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cgroup.c

/*
 *  Generic process-grouping system.
 *
 *  Based originally on the cpuset system, extracted by Paul Menage
 *  Copyright (C) 2006 Google, Inc
 *
 *  Copyright notices from the original cpuset code:
 *  --------------------------------------------------
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *
 *  2003-10-10 Written by Simon Derr.
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson.
 *  ---------------------------------------------------
 *
 *  This file is subject to the terms and conditions of the GNU General Public
 *  License.  See the file COPYING in the main directory of the Linux
 *  distribution for more details.
 */

#include <linux/cgroup.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/mutex.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/proc_fs.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/backing-dev.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/magic.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/sort.h>
#include <linux/kmod.h>
#include <linux/delayacct.h>
#include <linux/cgroupstats.h>
#include <linux/hash.h>
#include <linux/namei.h>
#include <linux/smp_lock.h>
#include <linux/pid_namespace.h>

#include <asm/atomic.h>

static DEFINE_MUTEX(cgroup_mutex);

/* Generate an array of cgroup subsystem pointers */
#define SUBSYS(_x) &_x ## _subsys,

static struct cgroup_subsys *subsys[] = {
#include <linux/cgroup_subsys.h>
};

/*
 * A cgroupfs_root represents the root of a cgroup hierarchy,
 * and may be associated with a superblock to form an active
 * hierarchy
 */
00068 struct cgroupfs_root {
      struct super_block *sb;

      /*
       * The bitmask of subsystems intended to be attached to this
       * hierarchy
       */
      unsigned long subsys_bits;

      /* The bitmask of subsystems currently attached to this hierarchy */
      unsigned long actual_subsys_bits;

      /* A list running through the attached subsystems */
      struct list_head subsys_list;

      /* The root cgroup for this hierarchy */
      struct cgroup top_cgroup;

      /* Tracks how many cgroups are currently defined in hierarchy.*/
      int number_of_cgroups;

      /* A list running through the active hierarchies */
      struct list_head root_list;

      /* Hierarchy-specific flags */
      unsigned long flags;

      /* The path to use for release notifications. */
      char release_agent_path[PATH_MAX];
};

/*
 * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
 * subsystems that are otherwise unattached - it never has more than a
 * single cgroup, and all tasks are part of that cgroup.
 */
static struct cgroupfs_root rootnode;

/*
 * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
 * cgroup_subsys->use_id != 0.
 */
#define CSS_ID_MAX      (65535)
00111 struct css_id {
      /*
       * The css to which this ID points. This pointer is set to valid value
       * after cgroup is populated. If cgroup is removed, this will be NULL.
       * This pointer is expected to be RCU-safe because destroy()
       * is called after synchronize_rcu(). But for safe use, css_is_removed()
       * css_tryget() should be used for avoiding race.
       */
      struct cgroup_subsys_state *css;
      /*
       * ID of this css.
       */
      unsigned short id;
      /*
       * Depth in hierarchy which this ID belongs to.
       */
      unsigned short depth;
      /*
       * ID is freed by RCU. (and lookup routine is RCU safe.)
       */
      struct rcu_head rcu_head;
      /*
       * Hierarchy of CSS ID belongs to.
       */
      unsigned short stack[0]; /* Array of Length (depth+1) */
};


/* The list of hierarchy roots */

static LIST_HEAD(roots);
static int root_count;

/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
#define dummytop (&rootnode.top_cgroup)

/* This flag indicates whether tasks in the fork and exit paths should
 * check for fork/exit handlers to call. This avoids us having to do
 * extra work in the fork/exit path if none of the subsystems need to
 * be called.
 */
static int need_forkexit_callback __read_mostly;

/* convenient tests for these bits */
inline int cgroup_is_removed(const struct cgroup *cgrp)
{
      return test_bit(CGRP_REMOVED, &cgrp->flags);
}

/* bits in struct cgroupfs_root flags field */
enum {
      ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
};

static int cgroup_is_releasable(const struct cgroup *cgrp)
{
      const int bits =
            (1 << CGRP_RELEASABLE) |
            (1 << CGRP_NOTIFY_ON_RELEASE);
      return (cgrp->flags & bits) == bits;
}

static int notify_on_release(const struct cgroup *cgrp)
{
      return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
}

/*
 * for_each_subsys() allows you to iterate on each subsystem attached to
 * an active hierarchy
 */
#define for_each_subsys(_root, _ss) \
list_for_each_entry(_ss, &_root->subsys_list, sibling)

/* for_each_active_root() allows you to iterate across the active hierarchies */
#define for_each_active_root(_root) \
list_for_each_entry(_root, &roots, root_list)

/* the list of cgroups eligible for automatic release. Protected by
 * release_list_lock */
static LIST_HEAD(release_list);
static DEFINE_SPINLOCK(release_list_lock);
static void cgroup_release_agent(struct work_struct *work);
static DECLARE_WORK(release_agent_work, cgroup_release_agent);
static void check_for_release(struct cgroup *cgrp);

/* Link structure for associating css_set objects with cgroups */
00198 struct cg_cgroup_link {
      /*
       * List running through cg_cgroup_links associated with a
       * cgroup, anchored on cgroup->css_sets
       */
      struct list_head cgrp_link_list;
      /*
       * List running through cg_cgroup_links pointing at a
       * single css_set object, anchored on css_set->cg_links
       */
      struct list_head cg_link_list;
      struct css_set *cg;
};

/* The default css_set - used by init and its children prior to any
 * hierarchies being mounted. It contains a pointer to the root state
 * for each subsystem. Also used to anchor the list of css_sets. Not
 * reference-counted, to improve performance when child cgroups
 * haven't been created.
 */

static struct css_set init_css_set;
static struct cg_cgroup_link init_css_set_link;

static int cgroup_subsys_init_idr(struct cgroup_subsys *ss);

/* css_set_lock protects the list of css_set objects, and the
 * chain of tasks off each css_set.  Nests outside task->alloc_lock
 * due to cgroup_iter_start() */
static DEFINE_RWLOCK(css_set_lock);
static int css_set_count;

/* hash table for cgroup groups. This improves the performance to
 * find an existing css_set */
#define CSS_SET_HASH_BITS     7
#define CSS_SET_TABLE_SIZE    (1 << CSS_SET_HASH_BITS)
static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];

static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
{
      int i;
      int index;
      unsigned long tmp = 0UL;

      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
            tmp += (unsigned long)css[i];
      tmp = (tmp >> 16) ^ tmp;

      index = hash_long(tmp, CSS_SET_HASH_BITS);

      return &css_set_table[index];
}

/* We don't maintain the lists running through each css_set to its
 * task until after the first call to cgroup_iter_start(). This
 * reduces the fork()/exit() overhead for people who have cgroups
 * compiled into their kernel but not actually in use */
static int use_task_css_set_links __read_mostly;

/* When we create or destroy a css_set, the operation simply
 * takes/releases a reference count on all the cgroups referenced
 * by subsystems in this css_set. This can end up multiple-counting
 * some cgroups, but that's OK - the ref-count is just a
 * busy/not-busy indicator; ensuring that we only count each cgroup
 * once would require taking a global lock to ensure that no
 * subsystems moved between hierarchies while we were doing so.
 *
 * Possible TODO: decide at boot time based on the number of
 * registered subsystems and the number of CPUs or NUMA nodes whether
 * it's better for performance to ref-count every subsystem, or to
 * take a global lock and only add one ref count to each hierarchy.
 */

/*
 * unlink a css_set from the list and free it
 */
static void unlink_css_set(struct css_set *cg)
{
      struct cg_cgroup_link *link;
      struct cg_cgroup_link *saved_link;

      hlist_del(&cg->hlist);
      css_set_count--;

      list_for_each_entry_safe(link, saved_link, &cg->cg_links,
                         cg_link_list) {
            list_del(&link->cg_link_list);
            list_del(&link->cgrp_link_list);
            kfree(link);
      }
}

static void __put_css_set(struct css_set *cg, int taskexit)
{
      int i;
      /*
       * Ensure that the refcount doesn't hit zero while any readers
       * can see it. Similar to atomic_dec_and_lock(), but for an
       * rwlock
       */
      if (atomic_add_unless(&cg->refcount, -1, 1))
            return;
      write_lock(&css_set_lock);
      if (!atomic_dec_and_test(&cg->refcount)) {
            write_unlock(&css_set_lock);
            return;
      }
      unlink_css_set(cg);
      write_unlock(&css_set_lock);

      rcu_read_lock();
      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup *cgrp = rcu_dereference(cg->subsys[i]->cgroup);
            if (atomic_dec_and_test(&cgrp->count) &&
                notify_on_release(cgrp)) {
                  if (taskexit)
                        set_bit(CGRP_RELEASABLE, &cgrp->flags);
                  check_for_release(cgrp);
            }
      }
      rcu_read_unlock();
      kfree(cg);
}

