180         * Scan tasks in the cgroup, using the scanner's "test_task" callback
3181         * to determine which are of interest, and using the scanner's
3182         * "process_task" callback to process any of them that need an update.
3183         * Since we don't want to hold any locks during the task updates,
3184         * gather tasks to be processed in a heap structure.
3185         * The heap is sorted by descending task start time.
3186         * If the statically-sized heap fills up, we overflow tasks that
3187         * started later, and in future iterations only consider tasks that
3188         * started after the latest task in the previous pass. This
3189         * guarantees forward progress and that we don't miss any tasks.
3190         */
3191        heap->size = 0;
3192        cgroup_iter_start(scan->cg, &it);
3193        while ((p = cgroup_iter_next(scan->cg, &it))) {
3194                /*
3195                 * Only affect tasks that qualify per the caller's callback,
3196                 * if he provided one
3197                 */
3198                if (scan->test_task && !scan->test_task(p, scan))
3199                        continue;
3200                /*
3201                 * Only process tasks that started after the last task
3202                 * we processed
3203                 */
3204                if (!started_after_time(p, &latest_time, latest_task))
3205                        continue;
3206                dropped = heap_insert(heap, p);
3207                if (dropped == NULL) {
3208                        /*
3209                         * The new task was inserted; the heap wasn't
3210                         * previously full
3211                         */
3212                        get_task_struct(p);
3213                } else if (dropped != p) {
3214                        /*
3215                         * The new task was inserted, and pushed out a
3216                         * different task
3217                         */
3218                        get_task_struct(p);
3219                        put_task_struct(dropped);
3220                }
3221                /*
3222                 * Else the new task was newer than anything already in
3223                 * the heap and wasn't inserted
3224                 */
3225        }
3226        cgroup_iter_end(scan->cg, &it);
3227
3228        if (heap->size) {
3229                for (i = 0; i < heap->size; i++) {
3230                        struct task_struct *q = heap->ptrs[i];
3231                        if (i == 0) {
3232                                latest_time = q->start_time;
3233                                latest_task = q;
3234                        }
3235                        /* Process the task per the caller's callback */
3236                        scan->process_task(q, scan);
3237                        put_task_struct(q);
3238                }
3239                /*
3240                 * If we had to process any tasks at all, scan again
3241                 * in case some of them were in the middle of forking
3242                 * children that didn't get processed.
3243                 * Not the most efficient way to do it, but it avoids
3244                 * having to take callback_mutex in the fork path
3245                 */
3246                goto again;
3247        }
3248        if (heap == &tmp_heap)
3249                heap_free(&tmp_heap);
3250        return 0;
3251}
3252
3253/*
3254 * Stuff for reading the 'tasks'/'procs' files.
3255 *
3256 * Reading this file can return large amounts of data if a cgroup has
3257 * *lots* of attached tasks. So it may need several calls to read(),
3258 * but we cannot guarantee that the information we produce is correct
3259 * unless we produce it entirely atomically.
3260 *
3261 */
3262
3263/* which pidlist file are we talking about? */
3264enum cgroup_filetype {
3265        CGROUP_FILE_PROCS,
3266        CGROUP_FILE_TASKS,
3267};
3268
3269/*
3270 * A pidlist is a list of pids that virtually represents the contents of one
3271 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
3272 * a pair (one each for procs, tasks) for each pid namespace that's relevant
3273 * to the cgroup.
3274 */
3275struct cgroup_pidlist {
3276        /*
3277         * used to find which pidlist is wanted. doesn't change as long as
3278         * this particular list stays in the list.
3279        */
3280        struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
3281        /* array of xids */
3282        pid_t *list;
3283        /* how many elements the above list has */
3284        int length;
3285        /* how many files are using the current array */
3286        int use_count;
3287        /* each of these stored in a list by its cgroup */
3288        struct list_head links;
3289        /* pointer to the cgroup we belong to, for list removal purposes */
3290        struct cgroup *owner;
3291        /* protects the other fields */
3292        struct rw_semaphore mutex;
3293};
3294
3295/*
3296 * The following two functions "fix" the issue where there are more pids
3297 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
3298 * TODO: replace with a kernel-wide solution to this problem
3299 */
3300#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
3301static void *pidlist_allocate(int count)
3302{
3303        if (PIDLIST_TOO_LARGE(count))
3304                return vmalloc(count * sizeof(pid_t));
3305        else
3306                return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
3307}
3308static void pidlist_free(void *p)
3309{
3310        if (is_vmalloc_addr(p))
3311                vfree(p);
3312        else
3313                kfree(p);
3314}
3315static void *pidlist_resize(void *p, int newcount)
3316{
3317        void *newlist;
3318        /* note: if new alloc fails, old p will still be valid either way */
3319        if (is_vmalloc_addr(p)) {
3320                newlist = vmalloc(newcount * sizeof(pid_t));
3321                if (!newlist)
3322                        return NULL;
3323                memcpy(newlist, p, newcount * sizeof(pid_t));
3324                vfree(p);
3325        } else {
3326                newlist = krealloc(p, newcount * sizeof(pid_t), GFP_KERNEL);
3327        }
3328        return newlist;
3329}
3330
3331/*
3332 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
3333 * If the new stripped list is sufficiently smaller and there's enough memory
3334 * to allocate a new buffer, will let go of the unneeded memory. Returns the
3335 * number of unique elements.
3336 */
3337/* is the size difference enough that we should re-allocate the array? */
3338#define PIDLIST_REALLOC_DIFFERENCE(old, new) ((old) - PAGE_SIZE >= (new))
3339static int pidlist_uniq(pid_t **p, int length)
3340{
3341        int src, dest = 1;
3342        pid_t *list = *p;
3343        pid_t *newlist;
3344
3345        /*
3346         * we presume the 0th element is unique, so i starts at 1. trivial
3347         * edge cases first; no work needs to be done for either
3348         */
3349        if (length == 0 || length == 1)
3350                return length;
3351        /* src and dest walk down the list; dest counts unique elements */
3352        for (src = 1; src < length; src++) {
3353                /* find next unique element */
3354                while (list[src] == list[src-1]) {
3355                        src++;
3356                        if (src == length)
3357                                goto after;
3358                }
3359                /* dest always points to where the next unique element goes */
3360                list[dest] = list[src];
3361                dest++;
3362        }
3363after:
3364        /*
3365         * if the length difference is large enough, we want to allocate a
3366         * smaller buffer to save memory. if this fails due to out of memory,
3367         * we'll just stay with what we've got.
3368         */
3369        if (PIDLIST_REALLOC_DIFFERENCE(length, dest)) {
3370                newlist = pidlist_resize(list, dest);
3371                if (newlist)
3372                        *p = newlist;
3373        }
3374        return dest;
3375}
3376
3377static int cmppid(const void *a, const void *b)
3378{
3379        return *(pid_t *)a - *(pid_t *)b;
3380}
3381
3382/*
3383 * find the appropriate pidlist for our purpose (given procs vs tasks)
3384 * returns with the lock on that pidlist already held, and takes care
3385 * of the use count, or returns NULL with no locks held if we're out of
3386 * memory.
3387 */
3388static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
3389                                                  enum cgroup_filetype type)
3390{
3391        struct cgroup_pidlist *l;
3392        /* don't need task_nsproxy() if we're looking at ourself */
3393        struct pid_namespace *ns = current->nsproxy->pid_ns;
3394
3395        /*
3396         * We can't drop the pidlist_mutex before taking the l->mutex in case
3397         * the last ref-holder is trying to remove l from the list at the same
3398         * time. Holding the pidlist_mutex precludes somebody taking whichever
3399         * list we find out from under us - compare release_pid_array().
3400         */
3401        mutex_lock(&cgrp->pidlist_mutex);
3402        list_for_each_entry(l, &cgrp->pidlists, links) {
3403                if (l->key.type == type && l->key.ns == ns) {
3404                        /* make sure l doesn't vanish out from under us */
3405                        down_write(&l->mutex);
3406                        mutex_unlock(&cgrp->pidlist_mutex);
3407                        return l;
3408                }
3409        }
3410        /* entry not found; create a new one */
3411        l = kmalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
3412        if (!l) {
3413                mutex_unlock(&cgrp->pidlist_mutex);
3414                return l;
3415        }
3416        init_rwsem(&l->mutex);
3417        down_write(&l->mutex);
3418        l->key.type = type;
3419        l->key.ns = get_pid_ns(ns);
3420        l->use_count = 0; /* don't increment here */
3421        l->list = NULL;
3422        l->owner = cgrp;
3423        list_add(&l->links, &cgrp->pidlists);
3424        mutex_unlock(&cgrp->pidlist_mutex);
3425        return l;
3426}
3427
3428/*
3429 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
3430 */
3431static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
3432                              struct cgroup_pidlist **lp)
3433{
3434        pid_t *array;
3435        int length;
3436        int pid, n = 0; /* used for populating the array */
3437        struct cgroup_iter it;
3438        struct task_struct *tsk;
3439        struct cgroup_pidlist *l;
3440
3441        /*
3442         * If cgroup gets more users after we read count, we won't have
3443         * enough space - tough.  This race is indistinguishable to the
3444         * caller from the case that the additional cgroup users didn't
3445         * show up until sometime later on.
3446         */
3447        length = cgroup_task_count(cgrp);
3448        array = pidlist_allocate(length);
3449        if (!array)
3450                return -ENOMEM;
3451        /* now, populate the array */
3452        cgroup_iter_start(cgrp, &it);
3453        while ((tsk = cgroup_iter_next(cgrp, &it))) {
3454                if (unlikely(n == length))
3455                        break;
3456                /* get tgid or pid for procs or tasks file respectively */
3457                if (type == CGROUP_FILE_PROCS)
3458                        pid = task_tgid_vnr(tsk);
3459                else
3460                        pid = task_pid_vnr(tsk);
3461                if (pid > 0) /* make sure to only use valid results */
3462                        array[n++] = pid;
3463        }
3464        cgroup_iter_end(cgrp, &it);
3465        length = n;
3466        /* now sort & (if procs) strip out duplicates */
3467        sort(array, length, sizeof(pid_t), cmppid, NULL);
3468        if (type == CGROUP_FILE_PROCS)
3469                length = pidlist_uniq(&array, length);
3470        l = cgroup_pidlist_find(cgrp, type);
3471        if (!l) {
3472                pidlist_free(array);
3473                return -ENOMEM;
3474        }
3475        /* store array, freeing old if necessary - lock already held */
3476        pidlist_free(l->list);
3477        l->list = array;
3478        l->length = length;
3479        l->use_count++;
3480        up_write(&l->mutex);
3481        *lp = l;
3482        return 0;
3483}
3484
3485/**
3486 * cgroupstats_build - build and fill cgroupstats
3487 * @stats: cgroupstats to fill information into
3488 * @dentry: A dentry entry belonging to the cgroup for which stats have
3489 * been requested.
