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 *  Copyright notices from the original cpuset code:
   8 *  --------------------------------------------------
   9 *  Copyright (C) 2003 BULL SA.
  10 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
  11 *
  12 *  Portions derived from Patrick Mochel's sysfs code.
  13 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
  14 *
  15 *  2003-10-10 Written by Simon Derr.
  16 *  2003-10-22 Updates by Stephen Hemminger.
  17 *  2004 May-July Rework by Paul Jackson.
  18 *  ---------------------------------------------------
  19 *
  20 *  This file is subject to the terms and conditions of the GNU General Public
  21 *  License.  See the file COPYING in the main directory of the Linux
  22 *  distribution for more details.
  23 */
  24
  25#include <linux/cgroup.h>
  26#include <linux/errno.h>
  27#include <linux/fs.h>
  28#include <linux/kernel.h>
  29#include <linux/list.h>
  30#include <linux/mm.h>
  31#include <linux/mutex.h>
  32#include <linux/mount.h>
  33#include <linux/pagemap.h>
  34#include <linux/proc_fs.h>
  35#include <linux/rcupdate.h>
  36#include <linux/sched.h>
  37#include <linux/backing-dev.h>
  38#include <linux/seq_file.h>
  39#include <linux/slab.h>
  40#include <linux/magic.h>
  41#include <linux/spinlock.h>
  42#include <linux/string.h>
  43#include <linux/sort.h>
  44#include <linux/kmod.h>
  45#include <linux/delayacct.h>
  46#include <linux/cgroupstats.h>
  47#include <linux/hash.h>
  48#include <linux/namei.h>
  49
  50#include <asm/atomic.h>
  51
  52static DEFINE_MUTEX(cgroup_mutex);
  53
  54/* Generate an array of cgroup subsystem pointers */
  55#define SUBSYS(_x) &_x ## _subsys,
  56
  57static struct cgroup_subsys *subsys[] = {
  58#include <linux/cgroup_subsys.h>
  59};
  60
  61/*
  62 * A cgroupfs_root represents the root of a cgroup hierarchy,
  63 * and may be associated with a superblock to form an active
  64 * hierarchy
  65 */
  66struct cgroupfs_root {
  67        struct super_block *sb;
  68
  69        /*
  70         * The bitmask of subsystems intended to be attached to this
  71         * hierarchy
  72         */
  73        unsigned long subsys_bits;
  74
  75        /* The bitmask of subsystems currently attached to this hierarchy */
  76        unsigned long actual_subsys_bits;
  77
  78        /* A list running through the attached subsystems */
  79        struct list_head subsys_list;
  80
  81        /* The root cgroup for this hierarchy */
  82        struct cgroup top_cgroup;
  83
  84        /* Tracks how many cgroups are currently defined in hierarchy.*/
  85        int number_of_cgroups;
  86
  87        /* A list running through the active hierarchies */
  88        struct list_head root_list;
  89
  90        /* Hierarchy-specific flags */
  91        unsigned long flags;
  92
  93        /* The path to use for release notifications. */
  94        char release_agent_path[PATH_MAX];
  95};
  96
  97/*
  98 * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
  99 * subsystems that are otherwise unattached - it never has more than a
 100 * single cgroup, and all tasks are part of that cgroup.
 101 */
 102static struct cgroupfs_root rootnode;
 103
 104/*
 105 * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
 106 * cgroup_subsys->use_id != 0.
 107 */
 108#define CSS_ID_MAX      (65535)
 109struct css_id {
 110        /*
 111         * The css to which this ID points. This pointer is set to valid value
 112         * after cgroup is populated. If cgroup is removed, this will be NULL.
 113         * This pointer is expected to be RCU-safe because destroy()
 114         * is called after synchronize_rcu(). But for safe use, css_is_removed()
 115         * css_tryget() should be used for avoiding race.
 116         */
 117        struct cgroup_subsys_state *css;
 118        /*
 119         * ID of this css.
 120         */
 121        unsigned short id;
 122        /*
 123         * Depth in hierarchy which this ID belongs to.
 124         */
 125        unsigned short depth;
 126        /*
 127         * ID is freed by RCU. (and lookup routine is RCU safe.)
 128         */
 129        struct rcu_head rcu_head;
 130        /*
 131         * Hierarchy of CSS ID belongs to.
 132         */
 133        unsigned short stack[0]; /* Array of Length (depth+1) */
 134};
 135
 136
 137/* The list of hierarchy roots */
 138
 139static LIST_HEAD(roots);
 140static int root_count;
 141
 142/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
 143#define dummytop (&rootnode.top_cgroup)
 144
 145/* This flag indicates whether tasks in the fork and exit paths should
 146 * check for fork/exit handlers to call. This avoids us having to do
 147 * extra work in the fork/exit path if none of the subsystems need to
 148 * be called.
 149 */
 150static int need_forkexit_callback __read_mostly;
 151
 152/* convenient tests for these bits */
 153inline int cgroup_is_removed(const struct cgroup *cgrp)
 154{
 155        return test_bit(CGRP_REMOVED, &cgrp->flags);
 156}
 157
 158/* bits in struct cgroupfs_root flags field */
 159enum {
 160        ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
 161};
 162
 163static int cgroup_is_releasable(const struct cgroup *cgrp)
 164{
 165        const int bits =
 166                (1 << CGRP_RELEASABLE) |
 167                (1 << CGRP_NOTIFY_ON_RELEASE);
 168        return (cgrp->flags & bits) == bits;
 169}
 170
 171static int notify_on_release(const struct cgroup *cgrp)
 172{
 173        return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
 174}
 175
 176/*
 177 * for_each_subsys() allows you to iterate on each subsystem attached to
 178 * an active hierarchy
 179 */
 180#define for_each_subsys(_root, _ss) \
 181list_for_each_entry(_ss, &_root->subsys_list, sibling)
 182
 183/* for_each_active_root() allows you to iterate across the active hierarchies */
 184#define for_each_active_root(_root) \
 185list_for_each_entry(_root, &roots, root_list)
 186
 187/* the list of cgroups eligible for automatic release. Protected by
 188 * release_list_lock */
 189static LIST_HEAD(release_list);
 190static DEFINE_SPINLOCK(release_list_lock);
 191static void cgroup_release_agent(struct work_struct *work);
 192static DECLARE_WORK(release_agent_work, cgroup_release_agent);
 193static void check_for_release(struct cgroup *cgrp);
 194
 195/* Link structure for associating css_set objects with cgroups */
 196struct cg_cgroup_link {
 197        /*
 198         * List running through cg_cgroup_links associated with a
 199         * cgroup, anchored on cgroup->css_sets
 200         */
 201        struct list_head cgrp_link_list;
 202        /*
 203         * List running through cg_cgroup_links pointing at a
 204         * single css_set object, anchored on css_set->cg_links
 205         */
 206        struct list_head cg_link_list;
 207        struct css_set *cg;
 208};
 209
 210/* The default css_set - used by init and its children prior to any
 211 * hierarchies being mounted. It contains a pointer to the root state
 212 * for each subsystem. Also used to anchor the list of css_sets. Not
 213 * reference-counted, to improve performance when child cgroups
 214 * haven't been created.
 215 */
 216
 217static struct css_set init_css_set;
 218static struct cg_cgroup_link init_css_set_link;
 219
 220static int cgroup_subsys_init_idr(struct cgroup_subsys *ss);
 221
 222/* css_set_lock protects the list of css_set objects, and the
 223 * chain of tasks off each css_set.  Nests outside task->alloc_lock
 224 * due to cgroup_iter_start() */
 225static DEFINE_RWLOCK(css_set_lock);
 226static int css_set_count;
 227
 228/* hash table for cgroup groups. This improves the performance to
 229 * find an existing css_set */
 230#define CSS_SET_HASH_BITS       7
 231#define CSS_SET_TABLE_SIZE      (1 << CSS_SET_HASH_BITS)
 232static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];
 233
 234static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
 235{
 236        int i;
 237        int index;
 238        unsigned long tmp = 0UL;
 239
 240        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
 241                tmp += (unsigned long)css[i];
 242        tmp = (tmp >> 16) ^ tmp;
 243
 244        index = hash_long(tmp, CSS_SET_HASH_BITS);
 245
 246        return &css_set_table[index];
 247}
 248
 249/* We don't maintain the lists running through each css_set to its
 250 * task until after the first call to cgroup_iter_start(). This
 251 * reduces the fork()/exit() overhead for people who have cgroups
 252 * compiled into their kernel but not actually in use */
 253static int use_task_css_set_links __read_mostly;
 254
 255/* When we create or destroy a css_set, the operation simply
 256 * takes/releases a reference count on all the cgroups referenced
 257 * by subsystems in this css_set. This can end up multiple-counting
 258 * some cgroups, but that's OK - the ref-count is just a
 259 * busy/not-busy indicator; ensuring that we only count each cgroup
 260 * once would require taking a global lock to ensure that no
 261 * subsystems moved between hierarchies while we were doing so.
 262 *
 263 * Possible TODO: decide at boot time based on the number of
 264 * registered subsystems and the number of CPUs or NUMA nodes whether
 265 * it's better for performance to ref-count every subsystem, or to
 266 * take a global lock and only add one ref count to each hierarchy.
 267 */
 268
 269/*
 270 * unlink a css_set from the list and free it
 271 */
 272static void unlink_css_set(struct css_set *cg)
 273{
 274        struct cg_cgroup_link *link;
 275        struct cg_cgroup_link *saved_link;
 276
 277        hlist_del(&cg->hlist);
 278        css_set_count--;
 279
 280        list_for_each_entry_safe(link, saved_link, &cg->cg_links,
 281                                 cg_link_list) {
 282                list_del(&link->cg_link_list);
 283                list_del(&link->cgrp_link_list);
 284                kfree(link);
 285        }
 286}
 287
 288static void __put_css_set(struct css_set *cg, int taskexit)
 289{
 290        int i;
 291        /*
 292         * Ensure that the refcount doesn't hit zero while any readers
 293         * can see it. Similar to atomic_dec_and_lock(), but for an
 294         * rwlock
 295         */
 296        if (atomic_add_unless(&cg->refcount, -1, 1))
 297                return;
 298        write_lock(&css_set_lock);
 299        if (!atomic_dec_and_test(&cg->refcount)) {
 300                write_unlock(&css_set_lock);
 301                return;
 302        }
 303        unlink_css_set(cg);
 304        write_unlock(&css_set_lock);
 305
 306        rcu_read_lock();
 307        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 308                struct cgroup *cgrp = rcu_dereference(cg->subsys[i]->cgroup);
 309                if (atomic_dec_and_test(&cgrp->count) &&
 310                    notify_on_release(cgrp)) {
 311                        if (taskexit)
 312                                set_bit(CGRP_RELEASABLE, &cgrp->flags);
 313                        check_for_release(cgrp);
 314                }
 315        }
 316        rcu_read_unlock();
 317        kfree(cg);
 318}
 319
 320/*
 321 * refcounted get/put for css_set objects
 322 */
 323static inline void get_css_set(struct css_set *cg)
 324{
 325        atomic_inc(&cg->refcount);
 326}
 327
 328static inline void put_css_set(struct css_set *cg)
 329{
 330        __put_css_set(cg, 0);
 331}
 332
 333static inline void put_css_set_taskexit(struct css_set *cg)
 334{
 335        __put_css_set(cg, 1);
 336}
 337
 338/*
 339 * find_existing_css_set() is a helper for
 340 * find_css_set(), and checks to see whether an existing
 341 * css_set is suitable.
 342 *
 343 * oldcg: the cgroup group that we're using before the cgroup
 344 * transition
 345 *
 346 * cgrp: the cgroup that we're moving into
 347 *
 348 * template: location in which to build the desired set of subsystem
 349 * state objects for the new cgroup group
 350 */
 351static struct css_set *find_existing_css_set(
 352        struct css_set *oldcg,
 353        struct cgroup *cgrp,
 354        struct cgroup_subsys_state *template[])
 355{
 356        int i;
 357        struct cgroupfs_root *root = cgrp->root;
 358        struct hlist_head *hhead;
 359        struct hlist_node *node;
 360        struct css_set *cg;
 361
 362        /* Built the set of subsystem state objects that we want to
 363         * see in the new css_set */
 364        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 365                if (root->subsys_bits & (1UL << i)) {
 366                        /* Subsystem is in this hierarchy. So we want
 367                         * the subsystem state from the new
 368                         * cgroup */
 369                        template[i] = cgrp->subsys[i];
 370                } else {
 371                        /* Subsystem is not in this hierarchy, so we
 372                         * don't want to change the subsystem state */
 373                        template[i] = oldcg->subsys[i];
 374                }
 375        }
 376
 377        hhead = css_set_hash(template);
 378        hlist_for_each_entry(cg, node, hhead, hlist) {
 379                if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
 380                        /* All subsystems matched */
 381                        return cg;
 382                }
 383        }
 384
 385        /* No existing cgroup group matched */
 386        return NULL;
 387}
 388
 389static void free_cg_links(struct list_head *tmp)
 390{
 391        struct cg_cgroup_link *link;
 392        struct cg_cgroup_link *saved_link;
 393
 394        list_for_each_entry_safe(link, saved_link, tmp, cgrp_link_list) {
 395                list_del(&link->cgrp_link_list);
 396                kfree(link);
 397        }
 398}
 399
 400/*
 401 * allocate_cg_links() allocates "count" cg_cgroup_link structures
 402 * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
 403 * success or a negative error
 404 */
 405static int allocate_cg_links(int count, struct list_head *tmp)
 406{
 407        struct cg_cgroup_link *link;
 408        int i;
 409        INIT_LIST_HEAD(tmp);
 410        for (i = 0; i < count; i++) {
 411                link = kmalloc(sizeof(*link), GFP_KERNEL);
 412                if (!link) {
 413                        free_cg_links(tmp);
 414                        return -ENOMEM;
 415                }
 416                list_add(&link->cgrp_link_list, tmp);
 417        }
 418        return 0;
 419}
 420
 421/**
 422 * link_css_set - a helper function to link a css_set to a cgroup
 423 * @tmp_cg_links: cg_cgroup_link objects allocated by allocate_cg_links()
 424 * @cg: the css_set to be linked
 425 * @cgrp: the destination cgroup
 426 */
 427static void link_css_set(struct list_head *tmp_cg_links,
 428                         struct css_set *cg, struct cgroup *cgrp)
 429{
 430        struct cg_cgroup_link *link;
 431
 432        BUG_ON(list_empty(tmp_cg_links));
 433        link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
 434                                cgrp_link_list);
 435        link->cg = cg;
 436        list_move(&link->cgrp_link_list, &cgrp->css_sets);
 437        list_add(&link->cg_link_list, &cg->cg_links);
 438}
 439
 440/*
 441 * find_css_set() takes an existing cgroup group and a
 442 * cgroup object, and returns a css_set object that's
 443 * equivalent to the old group, but with the given cgroup
 444 * substituted into the appropriate hierarchy. Must be called with
 445 * cgroup_mutex held
 446 */
 447static struct css_set *find_css_set(
 448        struct css_set *oldcg, struct cgroup *cgrp)
 449{
 450        struct css_set *res;
 451        struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
 452        int i;
 453
 454        struct list_head tmp_cg_links;
 455
 456        struct hlist_head *hhead;
 457
 458        /* First see if we already have a cgroup group that matches
 459         * the desired set */
 460        read_lock(&css_set_lock);
 461        res = find_existing_css_set(oldcg, cgrp, template);
 462        if (res)
 463                get_css_set(res);
 464        read_unlock(&css_set_lock);
 465
 466        if (res)
 467                return res;
 468
 469        res = kmalloc(sizeof(*res), GFP_KERNEL);
 470        if (!res)
 471                return NULL;
 472
 473        /* Allocate all the cg_cgroup_link objects that we'll need */
 474        if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
 475                kfree(res);
 476                return NULL;
 477        }
 478
 479        atomic_set(&res->refcount, 1);
 480        INIT_LIST_HEAD(&res->cg_links);
 481        INIT_LIST_HEAD(&res->tasks);
 482        INIT_HLIST_NODE(&res->hlist);
 483
 484        /* Copy the set of subsystem state objects generated in
 485         * find_existing_css_set() */
 486        memcpy(res->subsys, template, sizeof(res->subsys));
 487
 488        write_lock(&css_set_lock);
 489        /* Add reference counts and links from the new css_set. */
 490        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 491                struct cgroup *cgrp = res->subsys[i]->cgroup;
 492                struct cgroup_subsys *ss = subsys[i];
 493                atomic_inc(&cgrp->count);
 494                /*
 495                 * We want to add a link once per cgroup, so we
 496                 * only do it for the first subsystem in each
 497                 * hierarchy
 498                 */
 499                if (ss->root->subsys_list.next == &ss->sibling)
 500                        link_css_set(&tmp_cg_links, res, cgrp);
 501        }
 502        if (list_empty(&rootnode.subsys_list))
 503                link_css_set(&tmp_cg_links, res, dummytop);
 504
 505        BUG_ON(!list_empty(&tmp_cg_links));
 506
 507        css_set_count++;
 508
 509        /* Add this cgroup group to the hash table */
 510        hhead = css_set_hash(res->subsys);
 511        hlist_add_head(&res->hlist, hhead);
 512
 513        write_unlock(&css_set_lock);
 514
 515        return res;
 516}
 517
 518/*
 519 * There is one global cgroup mutex. We also require taking
 520 * task_lock() when dereferencing a task's cgroup subsys pointers.