/*
 * refcounted get/put for css_set objects
 */
static inline void get_css_set(struct css_set *cg)
{
      atomic_inc(&cg->refcount);
}

static inline void put_css_set(struct css_set *cg)
{
      __put_css_set(cg, 0);
}

static inline void put_css_set_taskexit(struct css_set *cg)
{
      __put_css_set(cg, 1);
}

/*
 * find_existing_css_set() is a helper for
 * find_css_set(), and checks to see whether an existing
 * css_set is suitable.
 *
 * oldcg: the cgroup group that we're using before the cgroup
 * transition
 *
 * cgrp: the cgroup that we're moving into
 *
 * template: location in which to build the desired set of subsystem
 * state objects for the new cgroup group
 */
static struct css_set *find_existing_css_set(
      struct css_set *oldcg,
      struct cgroup *cgrp,
      struct cgroup_subsys_state *template[])
{
      int i;
      struct cgroupfs_root *root = cgrp->root;
      struct hlist_head *hhead;
      struct hlist_node *node;
      struct css_set *cg;

      /* Built the set of subsystem state objects that we want to
       * see in the new css_set */
      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            if (root->subsys_bits & (1UL << i)) {
                  /* Subsystem is in this hierarchy. So we want
                   * the subsystem state from the new
                   * cgroup */
                  template[i] = cgrp->subsys[i];
            } else {
                  /* Subsystem is not in this hierarchy, so we
                   * don't want to change the subsystem state */
                  template[i] = oldcg->subsys[i];
            }
      }

      hhead = css_set_hash(template);
      hlist_for_each_entry(cg, node, hhead, hlist) {
            if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
                  /* All subsystems matched */
                  return cg;
            }
      }

      /* No existing cgroup group matched */
      return NULL;
}

static void free_cg_links(struct list_head *tmp)
{
      struct cg_cgroup_link *link;
      struct cg_cgroup_link *saved_link;

      list_for_each_entry_safe(link, saved_link, tmp, cgrp_link_list) {
            list_del(&link->cgrp_link_list);
            kfree(link);
      }
}

/*
 * allocate_cg_links() allocates "count" cg_cgroup_link structures
 * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
 * success or a negative error
 */
static int allocate_cg_links(int count, struct list_head *tmp)
{
      struct cg_cgroup_link *link;
      int i;
      INIT_LIST_HEAD(tmp);
      for (i = 0; i < count; i++) {
            link = kmalloc(sizeof(*link), GFP_KERNEL);
            if (!link) {
                  free_cg_links(tmp);
                  return -ENOMEM;
            }
            list_add(&link->cgrp_link_list, tmp);
      }
      return 0;
}

/**
 * link_css_set - a helper function to link a css_set to a cgroup
 * @tmp_cg_links: cg_cgroup_link objects allocated by allocate_cg_links()
 * @cg: the css_set to be linked
 * @cgrp: the destination cgroup
 */
static void link_css_set(struct list_head *tmp_cg_links,
                   struct css_set *cg, struct cgroup *cgrp)
{
      struct cg_cgroup_link *link;

      BUG_ON(list_empty(tmp_cg_links));
      link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
                        cgrp_link_list);
      link->cg = cg;
      list_move(&link->cgrp_link_list, &cgrp->css_sets);
      list_add(&link->cg_link_list, &cg->cg_links);
}

/*
 * find_css_set() takes an existing cgroup group and a
 * cgroup object, and returns a css_set object that's
 * equivalent to the old group, but with the given cgroup
 * substituted into the appropriate hierarchy. Must be called with
 * cgroup_mutex held
 */
static struct css_set *find_css_set(
      struct css_set *oldcg, struct cgroup *cgrp)
{
      struct css_set *res;
      struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
      int i;

      struct list_head tmp_cg_links;

      struct hlist_head *hhead;

      /* First see if we already have a cgroup group that matches
       * the desired set */
      read_lock(&css_set_lock);
      res = find_existing_css_set(oldcg, cgrp, template);
      if (res)
            get_css_set(res);
      read_unlock(&css_set_lock);

      if (res)
            return res;

      res = kmalloc(sizeof(*res), GFP_KERNEL);
      if (!res)
            return NULL;

      /* Allocate all the cg_cgroup_link objects that we'll need */
      if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
            kfree(res);
            return NULL;
      }

      atomic_set(&res->refcount, 1);
      INIT_LIST_HEAD(&res->cg_links);
      INIT_LIST_HEAD(&res->tasks);
      INIT_HLIST_NODE(&res->hlist);

      /* Copy the set of subsystem state objects generated in
       * find_existing_css_set() */
      memcpy(res->subsys, template, sizeof(res->subsys));

      write_lock(&css_set_lock);
      /* Add reference counts and links from the new css_set. */
      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup *cgrp = res->subsys[i]->cgroup;
            struct cgroup_subsys *ss = subsys[i];
            atomic_inc(&cgrp->count);
            /*
             * We want to add a link once per cgroup, so we
             * only do it for the first subsystem in each
             * hierarchy
             */
            if (ss->root->subsys_list.next == &ss->sibling)
                  link_css_set(&tmp_cg_links, res, cgrp);
      }
      if (list_empty(&rootnode.subsys_list))
            link_css_set(&tmp_cg_links, res, dummytop);

      BUG_ON(!list_empty(&tmp_cg_links));

      css_set_count++;

      /* Add this cgroup group to the hash table */
      hhead = css_set_hash(res->subsys);
      hlist_add_head(&res->hlist, hhead);

      write_unlock(&css_set_lock);

      return res;
}

/*
 * There is one global cgroup mutex. We also require taking
 * task_lock() when dereferencing a task's cgroup subsys pointers.
 * See "The task_lock() exception", at the end of this comment.
 *
 * A task must hold cgroup_mutex to modify cgroups.
 *
 * Any task can increment and decrement the count field without lock.
 * So in general, code holding cgroup_mutex can't rely on the count
 * field not changing.  However, if the count goes to zero, then only
 * cgroup_attach_task() can increment it again.  Because a count of zero
 * means that no tasks are currently attached, therefore there is no
 * way a task attached to that cgroup can fork (the other way to
 * increment the count).  So code holding cgroup_mutex can safely
 * assume that if the count is zero, it will stay zero. Similarly, if
 * a task holds cgroup_mutex on a cgroup with zero count, it
 * knows that the cgroup won't be removed, as cgroup_rmdir()
 * needs that mutex.
 *
 * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
 * (usually) take cgroup_mutex.  These are the two most performance
 * critical pieces of code here.  The exception occurs on cgroup_exit(),
 * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
 * is taken, and if the cgroup count is zero, a usermode call made
 * to the release agent with the name of the cgroup (path relative to
 * the root of cgroup file system) as the argument.
 *
 * A cgroup can only be deleted if both its 'count' of using tasks
 * is zero, and its list of 'children' cgroups is empty.  Since all
 * tasks in the system use _some_ cgroup, and since there is always at
 * least one task in the system (init, pid == 1), therefore, top_cgroup
 * always has either children cgroups and/or using tasks.  So we don't
 * need a special hack to ensure that top_cgroup cannot be deleted.
 *
 *    The task_lock() exception
 *
 * The need for this exception arises from the action of
 * cgroup_attach_task(), which overwrites one tasks cgroup pointer with
 * another.  It does so using cgroup_mutex, however there are
 * several performance critical places that need to reference
 * task->cgroup without the expense of grabbing a system global
 * mutex.  Therefore except as noted below, when dereferencing or, as
 * in cgroup_attach_task(), modifying a task'ss cgroup pointer we use
 * task_lock(), which acts on a spinlock (task->alloc_lock) already in
 * the task_struct routinely used for such matters.
 *
 * P.S.  One more locking exception.  RCU is used to guard the
 * update of a tasks cgroup pointer by cgroup_attach_task()
 */

/**
 * cgroup_lock - lock out any changes to cgroup structures
 *
 */
void cgroup_lock(void)
{
      mutex_lock(&cgroup_mutex);
}

/**
 * cgroup_unlock - release lock on cgroup changes
 *
 * Undo the lock taken in a previous cgroup_lock() call.
 */
void cgroup_unlock(void)
{
      mutex_unlock(&cgroup_mutex);
}

/*
 * A couple of forward declarations required, due to cyclic reference loop:
 * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
 * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
 * -> cgroup_mkdir.
 */

static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);
static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
static int cgroup_populate_dir(struct cgroup *cgrp);
static struct inode_operations cgroup_dir_inode_operations;
static struct file_operations proc_cgroupstats_operations;

static struct backing_dev_info cgroup_backing_dev_info = {
      .capabilities     = BDI_CAP_NO_ACCT_AND_WRITEBACK,
};

static int alloc_css_id(struct cgroup_subsys *ss,
                  struct cgroup *parent, struct cgroup *child);

static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
{
      struct inode *inode = new_inode(sb);

      if (inode) {
            inode->i_mode = mode;
            inode->i_uid = current_fsuid();
            inode->i_gid = current_fsgid();
            inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
            inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
      }
      return inode;
}