3490 *
3491 * Build and fill cgroupstats so that taskstats can export it to user
3492 * space.
3493 */
3494int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
3495{
3496        int ret = -EINVAL;
3497        struct cgroup *cgrp;
3498        struct cgroup_iter it;
3499        struct task_struct *tsk;
3500
3501        /*
3502         * Validate dentry by checking the superblock operations,
3503         * and make sure it's a directory.
3504         */
3505        if (dentry->d_sb->s_op != &cgroup_ops ||
3506            !S_ISDIR(dentry->d_inode->i_mode))
3507                 goto err;
3508
3509        ret = 0;
3510        cgrp = dentry->d_fsdata;
3511
3512        cgroup_iter_start(cgrp, &it);
3513        while ((tsk = cgroup_iter_next(cgrp, &it))) {
3514                switch (tsk->state) {
3515                case TASK_RUNNING:
3516                        stats->nr_running++;
3517                        break;
3518                case TASK_INTERRUPTIBLE:
3519                        stats->nr_sleeping++;
3520                        break;
3521                case TASK_UNINTERRUPTIBLE:
3522                        stats->nr_uninterruptible++;
3523                        break;
3524                case TASK_STOPPED:
3525                        stats->nr_stopped++;
3526                        break;
3527                default:
3528                        if (delayacct_is_task_waiting_on_io(tsk))
3529                                stats->nr_io_wait++;
3530                        break;
3531                }
3532        }
3533        cgroup_iter_end(cgrp, &it);
3534
3535err:
3536        return ret;
3537}
3538
3539
3540/*
3541 * seq_file methods for the tasks/procs files. The seq_file position is the
3542 * next pid to display; the seq_file iterator is a pointer to the pid
3543 * in the cgroup->l->list array.
3544 */
3545
3546static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
3547{
3548        /*
3549         * Initially we receive a position value that corresponds to
3550         * one more than the last pid shown (or 0 on the first call or
3551         * after a seek to the start). Use a binary-search to find the
3552         * next pid to display, if any
3553         */
3554        struct cgroup_pidlist *l = s->private;
3555        int index = 0, pid = *pos;
3556        int *iter;
3557
3558        down_read(&l->mutex);
3559        if (pid) {
3560                int end = l->length;
3561
3562                while (index < end) {
3563                        int mid = (index + end) / 2;
3564                        if (l->list[mid] == pid) {
3565                                index = mid;
3566                                break;
3567                        } else if (l->list[mid] <= pid)
3568                                index = mid + 1;
3569                        else
3570                                end = mid;
3571                }
3572        }
3573        /* If we're off the end of the array, we're done */
3574        if (index >= l->length)
3575                return NULL;
3576        /* Update the abstract position to be the actual pid that we found */
3577        iter = l->list + index;
3578        *pos = *iter;
3579        return iter;
3580}
3581
3582static void cgroup_pidlist_stop(struct seq_file *s, void *v)
3583{
3584        struct cgroup_pidlist *l = s->private;
3585        up_read(&l->mutex);
3586}
3587
3588static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
3589{
3590        struct cgroup_pidlist *l = s->private;
3591        pid_t *p = v;
3592        pid_t *end = l->list + l->length;
3593        /*
3594         * Advance to the next pid in the array. If this goes off the
3595         * end, we're done
3596         */
3597        p++;
3598        if (p >= end) {
3599                return NULL;
3600        } else {
3601                *pos = *p;
3602                return p;
3603        }
3604}
3605
3606static int cgroup_pidlist_show(struct seq_file *s, void *v)
3607{
3608        return seq_printf(s, "%d\n", *(int *)v);
3609}
3610
3611/*
3612 * seq_operations functions for iterating on pidlists through seq_file -
3613 * independent of whether it's tasks or procs
3614 */
3615static const struct seq_operations cgroup_pidlist_seq_operations = {
3616        .start = cgroup_pidlist_start,
3617        .stop = cgroup_pidlist_stop,
3618        .next = cgroup_pidlist_next,
3619        .show = cgroup_pidlist_show,
3620};
3621
3622static void cgroup_release_pid_array(struct cgroup_pidlist *l)
3623{
3624        /*
3625         * the case where we're the last user of this particular pidlist will
3626         * have us remove it from the cgroup's list, which entails taking the
3627         * mutex. since in pidlist_find the pidlist->lock depends on cgroup->
3628         * pidlist_mutex, we have to take pidlist_mutex first.
3629         */
3630        mutex_lock(&l->owner->pidlist_mutex);
3631        down_write(&l->mutex);
3632        BUG_ON(!l->use_count);
3633        if (!--l->use_count) {
3634                /* we're the last user if refcount is 0; remove and free */
3635                list_del(&l->links);
3636                mutex_unlock(&l->owner->pidlist_mutex);
3637                pidlist_free(l->list);
3638                put_pid_ns(l->key.ns);
3639                up_write(&l->mutex);
3640                kfree(l);
3641                return;
3642        }
3643        mutex_unlock(&l->owner->pidlist_mutex);
3644        up_write(&l->mutex);
3645}
3646
3647static int cgroup_pidlist_release(struct inode *inode, struct file *file)
3648{
3649        struct cgroup_pidlist *l;
3650        if (!(file->f_mode & FMODE_READ))
3651                return 0;
3652        /*
3653         * the seq_file will only be initialized if the file was opened for
3654         * reading; hence we check if it's not null only in that case.
3655         */
3656        l = ((struct seq_file *)file->private_data)->private;
3657        cgroup_release_pid_array(l);
3658        return seq_release(inode, file);
3659}
3660
3661static const struct file_operations cgroup_pidlist_operations = {
3662        .read = seq_read,
3663        .llseek = seq_lseek,
3664        .write = cgroup_file_write,
3665        .release = cgroup_pidlist_release,
3666};
3667
3668/*
3669 * The following functions handle opens on a file that displays a pidlist
3670 * (tasks or procs). Prepare an array of the process/thread IDs of whoever's
3671 * in the cgroup.
3672 */
3673/* helper function for the two below it */
3674static int cgroup_pidlist_open(struct file *file, enum cgroup_filetype type)
3675{
3676        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
3677        struct cgroup_pidlist *l;
3678        int retval;
3679
3680        /* Nothing to do for write-only files */
3681        if (!(file->f_mode & FMODE_READ))
3682                return 0;
3683
3684        /* have the array populated */
3685        retval = pidlist_array_load(cgrp, type, &l);
3686        if (retval)
3687                return retval;
3688        /* configure file information */
3689        file->f_op = &cgroup_pidlist_operations;
3690
3691        retval = seq_open(file, &cgroup_pidlist_seq_operations);
3692        if (retval) {
3693                cgroup_release_pid_array(l);
3694                return retval;
3695        }
3696        ((struct seq_file *)file->private_data)->private = l;
3697        return 0;
3698}
3699static int cgroup_tasks_open(struct inode *unused, struct file *file)
3700{
3701        return cgroup_pidlist_open(file, CGROUP_FILE_TASKS);
3702}
3703static int cgroup_procs_open(struct inode *unused, struct file *file)
3704{
3705        return cgroup_pidlist_open(file, CGROUP_FILE_PROCS);
3706}
3707
3708static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
3709                                            struct cftype *cft)
3710{
3711        return notify_on_release(cgrp);
3712}
3713
3714static int cgroup_write_notify_on_release(struct cgroup *cgrp,
3715                                          struct cftype *cft,
3716                                          u64 val)
3717{
3718        clear_bit(CGRP_RELEASABLE, &cgrp->flags);
3719        if (val)
3720                set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3721        else
3722                clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
3723        return 0;
3724}
3725
3726/*
3727 * Unregister event and free resources.
3728 *
3729 * Gets called from workqueue.
3730 */
3731static void cgroup_event_remove(struct work_struct *work)
3732{
3733        struct cgroup_event *event = container_of(work, struct cgroup_event,
3734                        remove);
3735        struct cgroup *cgrp = event->cgrp;
3736
3737        event->cft->unregister_event(cgrp, event->cft, event->eventfd);
3738
3739        eventfd_ctx_put(event->eventfd);
3740        kfree(event);
3741        dput(cgrp->dentry);
3742}
3743
3744/*
3745 * Gets called on POLLHUP on eventfd when user closes it.
3746 *
3747 * Called with wqh->lock held and interrupts disabled.
3748 */
3749static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
3750                int sync, void *key)
3751{
3752        struct cgroup_event *event = container_of(wait,
3753                        struct cgroup_event, wait);
3754        struct cgroup *cgrp = event->cgrp;
3755        unsigned long flags = (unsigned long)key;
3756
3757        if (flags & POLLHUP) {
3758                __remove_wait_queue(event->wqh, &event->wait);
3759                spin_lock(&cgrp->event_list_lock);
3760                list_del(&event->list);
3761                spin_unlock(&cgrp->event_list_lock);
3762                /*
3763                 * We are in atomic context, but cgroup_event_remove() may
3764                 * sleep, so we have to call it in workqueue.
3765                 */
3766                schedule_work(&event->remove);
3767        }
3768
3769        return 0;
3770}
3771
3772static void cgroup_event_ptable_queue_proc(struct file *file,
3773                wait_queue_head_t *wqh, poll_table *pt)
3774{
3775        struct cgroup_event *event = container_of(pt,
3776                        struct cgroup_event, pt);
3777
3778        event->wqh = wqh;
3779        add_wait_queue(wqh, &event->wait);
3780}
3781
3782/*
3783 * Parse input and register new cgroup event handler.
3784 *
3785 * Input must be in format '<event_fd> <control_fd> <args>'.
3786 * Interpretation of args is defined by control file implementation.