 521 * See "The task_lock() exception", at the end of this comment.
 522 *
 523 * A task must hold cgroup_mutex to modify cgroups.
 524 *
 525 * Any task can increment and decrement the count field without lock.
 526 * So in general, code holding cgroup_mutex can't rely on the count
 527 * field not changing.  However, if the count goes to zero, then only
 528 * cgroup_attach_task() can increment it again.  Because a count of zero
 529 * means that no tasks are currently attached, therefore there is no
 530 * way a task attached to that cgroup can fork (the other way to
 531 * increment the count).  So code holding cgroup_mutex can safely
 532 * assume that if the count is zero, it will stay zero. Similarly, if
 533 * a task holds cgroup_mutex on a cgroup with zero count, it
 534 * knows that the cgroup won't be removed, as cgroup_rmdir()
 535 * needs that mutex.
 536 *
 537 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
 538 * (usually) take cgroup_mutex.  These are the two most performance
 539 * critical pieces of code here.  The exception occurs on cgroup_exit(),
 540 * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
 541 * is taken, and if the cgroup count is zero, a usermode call made
 542 * to the release agent with the name of the cgroup (path relative to
 543 * the root of cgroup file system) as the argument.
 544 *
 545 * A cgroup can only be deleted if both its 'count' of using tasks
 546 * is zero, and its list of 'children' cgroups is empty.  Since all
 547 * tasks in the system use _some_ cgroup, and since there is always at
 548 * least one task in the system (init, pid == 1), therefore, top_cgroup
 549 * always has either children cgroups and/or using tasks.  So we don't
 550 * need a special hack to ensure that top_cgroup cannot be deleted.
 551 *
 552 *      The task_lock() exception
 553 *
 554 * The need for this exception arises from the action of
 555 * cgroup_attach_task(), which overwrites one tasks cgroup pointer with
 556 * another.  It does so using cgroup_mutex, however there are
 557 * several performance critical places that need to reference
 558 * task->cgroup without the expense of grabbing a system global
 559 * mutex.  Therefore except as noted below, when dereferencing or, as
 560 * in cgroup_attach_task(), modifying a task'ss cgroup pointer we use
 561 * task_lock(), which acts on a spinlock (task->alloc_lock) already in
 562 * the task_struct routinely used for such matters.
 563 *
 564 * P.S.  One more locking exception.  RCU is used to guard the
 565 * update of a tasks cgroup pointer by cgroup_attach_task()
 566 */
 567
 568/**
 569 * cgroup_lock - lock out any changes to cgroup structures
 570 *
 571 */
 572void cgroup_lock(void)
 573{
 574        mutex_lock(&cgroup_mutex);
 575}
 576
 577/**
 578 * cgroup_unlock - release lock on cgroup changes
 579 *
 580 * Undo the lock taken in a previous cgroup_lock() call.
 581 */
 582void cgroup_unlock(void)
 583{
 584        mutex_unlock(&cgroup_mutex);
 585}
 586
 587/*
 588 * A couple of forward declarations required, due to cyclic reference loop:
 589 * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
 590 * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
 591 * -> cgroup_mkdir.
 592 */
 593
 594static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);
 595static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
 596static int cgroup_populate_dir(struct cgroup *cgrp);
 597static struct inode_operations cgroup_dir_inode_operations;
 598static struct file_operations proc_cgroupstats_operations;
 599
 600static struct backing_dev_info cgroup_backing_dev_info = {
 601        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
 602};
 603
 604static int alloc_css_id(struct cgroup_subsys *ss,
 605                        struct cgroup *parent, struct cgroup *child);
 606
 607static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
 608{
 609        struct inode *inode = new_inode(sb);
 610
 611        if (inode) {
 612                inode->i_mode = mode;
 613                inode->i_uid = current_fsuid();
 614                inode->i_gid = current_fsgid();
 615                inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 616                inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
 617        }
 618        return inode;
 619}
 620
 621/*
 622 * Call subsys's pre_destroy handler.
 623 * This is called before css refcnt check.
 624 */
 625static int cgroup_call_pre_destroy(struct cgroup *cgrp)
 626{
 627        struct cgroup_subsys *ss;
 628        int ret = 0;
 629
 630        for_each_subsys(cgrp->root, ss)
 631                if (ss->pre_destroy) {
 632                        ret = ss->pre_destroy(ss, cgrp);
 633                        if (ret)
 634                                break;
 635                }
 636        return ret;
 637}
 638
 639static void free_cgroup_rcu(struct rcu_head *obj)
 640{
 641        struct cgroup *cgrp = container_of(obj, struct cgroup, rcu_head);
 642
 643        kfree(cgrp);
 644}
 645
 646static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 647{
 648        /* is dentry a directory ? if so, kfree() associated cgroup */
 649        if (S_ISDIR(inode->i_mode)) {
 650                struct cgroup *cgrp = dentry->d_fsdata;
 651                struct cgroup_subsys *ss;
 652                BUG_ON(!(cgroup_is_removed(cgrp)));
 653                /* It's possible for external users to be holding css
 654                 * reference counts on a cgroup; css_put() needs to
 655                 * be able to access the cgroup after decrementing
 656                 * the reference count in order to know if it needs to
 657                 * queue the cgroup to be handled by the release
 658                 * agent */
 659                synchronize_rcu();
 660
 661                mutex_lock(&cgroup_mutex);
 662                /*
 663                 * Release the subsystem state objects.
 664                 */
 665                for_each_subsys(cgrp->root, ss)
 666                        ss->destroy(ss, cgrp);
 667
 668                cgrp->root->number_of_cgroups--;
 669                mutex_unlock(&cgroup_mutex);
 670
 671                /*
 672                 * Drop the active superblock reference that we took when we
 673                 * created the cgroup
 674                 */
 675                deactivate_super(cgrp->root->sb);
 676
 677                call_rcu(&cgrp->rcu_head, free_cgroup_rcu);
 678        }
 679        iput(inode);
 680}
 681
 682static void remove_dir(struct dentry *d)
 683{
 684        struct dentry *parent = dget(d->d_parent);
 685
 686        d_delete(d);
 687        simple_rmdir(parent->d_inode, d);
 688        dput(parent);
 689}
 690
 691static void cgroup_clear_directory(struct dentry *dentry)
 692{
 693        struct list_head *node;
 694
 695        BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
 696        spin_lock(&dcache_lock);
 697        node = dentry->d_subdirs.next;
 698        while (node != &dentry->d_subdirs) {
 699                struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
 700                list_del_init(node);
 701                if (d->d_inode) {
 702                        /* This should never be called on a cgroup
 703                         * directory with child cgroups */
 704                        BUG_ON(d->d_inode->i_mode & S_IFDIR);
 705                        d = dget_locked(d);
 706                        spin_unlock(&dcache_lock);
 707                        d_delete(d);
 708                        simple_unlink(dentry->d_inode, d);
 709                        dput(d);
 710                        spin_lock(&dcache_lock);
 711                }
 712                node = dentry->d_subdirs.next;
 713        }
 714        spin_unlock(&dcache_lock);
 715}
 716
 717/*
 718 * NOTE : the dentry must have been dget()'ed
 719 */
 720static void cgroup_d_remove_dir(struct dentry *dentry)
 721{
 722        cgroup_clear_directory(dentry);
 723
 724        spin_lock(&dcache_lock);
 725        list_del_init(&dentry->d_u.d_child);
 726        spin_unlock(&dcache_lock);
 727        remove_dir(dentry);
 728}
 729
 730/*
 731 * A queue for waiters to do rmdir() cgroup. A tasks will sleep when
 732 * cgroup->count == 0 && list_empty(&cgroup->children) && subsys has some
 733 * reference to css->refcnt. In general, this refcnt is expected to goes down
 734 * to zero, soon.
 735 *
 736 * CGRP_WAIT_ON_RMDIR flag is modified under cgroup's inode->i_mutex;
 737 */
 738DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
 739
 740static void cgroup_wakeup_rmdir_waiters(const struct cgroup *cgrp)
 741{
 742        if (unlikely(test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
 743                wake_up_all(&cgroup_rmdir_waitq);
 744}
 745
 746static int rebind_subsystems(struct cgroupfs_root *root,
 747                              unsigned long final_bits)
 748{
 749        unsigned long added_bits, removed_bits;
 750        struct cgroup *cgrp = &root->top_cgroup;
 751        int i;
 752
 753        removed_bits = root->actual_subsys_bits & ~final_bits;
 754        added_bits = final_bits & ~root->actual_subsys_bits;
 755        /* Check that any added subsystems are currently free */
 756        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 757                unsigned long bit = 1UL << i;
 758                struct cgroup_subsys *ss = subsys[i];
 759                if (!(bit & added_bits))
 760                        continue;
 761                if (ss->root != &rootnode) {
 762                        /* Subsystem isn't free */
 763                        return -EBUSY;
 764                }
 765        }
 766
 767        /* Currently we don't handle adding/removing subsystems when
 768         * any child cgroups exist. This is theoretically supportable
 769         * but involves complex error handling, so it's being left until
 770         * later */
 771        if (root->number_of_cgroups > 1)
 772                return -EBUSY;
 773
 774        /* Process each subsystem */
 775        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 776                struct cgroup_subsys *ss = subsys[i];
 777                unsigned long bit = 1UL << i;
 778                if (bit & added_bits) {
 779                        /* We're binding this subsystem to this hierarchy */
 780                        BUG_ON(cgrp->subsys[i]);
 781                        BUG_ON(!dummytop->subsys[i]);
 782                        BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
 783                        mutex_lock(&ss->hierarchy_mutex);
 784                        cgrp->subsys[i] = dummytop->subsys[i];
 785                        cgrp->subsys[i]->cgroup = cgrp;
 786                        list_move(&ss->sibling, &root->subsys_list);
 787                        ss->root = root;
 788                        if (ss->bind)
 789                                ss->bind(ss, cgrp);
 790                        mutex_unlock(&ss->hierarchy_mutex);
 791                } else if (bit & removed_bits) {
 792                        /* We're removing this subsystem */
 793                        BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
 794                        BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
 795                        mutex_lock(&ss->hierarchy_mutex);
 796                        if (ss->bind)
 797                                ss->bind(ss, dummytop);
 798                        dummytop->subsys[i]->cgroup = dummytop;
 799                        cgrp->subsys[i] = NULL;
 800                        subsys[i]->root = &rootnode;
 801                        list_move(&ss->sibling, &rootnode.subsys_list);
 802                        mutex_unlock(&ss->hierarchy_mutex);
 803                } else if (bit & final_bits) {
 804                        /* Subsystem state should already exist */
 805                        BUG_ON(!cgrp->subsys[i]);
 806                } else {
 807                        /* Subsystem state shouldn't exist */
 808                        BUG_ON(cgrp->subsys[i]);
 809                }
 810        }
 811        root->subsys_bits = root->actual_subsys_bits = final_bits;
 812        synchronize_rcu();
 813
 814        return 0;
 815}
 816
 817static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
 818{
 819        struct cgroupfs_root *root = vfs->mnt_sb->s_fs_info;
 820        struct cgroup_subsys *ss;
 821
 822        mutex_lock(&cgroup_mutex);
 823        for_each_subsys(root, ss)
 824                seq_printf(seq, ",%s", ss->name);
 825        if (test_bit(ROOT_NOPREFIX, &root->flags))
 826                seq_puts(seq, ",noprefix");
 827        if (strlen(root->release_agent_path))
 828                seq_printf(seq, ",release_agent=%s", root->release_agent_path);
 829        mutex_unlock(&cgroup_mutex);
 830        return 0;
 831}
 832
 833struct cgroup_sb_opts {
 834        unsigned long subsys_bits;
 835        unsigned long flags;
 836        char *release_agent;
 837};
 838
 839/* Convert a hierarchy specifier into a bitmask of subsystems and
 840 * flags. */
 841static int parse_cgroupfs_options(char *data,
 842                                     struct cgroup_sb_opts *opts)
 843{
 844        char *token, *o = data ?: "all";
 845
 846        opts->subsys_bits = 0;
 847        opts->flags = 0;
 848        opts->release_agent = NULL;
 849
 850        while ((token = strsep(&o, ",")) != NULL) {
 851                if (!*token)
 852                        return -EINVAL;
 853                if (!strcmp(token, "all")) {
 854                        /* Add all non-disabled subsystems */
 855                        int i;
 856                        opts->subsys_bits = 0;
 857                        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 858                                struct cgroup_subsys *ss = subsys[i];
 859                                if (!ss->disabled)
 860                                        opts->subsys_bits |= 1ul << i;
 861                        }
 862                } else if (!strcmp(token, "noprefix")) {
 863                        set_bit(ROOT_NOPREFIX, &opts->flags);
 864                } else if (!strncmp(token, "release_agent=", 14)) {
 865                        /* Specifying two release agents is forbidden */
 866                        if (opts->release_agent)
 867                                return -EINVAL;
 868                        opts->release_agent = kzalloc(PATH_MAX, GFP_KERNEL);
 869                        if (!opts->release_agent)
 870                                return -ENOMEM;
 871                        strncpy(opts->release_agent, token + 14, PATH_MAX - 1);
 872                        opts->release_agent[PATH_MAX - 1] = 0;
 873                } else {
 874                        struct cgroup_subsys *ss;
 875                        int i;
 876                        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 877                                ss = subsys[i];
 878                                if (!strcmp(token, ss->name)) {
 879                                        if (!ss->disabled)
 880                                                set_bit(i, &opts->subsys_bits);
 881                                        break;
 882                                }
 883                        }
 884                        if (i == CGROUP_SUBSYS_COUNT)