/*
 * Call subsys's pre_destroy handler.
 * This is called before css refcnt check.
 */
static int cgroup_call_pre_destroy(struct cgroup *cgrp)
{
      struct cgroup_subsys *ss;
      int ret = 0;

      for_each_subsys(cgrp->root, ss)
            if (ss->pre_destroy) {
                  ret = ss->pre_destroy(ss, cgrp);
                  if (ret)
                        break;
            }
      return ret;
}

static void free_cgroup_rcu(struct rcu_head *obj)
{
      struct cgroup *cgrp = container_of(obj, struct cgroup, rcu_head);

      kfree(cgrp);
}

static void cgroup_diput(struct dentry *dentry, struct inode *inode)
{
      /* is dentry a directory ? if so, kfree() associated cgroup */
      if (S_ISDIR(inode->i_mode)) {
            struct cgroup *cgrp = dentry->d_fsdata;
            struct cgroup_subsys *ss;
            BUG_ON(!(cgroup_is_removed(cgrp)));
            /* It's possible for external users to be holding css
             * reference counts on a cgroup; css_put() needs to
             * be able to access the cgroup after decrementing
             * the reference count in order to know if it needs to
             * queue the cgroup to be handled by the release
             * agent */
            synchronize_rcu();

            mutex_lock(&cgroup_mutex);
            /*
             * Release the subsystem state objects.
             */
            for_each_subsys(cgrp->root, ss)
                  ss->destroy(ss, cgrp);

            cgrp->root->number_of_cgroups--;
            mutex_unlock(&cgroup_mutex);

            /*
             * Drop the active superblock reference that we took when we
             * created the cgroup
             */
            deactivate_super(cgrp->root->sb);

            call_rcu(&cgrp->rcu_head, free_cgroup_rcu);
      }
      iput(inode);
}

static void remove_dir(struct dentry *d)
{
      struct dentry *parent = dget(d->d_parent);

      d_delete(d);
      simple_rmdir(parent->d_inode, d);
      dput(parent);
}

static void cgroup_clear_directory(struct dentry *dentry)
{
      struct list_head *node;

      BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
      spin_lock(&dcache_lock);
      node = dentry->d_subdirs.next;
      while (node != &dentry->d_subdirs) {
            struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
            list_del_init(node);
            if (d->d_inode) {
                  /* This should never be called on a cgroup
                   * directory with child cgroups */
                  BUG_ON(d->d_inode->i_mode & S_IFDIR);
                  d = dget_locked(d);
                  spin_unlock(&dcache_lock);
                  d_delete(d);
                  simple_unlink(dentry->d_inode, d);
                  dput(d);
                  spin_lock(&dcache_lock);
            }
            node = dentry->d_subdirs.next;
      }
      spin_unlock(&dcache_lock);
}

/*
 * NOTE : the dentry must have been dget()'ed
 */
static void cgroup_d_remove_dir(struct dentry *dentry)
{
      cgroup_clear_directory(dentry);

      spin_lock(&dcache_lock);
      list_del_init(&dentry->d_u.d_child);
      spin_unlock(&dcache_lock);
      remove_dir(dentry);
}

/*
 * A queue for waiters to do rmdir() cgroup. A tasks will sleep when
 * cgroup->count == 0 && list_empty(&cgroup->children) && subsys has some
 * reference to css->refcnt. In general, this refcnt is expected to goes down
 * to zero, soon.
 *
 * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
 */
DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);

static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
{
      if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
            wake_up_all(&cgroup_rmdir_waitq);
}

void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
{
      css_get(css);
}

void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
{
      cgroup_wakeup_rmdir_waiter(css->cgroup);
      css_put(css);
}


static int rebind_subsystems(struct cgroupfs_root *root,
                        unsigned long final_bits)
{
      unsigned long added_bits, removed_bits;
      struct cgroup *cgrp = &root->top_cgroup;
      int i;

      removed_bits = root->actual_subsys_bits & ~final_bits;
      added_bits = final_bits & ~root->actual_subsys_bits;
      /* Check that any added subsystems are currently free */
      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            unsigned long bit = 1UL << i;
            struct cgroup_subsys *ss = subsys[i];
            if (!(bit & added_bits))
                  continue;
            if (ss->root != &rootnode) {
                  /* Subsystem isn't free */
                  return -EBUSY;
            }
      }

      /* Currently we don't handle adding/removing subsystems when
       * any child cgroups exist. This is theoretically supportable
       * but involves complex error handling, so it's being left until
       * later */
      if (root->number_of_cgroups > 1)
            return -EBUSY;

      /* Process each subsystem */
      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup_subsys *ss = subsys[i];
            unsigned long bit = 1UL << i;
            if (bit & added_bits) {
                  /* We're binding this subsystem to this hierarchy */
                  BUG_ON(cgrp->subsys[i]);
                  BUG_ON(!dummytop->subsys[i]);
                  BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
                  mutex_lock(&ss->hierarchy_mutex);
                  cgrp->subsys[i] = dummytop->subsys[i];
                  cgrp->subsys[i]->cgroup = cgrp;
                  list_move(&ss->sibling, &root->subsys_list);
                  ss->root = root;
                  if (ss->bind)
                        ss->bind(ss, cgrp);
                  mutex_unlock(&ss->hierarchy_mutex);
            } else if (bit & removed_bits) {
                  /* We're removing this subsystem */
                  BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
                  BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
                  mutex_lock(&ss->hierarchy_mutex);
                  if (ss->bind)
                        ss->bind(ss, dummytop);
                  dummytop->subsys[i]->cgroup = dummytop;
                  cgrp->subsys[i] = NULL;
                  subsys[i]->root = &rootnode;
                  list_move(&ss->sibling, &rootnode.subsys_list);
                  mutex_unlock(&ss->hierarchy_mutex);
            } else if (bit & final_bits) {
                  /* Subsystem state should already exist */
                  BUG_ON(!cgrp->subsys[i]);
            } else {
                  /* Subsystem state shouldn't exist */
                  BUG_ON(cgrp->subsys[i]);
            }
      }
      root->subsys_bits = root->actual_subsys_bits = final_bits;
      synchronize_rcu();

      return 0;
}

static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
{
      struct cgroupfs_root *root = vfs->mnt_sb->s_fs_info;
      struct cgroup_subsys *ss;

      mutex_lock(&cgroup_mutex);
      for_each_subsys(root, ss)
            seq_printf(seq, ",%s", ss->name);
      if (test_bit(ROOT_NOPREFIX, &root->flags))
            seq_puts(seq, ",noprefix");
      if (strlen(root->release_agent_path))
            seq_printf(seq, ",release_agent=%s", root->release_agent_path);
      mutex_unlock(&cgroup_mutex);
      return 0;
}

00847 struct cgroup_sb_opts {
      unsigned long subsys_bits;
      unsigned long flags;
      char *release_agent;
};

/* Convert a hierarchy specifier into a bitmask of subsystems and
 * flags. */
static int parse_cgroupfs_options(char *data,
                             struct cgroup_sb_opts *opts)
{
      char *token, *o = data ?: "all";
      unsigned long mask = (unsigned long)-1;

#ifdef CONFIG_CPUSETS
      mask = ~(1UL << cpuset_subsys_id);
#endif

      opts->subsys_bits = 0;
      opts->flags = 0;
      opts->release_agent = NULL;

      while ((token = strsep(&o, ",")) != NULL) {
            if (!*token)
                  return -EINVAL;
            if (!strcmp(token, "all")) {
                  /* Add all non-disabled subsystems */
                  int i;
                  opts->subsys_bits = 0;
                  for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                        struct cgroup_subsys *ss = subsys[i];
                        if (!ss->disabled)
                              opts->subsys_bits |= 1ul << i;
                  }
            } else if (!strcmp(token, "noprefix")) {
                  set_bit(ROOT_NOPREFIX, &opts->flags);
            } else if (!strncmp(token, "release_agent=", 14)) {
                  /* Specifying two release agents is forbidden */
                  if (opts->release_agent)
                        return -EINVAL;
                  opts->release_agent = kzalloc(PATH_MAX, GFP_KERNEL);
                  if (!opts->release_agent)
                        return -ENOMEM;
                  strncpy(opts->release_agent, token + 14, PATH_MAX - 1);
                  opts->release_agent[PATH_MAX - 1] = 0;
            } else {
                  struct cgroup_subsys *ss;
                  int i;
                  for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                        ss = subsys[i];
                        if (!strcmp(token, ss->name)) {
                              if (!ss->disabled)
                                    set_bit(i, &opts->subsys_bits);
                              break;
                        }
                  }
                  if (i == CGROUP_SUBSYS_COUNT)
                        return -ENOENT;
            }
      }

      /*
       * Option noprefix was introduced just for backward compatibility
       * with the old cpuset, so we allow noprefix only if mounting just
       * the cpuset subsystem.
       */
      if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
          (opts->subsys_bits & mask))
            return -EINVAL;