3787 */
3788static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
3789                                      const char *buffer)
3790{
3791        struct cgroup_event *event = NULL;
3792        unsigned int efd, cfd;
3793        struct file *efile = NULL;
3794        struct file *cfile = NULL;
3795        char *endp;
3796        int ret;
3797
3798        efd = simple_strtoul(buffer, &endp, 10);
3799        if (*endp != ' ')
3800                return -EINVAL;
3801        buffer = endp + 1;
3802
3803        cfd = simple_strtoul(buffer, &endp, 10);
3804        if ((*endp != ' ') && (*endp != '\0'))
3805                return -EINVAL;
3806        buffer = endp + 1;
3807
3808        event = kzalloc(sizeof(*event), GFP_KERNEL);
3809        if (!event)
3810                return -ENOMEM;
3811        event->cgrp = cgrp;
3812        INIT_LIST_HEAD(&event->list);
3813        init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
3814        init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
3815        INIT_WORK(&event->remove, cgroup_event_remove);
3816
3817        efile = eventfd_fget(efd);
3818        if (IS_ERR(efile)) {
3819                ret = PTR_ERR(efile);
3820                goto fail;
3821        }
3822
3823        event->eventfd = eventfd_ctx_fileget(efile);
3824        if (IS_ERR(event->eventfd)) {
3825                ret = PTR_ERR(event->eventfd);
3826                goto fail;
3827        }
3828
3829        cfile = fget(cfd);
3830        if (!cfile) {
3831                ret = -EBADF;
3832                goto fail;
3833        }
3834
3835        /* the process need read permission on control file */
3836        /* AV: shouldn't we check that it's been opened for read instead? */
3837        ret = inode_permission(cfile->f_path.dentry->d_inode, MAY_READ);
3838        if (ret < 0)
3839                goto fail;
3840
3841        event->cft = __file_cft(cfile);
3842        if (IS_ERR(event->cft)) {
3843                ret = PTR_ERR(event->cft);
3844                goto fail;
3845        }
3846
3847        if (!event->cft->register_event || !event->cft->unregister_event) {
3848                ret = -EINVAL;
3849                goto fail;
3850        }
3851
3852        ret = event->cft->register_event(cgrp, event->cft,
3853                        event->eventfd, buffer);
3854        if (ret)
3855                goto fail;
3856
3857        if (efile->f_op->poll(efile, &event->pt) & POLLHUP) {
3858                event->cft->unregister_event(cgrp, event->cft, event->eventfd);
3859                ret = 0;
3860                goto fail;
3861        }
3862
3863        /*
3864         * Events should be removed after rmdir of cgroup directory, but before
3865         * destroying subsystem state objects. Let's take reference to cgroup
3866         * directory dentry to do that.
3867         */
3868        dget(cgrp->dentry);
3869
3870        spin_lock(&cgrp->event_list_lock);
3871        list_add(&event->list, &cgrp->event_list);
3872        spin_unlock(&cgrp->event_list_lock);
3873
3874        fput(cfile);
3875        fput(efile);
3876
3877        return 0;
3878
3879fail:
3880        if (cfile)
3881                fput(cfile);
3882
3883        if (event && event->eventfd && !IS_ERR(event->eventfd))
3884                eventfd_ctx_put(event->eventfd);
3885
3886        if (!IS_ERR_OR_NULL(efile))
3887                fput(efile);
3888
3889        kfree(event);
3890
3891        return ret;
3892}
3893
3894static u64 cgroup_clone_children_read(struct cgroup *cgrp,
3895                                    struct cftype *cft)
3896{
3897        return clone_children(cgrp);
3898}
3899
3900static int cgroup_clone_children_write(struct cgroup *cgrp,
3901                                     struct cftype *cft,
3902                                     u64 val)
3903{
3904        if (val)
3905                set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
3906        else
3907                clear_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
3908        return 0;
3909}
3910
3911/*
3912 * for the common functions, 'private' gives the type of file
3913 */
3914/* for hysterical raisins, we can't put this on the older files */
3915#define CGROUP_FILE_GENERIC_PREFIX "cgroup."
3916static struct cftype files[] = {
3917        {
3918                .name = "tasks",
3919                .open = cgroup_tasks_open,
3920                .write_u64 = cgroup_tasks_write,
3921                .release = cgroup_pidlist_release,
3922                .mode = S_IRUGO | S_IWUSR,
3923        },
3924        {
3925                .name = CGROUP_FILE_GENERIC_PREFIX "procs",
3926                .open = cgroup_procs_open,
3927                .write_u64 = cgroup_procs_write,
3928                .release = cgroup_pidlist_release,
3929                .mode = S_IRUGO | S_IWUSR,
3930        },
3931        {
3932                .name = "notify_on_release",
3933                .read_u64 = cgroup_read_notify_on_release,
3934                .write_u64 = cgroup_write_notify_on_release,
3935        },
3936        {
3937                .name = CGROUP_FILE_GENERIC_PREFIX "event_control",
3938                .write_string = cgroup_write_event_control,
3939                .mode = S_IWUGO,
3940        },
3941        {
3942                .name = "cgroup.clone_children",
3943                .read_u64 = cgroup_clone_children_read,
3944                .write_u64 = cgroup_clone_children_write,
3945        },
3946        {
3947                .name = "release_agent",
3948                .flags = CFTYPE_ONLY_ON_ROOT,
3949                .read_seq_string = cgroup_release_agent_show,
3950                .write_string = cgroup_release_agent_write,
3951                .max_write_len = PATH_MAX,
3952        },
3953        { }     /* terminate */
3954};
3955
3956/**
3957 * cgroup_populate_dir - selectively creation of files in a directory
3958 * @cgrp: target cgroup
3959 * @base_files: true if the base files should be added
3960 * @subsys_mask: mask of the subsystem ids whose files should be added
3961 */
3962static int cgroup_populate_dir(struct cgroup *cgrp, bool base_files,
3963                               unsigned long subsys_mask)
3964{
3965        int err;
3966        struct cgroup_subsys *ss;
3967
3968        if (base_files) {
3969                err = cgroup_addrm_files(cgrp, NULL, files, true);
3970                if (err < 0)
3971                        return err;
3972        }
3973
3974        /* process cftsets of each subsystem */
3975        for_each_subsys(cgrp->root, ss) {
3976                struct cftype_set *set;
3977                if (!test_bit(ss->subsys_id, &subsys_mask))
3978                        continue;
3979
3980                list_for_each_entry(set, &ss->cftsets, node)
3981                        cgroup_addrm_files(cgrp, ss, set->cfts, true);
3982        }
3983
3984        /* This cgroup is ready now */
3985        for_each_subsys(cgrp->root, ss) {
3986                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
3987                /*
3988                 * Update id->css pointer and make this css visible from
3989                 * CSS ID functions. This pointer will be dereferened
3990                 * from RCU-read-side without locks.
3991                 */
3992                if (css->id)
3993                        rcu_assign_pointer(css->id->css, css);
3994        }
3995
3996        return 0;
3997}
3998
3999static void css_dput_fn(struct work_struct *work)
4000{
4001        struct cgroup_subsys_state *css =
4002                container_of(work, struct cgroup_subsys_state, dput_work);
4003        struct dentry *dentry = css->cgroup->dentry;
4004        struct super_block *sb = dentry->d_sb;
4005
4006        atomic_inc(&sb->s_active);
4007        dput(dentry);
4008        deactivate_super(sb);
4009}
4010
4011static void init_cgroup_css(struct cgroup_subsys_state *css,
4012                               struct cgroup_subsys *ss,
4013                               struct cgroup *cgrp)
4014{
4015        css->cgroup = cgrp;
4016        atomic_set(&css->refcnt, 1);
4017        css->flags = 0;
4018        css->id = NULL;
4019        if (cgrp == dummytop)
4020                set_bit(CSS_ROOT, &css->flags);
4021        BUG_ON(cgrp->subsys[ss->subsys_id]);
4022        cgrp->subsys[ss->subsys_id] = css;
4023
4024        /*
4025         * If !clear_css_refs, css holds an extra ref to @cgrp->dentry
4026         * which is put on the last css_put().  dput() requires process
4027         * context, which css_put() may be called without.  @css->dput_work
4028         * will be used to invoke dput() asynchronously from css_put().