 885                                return -ENOENT;
 886                }
 887        }
 888
 889        /* We can't have an empty hierarchy */
 890        if (!opts->subsys_bits)
 891                return -EINVAL;
 892
 893        return 0;
 894}
 895
 896static int cgroup_remount(struct super_block *sb, int *flags, char *data)
 897{
 898        int ret = 0;
 899        struct cgroupfs_root *root = sb->s_fs_info;
 900        struct cgroup *cgrp = &root->top_cgroup;
 901        struct cgroup_sb_opts opts;
 902
 903        mutex_lock(&cgrp->dentry->d_inode->i_mutex);
 904        mutex_lock(&cgroup_mutex);
 905
 906        /* See what subsystems are wanted */
 907        ret = parse_cgroupfs_options(data, &opts);
 908        if (ret)
 909                goto out_unlock;
 910
 911        /* Don't allow flags to change at remount */
 912        if (opts.flags != root->flags) {
 913                ret = -EINVAL;
 914                goto out_unlock;
 915        }
 916
 917        ret = rebind_subsystems(root, opts.subsys_bits);
 918        if (ret)
 919                goto out_unlock;
 920
 921        /* (re)populate subsystem files */
 922        cgroup_populate_dir(cgrp);
 923
 924        if (opts.release_agent)
 925                strcpy(root->release_agent_path, opts.release_agent);
 926 out_unlock:
 927        kfree(opts.release_agent);
 928        mutex_unlock(&cgroup_mutex);
 929        mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
 930        return ret;
 931}
 932
 933static struct super_operations cgroup_ops = {
 934        .statfs = simple_statfs,
 935        .drop_inode = generic_delete_inode,
 936        .show_options = cgroup_show_options,
 937        .remount_fs = cgroup_remount,
 938};
 939
 940static void init_cgroup_housekeeping(struct cgroup *cgrp)
 941{
 942        INIT_LIST_HEAD(&cgrp->sibling);
 943        INIT_LIST_HEAD(&cgrp->children);
 944        INIT_LIST_HEAD(&cgrp->css_sets);
 945        INIT_LIST_HEAD(&cgrp->release_list);
 946        init_rwsem(&cgrp->pids_mutex);
 947}
 948static void init_cgroup_root(struct cgroupfs_root *root)
 949{
 950        struct cgroup *cgrp = &root->top_cgroup;
 951        INIT_LIST_HEAD(&root->subsys_list);
 952        INIT_LIST_HEAD(&root->root_list);
 953        root->number_of_cgroups = 1;
 954        cgrp->root = root;
 955        cgrp->top_cgroup = cgrp;
 956        init_cgroup_housekeeping(cgrp);
 957}
 958
 959static int cgroup_test_super(struct super_block *sb, void *data)
 960{
 961        struct cgroupfs_root *new = data;
 962        struct cgroupfs_root *root = sb->s_fs_info;
 963
 964        /* First check subsystems */
 965        if (new->subsys_bits != root->subsys_bits)
 966            return 0;
 967
 968        /* Next check flags */
 969        if (new->flags != root->flags)
 970                return 0;
 971
 972        return 1;
 973}
 974
 975static int cgroup_set_super(struct super_block *sb, void *data)
 976{
 977        int ret;
 978        struct cgroupfs_root *root = data;
 979
 980        ret = set_anon_super(sb, NULL);
 981        if (ret)
 982                return ret;
 983
 984        sb->s_fs_info = root;
 985        root->sb = sb;
 986
 987        sb->s_blocksize = PAGE_CACHE_SIZE;
 988        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
 989        sb->s_magic = CGROUP_SUPER_MAGIC;
 990        sb->s_op = &cgroup_ops;
 991
 992        return 0;
 993}
 994
 995static int cgroup_get_rootdir(struct super_block *sb)
 996{
 997        struct inode *inode =
 998                cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
 999        struct dentry *dentry;
1000
1001        if (!inode)
1002                return -ENOMEM;
1003
1004        inode->i_fop = &simple_dir_operations;
1005        inode->i_op = &cgroup_dir_inode_operations;
1006        /* directories start off with i_nlink == 2 (for "." entry) */
1007        inc_nlink(inode);
1008        dentry = d_alloc_root(inode);
1009        if (!dentry) {
1010                iput(inode);
1011                return -ENOMEM;
1012        }
1013        sb->s_root = dentry;
1014        return 0;
1015}
1016
1017static int cgroup_get_sb(struct file_system_type *fs_type,
1018                         int flags, const char *unused_dev_name,
1019                         void *data, struct vfsmount *mnt)
1020{
1021        struct cgroup_sb_opts opts;
1022        int ret = 0;
1023        struct super_block *sb;
1024        struct cgroupfs_root *root;
1025        struct list_head tmp_cg_links;
1026
1027        /* First find the desired set of subsystems */
1028        ret = parse_cgroupfs_options(data, &opts);
1029        if (ret) {
1030                kfree(opts.release_agent);
1031                return ret;
1032        }
1033
1034        root = kzalloc(sizeof(*root), GFP_KERNEL);
1035        if (!root) {
1036                kfree(opts.release_agent);
1037                return -ENOMEM;
1038        }
1039
1040        init_cgroup_root(root);
1041        root->subsys_bits = opts.subsys_bits;
1042        root->flags = opts.flags;
1043        if (opts.release_agent) {
1044                strcpy(root->release_agent_path, opts.release_agent);
1045                kfree(opts.release_agent);
1046        }
1047
1048        sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);
1049
1050        if (IS_ERR(sb)) {
1051                kfree(root);
1052                return PTR_ERR(sb);
1053        }
1054
1055        if (sb->s_fs_info != root) {
1056                /* Reusing an existing superblock */
1057                BUG_ON(sb->s_root == NULL);
1058                kfree(root);
1059                root = NULL;
1060        } else {
1061                /* New superblock */
1062                struct cgroup *root_cgrp = &root->top_cgroup;
1063                struct inode *inode;
1064                int i;
1065
1066                BUG_ON(sb->s_root != NULL);
1067
1068                ret = cgroup_get_rootdir(sb);
1069                if (ret)
1070                        goto drop_new_super;
1071                inode = sb->s_root->d_inode;
1072
1073                mutex_lock(&inode->i_mutex);
1074                mutex_lock(&cgroup_mutex);
1075
1076                /*
1077                 * We're accessing css_set_count without locking
1078                 * css_set_lock here, but that's OK - it can only be
1079                 * increased by someone holding cgroup_lock, and
1080                 * that's us. The worst that can happen is that we
1081                 * have some link structures left over
1082                 */
1083                ret = allocate_cg_links(css_set_count, &tmp_cg_links);
1084                if (ret) {
1085                        mutex_unlock(&cgroup_mutex);
1086                        mutex_unlock(&inode->i_mutex);
1087                        goto drop_new_super;
1088                }
1089
1090                ret = rebind_subsystems(root, root->subsys_bits);
1091                if (ret == -EBUSY) {
1092                        mutex_unlock(&cgroup_mutex);
1093                        mutex_unlock(&inode->i_mutex);
1094                        goto free_cg_links;
1095                }
1096
1097                /* EBUSY should be the only error here */
1098                BUG_ON(ret);
1099
1100                list_add(&root->root_list, &roots);
1101                root_count++;
1102
1103                sb->s_root->d_fsdata = root_cgrp;
1104                root->top_cgroup.dentry = sb->s_root;
1105
1106                /* Link the top cgroup in this hierarchy into all
1107                 * the css_set objects */
1108                write_lock(&css_set_lock);
1109                for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
1110                        struct hlist_head *hhead = &css_set_table[i];
1111                        struct hlist_node *node;
1112                        struct css_set *cg;
1113
1114                        hlist_for_each_entry(cg, node, hhead, hlist)
1115                                link_css_set(&tmp_cg_links, cg, root_cgrp);
1116                }
1117                write_unlock(&css_set_lock);
1118
1119                free_cg_links(&tmp_cg_links);
1120
1121                BUG_ON(!list_empty(&root_cgrp->sibling));
1122                BUG_ON(!list_empty(&root_cgrp->children));
1123                BUG_ON(root->number_of_cgroups != 1);
1124
1125                cgroup_populate_dir(root_cgrp);
1126                mutex_unlock(&inode->i_mutex);
1127                mutex_unlock(&cgroup_mutex);
1128        }
1129
1130        simple_set_mnt(mnt, sb);
1131        return 0;
1132
1133 free_cg_links:
1134        free_cg_links(&tmp_cg_links);
1135 drop_new_super:
1136        deactivate_locked_super(sb);
1137        return ret;
1138}
1139
1140static void cgroup_kill_sb(struct super_block *sb) {
1141        struct cgroupfs_root *root = sb->s_fs_info;
1142        struct cgroup *cgrp = &root->top_cgroup;
1143        int ret;
1144        struct cg_cgroup_link *link;
1145        struct cg_cgroup_link *saved_link;
1146
1147        BUG_ON(!root);
1148
1149        BUG_ON(root->number_of_cgroups != 1);
1150        BUG_ON(!list_empty(&cgrp->children));
1151        BUG_ON(!list_empty(&cgrp->sibling));
1152
1153        mutex_lock(&cgroup_mutex);
1154
1155        /* Rebind all subsystems back to the default hierarchy */
1156        ret = rebind_subsystems(root, 0);
1157        /* Shouldn't be able to fail ... */
1158        BUG_ON(ret);
1159
1160        /*
1161         * Release all the links from css_sets to this hierarchy's
1162         * root cgroup
1163         */
1164        write_lock(&css_set_lock);
1165
1166        list_for_each_entry_safe(link, saved_link, &cgrp->css_sets,
1167                                 cgrp_link_list) {
1168                list_del(&link->cg_link_list);
1169                list_del(&link->cgrp_link_list);
1170                kfree(link);
1171        }
1172        write_unlock(&css_set_lock);
1173
1174        if (!list_empty(&root->root_list)) {
1175                list_del(&root->root_list);
1176                root_count--;
1177        }
1178
1179        mutex_unlock(&cgroup_mutex);
1180
1181        kill_litter_super(sb);
1182        kfree(root);
1183}
1184
1185static struct file_system_type cgroup_fs_type = {
1186        .name = "cgroup",
1187        .get_sb = cgroup_get_sb,
1188        .kill_sb = cgroup_kill_sb,
1189};
1190
1191static inline struct cgroup *__d_cgrp(struct dentry *dentry)
1192{
1193        return dentry->d_fsdata;
1194}
1195
1196static inline struct cftype *__d_cft(struct dentry *dentry)
1197{
1198        return dentry->d_fsdata;
1199}
1200
1201/**
1202 * cgroup_path - generate the path of a cgroup
1203 * @cgrp: the cgroup in question
1204 * @buf: the buffer to write the path into
1205 * @buflen: the length of the buffer
1206 *
1207 * Called with cgroup_mutex held or else with an RCU-protected cgroup
1208 * reference.  Writes path of cgroup into buf.  Returns 0 on success,
1209 * -errno on error.
1210 */
1211int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
1212{
1213        char *start;
1214        struct dentry *dentry = rcu_dereference(cgrp->dentry);
1215
1216        if (!dentry || cgrp == dummytop) {
1217                /*
1218                 * Inactive subsystems have no dentry for their root
1219                 * cgroup
1220                 */
1221                strcpy(buf, "/");
1222                return 0;
1223        }
1224
1225        start = buf + buflen;
1226
1227        *--start = '\0';
1228        for (;;) {
1229                int len = dentry->d_name.len;
1230                if ((start -= len) < buf)
1231                        return -ENAMETOOLONG;
1232                memcpy(start, cgrp->dentry->d_name.name, len);
1233                cgrp = cgrp->parent;
1234                if (!cgrp)
1235                        break;
1236                dentry = rcu_dereference(cgrp->dentry);
1237                if (!cgrp->parent)
1238                        continue;
1239                if (--start < buf)
1240                        return -ENAMETOOLONG;
1241                *start = '/';
1242        }
1243        memmove(buf, start, buf + buflen - start);
1244        return 0;
1245}
1246
1247/*
1248 * Return the first subsystem attached to a cgroup's hierarchy, and
1249 * its subsystem id.
1250 */
1251
1252static void get_first_subsys(const struct cgroup *cgrp,
1253                        struct cgroup_subsys_state **css, int *subsys_id)
1254{
1255        const struct cgroupfs_root *root = cgrp->root;
1256        const struct cgroup_subsys *test_ss;
1257        BUG_ON(list_empty(&root->subsys_list));
1258        test_ss = list_entry(root->subsys_list.next,
1259                             struct cgroup_subsys, sibling);
1260        if (css) {
1261                *css = cgrp->subsys[test_ss->subsys_id];
1262                BUG_ON(!*css);
1263        }
1264        if (subsys_id)
1265                *subsys_id = test_ss->subsys_id;
1266}
1267
1268/**
1269 * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
1270 * @cgrp: the cgroup the task is attaching to
1271 * @tsk: the task to be attached
1272 *
1273 * Call holding cgroup_mutex. May take task_lock of
1274 * the task 'tsk' during call.
1275 */
1276int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
1277{
1278        int retval = 0;
1279        struct cgroup_subsys *ss;
1280        struct cgroup *oldcgrp;
1281        struct css_set *cg;
1282        struct css_set *newcg;
1283        struct cgroupfs_root *root = cgrp->root;
1284        int subsys_id;
1285
1286        get_first_subsys(cgrp, NULL, &subsys_id);
1287
1288        /* Nothing to do if the task is already in that cgroup */
1289        oldcgrp = task_cgroup(tsk, subsys_id);
1290        if (cgrp == oldcgrp)
1291                return 0;
1292
1293        for_each_subsys(root, ss) {
1294                if (ss->can_attach) {
1295                        retval = ss->can_attach(ss, cgrp, tsk);
1296                        if (retval)
1297                                return retval;
1298                }
1299        }
1300
1301        task_lock(tsk);
1302        cg = tsk->cgroups;
1303        get_css_set(cg);
1304        task_unlock(tsk);
1305        /*
1306         * Locate or allocate a new css_set for this task,
1307         * based on its final set of cgroups
1308         */
1309        newcg = find_css_set(cg, cgrp);
1310        put_css_set(cg);
1311        if (!newcg)
1312                return -ENOMEM;
1313
1314        task_lock(tsk);
1315        if (tsk->flags & PF_EXITING) {
1316                task_unlock(tsk);
1317                put_css_set(newcg);
1318                return -ESRCH;
1319        }
1320        rcu_assign_pointer(tsk->cgroups, newcg);
1321        task_unlock(tsk);
1322
1323        /* Update the css_set linked lists if we're using them */
1324        write_lock(&css_set_lock);
1325        if (!list_empty(&tsk->cg_list)) {
1326                list_del(&tsk->cg_list);
1327                list_add(&tsk->cg_list, &newcg->tasks);
1328        }
1329        write_unlock(&css_set_lock);
1330
1331        for_each_subsys(root, ss) {
1332                if (ss->attach)
1333                        ss->attach(ss, cgrp, oldcgrp, tsk);
1334        }
1335        set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
1336        synchronize_rcu();
1337        put_css_set(cg);
1338
1339        /*
1340         * wake up rmdir() waiter. the rmdir should fail since the cgroup
1341         * is no longer empty.