      /* We can't have an empty hierarchy */
      if (!opts->subsys_bits)
            return -EINVAL;

      return 0;
}

static int cgroup_remount(struct super_block *sb, int *flags, char *data)
{
      int ret = 0;
      struct cgroupfs_root *root = sb->s_fs_info;
      struct cgroup *cgrp = &root->top_cgroup;
      struct cgroup_sb_opts opts;

      lock_kernel();
      mutex_lock(&cgrp->dentry->d_inode->i_mutex);
      mutex_lock(&cgroup_mutex);

      /* See what subsystems are wanted */
      ret = parse_cgroupfs_options(data, &opts);
      if (ret)
            goto out_unlock;

      /* Don't allow flags to change at remount */
      if (opts.flags != root->flags) {
            ret = -EINVAL;
            goto out_unlock;
      }

      ret = rebind_subsystems(root, opts.subsys_bits);
      if (ret)
            goto out_unlock;

      /* (re)populate subsystem files */
      cgroup_populate_dir(cgrp);

      if (opts.release_agent)
            strcpy(root->release_agent_path, opts.release_agent);
 out_unlock:
      kfree(opts.release_agent);
      mutex_unlock(&cgroup_mutex);
      mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
      unlock_kernel();
      return ret;
}

static struct super_operations cgroup_ops = {
      .statfs = simple_statfs,
      .drop_inode = generic_delete_inode,
      .show_options = cgroup_show_options,
      .remount_fs = cgroup_remount,
};

static void init_cgroup_housekeeping(struct cgroup *cgrp)
{
      INIT_LIST_HEAD(&cgrp->sibling);
      INIT_LIST_HEAD(&cgrp->children);
      INIT_LIST_HEAD(&cgrp->css_sets);
      INIT_LIST_HEAD(&cgrp->release_list);
      INIT_LIST_HEAD(&cgrp->pids_list);
      init_rwsem(&cgrp->pids_mutex);
}
static void init_cgroup_root(struct cgroupfs_root *root)
{
      struct cgroup *cgrp = &root->top_cgroup;
      INIT_LIST_HEAD(&root->subsys_list);
      INIT_LIST_HEAD(&root->root_list);
      root->number_of_cgroups = 1;
      cgrp->root = root;
      cgrp->top_cgroup = cgrp;
      init_cgroup_housekeeping(cgrp);
}

static int cgroup_test_super(struct super_block *sb, void *data)
{
      struct cgroupfs_root *new = data;
      struct cgroupfs_root *root = sb->s_fs_info;

      /* First check subsystems */
      if (new->subsys_bits != root->subsys_bits)
          return 0;

      /* Next check flags */
      if (new->flags != root->flags)
            return 0;

      return 1;
}

static int cgroup_set_super(struct super_block *sb, void *data)
{
      int ret;
      struct cgroupfs_root *root = data;

      ret = set_anon_super(sb, NULL);
      if (ret)
            return ret;

      sb->s_fs_info = root;
      root->sb = sb;

      sb->s_blocksize = PAGE_CACHE_SIZE;
      sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
      sb->s_magic = CGROUP_SUPER_MAGIC;
      sb->s_op = &cgroup_ops;

      return 0;
}

static int cgroup_get_rootdir(struct super_block *sb)
{
      struct inode *inode =
            cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
      struct dentry *dentry;

      if (!inode)
            return -ENOMEM;

      inode->i_fop = &simple_dir_operations;
      inode->i_op = &cgroup_dir_inode_operations;
      /* directories start off with i_nlink == 2 (for "." entry) */
      inc_nlink(inode);
      dentry = d_alloc_root(inode);
      if (!dentry) {
            iput(inode);
            return -ENOMEM;
      }
      sb->s_root = dentry;
      return 0;
}

static int cgroup_get_sb(struct file_system_type *fs_type,
                   int flags, const char *unused_dev_name,
                   void *data, struct vfsmount *mnt)
{
      struct cgroup_sb_opts opts;
      int ret = 0;
      struct super_block *sb;
      struct cgroupfs_root *root;
      struct list_head tmp_cg_links;

      /* First find the desired set of subsystems */
      ret = parse_cgroupfs_options(data, &opts);
      if (ret) {
            kfree(opts.release_agent);
            return ret;
      }

      root = kzalloc(sizeof(*root), GFP_KERNEL);
      if (!root) {
            kfree(opts.release_agent);
            return -ENOMEM;
      }

      init_cgroup_root(root);
      root->subsys_bits = opts.subsys_bits;
      root->flags = opts.flags;
      if (opts.release_agent) {
            strcpy(root->release_agent_path, opts.release_agent);
            kfree(opts.release_agent);
      }

      sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);

      if (IS_ERR(sb)) {
            kfree(root);
            return PTR_ERR(sb);
      }

      if (sb->s_fs_info != root) {
            /* Reusing an existing superblock */
            BUG_ON(sb->s_root == NULL);
            kfree(root);
            root = NULL;
      } else {
            /* New superblock */
            struct cgroup *root_cgrp = &root->top_cgroup;
            struct inode *inode;
            int i;

            BUG_ON(sb->s_root != NULL);

            ret = cgroup_get_rootdir(sb);
            if (ret)
                  goto drop_new_super;
            inode = sb->s_root->d_inode;

            mutex_lock(&inode->i_mutex);
            mutex_lock(&cgroup_mutex);

            /*
             * We're accessing css_set_count without locking
             * css_set_lock here, but that's OK - it can only be
             * increased by someone holding cgroup_lock, and
             * that's us. The worst that can happen is that we
             * have some link structures left over
             */
            ret = allocate_cg_links(css_set_count, &tmp_cg_links);
            if (ret) {
                  mutex_unlock(&cgroup_mutex);
                  mutex_unlock(&inode->i_mutex);
                  goto drop_new_super;
            }

            ret = rebind_subsystems(root, root->subsys_bits);
            if (ret == -EBUSY) {
                  mutex_unlock(&cgroup_mutex);
                  mutex_unlock(&inode->i_mutex);
                  goto free_cg_links;
            }

            /* EBUSY should be the only error here */
            BUG_ON(ret);

            list_add(&root->root_list, &roots);
            root_count++;

            sb->s_root->d_fsdata = root_cgrp;
            root->top_cgroup.dentry = sb->s_root;

            /* Link the top cgroup in this hierarchy into all
             * the css_set objects */
            write_lock(&css_set_lock);
            for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
                  struct hlist_head *hhead = &css_set_table[i];
                  struct hlist_node *node;
                  struct css_set *cg;

                  hlist_for_each_entry(cg, node, hhead, hlist)
                        link_css_set(&tmp_cg_links, cg, root_cgrp);
            }
            write_unlock(&css_set_lock);

            free_cg_links(&tmp_cg_links);

            BUG_ON(!list_empty(&root_cgrp->sibling));
            BUG_ON(!list_empty(&root_cgrp->children));
            BUG_ON(root->number_of_cgroups != 1);

            cgroup_populate_dir(root_cgrp);
            mutex_unlock(&inode->i_mutex);
            mutex_unlock(&cgroup_mutex);
      }

      simple_set_mnt(mnt, sb);
      return 0;

 free_cg_links:
      free_cg_links(&tmp_cg_links);
 drop_new_super:
      deactivate_locked_super(sb);
      return ret;
}

static void cgroup_kill_sb(struct super_block *sb) {
      struct cgroupfs_root *root = sb->s_fs_info;
      struct cgroup *cgrp = &root->top_cgroup;
      int ret;
      struct cg_cgroup_link *link;
      struct cg_cgroup_link *saved_link;

      BUG_ON(!root);

      BUG_ON(root->number_of_cgroups != 1);
      BUG_ON(!list_empty(&cgrp->children));
      BUG_ON(!list_empty(&cgrp->sibling));

      mutex_lock(&cgroup_mutex);

      /* Rebind all subsystems back to the default hierarchy */
      ret = rebind_subsystems(root, 0);
      /* Shouldn't be able to fail ... */
      BUG_ON(ret);

      /*
       * Release all the links from css_sets to this hierarchy's
       * root cgroup
       */
      write_lock(&css_set_lock);

      list_for_each_entry_safe(link, saved_link, &cgrp->css_sets,
                         cgrp_link_list) {
            list_del(&link->cg_link_list);
            list_del(&link->cgrp_link_list);
            kfree(link);
      }
      write_unlock(&css_set_lock);

      if (!list_empty(&root->root_list)) {
            list_del(&root->root_list);
            root_count--;
      }

      mutex_unlock(&cgroup_mutex);

      kill_litter_super(sb);
      kfree(root);
}

static struct file_system_type cgroup_fs_type = {
      .name = "cgroup",
      .get_sb = cgroup_get_sb,
      .kill_sb = cgroup_kill_sb,
};

static inline struct cgroup *__d_cgrp(struct dentry *dentry)
{
      return dentry->d_fsdata;
}

static inline struct cftype *__d_cft(struct dentry *dentry)
{
      return dentry->d_fsdata;
}