4029         */
4030        INIT_WORK(&css->dput_work, css_dput_fn);
4031        if (ss->__DEPRECATED_clear_css_refs)
4032                set_bit(CSS_CLEAR_CSS_REFS, &css->flags);
4033}
4034
4035/*
4036 * cgroup_create - create a cgroup
4037 * @parent: cgroup that will be parent of the new cgroup
4038 * @dentry: dentry of the new cgroup
4039 * @mode: mode to set on new inode
4040 *
4041 * Must be called with the mutex on the parent inode held
4042 */
4043static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
4044                             umode_t mode)
4045{
4046        struct cgroup *cgrp;
4047        struct cgroupfs_root *root = parent->root;
4048        int err = 0;
4049        struct cgroup_subsys *ss;
4050        struct super_block *sb = root->sb;
4051
4052        cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
4053        if (!cgrp)
4054                return -ENOMEM;
4055
4056        /* Grab a reference on the superblock so the hierarchy doesn't
4057         * get deleted on unmount if there are child cgroups.  This
4058         * can be done outside cgroup_mutex, since the sb can't
4059         * disappear while someone has an open control file on the
4060         * fs */
4061        atomic_inc(&sb->s_active);
4062
4063        mutex_lock(&cgroup_mutex);
4064
4065        init_cgroup_housekeeping(cgrp);
4066
4067        cgrp->parent = parent;
4068        cgrp->root = parent->root;
4069        cgrp->top_cgroup = parent->top_cgroup;
4070
4071        if (notify_on_release(parent))
4072                set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
4073
4074        if (clone_children(parent))
4075                set_bit(CGRP_CLONE_CHILDREN, &cgrp->flags);
4076
4077        for_each_subsys(root, ss) {
4078                struct cgroup_subsys_state *css;
4079
4080                css = ss->create(cgrp);
4081                if (IS_ERR(css)) {
4082                        err = PTR_ERR(css);
4083                        goto err_destroy;
4084                }
4085                init_cgroup_css(css, ss, cgrp);
4086                if (ss->use_id) {
4087                        err = alloc_css_id(ss, parent, cgrp);
4088                        if (err)
4089                                goto err_destroy;
4090                }
4091                /* At error, ->destroy() callback has to free assigned ID. */
4092                if (clone_children(parent) && ss->post_clone)
4093                        ss->post_clone(cgrp);
4094
4095                if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
4096                    parent->parent) {
4097                        pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
4098                                   current->comm, current->pid, ss->name);
4099                        if (!strcmp(ss->name, "memory"))
4100                                pr_warning("cgroup: \"memory\" requires setting use_hierarchy to 1 on the root.\n");
4101                        ss->warned_broken_hierarchy = true;
4102                }
4103        }
4104
4105        list_add(&cgrp->sibling, &cgrp->parent->children);
4106        root->number_of_cgroups++;
4107
4108        err = cgroup_create_dir(cgrp, dentry, mode);
4109        if (err < 0)
4110                goto err_remove;
4111
4112        /* If !clear_css_refs, each css holds a ref to the cgroup's dentry */
4113        for_each_subsys(root, ss)
4114                if (!ss->__DEPRECATED_clear_css_refs)
4115                        dget(dentry);
4116
4117        /* The cgroup directory was pre-locked for us */
4118        BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
4119
4120        list_add_tail(&cgrp->allcg_node, &root->allcg_list);
4121
4122        err = cgroup_populate_dir(cgrp, true, root->subsys_mask);
4123        /* If err < 0, we have a half-filled directory - oh well ;) */
4124
4125        mutex_unlock(&cgroup_mutex);
4126        mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
4127
4128        return 0;
4129
4130 err_remove:
4131
4132        list_del(&cgrp->sibling);
4133        root->number_of_cgroups--;
4134
4135 err_destroy:
4136
4137        for_each_subsys(root, ss) {
4138                if (cgrp->subsys[ss->subsys_id])
4139                        ss->destroy(cgrp);
4140        }
4141
4142        mutex_unlock(&cgroup_mutex);
4143
4144        /* Release the reference count that we took on the superblock */
4145        deactivate_super(sb);
4146
4147        kfree(cgrp);
4148        return err;
4149}
4150
4151static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
4152{
4153        struct cgroup *c_parent = dentry->d_parent->d_fsdata;
4154
4155        /* the vfs holds inode->i_mutex already */
4156        return cgroup_create(c_parent, dentry, mode | S_IFDIR);
4157}
4158
4159/*
4160 * Check the reference count on each subsystem. Since we already
4161 * established that there are no tasks in the cgroup, if the css refcount
4162 * is also 1, then there should be no outstanding references, so the
4163 * subsystem is safe to destroy. We scan across all subsystems rather than
4164 * using the per-hierarchy linked list of mounted subsystems since we can
4165 * be called via check_for_release() with no synchronization other than
4166 * RCU, and the subsystem linked list isn't RCU-safe.
4167 */
4168static int cgroup_has_css_refs(struct cgroup *cgrp)
4169{
4170        int i;
4171
4172        /*
4173         * We won't need to lock the subsys array, because the subsystems
4174         * we're concerned about aren't going anywhere since our cgroup root
4175         * has a reference on them.
4176         */
4177        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4178                struct cgroup_subsys *ss = subsys[i];
4179                struct cgroup_subsys_state *css;
4180
4181                /* Skip subsystems not present or not in this hierarchy */
4182                if (ss == NULL || ss->root != cgrp->root)
4183                        continue;
4184
4185                css = cgrp->subsys[ss->subsys_id];
4186                /*
4187                 * When called from check_for_release() it's possible
4188                 * that by this point the cgroup has been removed
4189                 * and the css deleted. But a false-positive doesn't
4190                 * matter, since it can only happen if the cgroup
4191                 * has been deleted and hence no longer needs the
4192                 * release agent to be called anyway.
4193                 */
4194                if (css && css_refcnt(css) > 1)
4195                        return 1;
4196        }
4197        return 0;
4198}
4199
4200/*
4201 * Atomically mark all (or else none) of the cgroup's CSS objects as
4202 * CSS_REMOVED. Return true on success, or false if the cgroup has
4203 * busy subsystems. Call with cgroup_mutex held
4204 *
4205 * Depending on whether a subsys has __DEPRECATED_clear_css_refs set or
4206 * not, cgroup removal behaves differently.
4207 *
4208 * If clear is set, css refcnt for the subsystem should be zero before
4209 * cgroup removal can be committed.  This is implemented by
4210 * CGRP_WAIT_ON_RMDIR and retry logic around ->pre_destroy(), which may be
4211 * called multiple times until all css refcnts reach zero and is allowed to
4212 * veto removal on any invocation.  This behavior is deprecated and will be
4213 * removed as soon as the existing user (memcg) is updated.
4214 *
4215 * If clear is not set, each css holds an extra reference to the cgroup's
4216 * dentry and cgroup removal proceeds regardless of css refs.
4217 * ->pre_destroy() will be called at least once and is not allowed to fail.
4218 * On the last put of each css, whenever that may be, the extra dentry ref
4219 * is put so that dentry destruction happens only after all css's are
4220 * released.
4221 */
4222static int cgroup_clear_css_refs(struct cgroup *cgrp)
4223{
4224        struct cgroup_subsys *ss;
4225        unsigned long flags;
4226        bool failed = false;
4227
4228        local_irq_save(flags);
4229
4230        /*
4231         * Block new css_tryget() by deactivating refcnt.  If all refcnts
4232         * for subsystems w/ clear_css_refs set were 1 at the moment of
4233         * deactivation, we succeeded.
4234         */
4235        for_each_subsys(cgrp->root, ss) {
4236                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
4237
4238                WARN_ON(atomic_read(&css->refcnt) < 0);
4239                atomic_add(CSS_DEACT_BIAS, &css->refcnt);
4240
4241                if (ss->__DEPRECATED_clear_css_refs)
4242                        failed |= css_refcnt(css) != 1;
4243        }
4244
4245        /*
4246         * If succeeded, set REMOVED and put all the base refs; otherwise,
4247         * restore refcnts to positive values.  Either way, all in-progress
4248         * css_tryget() will be released.
4249         */
4250        for_each_subsys(cgrp->root, ss) {
4251                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
4252
4253                if (!failed) {
4254                        set_bit(CSS_REMOVED, &css->flags);
4255                        css_put(css);
4256                } else {
4257                        atomic_sub(CSS_DEACT_BIAS, &css->refcnt);
4258                }
4259        }
4260
4261        local_irq_restore(flags);
4262        return !failed;
4263}
4264
4265static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
4266{
4267        struct cgroup *cgrp = dentry->d_fsdata;
4268        struct dentry *d;
4269        struct cgroup *parent;
4270        DEFINE_WAIT(wait);
4271        struct cgroup_event *event, *tmp;
4272        int ret;
4273
4274        /* the vfs holds both inode->i_mutex already */
4275again:
4276        mutex_lock(&cgroup_mutex);
4277        if (atomic_read(&cgrp->count) != 0) {
4278                mutex_unlock(&cgroup_mutex);
4279                return -EBUSY;
4280        }
4281        if (!list_empty(&cgrp->children)) {
4282                mutex_unlock(&cgroup_mutex);
4283                return -EBUSY;
4284        }
4285        mutex_unlock(&cgroup_mutex);
4286
4287        /*
4288         * In general, subsystem has no css->refcnt after pre_destroy(). But
4289         * in racy cases, subsystem may have to get css->refcnt after
4290         * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
4291         * make rmdir return -EBUSY too often. To avoid that, we use waitqueue
4292         * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
4293         * and subsystem's reference count handling. Please see css_get/put
4294         * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
4295         */
4296        set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4297
4298        /*
4299         * Call pre_destroy handlers of subsys. Notify subsystems
4300         * that rmdir() request comes.
4301         */
4302        ret = cgroup_call_pre_destroy(cgrp);
4303        if (ret) {
4304                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4305                return ret;
4306        }
4307
4308        mutex_lock(&cgroup_mutex);
4309        parent = cgrp->parent;
4310        if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
4311                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4312                mutex_unlock(&cgroup_mutex);
4313                return -EBUSY;
4314        }
4315        prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
4316        if (!cgroup_clear_css_refs(cgrp)) {
4317                mutex_unlock(&cgroup_mutex);
4318                /*
4319                 * Because someone may call cgroup_wakeup_rmdir_waiter() before
4320                 * prepare_to_wait(), we need to check this flag.
4321                 */
4322                if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
4323                        schedule();
4324                finish_wait(&cgroup_rmdir_waitq, &wait);
4325                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4326                if (signal_pending(current))
4327                        return -EINTR;
4328                goto again;
4329        }
4330        /* NO css_tryget() can success after here. */
4331        finish_wait(&cgroup_rmdir_waitq, &wait);
4332        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
4333
4334        raw_spin_lock(&release_list_lock);
4335        set_bit(CGRP_REMOVED, &cgrp->flags);
4336        if (!list_empty(&cgrp->release_list))
4337                list_del_init(&cgrp->release_list);
4338        raw_spin_unlock(&release_list_lock);
4339
4340        /* delete this cgroup from parent->children */
4341        list_del_init(&cgrp->sibling);
4342
4343        list_del_init(&cgrp->allcg_node);
4344
4345        d = dget(cgrp->dentry);
4346
4347        cgroup_d_remove_dir(d);
4348        dput(d);
4349
4350        set_bit(CGRP_RELEASABLE, &parent->flags);
4351        check_for_release(parent);
4352
4353        /*
4354         * Unregister events and notify userspace.
4355         * Notify userspace about cgroup removing only after rmdir of cgroup
4356         * directory to avoid race between userspace and kernelspace
4357         */
4358        spin_lock(&cgrp->event_list_lock);
4359        list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
4360                list_del(&event->list);
4361                remove_wait_queue(event->wqh, &event->wait);
4362                eventfd_signal(event->eventfd, 1);
4363                schedule_work(&event->remove);
4364        }
4365        spin_unlock(&cgrp->event_list_lock);
4366
4367        mutex_unlock(&cgroup_mutex);
4368        return 0;
4369}
4370
4371static void __init_or_module cgroup_init_cftsets(struct cgroup_subsys *ss)
4372{
4373        INIT_LIST_HEAD(&ss->cftsets);
4374
4375        /*
4376         * base_cftset is embedded in subsys itself, no need to worry about
4377         * deregistration.