1342         */
1343        cgroup_wakeup_rmdir_waiters(cgrp);
1344        return 0;
1345}
1346
1347/*
1348 * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
1349 * held. May take task_lock of task
1350 */
1351static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
1352{
1353        struct task_struct *tsk;
1354        const struct cred *cred = current_cred(), *tcred;
1355        int ret;
1356
1357        if (pid) {
1358                rcu_read_lock();
1359                tsk = find_task_by_vpid(pid);
1360                if (!tsk || tsk->flags & PF_EXITING) {
1361                        rcu_read_unlock();
1362                        return -ESRCH;
1363                }
1364
1365                tcred = __task_cred(tsk);
1366                if (cred->euid &&
1367                    cred->euid != tcred->uid &&
1368                    cred->euid != tcred->suid) {
1369                        rcu_read_unlock();
1370                        return -EACCES;
1371                }
1372                get_task_struct(tsk);
1373                rcu_read_unlock();
1374        } else {
1375                tsk = current;
1376                get_task_struct(tsk);
1377        }
1378
1379        ret = cgroup_attach_task(cgrp, tsk);
1380        put_task_struct(tsk);
1381        return ret;
1382}
1383
1384static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
1385{
1386        int ret;
1387        if (!cgroup_lock_live_group(cgrp))
1388                return -ENODEV;
1389        ret = attach_task_by_pid(cgrp, pid);
1390        cgroup_unlock();
1391        return ret;
1392}
1393
1394/* The various types of files and directories in a cgroup file system */
1395enum cgroup_filetype {
1396        FILE_ROOT,
1397        FILE_DIR,
1398        FILE_TASKLIST,
1399        FILE_NOTIFY_ON_RELEASE,
1400        FILE_RELEASE_AGENT,
1401};
1402
1403/**
1404 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
1405 * @cgrp: the cgroup to be checked for liveness
1406 *
1407 * On success, returns true; the lock should be later released with
1408 * cgroup_unlock(). On failure returns false with no lock held.
1409 */
1410bool cgroup_lock_live_group(struct cgroup *cgrp)
1411{
1412        mutex_lock(&cgroup_mutex);
1413        if (cgroup_is_removed(cgrp)) {
1414                mutex_unlock(&cgroup_mutex);
1415                return false;
1416        }
1417        return true;
1418}
1419
1420static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
1421                                      const char *buffer)
1422{
1423        BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
1424        if (!cgroup_lock_live_group(cgrp))
1425                return -ENODEV;
1426        strcpy(cgrp->root->release_agent_path, buffer);
1427        cgroup_unlock();
1428        return 0;
1429}
1430
1431static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
1432                                     struct seq_file *seq)
1433{
1434        if (!cgroup_lock_live_group(cgrp))
1435                return -ENODEV;
1436        seq_puts(seq, cgrp->root->release_agent_path);
1437        seq_putc(seq, '\n');
1438        cgroup_unlock();
1439        return 0;
1440}
1441
1442/* A buffer size big enough for numbers or short strings */
1443#define CGROUP_LOCAL_BUFFER_SIZE 64
1444
1445static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
1446                                struct file *file,
1447                                const char __user *userbuf,
1448                                size_t nbytes, loff_t *unused_ppos)
1449{
1450        char buffer[CGROUP_LOCAL_BUFFER_SIZE];
1451        int retval = 0;
1452        char *end;
1453
1454        if (!nbytes)
1455                return -EINVAL;
1456        if (nbytes >= sizeof(buffer))
1457                return -E2BIG;
1458        if (copy_from_user(buffer, userbuf, nbytes))
1459                return -EFAULT;
1460
1461        buffer[nbytes] = 0;     /* nul-terminate */
1462        strstrip(buffer);
1463        if (cft->write_u64) {
1464                u64 val = simple_strtoull(buffer, &end, 0);
1465                if (*end)
1466                        return -EINVAL;
1467                retval = cft->write_u64(cgrp, cft, val);
1468        } else {
1469                s64 val = simple_strtoll(buffer, &end, 0);
1470                if (*end)
1471                        return -EINVAL;
1472                retval = cft->write_s64(cgrp, cft, val);
1473        }
1474        if (!retval)
1475                retval = nbytes;
1476        return retval;
1477}
1478
1479static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
1480                                   struct file *file,
1481                                   const char __user *userbuf,
1482                                   size_t nbytes, loff_t *unused_ppos)
1483{
1484        char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
1485        int retval = 0;
1486        size_t max_bytes = cft->max_write_len;
1487        char *buffer = local_buffer;
1488
1489        if (!max_bytes)
1490                max_bytes = sizeof(local_buffer) - 1;
1491        if (nbytes >= max_bytes)
1492                return -E2BIG;
1493        /* Allocate a dynamic buffer if we need one */
1494        if (nbytes >= sizeof(local_buffer)) {
1495                buffer = kmalloc(nbytes + 1, GFP_KERNEL);
1496                if (buffer == NULL)
1497                        return -ENOMEM;
1498        }
1499        if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
1500                retval = -EFAULT;
1501                goto out;
1502        }
1503
1504        buffer[nbytes] = 0;     /* nul-terminate */
1505        strstrip(buffer);
1506        retval = cft->write_string(cgrp, cft, buffer);
1507        if (!retval)
1508                retval = nbytes;
1509out:
1510        if (buffer != local_buffer)
1511                kfree(buffer);
1512        return retval;
1513}
1514
1515static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
1516                                                size_t nbytes, loff_t *ppos)
1517{
1518        struct cftype *cft = __d_cft(file->f_dentry);
1519        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
1520
1521        if (cgroup_is_removed(cgrp))
1522                return -ENODEV;
1523        if (cft->write)
1524                return cft->write(cgrp, cft, file, buf, nbytes, ppos);
1525        if (cft->write_u64 || cft->write_s64)
1526                return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
1527        if (cft->write_string)
1528                return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
1529        if (cft->trigger) {
1530                int ret = cft->trigger(cgrp, (unsigned int)cft->private);
1531                return ret ? ret : nbytes;
1532        }
1533        return -EINVAL;
1534}
1535
1536static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
1537                               struct file *file,
1538                               char __user *buf, size_t nbytes,
1539                               loff_t *ppos)
1540{
1541        char tmp[CGROUP_LOCAL_BUFFER_SIZE];
1542        u64 val = cft->read_u64(cgrp, cft);
1543        int len = sprintf(tmp, "%llu\n", (unsigned long long) val);
1544
1545        return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
1546}
1547
1548static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
1549                               struct file *file,
1550                               char __user *buf, size_t nbytes,
1551                               loff_t *ppos)
1552{
1553        char tmp[CGROUP_LOCAL_BUFFER_SIZE];
1554        s64 val = cft->read_s64(cgrp, cft);
1555        int len = sprintf(tmp, "%lld\n", (long long) val);
1556
1557        return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
1558}
1559
1560static ssize_t cgroup_file_read(struct file *file, char __user *buf,
1561                                   size_t nbytes, loff_t *ppos)
1562{
1563        struct cftype *cft = __d_cft(file->f_dentry);
1564        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
1565
1566        if (cgroup_is_removed(cgrp))
1567                return -ENODEV;
1568
1569        if (cft->read)
1570                return cft->read(cgrp, cft, file, buf, nbytes, ppos);
1571        if (cft->read_u64)
1572                return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
1573        if (cft->read_s64)
1574                return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
1575        return -EINVAL;
1576}
1577
1578/*
1579 * seqfile ops/methods for returning structured data. Currently just
1580 * supports string->u64 maps, but can be extended in future.
1581 */
1582
1583struct cgroup_seqfile_state {
1584        struct cftype *cft;
1585        struct cgroup *cgroup;
1586};
1587
1588static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
1589{
1590        struct seq_file *sf = cb->state;
1591        return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
1592}
1593
1594static int cgroup_seqfile_show(struct seq_file *m, void *arg)
1595{
1596        struct cgroup_seqfile_state *state = m->private;
1597        struct cftype *cft = state->cft;
1598        if (cft->read_map) {
1599                struct cgroup_map_cb cb = {
1600                        .fill = cgroup_map_add,
1601                        .state = m,
1602                };
1603                return cft->read_map(state->cgroup, cft, &cb);
1604        }
1605        return cft->read_seq_string(state->cgroup, cft, m);
1606}
1607
1608static int cgroup_seqfile_release(struct inode *inode, struct file *file)
1609{
1610        struct seq_file *seq = file->private_data;
1611        kfree(seq->private);
1612        return single_release(inode, file);
1613}
1614
1615static struct file_operations cgroup_seqfile_operations = {
1616        .read = seq_read,
1617        .write = cgroup_file_write,
1618        .llseek = seq_lseek,
1619        .release = cgroup_seqfile_release,
1620};
1621
1622static int cgroup_file_open(struct inode *inode, struct file *file)
1623{
1624        int err;
1625        struct cftype *cft;
1626
1627        err = generic_file_open(inode, file);
1628        if (err)
1629                return err;
1630        cft = __d_cft(file->f_dentry);
1631
1632        if (cft->read_map || cft->read_seq_string) {
1633                struct cgroup_seqfile_state *state =
1634                        kzalloc(sizeof(*state), GFP_USER);
1635                if (!state)
1636                        return -ENOMEM;
1637                state->cft = cft;
1638                state->cgroup = __d_cgrp(file->f_dentry->d_parent);
1639                file->f_op = &cgroup_seqfile_operations;
1640                err = single_open(file, cgroup_seqfile_show, state);
1641                if (err < 0)
1642                        kfree(state);
1643        } else if (cft->open)
1644                err = cft->open(inode, file);
1645        else
1646                err = 0;
1647
1648        return err;
1649}
1650
1651static int cgroup_file_release(struct inode *inode, struct file *file)
1652{
1653        struct cftype *cft = __d_cft(file->f_dentry);
1654        if (cft->release)
1655                return cft->release(inode, file);
1656        return 0;
1657}
1658
1659/*
1660 * cgroup_rename - Only allow simple rename of directories in place.
1661 */
1662static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
1663                            struct inode *new_dir, struct dentry *new_dentry)
1664{
1665        if (!S_ISDIR(old_dentry->d_inode->i_mode))
1666                return -ENOTDIR;
1667        if (new_dentry->d_inode)
1668                return -EEXIST;
1669        if (old_dir != new_dir)
1670                return -EIO;
1671        return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
1672}
1673
1674static struct file_operations cgroup_file_operations = {
1675        .read = cgroup_file_read,
1676        .write = cgroup_file_write,
1677        .llseek = generic_file_llseek,
1678        .open = cgroup_file_open,
1679        .release = cgroup_file_release,
1680};
1681
1682static struct inode_operations cgroup_dir_inode_operations = {
1683        .lookup = simple_lookup,
1684        .mkdir = cgroup_mkdir,
1685        .rmdir = cgroup_rmdir,
1686        .rename = cgroup_rename,
1687};
1688
1689static int cgroup_create_file(struct dentry *dentry, mode_t mode,
1690                                struct super_block *sb)
1691{
1692        static const struct dentry_operations cgroup_dops = {
1693                .d_iput = cgroup_diput,
1694        };
1695
1696        struct inode *inode;
1697
1698        if (!dentry)
1699                return -ENOENT;
1700        if (dentry->d_inode)
1701                return -EEXIST;
1702
1703        inode = cgroup_new_inode(mode, sb);
1704        if (!inode)
1705                return -ENOMEM;
1706
1707        if (S_ISDIR(mode)) {
1708                inode->i_op = &cgroup_dir_inode_operations;
1709                inode->i_fop = &simple_dir_operations;
1710
1711                /* start off with i_nlink == 2 (for "." entry) */
1712                inc_nlink(inode);
1713
1714                /* start with the directory inode held, so that we can
1715                 * populate it without racing with another mkdir */
1716                mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
1717        } else if (S_ISREG(mode)) {
1718                inode->i_size = 0;
1719                inode->i_fop = &cgroup_file_operations;
1720        }
1721        dentry->d_op = &cgroup_dops;
1722        d_instantiate(dentry, inode);
1723        dget(dentry);   /* Extra count - pin the dentry in core */
1724        return 0;
1725}
1726
1727/*
1728 * cgroup_create_dir - create a directory for an object.
1729 * @cgrp: the cgroup we create the directory for. It must have a valid
1730 *        ->parent field. And we are going to fill its ->dentry field.
1731 * @dentry: dentry of the new cgroup
1732 * @mode: mode to set on new directory.
1733 */
1734static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
1735                                mode_t mode)
1736{
1737        struct dentry *parent;
1738        int error = 0;
1739
1740        parent = cgrp->parent->dentry;
1741        error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb);
1742        if (!error) {
1743                dentry->d_fsdata = cgrp;
1744                inc_nlink(parent->d_inode);
1745                rcu_assign_pointer(cgrp->dentry, dentry);
1746                dget(dentry);
1747        }
1748        dput(dentry);
1749
1750        return error;
1751}
1752
1753/**
1754 * cgroup_file_mode - deduce file mode of a control file
1755 * @cft: the control file in question
1756 *
1757 * returns cft->mode if ->mode is not 0
1758 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
1759 * returns S_IRUGO if it has only a read handler
1760 * returns S_IWUSR if it has only a write hander
1761 */
1762static mode_t cgroup_file_mode(const struct cftype *cft)
1763{
1764        mode_t mode = 0;
1765
1766        if (cft->mode)
1767                return cft->mode;
1768
1769        if (cft->read || cft->read_u64 || cft->read_s64 ||
1770            cft->read_map || cft->read_seq_string)
1771                mode |= S_IRUGO;
1772
1773        if (cft->write || cft->write_u64 || cft->write_s64 ||
1774            cft->write_string || cft->trigger)
1775                mode |= S_IWUSR;
1776
1777        return mode;
1778}
1779
1780int cgroup_add_file(struct cgroup *cgrp,
1781                       struct cgroup_subsys *subsys,
1782                       const struct cftype *cft)
1783{
1784        struct dentry *dir = cgrp->dentry;
1785        struct dentry *dentry;
1786        int error;
1787        mode_t mode;
1788
1789        char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
1790        if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
1791                strcpy(name, subsys->name);
1792                strcat(name, ".");
1793        }
1794        strcat(name, cft->name);
1795        BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
1796        dentry = lookup_one_len(name, dir, strlen(name));
1797        if (!IS_ERR(dentry)) {
1798                mode = cgroup_file_mode(cft);
1799                error = cgroup_create_file(dentry, mode | S_IFREG,
1800                                                cgrp->root->sb);
1801                if (!error)
1802                        dentry->d_fsdata = (void *)cft;
1803                dput(dentry);
1804        } else
1805                error = PTR_ERR(dentry);
1806        return error;
1807}
1808
1809int cgroup_add_files(struct cgroup *cgrp,
1810                        struct cgroup_subsys *subsys,
1811                        const struct cftype cft[],
1812                        int count)
1813{
1814        int i, err;
1815        for (i = 0; i < count; i++) {
1816                err = cgroup_add_file(cgrp, subsys, &cft[i]);
1817                if (err)
1818                        return err;
1819        }
1820        return 0;
1821}
1822
1823/**
1824 * cgroup_task_count - count the number of tasks in a cgroup.