/**
 * cgroup_path - generate the path of a cgroup
 * @cgrp: the cgroup in question
 * @buf: the buffer to write the path into
 * @buflen: the length of the buffer
 *
 * Called with cgroup_mutex held or else with an RCU-protected cgroup
 * reference.  Writes path of cgroup into buf.  Returns 0 on success,
 * -errno on error.
 */
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
{
      char *start;
      struct dentry *dentry = rcu_dereference(cgrp->dentry);

      if (!dentry || cgrp == dummytop) {
            /*
             * Inactive subsystems have no dentry for their root
             * cgroup
             */
            strcpy(buf, "/");
            return 0;
      }

      start = buf + buflen;

      *--start = '\0';
      for (;;) {
            int len = dentry->d_name.len;
            if ((start -= len) < buf)
                  return -ENAMETOOLONG;
            memcpy(start, cgrp->dentry->d_name.name, len);
            cgrp = cgrp->parent;
            if (!cgrp)
                  break;
            dentry = rcu_dereference(cgrp->dentry);
            if (!cgrp->parent)
                  continue;
            if (--start < buf)
                  return -ENAMETOOLONG;
            *start = '/';
      }
      memmove(buf, start, buf + buflen - start);
      return 0;
}

/*
 * Return the first subsystem attached to a cgroup's hierarchy, and
 * its subsystem id.
 */

static void get_first_subsys(const struct cgroup *cgrp,
                  struct cgroup_subsys_state **css, int *subsys_id)
{
      const struct cgroupfs_root *root = cgrp->root;
      const struct cgroup_subsys *test_ss;
      BUG_ON(list_empty(&root->subsys_list));
      test_ss = list_entry(root->subsys_list.next,
                       struct cgroup_subsys, sibling);
      if (css) {
            *css = cgrp->subsys[test_ss->subsys_id];
            BUG_ON(!*css);
      }
      if (subsys_id)
            *subsys_id = test_ss->subsys_id;
}

/**
 * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
 * @cgrp: the cgroup the task is attaching to
 * @tsk: the task to be attached
 *
 * Call holding cgroup_mutex. May take task_lock of
 * the task 'tsk' during call.
 */
int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
      int retval = 0;
      struct cgroup_subsys *ss;
      struct cgroup *oldcgrp;
      struct css_set *cg;
      struct css_set *newcg;
      struct cgroupfs_root *root = cgrp->root;
      int subsys_id;

      get_first_subsys(cgrp, NULL, &subsys_id);

      /* Nothing to do if the task is already in that cgroup */
      oldcgrp = task_cgroup(tsk, subsys_id);
      if (cgrp == oldcgrp)
            return 0;

      for_each_subsys(root, ss) {
            if (ss->can_attach) {
                  retval = ss->can_attach(ss, cgrp, tsk);
                  if (retval)
                        return retval;
            }
      }

      task_lock(tsk);
      cg = tsk->cgroups;
      get_css_set(cg);
      task_unlock(tsk);
      /*
       * Locate or allocate a new css_set for this task,
       * based on its final set of cgroups
       */
      newcg = find_css_set(cg, cgrp);
      put_css_set(cg);
      if (!newcg)
            return -ENOMEM;

      task_lock(tsk);
      if (tsk->flags & PF_EXITING) {
            task_unlock(tsk);
            put_css_set(newcg);
            return -ESRCH;
      }
      rcu_assign_pointer(tsk->cgroups, newcg);
      task_unlock(tsk);

      /* Update the css_set linked lists if we're using them */
      write_lock(&css_set_lock);
      if (!list_empty(&tsk->cg_list)) {
            list_del(&tsk->cg_list);
            list_add(&tsk->cg_list, &newcg->tasks);
      }
      write_unlock(&css_set_lock);

      for_each_subsys(root, ss) {
            if (ss->attach)
                  ss->attach(ss, cgrp, oldcgrp, tsk);
      }
      set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
      synchronize_rcu();
      put_css_set(cg);

      /*
       * wake up rmdir() waiter. the rmdir should fail since the cgroup
       * is no longer empty.
       */
      cgroup_wakeup_rmdir_waiter(cgrp);
      return 0;
}

/*
 * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
 * held. May take task_lock of task
 */
static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
{
      struct task_struct *tsk;
      const struct cred *cred = current_cred(), *tcred;
      int ret;

      if (pid) {
            rcu_read_lock();
            tsk = find_task_by_vpid(pid);
            if (!tsk || tsk->flags & PF_EXITING) {
                  rcu_read_unlock();
                  return -ESRCH;
            }

            tcred = __task_cred(tsk);
            if (cred->euid &&
                cred->euid != tcred->uid &&
                cred->euid != tcred->suid) {
                  rcu_read_unlock();
                  return -EACCES;
            }
            get_task_struct(tsk);
            rcu_read_unlock();
      } else {
            tsk = current;
            get_task_struct(tsk);
      }

      ret = cgroup_attach_task(cgrp, tsk);
      put_task_struct(tsk);
      return ret;
}

static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
{
      int ret;
      if (!cgroup_lock_live_group(cgrp))
            return -ENODEV;
      ret = attach_task_by_pid(cgrp, pid);
      cgroup_unlock();
      return ret;
}

/* The various types of files and directories in a cgroup file system */
enum cgroup_filetype {
      FILE_ROOT,
      FILE_DIR,
      FILE_TASKLIST,
      FILE_NOTIFY_ON_RELEASE,
      FILE_RELEASE_AGENT,
};

/**
 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
 * @cgrp: the cgroup to be checked for liveness
 *
 * On success, returns true; the lock should be later released with
 * cgroup_unlock(). On failure returns false with no lock held.
 */
bool cgroup_lock_live_group(struct cgroup *cgrp)
{
      mutex_lock(&cgroup_mutex);
      if (cgroup_is_removed(cgrp)) {
            mutex_unlock(&cgroup_mutex);
            return false;
      }
      return true;
}

static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
                              const char *buffer)
{
      BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
      if (!cgroup_lock_live_group(cgrp))
            return -ENODEV;
      strcpy(cgrp->root->release_agent_path, buffer);
      cgroup_unlock();
      return 0;
}

static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
                             struct seq_file *seq)
{
      if (!cgroup_lock_live_group(cgrp))
            return -ENODEV;
      seq_puts(seq, cgrp->root->release_agent_path);
      seq_putc(seq, '\n');
      cgroup_unlock();
      return 0;
}

/* A buffer size big enough for numbers or short strings */
#define CGROUP_LOCAL_BUFFER_SIZE 64

static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
                        struct file *file,
                        const char __user *userbuf,
                        size_t nbytes, loff_t *unused_ppos)
{
      char buffer[CGROUP_LOCAL_BUFFER_SIZE];
      int retval = 0;
      char *end;

      if (!nbytes)
            return -EINVAL;
      if (nbytes >= sizeof(buffer))
            return -E2BIG;
      if (copy_from_user(buffer, userbuf, nbytes))
            return -EFAULT;

      buffer[nbytes] = 0;     /* nul-terminate */
      strstrip(buffer);
      if (cft->write_u64) {
            u64 val = simple_strtoull(buffer, &end, 0);
            if (*end)
                  return -EINVAL;
            retval = cft->write_u64(cgrp, cft, val);
      } else {
            s64 val = simple_strtoll(buffer, &end, 0);
            if (*end)
                  return -EINVAL;
            retval = cft->write_s64(cgrp, cft, val);
      }
      if (!retval)
            retval = nbytes;
      return retval;
}

static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
                           struct file *file,
                           const char __user *userbuf,
                           size_t nbytes, loff_t *unused_ppos)
{
      char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
      int retval = 0;
      size_t max_bytes = cft->max_write_len;
      char *buffer = local_buffer;

      if (!max_bytes)
            max_bytes = sizeof(local_buffer) - 1;
      if (nbytes >= max_bytes)
            return -E2BIG;
      /* Allocate a dynamic buffer if we need one */
      if (nbytes >= sizeof(local_buffer)) {
            buffer = kmalloc(nbytes + 1, GFP_KERNEL);
            if (buffer == NULL)
                  return -ENOMEM;
      }
      if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
            retval = -EFAULT;
            goto out;
      }

      buffer[nbytes] = 0;     /* nul-terminate */
      strstrip(buffer);
      retval = cft->write_string(cgrp, cft, buffer);
      if (!retval)
            retval = nbytes;
out:
      if (buffer != local_buffer)
            kfree(buffer);
      return retval;
}

static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
                                    size_t nbytes, loff_t *ppos)
{
      struct cftype *cft = __d_cft(file->f_dentry);
      struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);

      if (cgroup_is_removed(cgrp))
            return -ENODEV;
      if (cft->write)
            return cft->write(cgrp, cft, file, buf, nbytes, ppos);
      if (cft->write_u64 || cft->write_s64)
            return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
      if (cft->write_string)
            return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
      if (cft->trigger) {
            int ret = cft->trigger(cgrp, (unsigned int)cft->private);
            return ret ? ret : nbytes;
      }
      return -EINVAL;
}

static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
                         struct file *file,
                         char __user *buf, size_t nbytes,
                         loff_t *ppos)
{
      char tmp[CGROUP_LOCAL_BUFFER_SIZE];
      u64 val = cft->read_u64(cgrp, cft);
      int len = sprintf(tmp, "%llu\n", (unsigned long long) val);

      return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
                         struct file *file,
                         char __user *buf, size_t nbytes,
                         loff_t *ppos)
{
      char tmp[CGROUP_LOCAL_BUFFER_SIZE];
      s64 val = cft->read_s64(cgrp, cft);
      int len = sprintf(tmp, "%lld\n", (long long) val);

      return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

static ssize_t cgroup_file_read(struct file *file, char __user *buf,
                           size_t nbytes, loff_t *ppos)
{
      struct cftype *cft = __d_cft(file->f_dentry);
      struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);

      if (cgroup_is_removed(cgrp))
            return -ENODEV;

      if (cft->read)
            return cft->read(cgrp, cft, file, buf, nbytes, ppos);
      if (cft->read_u64)
            return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
      if (cft->read_s64)
            return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
      return -EINVAL;
}