4378         */
4379        if (ss->base_cftypes) {
4380                ss->base_cftset.cfts = ss->base_cftypes;
4381                list_add_tail(&ss->base_cftset.node, &ss->cftsets);
4382        }
4383}
4384
4385static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
4386{
4387        struct cgroup_subsys_state *css;
4388
4389        printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
4390
4391        /* init base cftset */
4392        cgroup_init_cftsets(ss);
4393
4394        /* Create the top cgroup state for this subsystem */
4395        list_add(&ss->sibling, &rootnode.subsys_list);
4396        ss->root = &rootnode;
4397        css = ss->create(dummytop);
4398        /* We don't handle early failures gracefully */
4399        BUG_ON(IS_ERR(css));
4400        init_cgroup_css(css, ss, dummytop);
4401
4402        /* Update the init_css_set to contain a subsys
4403         * pointer to this state - since the subsystem is
4404         * newly registered, all tasks and hence the
4405         * init_css_set is in the subsystem's top cgroup. */
4406        init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
4407
4408        need_forkexit_callback |= ss->fork || ss->exit;
4409
4410        /* At system boot, before all subsystems have been
4411         * registered, no tasks have been forked, so we don't
4412         * need to invoke fork callbacks here. */
4413        BUG_ON(!list_empty(&init_task.tasks));
4414
4415        ss->active = 1;
4416
4417        /* this function shouldn't be used with modular subsystems, since they
4418         * need to register a subsys_id, among other things */
4419        BUG_ON(ss->module);
4420}
4421
4422/**
4423 * cgroup_load_subsys: load and register a modular subsystem at runtime
4424 * @ss: the subsystem to load
4425 *
4426 * This function should be called in a modular subsystem's initcall. If the
4427 * subsystem is built as a module, it will be assigned a new subsys_id and set
4428 * up for use. If the subsystem is built-in anyway, work is delegated to the
4429 * simpler cgroup_init_subsys.
4430 */
4431int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
4432{
4433        int i;
4434        struct cgroup_subsys_state *css;
4435
4436        /* check name and function validity */
4437        if (ss->name == NULL || strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN ||
4438            ss->create == NULL || ss->destroy == NULL)
4439                return -EINVAL;
4440
4441        /*
4442         * we don't support callbacks in modular subsystems. this check is
4443         * before the ss->module check for consistency; a subsystem that could
4444         * be a module should still have no callbacks even if the user isn't
4445         * compiling it as one.
4446         */
4447        if (ss->fork || ss->exit)
4448                return -EINVAL;
4449
4450        /*
4451         * an optionally modular subsystem is built-in: we want to do nothing,
4452         * since cgroup_init_subsys will have already taken care of it.
4453         */
4454        if (ss->module == NULL) {
4455                /* a sanity check */
4456                BUG_ON(subsys[ss->subsys_id] != ss);
4457                return 0;
4458        }
4459
4460        /* init base cftset */
4461        cgroup_init_cftsets(ss);
4462
4463        mutex_lock(&cgroup_mutex);
4464        subsys[ss->subsys_id] = ss;
4465
4466        /*
4467         * no ss->create seems to need anything important in the ss struct, so
4468         * this can happen first (i.e. before the rootnode attachment).
4469         */
4470        css = ss->create(dummytop);
4471        if (IS_ERR(css)) {
4472                /* failure case - need to deassign the subsys[] slot. */
4473                subsys[ss->subsys_id] = NULL;
4474                mutex_unlock(&cgroup_mutex);
4475                return PTR_ERR(css);
4476        }
4477
4478        list_add(&ss->sibling, &rootnode.subsys_list);
4479        ss->root = &rootnode;
4480
4481        /* our new subsystem will be attached to the dummy hierarchy. */
4482        init_cgroup_css(css, ss, dummytop);
4483        /* init_idr must be after init_cgroup_css because it sets css->id. */
4484        if (ss->use_id) {
4485                int ret = cgroup_init_idr(ss, css);
4486                if (ret) {
4487                        dummytop->subsys[ss->subsys_id] = NULL;
4488                        ss->destroy(dummytop);
4489                        subsys[ss->subsys_id] = NULL;
4490                        mutex_unlock(&cgroup_mutex);
4491                        return ret;
4492                }
4493        }
4494
4495        /*
4496         * Now we need to entangle the css into the existing css_sets. unlike
4497         * in cgroup_init_subsys, there are now multiple css_sets, so each one
4498         * will need a new pointer to it; done by iterating the css_set_table.
4499         * furthermore, modifying the existing css_sets will corrupt the hash
4500         * table state, so each changed css_set will need its hash recomputed.
4501         * this is all done under the css_set_lock.
4502         */
4503        write_lock(&css_set_lock);
4504        for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
4505                struct css_set *cg;
4506                struct hlist_node *node, *tmp;
4507                struct hlist_head *bucket = &css_set_table[i], *new_bucket;
4508
4509                hlist_for_each_entry_safe(cg, node, tmp, bucket, hlist) {
4510                        /* skip entries that we already rehashed */
4511                        if (cg->subsys[ss->subsys_id])
4512                                continue;
4513                        /* remove existing entry */
4514                        hlist_del(&cg->hlist);
4515                        /* set new value */
4516                        cg->subsys[ss->subsys_id] = css;
4517                        /* recompute hash and restore entry */
4518                        new_bucket = css_set_hash(cg->subsys);
4519                        hlist_add_head(&cg->hlist, new_bucket);
4520                }
4521        }
4522        write_unlock(&css_set_lock);
4523
4524        ss->active = 1;
4525
4526        /* success! */
4527        mutex_unlock(&cgroup_mutex);
4528        return 0;
4529}
4530EXPORT_SYMBOL_GPL(cgroup_load_subsys);
4531
4532/**
4533 * cgroup_unload_subsys: unload a modular subsystem
4534 * @ss: the subsystem to unload
4535 *
4536 * This function should be called in a modular subsystem's exitcall. When this
4537 * function is invoked, the refcount on the subsystem's module will be 0, so
4538 * the subsystem will not be attached to any hierarchy.
4539 */
4540void cgroup_unload_subsys(struct cgroup_subsys *ss)
4541{
4542        struct cg_cgroup_link *link;
4543        struct hlist_head *hhead;
4544
4545        BUG_ON(ss->module == NULL);
4546
4547        /*
4548         * we shouldn't be called if the subsystem is in use, and the use of
4549         * try_module_get in parse_cgroupfs_options should ensure that it
4550         * doesn't start being used while we're killing it off.
4551         */
4552        BUG_ON(ss->root != &rootnode);
4553
4554        mutex_lock(&cgroup_mutex);
4555        /* deassign the subsys_id */
4556        subsys[ss->subsys_id] = NULL;
4557
4558        /* remove subsystem from rootnode's list of subsystems */
4559        list_del_init(&ss->sibling);
4560
4561        /*
4562         * disentangle the css from all css_sets attached to the dummytop. as
4563         * in loading, we need to pay our respects to the hashtable gods.
4564         */
4565        write_lock(&css_set_lock);
4566        list_for_each_entry(link, &dummytop->css_sets, cgrp_link_list) {
4567                struct css_set *cg = link->cg;
4568
4569                hlist_del(&cg->hlist);
4570                BUG_ON(!cg->subsys[ss->subsys_id]);
4571                cg->subsys[ss->subsys_id] = NULL;
4572                hhead = css_set_hash(cg->subsys);
4573                hlist_add_head(&cg->hlist, hhead);
4574        }
4575        write_unlock(&css_set_lock);
4576
4577        /*
4578         * remove subsystem's css from the dummytop and free it - need to free
4579         * before marking as null because ss->destroy needs the cgrp->subsys
4580         * pointer to find their state. note that this also takes care of
4581         * freeing the css_id.
4582         */
4583        ss->destroy(dummytop);
4584        dummytop->subsys[ss->subsys_id] = NULL;
4585
4586        mutex_unlock(&cgroup_mutex);
4587}
4588EXPORT_SYMBOL_GPL(cgroup_unload_subsys);
4589
4590/**
4591 * cgroup_init_early - cgroup initialization at system boot
4592 *
4593 * Initialize cgroups at system boot, and initialize any
4594 * subsystems that request early init.
4595 */
4596int __init cgroup_init_early(void)
4597{
4598        int i;
4599        atomic_set(&init_css_set.refcount, 1);
4600        INIT_LIST_HEAD(&init_css_set.cg_links);
4601        INIT_LIST_HEAD(&init_css_set.tasks);
4602        INIT_HLIST_NODE(&init_css_set.hlist);
4603        css_set_count = 1;
4604        init_cgroup_root(&rootnode);
4605        root_count = 1;
4606        init_task.cgroups = &init_css_set;
4607
4608        init_css_set_link.cg = &init_css_set;
4609        init_css_set_link.cgrp = dummytop;
4610        list_add(&init_css_set_link.cgrp_link_list,
4611                 &rootnode.top_cgroup.css_sets);
4612        list_add(&init_css_set_link.cg_link_list,
4613                 &init_css_set.cg_links);
4614
4615        for (i = 0; i < CSS_SET_TABLE_SIZE; i++)
4616                INIT_HLIST_HEAD(&css_set_table[i]);
4617
4618        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4619                struct cgroup_subsys *ss = subsys[i];
4620
4621                /* at bootup time, we don't worry about modular subsystems */
4622                if (!ss || ss->module)
4623                        continue;
4624
4625                BUG_ON(!ss->name);
4626                BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
4627                BUG_ON(!ss->create);
4628                BUG_ON(!ss->destroy);
4629                if (ss->subsys_id != i) {
4630                        printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
4631                               ss->name, ss->subsys_id);
4632                        BUG();
4633                }
4634
4635                if (ss->early_init)
4636                        cgroup_init_subsys(ss);
4637        }
4638        return 0;
4639}
4640
4641/**
4642 * cgroup_init - cgroup initialization
4643 *
4644 * Register cgroup filesystem and /proc file, and initialize
4645 * any subsystems that didn't request early init.