1825 * @cgrp: the cgroup in question
1826 *
1827 * Return the number of tasks in the cgroup.
1828 */
1829int cgroup_task_count(const struct cgroup *cgrp)
1830{
1831        int count = 0;
1832        struct cg_cgroup_link *link;
1833
1834        read_lock(&css_set_lock);
1835        list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
1836                count += atomic_read(&link->cg->refcount);
1837        }
1838        read_unlock(&css_set_lock);
1839        return count;
1840}
1841
1842/*
1843 * Advance a list_head iterator.  The iterator should be positioned at
1844 * the start of a css_set
1845 */
1846static void cgroup_advance_iter(struct cgroup *cgrp,
1847                                          struct cgroup_iter *it)
1848{
1849        struct list_head *l = it->cg_link;
1850        struct cg_cgroup_link *link;
1851        struct css_set *cg;
1852
1853        /* Advance to the next non-empty css_set */
1854        do {
1855                l = l->next;
1856                if (l == &cgrp->css_sets) {
1857                        it->cg_link = NULL;
1858                        return;
1859                }
1860                link = list_entry(l, struct cg_cgroup_link, cgrp_link_list);
1861                cg = link->cg;
1862        } while (list_empty(&cg->tasks));
1863        it->cg_link = l;
1864        it->task = cg->tasks.next;
1865}
1866
1867/*
1868 * To reduce the fork() overhead for systems that are not actually
1869 * using their cgroups capability, we don't maintain the lists running
1870 * through each css_set to its tasks until we see the list actually
1871 * used - in other words after the first call to cgroup_iter_start().
1872 *
1873 * The tasklist_lock is not held here, as do_each_thread() and
1874 * while_each_thread() are protected by RCU.
1875 */
1876static void cgroup_enable_task_cg_lists(void)
1877{
1878        struct task_struct *p, *g;
1879        write_lock(&css_set_lock);
1880        use_task_css_set_links = 1;
1881        do_each_thread(g, p) {
1882                task_lock(p);
1883                /*
1884                 * We should check if the process is exiting, otherwise
1885                 * it will race with cgroup_exit() in that the list
1886                 * entry won't be deleted though the process has exited.
1887                 */
1888                if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
1889                        list_add(&p->cg_list, &p->cgroups->tasks);
1890                task_unlock(p);
1891        } while_each_thread(g, p);
1892        write_unlock(&css_set_lock);
1893}
1894
1895void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
1896{
1897        /*
1898         * The first time anyone tries to iterate across a cgroup,
1899         * we need to enable the list linking each css_set to its
1900         * tasks, and fix up all existing tasks.
1901         */
1902        if (!use_task_css_set_links)
1903                cgroup_enable_task_cg_lists();
1904
1905        read_lock(&css_set_lock);
1906        it->cg_link = &cgrp->css_sets;
1907        cgroup_advance_iter(cgrp, it);
1908}
1909
1910struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
1911                                        struct cgroup_iter *it)
1912{
1913        struct task_struct *res;
1914        struct list_head *l = it->task;
1915        struct cg_cgroup_link *link;
1916
1917        /* If the iterator cg is NULL, we have no tasks */
1918        if (!it->cg_link)
1919                return NULL;
1920        res = list_entry(l, struct task_struct, cg_list);
1921        /* Advance iterator to find next entry */
1922        l = l->next;
1923        link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list);
1924        if (l == &link->cg->tasks) {
1925                /* We reached the end of this task list - move on to
1926                 * the next cg_cgroup_link */
1927                cgroup_advance_iter(cgrp, it);
1928        } else {
1929                it->task = l;
1930        }
1931        return res;
1932}
1933
1934void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
1935{
1936        read_unlock(&css_set_lock);
1937}
1938
1939static inline int started_after_time(struct task_struct *t1,
1940                                     struct timespec *time,
1941                                     struct task_struct *t2)
1942{
1943        int start_diff = timespec_compare(&t1->start_time, time);
1944        if (start_diff > 0) {
1945                return 1;
1946        } else if (start_diff < 0) {
1947                return 0;
1948        } else {
1949                /*
1950                 * Arbitrarily, if two processes started at the same
1951                 * time, we'll say that the lower pointer value
1952                 * started first. Note that t2 may have exited by now
1953                 * so this may not be a valid pointer any longer, but
1954                 * that's fine - it still serves to distinguish
1955                 * between two tasks started (effectively) simultaneously.
1956                 */
1957                return t1 > t2;
1958        }
1959}
1960
1961/*
1962 * This function is a callback from heap_insert() and is used to order
1963 * the heap.
1964 * In this case we order the heap in descending task start time.
1965 */
1966static inline int started_after(void *p1, void *p2)
1967{
1968        struct task_struct *t1 = p1;
1969        struct task_struct *t2 = p2;
1970        return started_after_time(t1, &t2->start_time, t2);
1971}
1972
1973/**
1974 * cgroup_scan_tasks - iterate though all the tasks in a cgroup
1975 * @scan: struct cgroup_scanner containing arguments for the scan
1976 *
1977 * Arguments include pointers to callback functions test_task() and
1978 * process_task().
1979 * Iterate through all the tasks in a cgroup, calling test_task() for each,
1980 * and if it returns true, call process_task() for it also.
1981 * The test_task pointer may be NULL, meaning always true (select all tasks).
1982 * Effectively duplicates cgroup_iter_{start,next,end}()
1983 * but does not lock css_set_lock for the call to process_task().
1984 * The struct cgroup_scanner may be embedded in any structure of the caller's
1985 * creation.
1986 * It is guaranteed that process_task() will act on every task that
1987 * is a member of the cgroup for the duration of this call. This
1988 * function may or may not call process_task() for tasks that exit
1989 * or move to a different cgroup during the call, or are forked or
1990 * move into the cgroup during the call.
1991 *
1992 * Note that test_task() may be called with locks held, and may in some
1993 * situations be called multiple times for the same task, so it should
1994 * be cheap.
1995 * If the heap pointer in the struct cgroup_scanner is non-NULL, a heap has been
1996 * pre-allocated and will be used for heap operations (and its "gt" member will
1997 * be overwritten), else a temporary heap will be used (allocation of which
1998 * may cause this function to fail).
1999 */
2000int cgroup_scan_tasks(struct cgroup_scanner *scan)
2001{
2002        int retval, i;
2003        struct cgroup_iter it;
2004        struct task_struct *p, *dropped;
2005        /* Never dereference latest_task, since it's not refcounted */
2006        struct task_struct *latest_task = NULL;
2007        struct ptr_heap tmp_heap;
2008        struct ptr_heap *heap;
2009        struct timespec latest_time = { 0, 0 };
2010
2011        if (scan->heap) {
2012                /* The caller supplied our heap and pre-allocated its memory */
2013                heap = scan->heap;
2014                heap->gt = &started_after;
2015        } else {
2016                /* We need to allocate our own heap memory */
2017                heap = &tmp_heap;
2018                retval = heap_init(heap, PAGE_SIZE, GFP_KERNEL, &started_after);
2019                if (retval)
2020                        /* cannot allocate the heap */
2021                        return retval;
2022        }
2023
2024 again:
2025        /*
2026         * Scan tasks in the cgroup, using the scanner's "test_task" callback
2027         * to determine which are of interest, and using the scanner's
2028         * "process_task" callback to process any of them that need an update.
2029         * Since we don't want to hold any locks during the task updates,
2030         * gather tasks to be processed in a heap structure.
2031         * The heap is sorted by descending task start time.
2032         * If the statically-sized heap fills up, we overflow tasks that
2033         * started later, and in future iterations only consider tasks that
2034         * started after the latest task in the previous pass. This
2035         * guarantees forward progress and that we don't miss any tasks.
2036         */
2037        heap->size = 0;
2038        cgroup_iter_start(scan->cg, &it);
2039        while ((p = cgroup_iter_next(scan->cg, &it))) {
2040                /*
2041                 * Only affect tasks that qualify per the caller's callback,
2042                 * if he provided one
2043                 */
2044                if (scan->test_task && !scan->test_task(p, scan))
2045                        continue;
2046                /*
2047                 * Only process tasks that started after the last task
2048                 * we processed
2049                 */
2050                if (!started_after_time(p, &latest_time, latest_task))
2051                        continue;
2052                dropped = heap_insert(heap, p);
2053                if (dropped == NULL) {
2054                        /*
2055                         * The new task was inserted; the heap wasn't
2056                         * previously full
2057                         */
2058                        get_task_struct(p);
2059                } else if (dropped != p) {
2060                        /*
2061                         * The new task was inserted, and pushed out a
2062                         * different task
2063                         */
2064                        get_task_struct(p);
2065                        put_task_struct(dropped);
2066                }
2067                /*
2068                 * Else the new task was newer than anything already in
2069                 * the heap and wasn't inserted
2070                 */
2071        }
2072        cgroup_iter_end(scan->cg, &it);
2073
2074        if (heap->size) {
2075                for (i = 0; i < heap->size; i++) {
2076                        struct task_struct *q = heap->ptrs[i];
2077                        if (i == 0) {
2078                                latest_time = q->start_time;
2079                                latest_task = q;
2080                        }
2081                        /* Process the task per the caller's callback */
2082                        scan->process_task(q, scan);
2083                        put_task_struct(q);
2084                }
2085                /*
2086                 * If we had to process any tasks at all, scan again
2087                 * in case some of them were in the middle of forking
2088                 * children that didn't get processed.
2089                 * Not the most efficient way to do it, but it avoids
2090                 * having to take callback_mutex in the fork path
2091                 */
2092                goto again;
2093        }
2094        if (heap == &tmp_heap)
2095                heap_free(&tmp_heap);
2096        return 0;
2097}
2098
2099/*
2100 * Stuff for reading the 'tasks' file.
2101 *
2102 * Reading this file can return large amounts of data if a cgroup has
2103 * *lots* of attached tasks. So it may need several calls to read(),
2104 * but we cannot guarantee that the information we produce is correct
2105 * unless we produce it entirely atomically.
2106 *
2107 */
2108
2109/*
2110 * Load into 'pidarray' up to 'npids' of the tasks using cgroup
2111 * 'cgrp'.  Return actual number of pids loaded.  No need to
2112 * task_lock(p) when reading out p->cgroup, since we're in an RCU
2113 * read section, so the css_set can't go away, and is
2114 * immutable after creation.
2115 */
2116static int pid_array_load(pid_t *pidarray, int npids, struct cgroup *cgrp)
2117{
2118        int n = 0, pid;
2119        struct cgroup_iter it;
2120        struct task_struct *tsk;
2121        cgroup_iter_start(cgrp, &it);
2122        while ((tsk = cgroup_iter_next(cgrp, &it))) {
2123                if (unlikely(n == npids))
2124                        break;
2125                pid = task_pid_vnr(tsk);
2126                if (pid > 0)
2127                        pidarray[n++] = pid;
2128        }
2129        cgroup_iter_end(cgrp, &it);
2130        return n;
2131}
2132
2133/**
2134 * cgroupstats_build - build and fill cgroupstats
2135 * @stats: cgroupstats to fill information into
2136 * @dentry: A dentry entry belonging to the cgroup for which stats have
2137 * been requested.
2138 *
2139 * Build and fill cgroupstats so that taskstats can export it to user
2140 * space.
2141 */
2142int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
2143{
2144        int ret = -EINVAL;
2145        struct cgroup *cgrp;
2146        struct cgroup_iter it;
2147        struct task_struct *tsk;
2148
2149        /*
2150         * Validate dentry by checking the superblock operations,
2151         * and make sure it's a directory.
2152         */
2153        if (dentry->d_sb->s_op != &cgroup_ops ||
2154            !S_ISDIR(dentry->d_inode->i_mode))
2155                 goto err;
2156
2157        ret = 0;
2158        cgrp = dentry->d_fsdata;
2159
2160        cgroup_iter_start(cgrp, &it);
2161        while ((tsk = cgroup_iter_next(cgrp, &it))) {
2162                switch (tsk->state) {
2163                case TASK_RUNNING:
2164                        stats->nr_running++;
2165                        break;
2166                case TASK_INTERRUPTIBLE:
2167                        stats->nr_sleeping++;
2168                        break;
2169                case TASK_UNINTERRUPTIBLE:
2170                        stats->nr_uninterruptible++;
2171                        break;
2172                case TASK_STOPPED:
2173                        stats->nr_stopped++;
2174                        break;
2175                default:
2176                        if (delayacct_is_task_waiting_on_io(tsk))
2177                                stats->nr_io_wait++;
2178                        break;
2179                }
2180        }
2181        cgroup_iter_end(cgrp, &it);
2182
2183err:
2184        return ret;
2185}
2186
2187static int cmppid(const void *a, const void *b)
2188{
2189        return *(pid_t *)a - *(pid_t *)b;
2190}
2191
2192
2193/*
2194 * seq_file methods for the "tasks" file. The seq_file position is the
2195 * next pid to display; the seq_file iterator is a pointer to the pid
2196 * in the cgroup->tasks_pids array.
2197 */
2198
2199static void *cgroup_tasks_start(struct seq_file *s, loff_t *pos)
2200{
2201        /*
2202         * Initially we receive a position value that corresponds to
2203         * one more than the last pid shown (or 0 on the first call or
2204         * after a seek to the start). Use a binary-search to find the
2205         * next pid to display, if any
2206         */
2207        struct cgroup *cgrp = s->private;
2208        int index = 0, pid = *pos;
2209        int *iter;
2210
2211        down_read(&cgrp->pids_mutex);
2212        if (pid) {
2213                int end = cgrp->pids_length;
2214
2215                while (index < end) {
2216                        int mid = (index + end) / 2;
2217                        if (cgrp->tasks_pids[mid] == pid) {
2218                                index = mid;
2219                                break;
2220                        } else if (cgrp->tasks_pids[mid] <= pid)
2221                                index = mid + 1;
2222                        else
2223                                end = mid;
2224                }
2225        }
2226        /* If we're off the end of the array, we're done */
2227        if (index >= cgrp->pids_length)
2228                return NULL;
2229        /* Update the abstract position to be the actual pid that we found */
2230        iter = cgrp->tasks_pids + index;
2231        *pos = *iter;
2232        return iter;
2233}
2234
2235static void cgroup_tasks_stop(struct seq_file *s, void *v)
2236{
2237        struct cgroup *cgrp = s->private;
2238        up_read(&cgrp->pids_mutex);
2239}
2240
2241static void *cgroup_tasks_next(struct seq_file *s, void *v, loff_t *pos)
2242{
2243        struct cgroup *cgrp = s->private;
2244        int *p = v;
2245        int *end = cgrp->tasks_pids + cgrp->pids_length;
2246
2247        /*
2248         * Advance to the next pid in the array. If this goes off the
2249         * end, we're done
2250         */
2251        p++;
2252        if (p >= end) {
2253                return NULL;
2254        } else {
2255                *pos = *p;
2256                return p;
2257        }
2258}
2259
2260static int cgroup_tasks_show(struct seq_file *s, void *v)
2261{
2262        return seq_printf(s, "%d\n", *(int *)v);
2263}
2264
2265static struct seq_operations cgroup_tasks_seq_operations = {
2266        .start = cgroup_tasks_start,
2267        .stop = cgroup_tasks_stop,
2268        .next = cgroup_tasks_next,
2269        .show = cgroup_tasks_show,
2270};
2271
2272static void release_cgroup_pid_array(struct cgroup *cgrp)
2273{
2274        down_write(&cgrp->pids_mutex);
2275        BUG_ON(!cgrp->pids_use_count);
2276        if (!--cgrp->pids_use_count) {
2277                kfree(cgrp->tasks_pids);
2278                cgrp->tasks_pids = NULL;
2279                cgrp->pids_length = 0;
2280        }
2281        up_write(&cgrp->pids_mutex);
2282}
2283
2284static int cgroup_tasks_release(struct inode *inode, struct file *file)
2285{
2286        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2287
2288        if (!(file->f_mode & FMODE_READ))
2289                return 0;
2290
2291        release_cgroup_pid_array(cgrp);
2292        return seq_release(inode, file);
2293}
2294
2295static struct file_operations cgroup_tasks_operations = {
2296        .read = seq_read,
2297        .llseek = seq_lseek,
2298        .write = cgroup_file_write,
2299        .release = cgroup_tasks_release,
2300};
2301
2302/*
2303 * Handle an open on 'tasks' file.  Prepare an array containing the
2304 * process id's of tasks currently attached to the cgroup being opened.