/*
 * seqfile ops/methods for returning structured data. Currently just
 * supports string->u64 maps, but can be extended in future.
 */

01614 struct cgroup_seqfile_state {
      struct cftype *cft;
      struct cgroup *cgroup;
};

static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
{
      struct seq_file *sf = cb->state;
      return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
}

static int cgroup_seqfile_show(struct seq_file *m, void *arg)
{
      struct cgroup_seqfile_state *state = m->private;
      struct cftype *cft = state->cft;
      if (cft->read_map) {
            struct cgroup_map_cb cb = {
                  .fill = cgroup_map_add,
                  .state = m,
            };
            return cft->read_map(state->cgroup, cft, &cb);
      }
      return cft->read_seq_string(state->cgroup, cft, m);
}

static int cgroup_seqfile_release(struct inode *inode, struct file *file)
{
      struct seq_file *seq = file->private_data;
      kfree(seq->private);
      return single_release(inode, file);
}

static struct file_operations cgroup_seqfile_operations = {
      .read = seq_read,
      .write = cgroup_file_write,
      .llseek = seq_lseek,
      .release = cgroup_seqfile_release,
};

static int cgroup_file_open(struct inode *inode, struct file *file)
{
      int err;
      struct cftype *cft;

      err = generic_file_open(inode, file);
      if (err)
            return err;
      cft = __d_cft(file->f_dentry);

      if (cft->read_map || cft->read_seq_string) {
            struct cgroup_seqfile_state *state =
                  kzalloc(sizeof(*state), GFP_USER);
            if (!state)
                  return -ENOMEM;
            state->cft = cft;
            state->cgroup = __d_cgrp(file->f_dentry->d_parent);
            file->f_op = &cgroup_seqfile_operations;
            err = single_open(file, cgroup_seqfile_show, state);
            if (err < 0)
                  kfree(state);
      } else if (cft->open)
            err = cft->open(inode, file);
      else
            err = 0;

      return err;
}

static int cgroup_file_release(struct inode *inode, struct file *file)
{
      struct cftype *cft = __d_cft(file->f_dentry);
      if (cft->release)
            return cft->release(inode, file);
      return 0;
}

/*
 * cgroup_rename - Only allow simple rename of directories in place.
 */
static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
                      struct inode *new_dir, struct dentry *new_dentry)
{
      if (!S_ISDIR(old_dentry->d_inode->i_mode))
            return -ENOTDIR;
      if (new_dentry->d_inode)
            return -EEXIST;
      if (old_dir != new_dir)
            return -EIO;
      return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
}

static struct file_operations cgroup_file_operations = {
      .read = cgroup_file_read,
      .write = cgroup_file_write,
      .llseek = generic_file_llseek,
      .open = cgroup_file_open,
      .release = cgroup_file_release,
};

static struct inode_operations cgroup_dir_inode_operations = {
      .lookup = simple_lookup,
      .mkdir = cgroup_mkdir,
      .rmdir = cgroup_rmdir,
      .rename = cgroup_rename,
};

static int cgroup_create_file(struct dentry *dentry, mode_t mode,
                        struct super_block *sb)
{
      static const struct dentry_operations cgroup_dops = {
            .d_iput = cgroup_diput,
      };

      struct inode *inode;

      if (!dentry)
            return -ENOENT;
      if (dentry->d_inode)
            return -EEXIST;

      inode = cgroup_new_inode(mode, sb);
      if (!inode)
            return -ENOMEM;

      if (S_ISDIR(mode)) {
            inode->i_op = &cgroup_dir_inode_operations;
            inode->i_fop = &simple_dir_operations;

            /* start off with i_nlink == 2 (for "." entry) */
            inc_nlink(inode);

            /* start with the directory inode held, so that we can
             * populate it without racing with another mkdir */
            mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
      } else if (S_ISREG(mode)) {
            inode->i_size = 0;
            inode->i_fop = &cgroup_file_operations;
      }
      dentry->d_op = &cgroup_dops;
      d_instantiate(dentry, inode);
      dget(dentry);     /* Extra count - pin the dentry in core */
      return 0;
}

/*
 * cgroup_create_dir - create a directory for an object.
 * @cgrp: the cgroup we create the directory for. It must have a valid
 *        ->parent field. And we are going to fill its ->dentry field.
 * @dentry: dentry of the new cgroup
 * @mode: mode to set on new directory.
 */
static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
                        mode_t mode)
{
      struct dentry *parent;
      int error = 0;

      parent = cgrp->parent->dentry;
      error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb);
      if (!error) {
            dentry->d_fsdata = cgrp;
            inc_nlink(parent->d_inode);
            rcu_assign_pointer(cgrp->dentry, dentry);
            dget(dentry);
      }
      dput(dentry);

      return error;
}

/**
 * cgroup_file_mode - deduce file mode of a control file
 * @cft: the control file in question
 *
 * returns cft->mode if ->mode is not 0
 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
 * returns S_IRUGO if it has only a read handler
 * returns S_IWUSR if it has only a write hander
 */
static mode_t cgroup_file_mode(const struct cftype *cft)
{
      mode_t mode = 0;

      if (cft->mode)
            return cft->mode;

      if (cft->read || cft->read_u64 || cft->read_s64 ||
          cft->read_map || cft->read_seq_string)
            mode |= S_IRUGO;

      if (cft->write || cft->write_u64 || cft->write_s64 ||
          cft->write_string || cft->trigger)
            mode |= S_IWUSR;

      return mode;
}

int cgroup_add_file(struct cgroup *cgrp,
                   struct cgroup_subsys *subsys,
                   const struct cftype *cft)
{
      struct dentry *dir = cgrp->dentry;
      struct dentry *dentry;
      int error;
      mode_t mode;

      char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
      if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
            strcpy(name, subsys->name);
            strcat(name, ".");
      }
      strcat(name, cft->name);
      BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
      dentry = lookup_one_len(name, dir, strlen(name));
      if (!IS_ERR(dentry)) {
            mode = cgroup_file_mode(cft);
            error = cgroup_create_file(dentry, mode | S_IFREG,
                                    cgrp->root->sb);
            if (!error)
                  dentry->d_fsdata = (void *)cft;
            dput(dentry);
      } else
            error = PTR_ERR(dentry);
      return error;
}

int cgroup_add_files(struct cgroup *cgrp,
                  struct cgroup_subsys *subsys,
                  const struct cftype cft[],
                  int count)
{
      int i, err;
      for (i = 0; i < count; i++) {
            err = cgroup_add_file(cgrp, subsys, &cft[i]);
            if (err)
                  return err;
      }
      return 0;
}

/**
 * cgroup_task_count - count the number of tasks in a cgroup.
 * @cgrp: the cgroup in question
 *
 * Return the number of tasks in the cgroup.
 */
int cgroup_task_count(const struct cgroup *cgrp)
{
      int count = 0;
      struct cg_cgroup_link *link;

      read_lock(&css_set_lock);
      list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
            count += atomic_read(&link->cg->refcount);
      }
      read_unlock(&css_set_lock);
      return count;
}

/*
 * Advance a list_head iterator.  The iterator should be positioned at
 * the start of a css_set
 */
static void cgroup_advance_iter(struct cgroup *cgrp,
                                struct cgroup_iter *it)
{
      struct list_head *l = it->cg_link;
      struct cg_cgroup_link *link;
      struct css_set *cg;

      /* Advance to the next non-empty css_set */
      do {
            l = l->next;
            if (l == &cgrp->css_sets) {
                  it->cg_link = NULL;
                  return;
            }
            link = list_entry(l, struct cg_cgroup_link, cgrp_link_list);
            cg = link->cg;
      } while (list_empty(&cg->tasks));
      it->cg_link = l;
      it->task = cg->tasks.next;
}