4646 */
4647int __init cgroup_init(void)
4648{
4649        int err;
4650        int i;
4651        struct hlist_head *hhead;
4652
4653        err = bdi_init(&cgroup_backing_dev_info);
4654        if (err)
4655                return err;
4656
4657        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4658                struct cgroup_subsys *ss = subsys[i];
4659
4660                /* at bootup time, we don't worry about modular subsystems */
4661                if (!ss || ss->module)
4662                        continue;
4663                if (!ss->early_init)
4664                        cgroup_init_subsys(ss);
4665                if (ss->use_id)
4666                        cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
4667        }
4668
4669        /* Add init_css_set to the hash table */
4670        hhead = css_set_hash(init_css_set.subsys);
4671        hlist_add_head(&init_css_set.hlist, hhead);
4672        BUG_ON(!init_root_id(&rootnode));
4673
4674        cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
4675        if (!cgroup_kobj) {
4676                err = -ENOMEM;
4677                goto out;
4678        }
4679
4680        err = register_filesystem(&cgroup_fs_type);
4681        if (err < 0) {
4682                kobject_put(cgroup_kobj);
4683                goto out;
4684        }
4685
4686        proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
4687
4688out:
4689        if (err)
4690                bdi_destroy(&cgroup_backing_dev_info);
4691
4692        return err;
4693}
4694
4695/*
4696 * proc_cgroup_show()
4697 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
4698 *  - Used for /proc/<pid>/cgroup.
4699 *  - No need to task_lock(tsk) on this tsk->cgroup reference, as it
4700 *    doesn't really matter if tsk->cgroup changes after we read it,
4701 *    and we take cgroup_mutex, keeping cgroup_attach_task() from changing it
4702 *    anyway.  No need to check that tsk->cgroup != NULL, thanks to
4703 *    the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
4704 *    cgroup to top_cgroup.
4705 */
4706
4707/* TODO: Use a proper seq_file iterator */
4708static int proc_cgroup_show(struct seq_file *m, void *v)
4709{
4710        struct pid *pid;
4711        struct task_struct *tsk;
4712        char *buf;
4713        int retval;
4714        struct cgroupfs_root *root;
4715
4716        retval = -ENOMEM;
4717        buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
4718        if (!buf)
4719                goto out;
4720
4721        retval = -ESRCH;
4722        pid = m->private;
4723        tsk = get_pid_task(pid, PIDTYPE_PID);
4724        if (!tsk)
4725                goto out_free;
4726
4727        retval = 0;
4728
4729        mutex_lock(&cgroup_mutex);
4730
4731        for_each_active_root(root) {
4732                struct cgroup_subsys *ss;
4733                struct cgroup *cgrp;
4734                int count = 0;
4735
4736                seq_printf(m, "%d:", root->hierarchy_id);
4737                for_each_subsys(root, ss)
4738                        seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
4739                if (strlen(root->name))
4740                        seq_printf(m, "%sname=%s", count ? "," : "",
4741                                   root->name);
4742                seq_putc(m, ':');
4743                cgrp = task_cgroup_from_root(tsk, root);
4744                retval = cgroup_path(cgrp, buf, PAGE_SIZE);
4745                if (retval < 0)
4746                        goto out_unlock;
4747                seq_puts(m, buf);
4748                seq_putc(m, '\n');
4749        }
4750
4751out_unlock:
4752        mutex_unlock(&cgroup_mutex);
4753        put_task_struct(tsk);
4754out_free:
4755        kfree(buf);
4756out:
4757        return retval;
4758}
4759
4760static int cgroup_open(struct inode *inode, struct file *file)
4761{
4762        struct pid *pid = PROC_I(inode)->pid;
4763        return single_open(file, proc_cgroup_show, pid);
4764}
4765
4766const struct file_operations proc_cgroup_operations = {
4767        .open           = cgroup_open,
4768        .read           = seq_read,
4769        .llseek         = seq_lseek,
4770        .release        = single_release,
4771};
4772
4773/* Display information about each subsystem and each hierarchy */
4774static int proc_cgroupstats_show(struct seq_file *m, void *v)
4775{
4776        int i;
4777
4778        seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
4779        /*
4780         * ideally we don't want subsystems moving around while we do this.
4781         * cgroup_mutex is also necessary to guarantee an atomic snapshot of
4782         * subsys/hierarchy state.
4783         */
4784        mutex_lock(&cgroup_mutex);
4785        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4786                struct cgroup_subsys *ss = subsys[i];
4787                if (ss == NULL)
4788                        continue;
4789                seq_printf(m, "%s\t%d\t%d\t%d\n",
4790                           ss->name, ss->root->hierarchy_id,
4791                           ss->root->number_of_cgroups, !ss->disabled);
4792        }
4793        mutex_unlock(&cgroup_mutex);
4794        return 0;
4795}
4796
4797static int cgroupstats_open(struct inode *inode, struct file *file)
4798{
4799        return single_open(file, proc_cgroupstats_show, NULL);
4800}
4801
4802static const struct file_operations proc_cgroupstats_operations = {
4803        .open = cgroupstats_open,
4804        .read = seq_read,
4805        .llseek = seq_lseek,
4806        .release = single_release,
4807};
4808
4809/**
4810 * cgroup_fork - attach newly forked task to its parents cgroup.
4811 * @child: pointer to task_struct of forking parent process.
4812 *
4813 * Description: A task inherits its parent's cgroup at fork().
4814 *
4815 * A pointer to the shared css_set was automatically copied in
4816 * fork.c by dup_task_struct().  However, we ignore that copy, since
4817 * it was not made under the protection of RCU or cgroup_mutex, so
4818 * might no longer be a valid cgroup pointer.  cgroup_attach_task() might
4819 * have already changed current->cgroups, allowing the previously
4820 * referenced cgroup group to be removed and freed.
4821 *
4822 * At the point that cgroup_fork() is called, 'current' is the parent
4823 * task, and the passed argument 'child' points to the child task.
4824 */
4825void cgroup_fork(struct task_struct *child)
4826{
4827        task_lock(current);
4828        child->cgroups = current->cgroups;
4829        get_css_set(child->cgroups);
4830        task_unlock(current);
4831        INIT_LIST_HEAD(&child->cg_list);
4832}
4833
4834/**
4835 * cgroup_fork_callbacks - run fork callbacks
4836 * @child: the new task
4837 *
4838 * Called on a new task very soon before adding it to the
4839 * tasklist. No need to take any locks since no-one can
4840 * be operating on this task.
4841 */
4842void cgroup_fork_callbacks(struct task_struct *child)
4843{
4844        if (need_forkexit_callback) {
4845                int i;
4846                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4847                        struct cgroup_subsys *ss = subsys[i];
4848
4849                        /*
4850                         * forkexit callbacks are only supported for
4851                         * builtin subsystems.
4852                         */
4853                        if (!ss || ss->module)
4854                                continue;
4855
4856                        if (ss->fork)
4857                                ss->fork(child);
4858                }
4859        }
4860}
4861
4862/**
4863 * cgroup_post_fork - called on a new task after adding it to the task list
4864 * @child: the task in question
4865 *
4866 * Adds the task to the list running through its css_set if necessary.
4867 * Has to be after the task is visible on the task list in case we race
4868 * with the first call to cgroup_iter_start() - to guarantee that the
4869 * new task ends up on its list.
4870 */
4871void cgroup_post_fork(struct task_struct *child)
4872{
4873        /*
4874         * use_task_css_set_links is set to 1 before we walk the tasklist
4875         * under the tasklist_lock and we read it here after we added the child
4876         * to the tasklist under the tasklist_lock as well. If the child wasn't
4877         * yet in the tasklist when we walked through it from
4878         * cgroup_enable_task_cg_lists(), then use_task_css_set_links value
4879         * should be visible now due to the paired locking and barriers implied
4880         * by LOCK/UNLOCK: it is written before the tasklist_lock unlock
4881         * in cgroup_enable_task_cg_lists() and read here after the tasklist_lock
4882         * lock on fork.
4883         */
4884        if (use_task_css_set_links) {
4885                write_lock(&css_set_lock);
4886                task_lock(child);
4887                if (list_empty(&child->cg_list))
4888                        list_add(&child->cg_list, &child->cgroups->tasks);
4889                task_unlock(child);
4890                write_unlock(&css_set_lock);
4891        }
4892}
4893/**
4894 * cgroup_exit - detach cgroup from exiting task
4895 * @tsk: pointer to task_struct of exiting process
4896 * @run_callback: run exit callbacks?
4897 *
4898 * Description: Detach cgroup from @tsk and release it.
4899 *
4900 * Note that cgroups marked notify_on_release force every task in
4901 * them to take the global cgroup_mutex mutex when exiting.
4902 * This could impact scaling on very large systems.  Be reluctant to
4903 * use notify_on_release cgroups where very high task exit scaling
4904 * is required on large systems.
4905 *
4906 * the_top_cgroup_hack:
4907 *
4908 *    Set the exiting tasks cgroup to the root cgroup (top_cgroup).
4909 *
4910 *    We call cgroup_exit() while the task is still competent to
4911 *    handle notify_on_release(), then leave the task attached to the
4912 *    root cgroup in each hierarchy for the remainder of its exit.
4913 *
4914 *    To do this properly, we would increment the reference count on
4915 *    top_cgroup, and near the very end of the kernel/exit.c do_exit()
4916 *    code we would add a second cgroup function call, to drop that
4917 *    reference.  This would just create an unnecessary hot spot on
4918 *    the top_cgroup reference count, to no avail.
4919 *
4920 *    Normally, holding a reference to a cgroup without bumping its
4921 *    count is unsafe.   The cgroup could go away, or someone could
4922 *    attach us to a different cgroup, decrementing the count on
4923 *    the first cgroup that we never incremented.  But in this case,
4924 *    top_cgroup isn't going away, and either task has PF_EXITING set,
4925 *    which wards off any cgroup_attach_task() attempts, or task is a failed
4926 *    fork, never visible to cgroup_attach_task.
4927 */
4928void cgroup_exit(struct task_struct *tsk, int run_callbacks)
4929{
4930        struct css_set *cg;
4931        int i;
4932
4933        /*
4934         * Unlink from the css_set task list if necessary.
4935         * Optimistically check cg_list before taking
4936         * css_set_lock
4937         */
4938        if (!list_empty(&tsk->cg_list)) {
4939                write_lock(&css_set_lock);
4940                if (!list_empty(&tsk->cg_list))
4941                        list_del_init(&tsk->cg_list);
4942                write_unlock(&css_set_lock);
4943        }
4944
4945        /* Reassign the task to the init_css_set. */
4946        task_lock(tsk);
4947        cg = tsk->cgroups;
4948        tsk->cgroups = &init_css_set;
4949
4950        if (run_callbacks && need_forkexit_callback) {
4951                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
4952                        struct cgroup_subsys *ss = subsys[i];
4953
4954                        /* modular subsystems can't use callbacks */
4955                        if (!ss || ss->module)
4956                                continue;
4957
4958                        if (ss->exit) {
4959                                struct cgroup *old_cgrp =
4960                                        rcu_dereference_raw(cg->subsys[i])->cgroup;
4961                                struct cgroup *cgrp = task_cgroup(tsk, i);
4962                                ss->exit(cgrp, old_cgrp, tsk);
4963                        }
4964                }
4965        }
4966        task_unlock(tsk);
4967
4968        if (cg)
4969                put_css_set_taskexit(cg);
4970}
4971
4972/**
4973 * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp
4974 * @cgrp: the cgroup in question
4975 * @task: the task in question
4976 *
4977 * See if @cgrp is a descendant of @task's cgroup in the appropriate
4978 * hierarchy.