2305 */
2306
2307static int cgroup_tasks_open(struct inode *unused, struct file *file)
2308{
2309        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
2310        pid_t *pidarray;
2311        int npids;
2312        int retval;
2313
2314        /* Nothing to do for write-only files */
2315        if (!(file->f_mode & FMODE_READ))
2316                return 0;
2317
2318        /*
2319         * If cgroup gets more users after we read count, we won't have
2320         * enough space - tough.  This race is indistinguishable to the
2321         * caller from the case that the additional cgroup users didn't
2322         * show up until sometime later on.
2323         */
2324        npids = cgroup_task_count(cgrp);
2325        pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
2326        if (!pidarray)
2327                return -ENOMEM;
2328        npids = pid_array_load(pidarray, npids, cgrp);
2329        sort(pidarray, npids, sizeof(pid_t), cmppid, NULL);
2330
2331        /*
2332         * Store the array in the cgroup, freeing the old
2333         * array if necessary
2334         */
2335        down_write(&cgrp->pids_mutex);
2336        kfree(cgrp->tasks_pids);
2337        cgrp->tasks_pids = pidarray;
2338        cgrp->pids_length = npids;
2339        cgrp->pids_use_count++;
2340        up_write(&cgrp->pids_mutex);
2341
2342        file->f_op = &cgroup_tasks_operations;
2343
2344        retval = seq_open(file, &cgroup_tasks_seq_operations);
2345        if (retval) {
2346                release_cgroup_pid_array(cgrp);
2347                return retval;
2348        }
2349        ((struct seq_file *)file->private_data)->private = cgrp;
2350        return 0;
2351}
2352
2353static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
2354                                            struct cftype *cft)
2355{
2356        return notify_on_release(cgrp);
2357}
2358
2359static int cgroup_write_notify_on_release(struct cgroup *cgrp,
2360                                          struct cftype *cft,
2361                                          u64 val)
2362{
2363        clear_bit(CGRP_RELEASABLE, &cgrp->flags);
2364        if (val)
2365                set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
2366        else
2367                clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
2368        return 0;
2369}
2370
2371/*
2372 * for the common functions, 'private' gives the type of file
2373 */
2374static struct cftype files[] = {
2375        {
2376                .name = "tasks",
2377                .open = cgroup_tasks_open,
2378                .write_u64 = cgroup_tasks_write,
2379                .release = cgroup_tasks_release,
2380                .private = FILE_TASKLIST,
2381                .mode = S_IRUGO | S_IWUSR,
2382        },
2383
2384        {
2385                .name = "notify_on_release",
2386                .read_u64 = cgroup_read_notify_on_release,
2387                .write_u64 = cgroup_write_notify_on_release,
2388                .private = FILE_NOTIFY_ON_RELEASE,
2389        },
2390};
2391
2392static struct cftype cft_release_agent = {
2393        .name = "release_agent",
2394        .read_seq_string = cgroup_release_agent_show,
2395        .write_string = cgroup_release_agent_write,
2396        .max_write_len = PATH_MAX,
2397        .private = FILE_RELEASE_AGENT,
2398};
2399
2400static int cgroup_populate_dir(struct cgroup *cgrp)
2401{
2402        int err;
2403        struct cgroup_subsys *ss;
2404
2405        /* First clear out any existing files */
2406        cgroup_clear_directory(cgrp->dentry);
2407
2408        err = cgroup_add_files(cgrp, NULL, files, ARRAY_SIZE(files));
2409        if (err < 0)
2410                return err;
2411
2412        if (cgrp == cgrp->top_cgroup) {
2413                if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0)
2414                        return err;
2415        }
2416
2417        for_each_subsys(cgrp->root, ss) {
2418                if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
2419                        return err;
2420        }
2421        /* This cgroup is ready now */
2422        for_each_subsys(cgrp->root, ss) {
2423                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
2424                /*
2425                 * Update id->css pointer and make this css visible from
2426                 * CSS ID functions. This pointer will be dereferened
2427                 * from RCU-read-side without locks.
2428                 */
2429                if (css->id)
2430                        rcu_assign_pointer(css->id->css, css);
2431        }
2432
2433        return 0;
2434}
2435
2436static void init_cgroup_css(struct cgroup_subsys_state *css,
2437                               struct cgroup_subsys *ss,
2438                               struct cgroup *cgrp)
2439{
2440        css->cgroup = cgrp;
2441        atomic_set(&css->refcnt, 1);
2442        css->flags = 0;
2443        css->id = NULL;
2444        if (cgrp == dummytop)
2445                set_bit(CSS_ROOT, &css->flags);
2446        BUG_ON(cgrp->subsys[ss->subsys_id]);
2447        cgrp->subsys[ss->subsys_id] = css;
2448}
2449
2450static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
2451{
2452        /* We need to take each hierarchy_mutex in a consistent order */
2453        int i;
2454
2455        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
2456                struct cgroup_subsys *ss = subsys[i];
2457                if (ss->root == root)
2458                        mutex_lock(&ss->hierarchy_mutex);
2459        }
2460}
2461
2462static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
2463{
2464        int i;
2465
2466        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
2467                struct cgroup_subsys *ss = subsys[i];
2468                if (ss->root == root)
2469                        mutex_unlock(&ss->hierarchy_mutex);
2470        }
2471}
2472
2473/*
2474 * cgroup_create - create a cgroup
2475 * @parent: cgroup that will be parent of the new cgroup
2476 * @dentry: dentry of the new cgroup
2477 * @mode: mode to set on new inode
2478 *
2479 * Must be called with the mutex on the parent inode held
2480 */
2481static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
2482                             mode_t mode)
2483{
2484        struct cgroup *cgrp;
2485        struct cgroupfs_root *root = parent->root;
2486        int err = 0;
2487        struct cgroup_subsys *ss;
2488        struct super_block *sb = root->sb;
2489
2490        cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
2491        if (!cgrp)
2492                return -ENOMEM;
2493
2494        /* Grab a reference on the superblock so the hierarchy doesn't
2495         * get deleted on unmount if there are child cgroups.  This
2496         * can be done outside cgroup_mutex, since the sb can't
2497         * disappear while someone has an open control file on the
2498         * fs */
2499        atomic_inc(&sb->s_active);
2500
2501        mutex_lock(&cgroup_mutex);
2502
2503        init_cgroup_housekeeping(cgrp);
2504
2505        cgrp->parent = parent;
2506        cgrp->root = parent->root;
2507        cgrp->top_cgroup = parent->top_cgroup;
2508
2509        if (notify_on_release(parent))
2510                set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
2511
2512        for_each_subsys(root, ss) {
2513                struct cgroup_subsys_state *css = ss->create(ss, cgrp);
2514                if (IS_ERR(css)) {
2515                        err = PTR_ERR(css);
2516                        goto err_destroy;
2517                }
2518                init_cgroup_css(css, ss, cgrp);
2519                if (ss->use_id)
2520                        if (alloc_css_id(ss, parent, cgrp))
2521                                goto err_destroy;
2522                /* At error, ->destroy() callback has to free assigned ID. */
2523        }
2524
2525        cgroup_lock_hierarchy(root);
2526        list_add(&cgrp->sibling, &cgrp->parent->children);
2527        cgroup_unlock_hierarchy(root);
2528        root->number_of_cgroups++;
2529
2530        err = cgroup_create_dir(cgrp, dentry, mode);
2531        if (err < 0)
2532                goto err_remove;
2533
2534        /* The cgroup directory was pre-locked for us */
2535        BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
2536
2537        err = cgroup_populate_dir(cgrp);
2538        /* If err < 0, we have a half-filled directory - oh well ;) */
2539
2540        mutex_unlock(&cgroup_mutex);
2541        mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
2542
2543        return 0;
2544
2545 err_remove:
2546
2547        cgroup_lock_hierarchy(root);
2548        list_del(&cgrp->sibling);
2549        cgroup_unlock_hierarchy(root);
2550        root->number_of_cgroups--;
2551
2552 err_destroy:
2553
2554        for_each_subsys(root, ss) {
2555                if (cgrp->subsys[ss->subsys_id])
2556                        ss->destroy(ss, cgrp);
2557        }
2558
2559        mutex_unlock(&cgroup_mutex);
2560
2561        /* Release the reference count that we took on the superblock */
2562        deactivate_super(sb);
2563
2564        kfree(cgrp);
2565        return err;
2566}
2567
2568static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)
2569{
2570        struct cgroup *c_parent = dentry->d_parent->d_fsdata;
2571
2572        /* the vfs holds inode->i_mutex already */
2573        return cgroup_create(c_parent, dentry, mode | S_IFDIR);
2574}
2575
2576static int cgroup_has_css_refs(struct cgroup *cgrp)
2577{
2578        /* Check the reference count on each subsystem. Since we
2579         * already established that there are no tasks in the
2580         * cgroup, if the css refcount is also 1, then there should
2581         * be no outstanding references, so the subsystem is safe to
2582         * destroy. We scan across all subsystems rather than using
2583         * the per-hierarchy linked list of mounted subsystems since
2584         * we can be called via check_for_release() with no
2585         * synchronization other than RCU, and the subsystem linked
2586         * list isn't RCU-safe */
2587        int i;
2588        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
2589                struct cgroup_subsys *ss = subsys[i];
2590                struct cgroup_subsys_state *css;
2591                /* Skip subsystems not in this hierarchy */
2592                if (ss->root != cgrp->root)
2593                        continue;
2594                css = cgrp->subsys[ss->subsys_id];
2595                /* When called from check_for_release() it's possible
2596                 * that by this point the cgroup has been removed
2597                 * and the css deleted. But a false-positive doesn't
2598                 * matter, since it can only happen if the cgroup
2599                 * has been deleted and hence no longer needs the
2600                 * release agent to be called anyway. */
2601                if (css && (atomic_read(&css->refcnt) > 1))
2602                        return 1;
2603        }
2604        return 0;
2605}
2606
2607/*
2608 * Atomically mark all (or else none) of the cgroup's CSS objects as
2609 * CSS_REMOVED. Return true on success, or false if the cgroup has
2610 * busy subsystems. Call with cgroup_mutex held
2611 */
2612
2613static int cgroup_clear_css_refs(struct cgroup *cgrp)
2614{
2615        struct cgroup_subsys *ss;
2616        unsigned long flags;
2617        bool failed = false;
2618        local_irq_save(flags);
2619        for_each_subsys(cgrp->root, ss) {
2620                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
2621                int refcnt;
2622                while (1) {
2623                        /* We can only remove a CSS with a refcnt==1 */
2624                        refcnt = atomic_read(&css->refcnt);
2625                        if (refcnt > 1) {
2626                                failed = true;
2627                                goto done;
2628                        }
2629                        BUG_ON(!refcnt);
2630                        /*
2631                         * Drop the refcnt to 0 while we check other
2632                         * subsystems. This will cause any racing
2633                         * css_tryget() to spin until we set the
2634                         * CSS_REMOVED bits or abort
2635                         */
2636                        if (atomic_cmpxchg(&css->refcnt, refcnt, 0) == refcnt)
2637                                break;
2638                        cpu_relax();
2639                }
2640        }
2641 done:
2642        for_each_subsys(cgrp->root, ss) {
2643                struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
2644                if (failed) {
2645                        /*
2646                         * Restore old refcnt if we previously managed
2647                         * to clear it from 1 to 0
2648                         */
2649                        if (!atomic_read(&css->refcnt))
2650                                atomic_set(&css->refcnt, 1);
2651                } else {
2652                        /* Commit the fact that the CSS is removed */
2653                        set_bit(CSS_REMOVED, &css->flags);
2654                }
2655        }
2656        local_irq_restore(flags);
2657        return !failed;
2658}
2659
2660static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
2661{
2662        struct cgroup *cgrp = dentry->d_fsdata;
2663        struct dentry *d;
2664        struct cgroup *parent;
2665        DEFINE_WAIT(wait);
2666        int ret;
2667
2668        /* the vfs holds both inode->i_mutex already */
2669again:
2670        mutex_lock(&cgroup_mutex);
2671        if (atomic_read(&cgrp->count) != 0) {
2672                mutex_unlock(&cgroup_mutex);
2673                return -EBUSY;
2674        }
2675        if (!list_empty(&cgrp->children)) {
2676                mutex_unlock(&cgroup_mutex);
2677                return -EBUSY;
2678        }
2679        mutex_unlock(&cgroup_mutex);
2680
2681        /*
2682         * Call pre_destroy handlers of subsys. Notify subsystems
2683         * that rmdir() request comes.
2684         */
2685        ret = cgroup_call_pre_destroy(cgrp);
2686        if (ret)
2687                return ret;
2688
2689        mutex_lock(&cgroup_mutex);
2690        parent = cgrp->parent;
2691        if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
2692                mutex_unlock(&cgroup_mutex);
2693                return -EBUSY;
2694        }
2695        /*
2696         * css_put/get is provided for subsys to grab refcnt to css. In typical
2697         * case, subsystem has no reference after pre_destroy(). But, under
2698         * hierarchy management, some *temporal* refcnt can be hold.
2699         * To avoid returning -EBUSY to a user, waitqueue is used. If subsys
2700         * is really busy, it should return -EBUSY at pre_destroy(). wake_up
2701         * is called when css_put() is called and refcnt goes down to 0.