/*
 * To reduce the fork() overhead for systems that are not actually
 * using their cgroups capability, we don't maintain the lists running
 * through each css_set to its tasks until we see the list actually
 * used - in other words after the first call to cgroup_iter_start().
 *
 * The tasklist_lock is not held here, as do_each_thread() and
 * while_each_thread() are protected by RCU.
 */
static void cgroup_enable_task_cg_lists(void)
{
      struct task_struct *p, *g;
      write_lock(&css_set_lock);
      use_task_css_set_links = 1;
      do_each_thread(g, p) {
            task_lock(p);
            /*
             * We should check if the process is exiting, otherwise
             * it will race with cgroup_exit() in that the list
             * entry won't be deleted though the process has exited.
             */
            if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
                  list_add(&p->cg_list, &p->cgroups->tasks);
            task_unlock(p);
      } while_each_thread(g, p);
      write_unlock(&css_set_lock);
}

void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
{
      /*
       * The first time anyone tries to iterate across a cgroup,
       * we need to enable the list linking each css_set to its
       * tasks, and fix up all existing tasks.
       */
      if (!use_task_css_set_links)
            cgroup_enable_task_cg_lists();

      read_lock(&css_set_lock);
      it->cg_link = &cgrp->css_sets;
      cgroup_advance_iter(cgrp, it);
}

struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
                              struct cgroup_iter *it)
{
      struct task_struct *res;
      struct list_head *l = it->task;
      struct cg_cgroup_link *link;

      /* If the iterator cg is NULL, we have no tasks */
      if (!it->cg_link)
            return NULL;
      res = list_entry(l, struct task_struct, cg_list);
      /* Advance iterator to find next entry */
      l = l->next;
      link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list);
      if (l == &link->cg->tasks) {
            /* We reached the end of this task list - move on to
             * the next cg_cgroup_link */
            cgroup_advance_iter(cgrp, it);
      } else {
            it->task = l;
      }
      return res;
}

void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
{
      read_unlock(&css_set_lock);
}

static inline int started_after_time(struct task_struct *t1,
                             struct timespec *time,
                             struct task_struct *t2)
{
      int start_diff = timespec_compare(&t1->start_time, time);
      if (start_diff > 0) {
            return 1;
      } else if (start_diff < 0) {
            return 0;
      } else {
            /*
             * Arbitrarily, if two processes started at the same
             * time, we'll say that the lower pointer value
             * started first. Note that t2 may have exited by now
             * so this may not be a valid pointer any longer, but
             * that's fine - it still serves to distinguish
             * between two tasks started (effectively) simultaneously.
             */
            return t1 > t2;
      }
}

/*
 * This function is a callback from heap_insert() and is used to order
 * the heap.
 * In this case we order the heap in descending task start time.
 */
static inline int started_after(void *p1, void *p2)
{
      struct task_struct *t1 = p1;
      struct task_struct *t2 = p2;
      return started_after_time(t1, &t2->start_time, t2);
}

/**
 * cgroup_scan_tasks - iterate though all the tasks in a cgroup
 * @scan: struct cgroup_scanner containing arguments for the scan
 *
 * Arguments include pointers to callback functions test_task() and
 * process_task().
 * Iterate through all the tasks in a cgroup, calling test_task() for each,
 * and if it returns true, call process_task() for it also.
 * The test_task pointer may be NULL, meaning always true (select all tasks).
 * Effectively duplicates cgroup_iter_{start,next,end}()
 * but does not lock css_set_lock for the call to process_task().
 * The struct cgroup_scanner may be embedded in any structure of the caller's
 * creation.
 * It is guaranteed that process_task() will act on every task that
 * is a member of the cgroup for the duration of this call. This
 * function may or may not call process_task() for tasks that exit
 * or move to a different cgroup during the call, or are forked or
 * move into the cgroup during the call.
 *
 * Note that test_task() may be called with locks held, and may in some
 * situations be called multiple times for the same task, so it should
 * be cheap.
 * If the heap pointer in the struct cgroup_scanner is non-NULL, a heap has been
 * pre-allocated and will be used for heap operations (and its "gt" member will
 * be overwritten), else a temporary heap will be used (allocation of which
 * may cause this function to fail).
 */
int cgroup_scan_tasks(struct cgroup_scanner *scan)
{
      int retval, i;
      struct cgroup_iter it;
      struct task_struct *p, *dropped;
      /* Never dereference latest_task, since it's not refcounted */
      struct task_struct *latest_task = NULL;
      struct ptr_heap tmp_heap;
      struct ptr_heap *heap;
      struct timespec latest_time = { 0, 0 };

      if (scan->heap) {
            /* The caller supplied our heap and pre-allocated its memory */
            heap = scan->heap;
            heap->gt = &started_after;
      } else {
            /* We need to allocate our own heap memory */
            heap = &tmp_heap;
            retval = heap_init(heap, PAGE_SIZE, GFP_KERNEL, &started_after);
            if (retval)
                  /* cannot allocate the heap */
                  return retval;
      }

 again:
      /*
       * Scan tasks in the cgroup, using the scanner's "test_task" callback
       * to determine which are of interest, and using the scanner's
       * "process_task" callback to process any of them that need an update.
       * Since we don't want to hold any locks during the task updates,
       * gather tasks to be processed in a heap structure.
       * The heap is sorted by descending task start time.
       * If the statically-sized heap fills up, we overflow tasks that
       * started later, and in future iterations only consider tasks that
       * started after the latest task in the previous pass. This
       * guarantees forward progress and that we don't miss any tasks.
       */
      heap->size = 0;
      cgroup_iter_start(scan->cg, &it);
      while ((p = cgroup_iter_next(scan->cg, &it))) {
            /*
             * Only affect tasks that qualify per the caller's callback,
             * if he provided one
             */
            if (scan->test_task && !scan->test_task(p, scan))
                  continue;
            /*
             * Only process tasks that started after the last task
             * we processed
             */
            if (!started_after_time(p, &latest_time, latest_task))
                  continue;
            dropped = heap_insert(heap, p);
            if (dropped == NULL) {
                  /*
                   * The new task was inserted; the heap wasn't
                   * previously full
                   */
                  get_task_struct(p);
            } else if (dropped != p) {
                  /*
                   * The new task was inserted, and pushed out a
                   * different task
                   */
                  get_task_struct(p);
                  put_task_struct(dropped);
            }
            /*
             * Else the new task was newer than anything already in
             * the heap and wasn't inserted
             */
      }
      cgroup_iter_end(scan->cg, &it);

      if (heap->size) {
            for (i = 0; i < heap->size; i++) {
                  struct task_struct *q = heap->ptrs[i];
                  if (i == 0) {
                        latest_time = q->start_time;
                        latest_task = q;
                  }
                  /* Process the task per the caller's callback */
                  scan->process_task(q, scan);
                  put_task_struct(q);
            }
            /*
             * If we had to process any tasks at all, scan again
             * in case some of them were in the middle of forking
             * children that didn't get processed.
             * Not the most efficient way to do it, but it avoids
             * having to take callback_mutex in the fork path
             */
            goto again;
      }
      if (heap == &tmp_heap)
            heap_free(&tmp_heap);
      return 0;
}

/*
 * Stuff for reading the 'tasks' file.
 *
 * Reading this file can return large amounts of data if a cgroup has
 * *lots* of attached tasks. So it may need several calls to read(),
 * but we cannot guarantee that the information we produce is correct
 * unless we produce it entirely atomically.
 *
 */

/*
 * Load into 'pidarray' up to 'npids' of the tasks using cgroup
 * 'cgrp'.  Return actual number of pids loaded.  No need to
 * task_lock(p) when reading out p->cgroup, since we're in an RCU
 * read section, so the css_set can't go away, and is
 * immutable after creation.
 */
static int pid_array_load(pid_t *pidarray, int npids, struct cgroup *cgrp)
{
      int n = 0, pid;
      struct cgroup_iter it;
      struct task_struct *tsk;
      cgroup_iter_start(cgrp, &it);
      while ((tsk = cgroup_iter_next(cgrp, &it))) {
            if (unlikely(n == npids))
                  break;
            pid = task_pid_vnr(tsk);
            if (pid > 0)
                  pidarray[n++] = pid;
      }
      cgroup_iter_end(cgrp, &it);
      return n;
}

/**
 * cgroupstats_build - build and fill cgroupstats
 * @stats: cgroupstats to fill information into
 * @dentry: A dentry entry belonging to the cgroup for which stats have
 * been requested.
 *
 * Build and fill cgroupstats so that taskstats can export it to user
 * space.
 */
int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
{
      int ret = -EINVAL;
      struct cgroup *cgrp;
      struct cgroup_iter it;
      struct task_struct *tsk;