4979 *
4980 * If we are sending in dummytop, then presumably we are creating
4981 * the top cgroup in the subsystem.
4982 *
4983 * Called only by the ns (nsproxy) cgroup.
4984 */
4985int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
4986{
4987        int ret;
4988        struct cgroup *target;
4989
4990        if (cgrp == dummytop)
4991                return 1;
4992
4993        target = task_cgroup_from_root(task, cgrp->root);
4994        while (cgrp != target && cgrp!= cgrp->top_cgroup)
4995                cgrp = cgrp->parent;
4996        ret = (cgrp == target);
4997        return ret;
4998}
4999
5000static void check_for_release(struct cgroup *cgrp)
5001{
5002        /* All of these checks rely on RCU to keep the cgroup
5003         * structure alive */
5004        if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count)
5005            && list_empty(&cgrp->children) && !cgroup_has_css_refs(cgrp)) {
5006                /* Control Group is currently removeable. If it's not
5007                 * already queued for a userspace notification, queue
5008                 * it now */
5009                int need_schedule_work = 0;
5010                raw_spin_lock(&release_list_lock);
5011                if (!cgroup_is_removed(cgrp) &&
5012                    list_empty(&cgrp->release_list)) {
5013                        list_add(&cgrp->release_list, &release_list);
5014                        need_schedule_work = 1;
5015                }
5016                raw_spin_unlock(&release_list_lock);
5017                if (need_schedule_work)
5018                        schedule_work(&release_agent_work);
5019        }
5020}
5021
5022/* Caller must verify that the css is not for root cgroup */
5023bool __css_tryget(struct cgroup_subsys_state *css)
5024{
5025        do {
5026                int v = css_refcnt(css);
5027
5028                if (atomic_cmpxchg(&css->refcnt, v, v + 1) == v)
5029                        return true;
5030                cpu_relax();
5031        } while (!test_bit(CSS_REMOVED, &css->flags));
5032
5033        return false;
5034}
5035EXPORT_SYMBOL_GPL(__css_tryget);
5036
5037/* Caller must verify that the css is not for root cgroup */
5038void __css_put(struct cgroup_subsys_state *css)
5039{
5040        struct cgroup *cgrp = css->cgroup;
5041        int v;
5042
5043        rcu_read_lock();
5044        v = css_unbias_refcnt(atomic_dec_return(&css->refcnt));
5045
5046        switch (v) {
5047        case 1:
5048                if (notify_on_release(cgrp)) {
5049                        set_bit(CGRP_RELEASABLE, &cgrp->flags);
5050                        check_for_release(cgrp);
5051                }
5052                cgroup_wakeup_rmdir_waiter(cgrp);
5053                break;
5054        case 0:
5055                if (!test_bit(CSS_CLEAR_CSS_REFS, &css->flags))
5056                        schedule_work(&css->dput_work);
5057                break;
5058        }
5059        rcu_read_unlock();
5060}
5061EXPORT_SYMBOL_GPL(__css_put);
5062
5063/*
5064 * Notify userspace when a cgroup is released, by running the
5065 * configured release agent with the name of the cgroup (path
5066 * relative to the root of cgroup file system) as the argument.
5067 *
5068 * Most likely, this user command will try to rmdir this cgroup.
5069 *
5070 * This races with the possibility that some other task will be
5071 * attached to this cgroup before it is removed, or that some other
5072 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
5073 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
5074 * unused, and this cgroup will be reprieved from its death sentence,
5075 * to continue to serve a useful existence.  Next time it's released,
5076 * we will get notified again, if it still has 'notify_on_release' set.
5077 *
5078 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
5079 * means only wait until the task is successfully execve()'d.  The
5080 * separate release agent task is forked by call_usermodehelper(),
5081 * then control in this thread returns here, without waiting for the
5082 * release agent task.  We don't bother to wait because the caller of
5083 * this routine has no use for the exit status of the release agent
5084 * task, so no sense holding our caller up for that.
5085 */
5086static void cgroup_release_agent(struct work_struct *work)
5087{
5088        BUG_ON(work != &release_agent_work);
5089        mutex_lock(&cgroup_mutex);
5090        raw_spin_lock(&release_list_lock);
5091        while (!list_empty(&release_list)) {
5092                char *argv[3], *envp[3];
5093                int i;
5094                char *pathbuf = NULL, *agentbuf = NULL;
5095                struct cgroup *cgrp = list_entry(release_list.next,
5096                                                    struct cgroup,
5097                                                    release_list);
5098                list_del_init(&cgrp->release_list);
5099                raw_spin_unlock(&release_list_lock);
5100                pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
5101                if (!pathbuf)
5102                        goto continue_free;
5103                if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
5104                        goto continue_free;
5105                agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
5106                if (!agentbuf)
5107                        goto continue_free;
5108
5109                i = 0;
5110                argv[i++] = agentbuf;
5111                argv[i++] = pathbuf;
5112                argv[i] = NULL;
5113
5114                i = 0;
5115                /* minimal command environment */
5116                envp[i++] = "HOME=/";
5117                envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
5118                envp[i] = NULL;
5119
5120                /* Drop the lock while we invoke the usermode helper,
5121                 * since the exec could involve hitting disk and hence
5122                 * be a slow process */
5123                mutex_unlock(&cgroup_mutex);
5124                call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
5125                mutex_lock(&cgroup_mutex);
5126 continue_free:
5127                kfree(pathbuf);
5128                kfree(agentbuf);
5129                raw_spin_lock(&release_list_lock);
5130        }
5131        raw_spin_unlock(&release_list_lock);
5132        mutex_unlock(&cgroup_mutex);
5133}
5134
5135static int __init cgroup_disable(char *str)
5136{
5137        int i;
5138        char *token;
5139
5140        while ((token = strsep(&str, ",")) != NULL) {
5141                if (!*token)
5142                        continue;
5143                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
5144                        struct cgroup_subsys *ss = subsys[i];
5145
5146                        /*
5147                         * cgroup_disable, being at boot time, can't
5148                         * know about module subsystems, so we don't
5149                         * worry about them.
5150                         */
5151                        if (!ss || ss->module)
5152                                continue;
5153
5154                        if (!strcmp(token, ss->name)) {
5155                                ss->disabled = 1;
5156                                printk(KERN_INFO "Disabling %s control group"
5157                                        " subsystem\n", ss->name);
5158                                break;
5159                        }
5160                }
5161        }
5162        return 1;
5163}
5164__setup("cgroup_disable=", cgroup_disable);
5165
5166/*
5167 * Functons for CSS ID.
5168 */
5169
5170/*
5171 *To get ID other than 0, this should be called when !cgroup_is_removed().
5172 */
5173unsigned short css_id(struct cgroup_subsys_state *css)
5174{
5175        struct css_id *cssid;
5176
5177        /*
5178         * This css_id() can return correct value when somone has refcnt
5179         * on this or this is under rcu_read_lock(). Once css->id is allocated,
5180         * it's unchanged until freed.
5181         */
5182        cssid = rcu_dereference_check(css->id, css_refcnt(css));
5183
5184        if (cssid)
5185                return cssid->id;
5186        return 0;
5187}
5188EXPORT_SYMBOL_GPL(css_id);
5189
5190unsigned short css_depth(struct cgroup_subsys_state *css)
5191{
5192        struct css_id *cssid;
5193
5194        cssid = rcu_dereference_check(css->id, css_refcnt(css));
5195
5196        if (cssid)
5197                return cssid->depth;
5198        return 0;
5199}
5200EXPORT_SYMBOL_GPL(css_depth);
5201
5202/**
5203 *  css_is_ancestor - test "root" css is an ancestor of "child"
5204 * @child: the css to be tested.
5205 * @root: the css supporsed to be an ancestor of the child.
5206 *
5207 * Returns true if "root" is an ancestor of "child" in its hierarchy. Because
5208 * this function reads css->id, the caller must hold rcu_read_lock().
5209 * But, considering usual usage, the csses should be valid objects after test.
5210 * Assuming that the caller will do some action to the child if this returns
5211 * returns true, the caller must take "child";s reference count.
5212 * If "child" is valid object and this returns true, "root" is valid, too.
5213 */
5214
5215bool css_is_ancestor(struct cgroup_subsys_state *child,
5216                    const struct cgroup_subsys_state *root)
5217{
5218        struct css_id *child_id;
5219        struct css_id *root_id;
5220
5221        child_id  = rcu_dereference(child->id);
5222        if (!child_id)
5223                return false;
5224        root_id = rcu_dereference(root->id);
5225        if (!root_id)
5226                return false;
5227        if (child_id->depth < root_id->depth)
5228                return false;
5229        if (child_id->stack[root_id->depth] != root_id->id)
5230                return false;
5231        return true;
5232}
5233
5234void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
5235{
5236        struct css_id *id = css->id;
5237        /* When this is called before css_id initialization, id can be NULL */
5238        if (!id)
5239                return;
5240
5241        BUG_ON(!ss->use_id);
5242
5243        rcu_assign_pointer(id->css, NULL);
5244        rcu_assign_pointer(css->id, NULL);
5245        spin_lock(&ss->id_lock);
5246        idr_remove(&ss->idr, id->id);
5247        spin_unlock(&ss->id_lock);
5248        kfree_rcu(id, rcu_head);
5249}
5250EXPORT_SYMBOL_GPL(free_css_id);
5251
5252/*
5253 * This is called by init or create(). Then, calls to this function are
5254 * always serialized (By cgroup_mutex() at create()).