2702         */
2703        set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
2704        prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
2705
2706        if (!cgroup_clear_css_refs(cgrp)) {
2707                mutex_unlock(&cgroup_mutex);
2708                schedule();
2709                finish_wait(&cgroup_rmdir_waitq, &wait);
2710                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
2711                if (signal_pending(current))
2712                        return -EINTR;
2713                goto again;
2714        }
2715        /* NO css_tryget() can success after here. */
2716        finish_wait(&cgroup_rmdir_waitq, &wait);
2717        clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
2718
2719        spin_lock(&release_list_lock);
2720        set_bit(CGRP_REMOVED, &cgrp->flags);
2721        if (!list_empty(&cgrp->release_list))
2722                list_del(&cgrp->release_list);
2723        spin_unlock(&release_list_lock);
2724
2725        cgroup_lock_hierarchy(cgrp->root);
2726        /* delete this cgroup from parent->children */
2727        list_del(&cgrp->sibling);
2728        cgroup_unlock_hierarchy(cgrp->root);
2729
2730        spin_lock(&cgrp->dentry->d_lock);
2731        d = dget(cgrp->dentry);
2732        spin_unlock(&d->d_lock);
2733
2734        cgroup_d_remove_dir(d);
2735        dput(d);
2736
2737        set_bit(CGRP_RELEASABLE, &parent->flags);
2738        check_for_release(parent);
2739
2740        mutex_unlock(&cgroup_mutex);
2741        return 0;
2742}
2743
2744static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
2745{
2746        struct cgroup_subsys_state *css;
2747
2748        printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
2749
2750        /* Create the top cgroup state for this subsystem */
2751        list_add(&ss->sibling, &rootnode.subsys_list);
2752        ss->root = &rootnode;
2753        css = ss->create(ss, dummytop);
2754        /* We don't handle early failures gracefully */
2755        BUG_ON(IS_ERR(css));
2756        init_cgroup_css(css, ss, dummytop);
2757
2758        /* Update the init_css_set to contain a subsys
2759         * pointer to this state - since the subsystem is
2760         * newly registered, all tasks and hence the
2761         * init_css_set is in the subsystem's top cgroup. */
2762        init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
2763
2764        need_forkexit_callback |= ss->fork || ss->exit;
2765
2766        /* At system boot, before all subsystems have been
2767         * registered, no tasks have been forked, so we don't
2768         * need to invoke fork callbacks here. */
2769        BUG_ON(!list_empty(&init_task.tasks));
2770
2771        mutex_init(&ss->hierarchy_mutex);
2772        lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
2773        ss->active = 1;
2774}
2775
2776/**
2777 * cgroup_init_early - cgroup initialization at system boot
2778 *
2779 * Initialize cgroups at system boot, and initialize any
2780 * subsystems that request early init.
2781 */
2782int __init cgroup_init_early(void)
2783{
2784        int i;
2785        atomic_set(&init_css_set.refcount, 1);
2786        INIT_LIST_HEAD(&init_css_set.cg_links);
2787        INIT_LIST_HEAD(&init_css_set.tasks);
2788        INIT_HLIST_NODE(&init_css_set.hlist);
2789        css_set_count = 1;
2790        init_cgroup_root(&rootnode);
2791        root_count = 1;
2792        init_task.cgroups = &init_css_set;
2793
2794        init_css_set_link.cg = &init_css_set;
2795        list_add(&init_css_set_link.cgrp_link_list,
2796                 &rootnode.top_cgroup.css_sets);
2797        list_add(&init_css_set_link.cg_link_list,
2798                 &init_css_set.cg_links);
2799
2800        for (i = 0; i < CSS_SET_TABLE_SIZE; i++)
2801                INIT_HLIST_HEAD(&css_set_table[i]);
2802
2803        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
2804                struct cgroup_subsys *ss = subsys[i];
2805
2806                BUG_ON(!ss->name);
2807                BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
2808                BUG_ON(!ss->create);
2809                BUG_ON(!ss->destroy);
2810                if (ss->subsys_id != i) {
2811                        printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
2812                               ss->name, ss->subsys_id);
2813                        BUG();
2814                }
2815
2816                if (ss->early_init)
2817                        cgroup_init_subsys(ss);
2818        }
2819        return 0;
2820}
2821
2822/**
2823 * cgroup_init - cgroup initialization
2824 *
2825 * Register cgroup filesystem and /proc file, and initialize
2826 * any subsystems that didn't request early init.
2827 */
2828int __init cgroup_init(void)
2829{
2830        int err;
2831        int i;
2832        struct hlist_head *hhead;
2833
2834        err = bdi_init(&cgroup_backing_dev_info);
2835        if (err)
2836                return err;
2837
2838        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
2839                struct cgroup_subsys *ss = subsys[i];
2840                if (!ss->early_init)
2841                        cgroup_init_subsys(ss);
2842                if (ss->use_id)
2843                        cgroup_subsys_init_idr(ss);
2844        }
2845
2846        /* Add init_css_set to the hash table */
2847        hhead = css_set_hash(init_css_set.subsys);
2848        hlist_add_head(&init_css_set.hlist, hhead);
2849
2850        err = register_filesystem(&cgroup_fs_type);
2851        if (err < 0)
2852                goto out;
2853
2854        proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);
2855
2856out:
2857        if (err)
2858                bdi_destroy(&cgroup_backing_dev_info);
2859
2860        return err;
2861}
2862
2863/*
2864 * proc_cgroup_show()
2865 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
2866 *  - Used for /proc/<pid>/cgroup.
2867 *  - No need to task_lock(tsk) on this tsk->cgroup reference, as it
2868 *    doesn't really matter if tsk->cgroup changes after we read it,
2869 *    and we take cgroup_mutex, keeping cgroup_attach_task() from changing it
2870 *    anyway.  No need to check that tsk->cgroup != NULL, thanks to
2871 *    the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
2872 *    cgroup to top_cgroup.
2873 */
2874
2875/* TODO: Use a proper seq_file iterator */
2876static int proc_cgroup_show(struct seq_file *m, void *v)
2877{
2878        struct pid *pid;
2879        struct task_struct *tsk;
2880        char *buf;
2881        int retval;
2882        struct cgroupfs_root *root;
2883
2884        retval = -ENOMEM;
2885        buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
2886        if (!buf)
2887                goto out;
2888
2889        retval = -ESRCH;
2890        pid = m->private;
2891        tsk = get_pid_task(pid, PIDTYPE_PID);
2892        if (!tsk)
2893                goto out_free;
2894
2895        retval = 0;
2896
2897        mutex_lock(&cgroup_mutex);
2898
2899        for_each_active_root(root) {
2900                struct cgroup_subsys *ss;
2901                struct cgroup *cgrp;
2902                int subsys_id;
2903                int count = 0;
2904
2905                seq_printf(m, "%lu:", root->subsys_bits);
2906                for_each_subsys(root, ss)
2907                        seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
2908                seq_putc(m, ':');
2909                get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
2910                cgrp = task_cgroup(tsk, subsys_id);
2911                retval = cgroup_path(cgrp, buf, PAGE_SIZE);
2912                if (retval < 0)
2913                        goto out_unlock;
2914                seq_puts(m, buf);
2915                seq_putc(m, '\n');
2916        }
2917
2918out_unlock:
2919        mutex_unlock(&cgroup_mutex);
2920        put_task_struct(tsk);
2921out_free:
2922        kfree(buf);
2923out:
2924        return retval;
2925}
2926
2927static int cgroup_open(struct inode *inode, struct file *file)
2928{
2929        struct pid *pid = PROC_I(inode)->pid;
2930        return single_open(file, proc_cgroup_show, pid);
2931}
2932
2933struct file_operations proc_cgroup_operations = {
2934        .open           = cgroup_open,
2935        .read           = seq_read,
2936        .llseek         = seq_lseek,
2937        .release        = single_release,
2938};
2939
2940/* Display information about each subsystem and each hierarchy */
2941static int proc_cgroupstats_show(struct seq_file *m, void *v)
2942{
2943        int i;
2944
2945        seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
2946        mutex_lock(&cgroup_mutex);
2947        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
2948                struct cgroup_subsys *ss = subsys[i];
2949                seq_printf(m, "%s\t%lu\t%d\t%d\n",
2950                           ss->name, ss->root->subsys_bits,
2951                           ss->root->number_of_cgroups, !ss->disabled);
2952        }
2953        mutex_unlock(&cgroup_mutex);
2954        return 0;
2955}
2956
2957static int cgroupstats_open(struct inode *inode, struct file *file)
2958{
2959        return single_open(file, proc_cgroupstats_show, NULL);
2960}
2961
2962static struct file_operations proc_cgroupstats_operations = {
2963        .open = cgroupstats_open,
2964        .read = seq_read,
2965        .llseek = seq_lseek,
2966        .release = single_release,
2967};
2968
2969/**
2970 * cgroup_fork - attach newly forked task to its parents cgroup.
2971 * @child: pointer to task_struct of forking parent process.
2972 *
2973 * Description: A task inherits its parent's cgroup at fork().
2974 *
2975 * A pointer to the shared css_set was automatically copied in
2976 * fork.c by dup_task_struct().  However, we ignore that copy, since
2977 * it was not made under the protection of RCU or cgroup_mutex, so
2978 * might no longer be a valid cgroup pointer.  cgroup_attach_task() might
2979 * have already changed current->cgroups, allowing the previously
2980 * referenced cgroup group to be removed and freed.
2981 *
2982 * At the point that cgroup_fork() is called, 'current' is the parent
2983 * task, and the passed argument 'child' points to the child task.
2984 */
2985void cgroup_fork(struct task_struct *child)
2986{
2987        task_lock(current);
2988        child->cgroups = current->cgroups;
2989        get_css_set(child->cgroups);
2990        task_unlock(current);
2991        INIT_LIST_HEAD(&child->cg_list);
2992}
2993
2994/**
2995 * cgroup_fork_callbacks - run fork callbacks
2996 * @child: the new task
2997 *
2998 * Called on a new task very soon before adding it to the
2999 * tasklist. No need to take any locks since no-one can
3000 * be operating on this task.
3001 */
3002void cgroup_fork_callbacks(struct task_struct *child)
3003{
3004        if (need_forkexit_callback) {
3005                int i;
3006                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3007                        struct cgroup_subsys *ss = subsys[i];
3008                        if (ss->fork)
3009                                ss->fork(ss, child);
3010                }
3011        }
3012}
3013
3014/**
3015 * cgroup_post_fork - called on a new task after adding it to the task list
3016 * @child: the task in question
3017 *
3018 * Adds the task to the list running through its css_set if necessary.
3019 * Has to be after the task is visible on the task list in case we race
3020 * with the first call to cgroup_iter_start() - to guarantee that the
3021 * new task ends up on its list.
3022 */
3023void cgroup_post_fork(struct task_struct *child)
3024{
3025        if (use_task_css_set_links) {
3026                write_lock(&css_set_lock);
3027                task_lock(child);
3028                if (list_empty(&child->cg_list))
3029                        list_add(&child->cg_list, &child->cgroups->tasks);
3030                task_unlock(child);
3031                write_unlock(&css_set_lock);
3032        }
3033}
3034/**
3035 * cgroup_exit - detach cgroup from exiting task
3036 * @tsk: pointer to task_struct of exiting process
3037 * @run_callback: run exit callbacks?
3038 *
3039 * Description: Detach cgroup from @tsk and release it.
3040 *
3041 * Note that cgroups marked notify_on_release force every task in
3042 * them to take the global cgroup_mutex mutex when exiting.
3043 * This could impact scaling on very large systems.  Be reluctant to
3044 * use notify_on_release cgroups where very high task exit scaling
3045 * is required on large systems.
3046 *
3047 * the_top_cgroup_hack:
3048 *
3049 *    Set the exiting tasks cgroup to the root cgroup (top_cgroup).
3050 *
3051 *    We call cgroup_exit() while the task is still competent to
3052 *    handle notify_on_release(), then leave the task attached to the
3053 *    root cgroup in each hierarchy for the remainder of its exit.
3054 *
3055 *    To do this properly, we would increment the reference count on
3056 *    top_cgroup, and near the very end of the kernel/exit.c do_exit()
3057 *    code we would add a second cgroup function call, to drop that
3058 *    reference.  This would just create an unnecessary hot spot on
3059 *    the top_cgroup reference count, to no avail.
3060 *
3061 *    Normally, holding a reference to a cgroup without bumping its
3062 *    count is unsafe.   The cgroup could go away, or someone could
3063 *    attach us to a different cgroup, decrementing the count on
3064 *    the first cgroup that we never incremented.  But in this case,
3065 *    top_cgroup isn't going away, and either task has PF_EXITING set,
3066 *    which wards off any cgroup_attach_task() attempts, or task is a failed
3067 *    fork, never visible to cgroup_attach_task.
3068 */
3069void cgroup_exit(struct task_struct *tsk, int run_callbacks)
3070{
3071        int i;
3072        struct css_set *cg;
3073
3074        if (run_callbacks && need_forkexit_callback) {
3075                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3076                        struct cgroup_subsys *ss = subsys[i];
3077                        if (ss->exit)
3078                                ss->exit(ss, tsk);
3079                }
3080        }
3081
3082        /*
3083         * Unlink from the css_set task list if necessary.
3084         * Optimistically check cg_list before taking
3085         * css_set_lock
3086         */
3087        if (!list_empty(&tsk->cg_list)) {
3088                write_lock(&css_set_lock);
3089                if (!list_empty(&tsk->cg_list))
3090                        list_del(&tsk->cg_list);
3091                write_unlock(&css_set_lock);
3092        }
3093
3094        /* Reassign the task to the init_css_set. */
3095        task_lock(tsk);
3096        cg = tsk->cgroups;
3097        tsk->cgroups = &init_css_set;
3098        task_unlock(tsk);
3099        if (cg)
3100                put_css_set_taskexit(cg);
3101}
3102
3103/**
3104 * cgroup_clone - clone the cgroup the given subsystem is attached to
3105 * @tsk: the task to be moved
3106 * @subsys: the given subsystem
3107 * @nodename: the name for the new cgroup
3108 *
3109 * Duplicate the current cgroup in the hierarchy that the given
3110 * subsystem is attached to, and move this task into the new
3111 * child.
3112 */
3113int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
3114                                                        char *nodename)
3115{
3116        struct dentry *dentry;
3117        int ret = 0;
3118        struct cgroup *parent, *child;
3119        struct inode *inode;
3120        struct css_set *cg;
3121        struct cgroupfs_root *root;
3122        struct cgroup_subsys *ss;
3123
3124        /* We shouldn't be called by an unregistered subsystem */
3125        BUG_ON(!subsys->active);
3126
3127        /* First figure out what hierarchy and cgroup we're dealing
3128         * with, and pin them so we can drop cgroup_mutex */
3129        mutex_lock(&cgroup_mutex);
3130 again:
3131        root = subsys->root;
3132        if (root == &rootnode) {
3133                mutex_unlock(&cgroup_mutex);
3134                return 0;
3135        }
3136
3137        /* Pin the hierarchy */
3138        if (!atomic_inc_not_zero(&root->sb->s_active)) {
3139                /* We race with the final deactivate_super() */
3140                mutex_unlock(&cgroup_mutex);
3141                return 0;
3142        }
3143
3144        /* Keep the cgroup alive */
3145        task_lock(tsk);
3146        parent = task_cgroup(tsk, subsys->subsys_id);
3147        cg = tsk->cgroups;
3148        get_css_set(cg);
3149        task_unlock(tsk);
3150
3151        mutex_unlock(&cgroup_mutex);
3152
3153        /* Now do the VFS work to create a cgroup */
3154        inode = parent->dentry->d_inode;
3155
3156        /* Hold the parent directory mutex across this operation to
3157         * stop anyone else deleting the new cgroup */
3158        mutex_lock(&inode->i_mutex);
3159        dentry = lookup_one_len(nodename, parent->dentry, strlen(nodename));
3160        if (IS_ERR(dentry)) {
3161                printk(KERN_INFO
3162                       "cgroup: Couldn't allocate dentry for %s: %ld\n", nodename,
3163                       PTR_ERR(dentry));
3164                ret = PTR_ERR(dentry);
3165                goto out_release;
3166        }
3167
3168        /* Create the cgroup directory, which also creates the cgroup */
3169        ret = vfs_mkdir(inode, dentry, 0755);
3170        child = __d_cgrp(dentry);
3171        dput(dentry);
3172        if (ret) {
3173                printk(KERN_INFO
3174                       "Failed to create cgroup %s: %d\n", nodename,
3175                       ret);
3176                goto out_release;
3177        }
3178
3179        /* The cgroup now exists. Retake cgroup_mutex and check
3180         * that we're still in the same state that we thought we
3181         * were. */
3182        mutex_lock(&cgroup_mutex);
3183        if ((root != subsys->root) ||
3184            (parent != task_cgroup(tsk, subsys->subsys_id))) {
3185                /* Aargh, we raced ... */
3186                mutex_unlock(&inode->i_mutex);
3187                put_css_set(cg);
3188
3189                deactivate_super(root->sb);
3190                /* The cgroup is still accessible in the VFS, but
3191                 * we're not going to try to rmdir() it at this
3192                 * point. */
3193                printk(KERN_INFO
3194                       "Race in cgroup_clone() - leaking cgroup %s\n",
3195                       nodename);
3196                goto again;
3197        }
3198
3199        /* do any required auto-setup */
3200        for_each_subsys(root, ss) {
3201                if (ss->post_clone)
3202                        ss->post_clone(ss, child);
3203        }
3204
3205        /* All seems fine. Finish by moving the task into the new cgroup */
3206        ret = cgroup_attach_task(child, tsk);
3207        mutex_unlock(&cgroup_mutex);
3208
3209 out_release:
3210        mutex_unlock(&inode->i_mutex);
3211
3212        mutex_lock(&cgroup_mutex);
3213        put_css_set(cg);
3214        mutex_unlock(&cgroup_mutex);
3215        deactivate_super(root->sb);
3216        return ret;
3217}
3218
3219/**
3220 * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp
3221 * @cgrp: the cgroup in question
3222 * @task: the task in question
3223 *
3224 * See if @cgrp is a descendant of @task's cgroup in the appropriate
3225 * hierarchy.
3226 *
3227 * If we are sending in dummytop, then presumably we are creating
3228 * the top cgroup in the subsystem.
3229 *
3230 * Called only by the ns (nsproxy) cgroup.
3231 */
3232int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
3233{
3234        int ret;
3235        struct cgroup *target;
3236        int subsys_id;
3237
3238        if (cgrp == dummytop)
3239                return 1;
3240
3241        get_first_subsys(cgrp, NULL, &subsys_id);
3242        target = task_cgroup(task, subsys_id);
3243        while (cgrp != target && cgrp!= cgrp->top_cgroup)
3244                cgrp = cgrp->parent;
3245        ret = (cgrp == target);
3246        return ret;
3247}
3248
3249static void check_for_release(struct cgroup *cgrp)
3250{
3251        /* All of these checks rely on RCU to keep the cgroup
3252         * structure alive */
3253        if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count)
3254            && list_empty(&cgrp->children) && !cgroup_has_css_refs(cgrp)) {
3255                /* Control Group is currently removeable. If it's not
3256                 * already queued for a userspace notification, queue
3257                 * it now */
3258                int need_schedule_work = 0;
3259                spin_lock(&release_list_lock);
3260                if (!cgroup_is_removed(cgrp) &&
3261                    list_empty(&cgrp->release_list)) {
3262                        list_add(&cgrp->release_list, &release_list);
3263                        need_schedule_work = 1;
3264                }
3265                spin_unlock(&release_list_lock);
3266                if (need_schedule_work)
3267                        schedule_work(&release_agent_work);
3268        }
3269}
3270
3271void __css_put(struct cgroup_subsys_state *css)
3272{
3273        struct cgroup *cgrp = css->cgroup;
3274        rcu_read_lock();
3275        if (atomic_dec_return(&css->refcnt) == 1) {
3276                if (notify_on_release(cgrp)) {
3277                        set_bit(CGRP_RELEASABLE, &cgrp->flags);
3278                        check_for_release(cgrp);
3279                }
3280                cgroup_wakeup_rmdir_waiters(cgrp);
3281        }
3282        rcu_read_unlock();
3283}
3284
3285/*
3286 * Notify userspace when a cgroup is released, by running the
3287 * configured release agent with the name of the cgroup (path
3288 * relative to the root of cgroup file system) as the argument.
3289 *
3290 * Most likely, this user command will try to rmdir this cgroup.
3291 *
3292 * This races with the possibility that some other task will be
3293 * attached to this cgroup before it is removed, or that some other
3294 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
3295 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
3296 * unused, and this cgroup will be reprieved from its death sentence,
3297 * to continue to serve a useful existence.  Next time it's released,
3298 * we will get notified again, if it still has 'notify_on_release' set.
3299 *
3300 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
3301 * means only wait until the task is successfully execve()'d.  The
3302 * separate release agent task is forked by call_usermodehelper(),
3303 * then control in this thread returns here, without waiting for the
3304 * release agent task.  We don't bother to wait because the caller of
3305 * this routine has no use for the exit status of the release agent
3306 * task, so no sense holding our caller up for that.
3307 */
3308static void cgroup_release_agent(struct work_struct *work)
3309{
3310        BUG_ON(work != &release_agent_work);
3311        mutex_lock(&cgroup_mutex);
3312        spin_lock(&release_list_lock);
3313        while (!list_empty(&release_list)) {
3314                char *argv[3], *envp[3];
3315                int i;
3316                char *pathbuf = NULL, *agentbuf = NULL;
3317                struct cgroup *cgrp = list_entry(release_list.next,
3318                                                    struct cgroup,
3319                                                    release_list);
3320                list_del_init(&cgrp->release_list);
3321                spin_unlock(&release_list_lock);
3322                pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
3323                if (!pathbuf)
3324                        goto continue_free;
3325                if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
3326                        goto continue_free;
3327                agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
3328                if (!agentbuf)
3329                        goto continue_free;
3330
3331                i = 0;
3332                argv[i++] = agentbuf;
3333                argv[i++] = pathbuf;
3334                argv[i] = NULL;
3335
3336                i = 0;
3337                /* minimal command environment */
3338                envp[i++] = "HOME=/";
3339                envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
3340                envp[i] = NULL;
3341
3342                /* Drop the lock while we invoke the usermode helper,
3343                 * since the exec could involve hitting disk and hence
3344                 * be a slow process */
3345                mutex_unlock(&cgroup_mutex);
3346                call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
3347                mutex_lock(&cgroup_mutex);
3348 continue_free:
3349                kfree(pathbuf);
3350                kfree(agentbuf);
3351                spin_lock(&release_list_lock);
3352        }
3353        spin_unlock(&release_list_lock);
3354        mutex_unlock(&cgroup_mutex);
3355}
3356
3357static int __init cgroup_disable(char *str)
3358{
3359        int i;
3360        char *token;
3361
3362        while ((token = strsep(&str, ",")) != NULL) {
3363                if (!*token)
3364                        continue;
3365
3366                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
3367                        struct cgroup_subsys *ss = subsys[i];
3368
3369                        if (!strcmp(token, ss->name)) {
3370                                ss->disabled = 1;
3371                                printk(KERN_INFO "Disabling %s control group"
3372                                        " subsystem\n", ss->name);
3373                                break;
3374                        }
3375                }
3376        }
3377        return 1;
3378}
3379__setup("cgroup_disable=", cgroup_disable);
3380
3381/*
3382 * Functons for CSS ID.
3383 */
3384
3385/*
3386 *To get ID other than 0, this should be called when !cgroup_is_removed().
3387 */
3388unsigned short css_id(struct cgroup_subsys_state *css)
3389{
3390        struct css_id *cssid = rcu_dereference(css->id);
3391
3392        if (cssid)
3393                return cssid->id;
3394        return 0;
3395}
3396
3397unsigned short css_depth(struct cgroup_subsys_state *css)
3398{
3399        struct css_id *cssid = rcu_dereference(css->id);
3400
3401        if (cssid)
3402                return cssid->depth;
3403        return 0;
3404}
3405
3406bool css_is_ancestor(struct cgroup_subsys_state *child,
3407                    const struct cgroup_subsys_state *root)
3408{
3409        struct css_id *child_id = rcu_dereference(child->id);
3410        struct css_id *root_id = rcu_dereference(root->id);
3411
3412        if (!child_id || !root_id || (child_id->depth < root_id->depth))
3413                return false;
3414        return child_id->stack[root_id->depth] == root_id->id;
3415}
3416
3417static void __free_css_id_cb(struct rcu_head *head)
3418{
3419        struct css_id *id;
3420
3421        id = container_of(head, struct css_id, rcu_head);
3422        kfree(id);
3423}
3424
3425void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
3426{
3427        struct css_id *id = css->id;
3428        /* When this is called before css_id initialization, id can be NULL */
3429        if (!id)
3430                return;
3431
3432        BUG_ON(!ss->use_id);
3433
3434        rcu_assign_pointer(id->css, NULL);
3435        rcu_assign_pointer(css->id, NULL);
3436        spin_lock(&ss->id_lock);
3437        idr_remove(&ss->idr, id->id);
3438        spin_unlock(&ss->id_lock);
3439        call_rcu(&id->rcu_head, __free_css_id_cb);
3440}
3441
3442/*
3443 * This is called by init or create(). Then, calls to this function are
3444 * always serialized (By cgroup_mutex() at create()).
3445 */
3446
3447static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
3448{
3449        struct css_id *newid;
3450        int myid, error, size;
3451
3452        BUG_ON(!ss->use_id);
3453
3454        size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
3455        newid = kzalloc(size, GFP_KERNEL);
3456        if (!newid)
3457                return ERR_PTR(-ENOMEM);
3458        /* get id */
3459        if (unlikely(!idr_pre_get(&ss->idr, GFP_KERNEL))) {
3460                error = -ENOMEM;
3461                goto err_out;
3462        }
3463        spin_lock(&ss->id_lock);
3464        /* Don't use 0. allocates an ID of 1-65535 */
3465        error = idr_get_new_above(&ss->idr, newid, 1, &myid);
3466        spin_unlock(&ss->id_lock);
3467
3468        /* Returns error when there are no free spaces for new ID.*/
3469        if (error) {
3470                error = -ENOSPC;
3471                goto err_out;
3472        }
3473        if (myid > CSS_ID_MAX)
3474                goto remove_idr;
3475
3476        newid->id = myid;
3477        newid->depth = depth;
3478        return newid;
3479remove_idr:
3480        error = -ENOSPC;
3481        spin_lock(&ss->id_lock);
3482        idr_remove(&ss->idr, myid);
3483        spin_unlock(&ss->id_lock);
3484err_out:
3485        kfree(newid);
3486        return ERR_PTR(error);
3487
3488}
3489
3490static int __init cgroup_subsys_init_idr(struct cgroup_subsys *ss)
3491{
3492        struct css_id *newid;
3493        struct cgroup_subsys_state *rootcss;
3494
3495        spin_lock_init(&ss->id_lock);
3496        idr_init(&ss->idr);
3497
3498        rootcss = init_css_set.subsys[ss->subsys_id];
3499        newid = get_new_cssid(ss, 0);
3500        if (IS_ERR(newid))
3501                return PTR_ERR(newid);
3502
3503        newid->stack[0] = newid->id;
3504        newid->css = rootcss;
3505        rootcss->id = newid;
3506        return 0;
3507}
3508
3509static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
3510                        struct cgroup *child)
3511{
3512        int subsys_id, i, depth = 0;
3513        struct cgroup_subsys_state *parent_css, *child_css;
3514        struct css_id *child_id, *parent_id = NULL;
3515
3516        subsys_id = ss->subsys_id;
3517        parent_css = parent->subsys[subsys_id];
3518        child_css = child->subsys[subsys_id];
3519        depth = css_depth(parent_css) + 1;
3520        parent_id = parent_css->id;
3521
3522        child_id = get_new_cssid(ss, depth);
3523        if (IS_ERR(child_id))
3524                return PTR_ERR(child_id);
3525
3526        for (i = 0; i < depth; i++)
3527                child_id->stack[i] = parent_id->stack[i];
3528        child_id->stack[depth] = child_id->id;
3529        /*
3530         * child_id->css pointer will be set after this cgroup is available
3531         * see cgroup_populate_dir()
3532         */
3533        rcu_assign_pointer(child_css->id, child_id);
3534
3535        return 0;
3536}
3537
3538/**
3539 * css_lookup - lookup css by id
3540 * @ss: cgroup subsys to be looked into.
3541 * @id: the id
3542 *
3543 * Returns pointer to cgroup_subsys_state if there is valid one with id.
3544 * NULL if not. Should be called under rcu_read_lock()
3545 */
3546struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
3547{
3548        struct css_id *cssid = NULL;
3549
3550        BUG_ON(!ss->use_id);
3551        cssid = idr_find(&ss->idr, id);
3552
3553        if (unlikely(!cssid))
3554                return NULL;
3555
3556        return rcu_dereference(cssid->css);
3557}
3558
3559/**
3560 * css_get_next - lookup next cgroup under specified hierarchy.
3561 * @ss: pointer to subsystem
3562 * @id: current position of iteration.
3563 * @root: pointer to css. search tree under this.
3564 * @foundid: position of found object.
3565 *
3566 * Search next css under the specified hierarchy of rootid. Calling under
3567 * rcu_read_lock() is necessary. Returns NULL if it reaches the end.
3568 */
3569struct cgroup_subsys_state *
3570css_get_next(struct cgroup_subsys *ss, int id,
3571             struct cgroup_subsys_state *root, int *foundid)
3572{
3573        struct cgroup_subsys_state *ret = NULL;
3574        struct css_id *tmp;
3575        int tmpid;
3576        int rootid = css_id(root);
3577        int depth = css_depth(root);
3578
3579        if (!rootid)
3580                return NULL;
3581
3582        BUG_ON(!ss->use_id);
3583        /* fill start point for scan */
3584        tmpid = id;
3585        while (1) {
3586                /*
3587                 * scan next entry from bitmap(tree), tmpid is updated after
3588                 * idr_get_next().
3589                 */
3590                spin_lock(&ss->id_lock);
3591                tmp = idr_get_next(&ss->idr, &tmpid);
3592                spin_unlock(&ss->id_lock);
3593
3594                if (!tmp)
3595                        break;
3596                if (tmp->depth >= depth && tmp->stack[depth] == rootid) {
3597                        ret = rcu_dereference(tmp->css);
3598                        if (ret) {
3599                                *foundid = tmpid;
3600                                break;
3601                        }
3602                }
3603                /* continue to scan from next id */
3604                tmpid = tmpid + 1;
3605        }
3606        return ret;
3607}
3608
3609