5255 */
5256
5257static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
5258{
5259        struct css_id *newid;
5260        int myid, error, size;
5261
5262        BUG_ON(!ss->use_id);
5263
5264        size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
5265        newid = kzalloc(size, GFP_KERNEL);
5266        if (!newid)
5267                return ERR_PTR(-ENOMEM);
5268        /* get id */
5269        if (unlikely(!idr_pre_get(&ss->idr, GFP_KERNEL))) {
5270                error = -ENOMEM;
5271                goto err_out;
5272        }
5273        spin_lock(&ss->id_lock);
5274        /* Don't use 0. allocates an ID of 1-65535 */
5275        error = idr_get_new_above(&ss->idr, newid, 1, &myid);
5276        spin_unlock(&ss->id_lock);
5277
5278        /* Returns error when there are no free spaces for new ID.*/
5279        if (error) {
5280                error = -ENOSPC;
5281                goto err_out;
5282        }
5283        if (myid > CSS_ID_MAX)
5284                goto remove_idr;
5285
5286        newid->id = myid;
5287        newid->depth = depth;
5288        return newid;
5289remove_idr:
5290        error = -ENOSPC;
5291        spin_lock(&ss->id_lock);
5292        idr_remove(&ss->idr, myid);
5293        spin_unlock(&ss->id_lock);
5294err_out:
5295        kfree(newid);
5296        return ERR_PTR(error);
5297
5298}
5299
5300static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
5301                                            struct cgroup_subsys_state *rootcss)
5302{
5303        struct css_id *newid;
5304
5305        spin_lock_init(&ss->id_lock);
5306        idr_init(&ss->idr);
5307
5308        newid = get_new_cssid(ss, 0);
5309        if (IS_ERR(newid))
5310                return PTR_ERR(newid);
5311
5312        newid->stack[0] = newid->id;
5313        newid->css = rootcss;
5314        rootcss->id = newid;
5315        return 0;
5316}
5317
5318static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
5319                        struct cgroup *child)
5320{
5321        int subsys_id, i, depth = 0;
5322        struct cgroup_subsys_state *parent_css, *child_css;
5323        struct css_id *child_id, *parent_id;
5324
5325        subsys_id = ss->subsys_id;
5326        parent_css = parent->subsys[subsys_id];
5327        child_css = child->subsys[subsys_id];
5328        parent_id = parent_css->id;
5329        depth = parent_id->depth + 1;
5330
5331        child_id = get_new_cssid(ss, depth);
5332        if (IS_ERR(child_id))
5333                return PTR_ERR(child_id);
5334
5335        for (i = 0; i < depth; i++)
5336                child_id->stack[i] = parent_id->stack[i];
5337        child_id->stack[depth] = child_id->id;
5338        /*
5339         * child_id->css pointer will be set after this cgroup is available
5340         * see cgroup_populate_dir()
5341         */
5342        rcu_assign_pointer(child_css->id, child_id);
5343
5344        return 0;
5345}
5346
5347/**
5348 * css_lookup - lookup css by id
5349 * @ss: cgroup subsys to be looked into.
5350 * @id: the id
5351 *
5352 * Returns pointer to cgroup_subsys_state if there is valid one with id.
5353 * NULL if not. Should be called under rcu_read_lock()
5354 */
5355struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
5356{
5357        struct css_id *cssid = NULL;
5358
5359        BUG_ON(!ss->use_id);
5360        cssid = idr_find(&ss->idr, id);
5361
5362        if (unlikely(!cssid))
5363                return NULL;
5364
5365        return rcu_dereference(cssid->css);
5366}
5367EXPORT_SYMBOL_GPL(css_lookup);
5368
5369/**
5370 * css_get_next - lookup next cgroup under specified hierarchy.
5371 * @ss: pointer to subsystem
5372 * @id: current position of iteration.
5373 * @root: pointer to css. search tree under this.
5374 * @foundid: position of found object.
5375 *
5376 * Search next css under the specified hierarchy of rootid. Calling under
5377 * rcu_read_lock() is necessary. Returns NULL if it reaches the end.
5378 */
5379struct cgroup_subsys_state *
5380css_get_next(struct cgroup_subsys *ss, int id,
5381             struct cgroup_subsys_state *root, int *foundid)
5382{
5383        struct cgroup_subsys_state *ret = NULL;
5384        struct css_id *tmp;
5385        int tmpid;
5386        int rootid = css_id(root);
5387        int depth = css_depth(root);
5388
5389        if (!rootid)
5390                return NULL;
5391
5392        BUG_ON(!ss->use_id);
5393        WARN_ON_ONCE(!rcu_read_lock_held());
5394
5395        /* fill start point for scan */
5396        tmpid = id;
5397        while (1) {
5398                /*
5399                 * scan next entry from bitmap(tree), tmpid is updated after
5400                 * idr_get_next().
5401                 */
5402                tmp = idr_get_next(&ss->idr, &tmpid);
5403                if (!tmp)
5404                        break;
5405                if (tmp->depth >= depth && tmp->stack[depth] == rootid) {
5406                        ret = rcu_dereference(tmp->css);
5407                        if (ret) {
5408                                *foundid = tmpid;
5409                                break;
5410                        }
5411                }
5412                /* continue to scan from next id */
5413                tmpid = tmpid + 1;
5414        }
5415        return ret;
5416}
5417
5418/*
5419 * get corresponding css from file open on cgroupfs directory
5420 */
5421struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
5422{
5423        struct cgroup *cgrp;
5424        struct inode *inode;
5425        struct cgroup_subsys_state *css;
5426
5427        inode = f->f_dentry->d_inode;
5428        /* check in cgroup filesystem dir */
5429        if (inode->i_op != &cgroup_dir_inode_operations)
5430                return ERR_PTR(-EBADF);
5431
5432        if (id < 0 || id >= CGROUP_SUBSYS_COUNT)
5433                return ERR_PTR(-EINVAL);
5434
5435        /* get cgroup */
5436        cgrp = __d_cgrp(f->f_dentry);
5437        css = cgrp->subsys[id];
5438        return css ? css : ERR_PTR(-ENOENT);
5439}
5440
5441#ifdef CONFIG_CGROUP_DEBUG
5442static struct cgroup_subsys_state *debug_create(struct cgroup *cont)
5443{
5444        struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL);
5445
5446        if (!css)
5447                return ERR_PTR(-ENOMEM);
5448
5449        return css;
5450}
5451
5452static void debug_destroy(struct cgroup *cont)
5453{
5454        kfree(cont->subsys[debug_subsys_id]);
5455}
5456
5457static u64 cgroup_refcount_read(struct cgroup *cont, struct cftype *cft)
5458{
5459        return atomic_read(&cont->count);
5460}
5461
5462static u64 debug_taskcount_read(struct cgroup *cont, struct cftype *cft)
5463{
5464        return cgroup_task_count(cont);
5465}
5466
5467static u64 current_css_set_read(struct cgroup *cont, struct cftype *cft)
5468{
5469        return (u64)(unsigned long)current->cgroups;
5470}
5471
5472static u64 current_css_set_refcount_read(struct cgroup *cont,
5473                                           struct cftype *cft)
5474{
5475        u64 count;
5476
5477        rcu_read_lock();
5478        count = atomic_read(&current->cgroups->refcount);
5479        rcu_read_unlock();
5480        return count;
5481}
5482
5483static int current_css_set_cg_links_read(struct cgroup *cont,
5484                                         struct cftype *cft,
5485                                         struct seq_file *seq)
5486{
5487        struct cg_cgroup_link *link;
5488        struct css_set *cg;
5489
5490        read_lock(&css_set_lock);
5491        rcu_read_lock();
5492        cg = rcu_dereference(current->cgroups);
5493        list_for_each_entry(link, &cg->cg_links, cg_link_list) {
5494                struct cgroup *c = link->cgrp;
5495                const char *name;
5496
5497                if (c->dentry)
5498                        name = c->dentry->d_name.name;
5499                else
5500                        name = "?";
5501                seq_printf(seq, "Root %d group %s\n",
5502                           c->root->hierarchy_id, name);
5503        }
5504        rcu_read_unlock();
5505        read_unlock(&css_set_lock);
5506        return 0;
5507}
5508
5509#define MAX_TASKS_SHOWN_PER_CSS 25
5510static int cgroup_css_links_read(struct cgroup *cont,
5511                                 struct cftype *cft,
5512                                 struct seq_file *seq)
5513{
5514        struct cg_cgroup_link *link;
5515
5516        read_lock(&css_set_lock);
5517        list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
5518                struct css_set *cg = link->cg;
5519                struct task_struct *task;
5520                int count = 0;
5521                seq_printf(seq, "css_set %p\n", cg);
5522                list_for_each_entry(task, &cg->tasks, cg_list) {
5523                        if (count++ > MAX_TASKS_SHOWN_PER_CSS) {
5524                                seq_puts(seq, "  ...\n");
5525                                break;
5526                        } else {
5527                                seq_printf(seq, "  task %d\n",
5528                                           task_pid_vnr(task));
5529                        }
5530                }
5531        }
5532        read_unlock(&css_set_lock);
5533        return 0;
5534}
5535
5536static u64 releasable_read(struct cgroup *cgrp, struct cftype *cft)
5537{
5538        return test_bit(CGRP_RELEASABLE, &cgrp->flags);
5539}
5540
5541static struct cftype debug_files[] =  {
5542        {
5543                .name = "cgroup_refcount",
5544                .read_u64 = cgroup_refcount_read,
5545        },
5546        {
5547                .name = "taskcount",
5548                .read_u64 = debug_taskcount_read,
5549        },
5550
5551        {
5552                .name = "current_css_set",
5553                .read_u64 = current_css_set_read,
5554        },
5555
5556        {
5557                .name = "current_css_set_refcount",
5558                .read_u64 = current_css_set_refcount_read,
5559        },
5560
5561        {
5562                .name = "current_css_set_cg_links",
5563                .read_seq_string = current_css_set_cg_links_read,
5564        },
5565
5566        {
5567                .name = "cgroup_css_links",
5568                .read_seq_string = cgroup_css_links_read,
5569        },
5570
5571        {
5572                .name = "releasable",
5573                .read_u64 = releasable_read,
5574        },
5575
5576        { }     /* terminate */
5577};
5578
5579struct cgroup_subsys debug_subsys = {
5580        .name = "debug",
5581        .create = debug_create,
5582        .destroy = debug_destroy,
5583        .subsys_id = debug_subsys_id,
5584        .base_cftypes = debug_files,
5585};
5586#endif /* CONFIG_CGROUP_DEBUG */
5587
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