      /*
       * Validate dentry by checking the superblock operations,
       * and make sure it's a directory.
       */
      if (dentry->d_sb->s_op != &cgroup_ops ||
          !S_ISDIR(dentry->d_inode->i_mode))
             goto err;

      ret = 0;
      cgrp = dentry->d_fsdata;

      cgroup_iter_start(cgrp, &it);
      while ((tsk = cgroup_iter_next(cgrp, &it))) {
            switch (tsk->state) {
            case TASK_RUNNING:
                  stats->nr_running++;
                  break;
            case TASK_INTERRUPTIBLE:
                  stats->nr_sleeping++;
                  break;
            case TASK_UNINTERRUPTIBLE:
                  stats->nr_uninterruptible++;
                  break;
            case TASK_STOPPED:
                  stats->nr_stopped++;
                  break;
            default:
                  if (delayacct_is_task_waiting_on_io(tsk))
                        stats->nr_io_wait++;
                  break;
            }
      }
      cgroup_iter_end(cgrp, &it);

err:
      return ret;
}

/*
 * Cache pids for all threads in the same pid namespace that are
 * opening the same "tasks" file.
 */
02222 struct cgroup_pids {
      /* The node in cgrp->pids_list */
      struct list_head list;
      /* The cgroup those pids belong to */
      struct cgroup *cgrp;
      /* The namepsace those pids belong to */
      struct pid_namespace *ns;
      /* Array of process ids in the cgroup */
      pid_t *tasks_pids;
      /* How many files are using the this tasks_pids array */
      int use_count;
      /* Length of the current tasks_pids array */
      int length;
};

static int cmppid(const void *a, const void *b)
{
      return *(pid_t *)a - *(pid_t *)b;
}

/*
 * seq_file methods for the "tasks" file. The seq_file position is the
 * next pid to display; the seq_file iterator is a pointer to the pid
 * in the cgroup->tasks_pids array.
 */

static void *cgroup_tasks_start(struct seq_file *s, loff_t *pos)
{
      /*
       * Initially we receive a position value that corresponds to
       * one more than the last pid shown (or 0 on the first call or
       * after a seek to the start). Use a binary-search to find the
       * next pid to display, if any
       */
      struct cgroup_pids *cp = s->private;
      struct cgroup *cgrp = cp->cgrp;
      int index = 0, pid = *pos;
      int *iter;

      down_read(&cgrp->pids_mutex);
      if (pid) {
            int end = cp->length;

            while (index < end) {
                  int mid = (index + end) / 2;
                  if (cp->tasks_pids[mid] == pid) {
                        index = mid;
                        break;
                  } else if (cp->tasks_pids[mid] <= pid)
                        index = mid + 1;
                  else
                        end = mid;
            }
      }
      /* If we're off the end of the array, we're done */
      if (index >= cp->length)
            return NULL;
      /* Update the abstract position to be the actual pid that we found */
      iter = cp->tasks_pids + index;
      *pos = *iter;
      return iter;
}

static void cgroup_tasks_stop(struct seq_file *s, void *v)
{
      struct cgroup_pids *cp = s->private;
      struct cgroup *cgrp = cp->cgrp;
      up_read(&cgrp->pids_mutex);
}

static void *cgroup_tasks_next(struct seq_file *s, void *v, loff_t *pos)
{
      struct cgroup_pids *cp = s->private;
      int *p = v;
      int *end = cp->tasks_pids + cp->length;

      /*
       * Advance to the next pid in the array. If this goes off the
       * end, we're done
       */
      p++;
      if (p >= end) {
            return NULL;
      } else {
            *pos = *p;
            return p;
      }
}

static int cgroup_tasks_show(struct seq_file *s, void *v)
{
      return seq_printf(s, "%d\n", *(int *)v);
}

static struct seq_operations cgroup_tasks_seq_operations = {
      .start = cgroup_tasks_start,
      .stop = cgroup_tasks_stop,
      .next = cgroup_tasks_next,
      .show = cgroup_tasks_show,
};

static void release_cgroup_pid_array(struct cgroup_pids *cp)
{
      struct cgroup *cgrp = cp->cgrp;

      down_write(&cgrp->pids_mutex);
      BUG_ON(!cp->use_count);
      if (!--cp->use_count) {
            list_del(&cp->list);
            put_pid_ns(cp->ns);
            kfree(cp->tasks_pids);
            kfree(cp);
      }
      up_write(&cgrp->pids_mutex);
}

static int cgroup_tasks_release(struct inode *inode, struct file *file)
{
      struct seq_file *seq;
      struct cgroup_pids *cp;

      if (!(file->f_mode & FMODE_READ))
            return 0;

      seq = file->private_data;
      cp = seq->private;

      release_cgroup_pid_array(cp);
      return seq_release(inode, file);
}

static struct file_operations cgroup_tasks_operations = {
      .read = seq_read,
      .llseek = seq_lseek,
      .write = cgroup_file_write,
      .release = cgroup_tasks_release,
};

/*
 * Handle an open on 'tasks' file.  Prepare an array containing the
 * process id's of tasks currently attached to the cgroup being opened.
 */

static int cgroup_tasks_open(struct inode *unused, struct file *file)
{
      struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
      struct pid_namespace *ns = current->nsproxy->pid_ns;
      struct cgroup_pids *cp;
      pid_t *pidarray;
      int npids;
      int retval;

      /* Nothing to do for write-only files */
      if (!(file->f_mode & FMODE_READ))
            return 0;

      /*
       * If cgroup gets more users after we read count, we won't have
       * enough space - tough.  This race is indistinguishable to the
       * caller from the case that the additional cgroup users didn't
       * show up until sometime later on.
       */
      npids = cgroup_task_count(cgrp);
      pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
      if (!pidarray)
            return -ENOMEM;
      npids = pid_array_load(pidarray, npids, cgrp);
      sort(pidarray, npids, sizeof(pid_t), cmppid, NULL);

      /*
       * Store the array in the cgroup, freeing the old
       * array if necessary
       */
      down_write(&cgrp->pids_mutex);

      list_for_each_entry(cp, &cgrp->pids_list, list) {
            if (ns == cp->ns)
                  goto found;
      }

      cp = kzalloc(sizeof(*cp), GFP_KERNEL);
      if (!cp) {
            up_write(&cgrp->pids_mutex);
            kfree(pidarray);
            return -ENOMEM;
      }
      cp->cgrp = cgrp;
      cp->ns = ns;
      get_pid_ns(ns);
      list_add(&cp->list, &cgrp->pids_list);
found:
      kfree(cp->tasks_pids);
      cp->tasks_pids = pidarray;
      cp->length = npids;
      cp->use_count++;
      up_write(&cgrp->pids_mutex);

      file->f_op = &cgroup_tasks_operations;

      retval = seq_open(file, &cgroup_tasks_seq_operations);
      if (retval) {
            release_cgroup_pid_array(cp);
            return retval;
      }
      ((struct seq_file *)file->private_data)->private = cp;
      return 0;
}

static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
                                  struct cftype *cft)
{
      return notify_on_release(cgrp);
}

static int cgroup_write_notify_on_release(struct cgroup *cgrp,
                                struct cftype *cft,
                                u64 val)
{
      clear_bit(CGRP_RELEASABLE, &cgrp->flags);
      if (val)
            set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
      else
            clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
      return 0;
}

/*
 * for the common functions, 'private' gives the type of file
 */
static struct cftype files[] = {
      {
            .name = "tasks",
            .open = cgroup_tasks_open,
            .write_u64 = cgroup_tasks_write,
            .release = cgroup_tasks_release,
            .private = FILE_TASKLIST,
            .mode = S_IRUGO | S_IWUSR,
      },

      {
            .name = "notify_on_release",
            .read_u64 = cgroup_read_notify_on_release,
            .write_u64 = cgroup_write_notify_on_release,
            .private = FILE_NOTIFY_ON_RELEASE,
      },
};

static struct cftype cft_release_agent = {
      .name = "release_agent",
      .read_seq_string = cgroup_release_agent_show,
      .write_string = cgroup_release_agent_write,
      .max_write_len = PATH_MAX,
      .private = FILE_RELEASE_AGENT,
};

static int cgroup_populate_dir(struct cgroup *cgrp)
{
      int err;
      struct cgroup_subsys *ss;

      /* First clear out any existing files */
      cgroup_clear_directory(cgrp->dentry);

      err = cgroup_add_files(cgrp, NULL, files, ARRAY_SIZE(files));
      if (err < 0)
            return err;

      if (cgrp == cgrp->top_cgroup) {
            if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0)
                  return err;
      }

      for_each_subsys(cgrp->root, ss) {
            if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
                  return err;
      }
      /* This cgroup is ready now */
      for_each_subsys(cgrp->root, ss) {
            struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
            /*
             * Update id->css pointer and make this css visible from
             * CSS ID functions. This pointer will be dereferened
             * from RCU-read-side without locks.
             */
            if (css->id)
                  rcu_assign_pointer(css->id->css, css);
      }

      return 0;
}

static void init_cgroup_css(struct cgroup_subsys_state *css,
                         struct cgroup_subsys *ss,
                         struct cgroup *cgrp)
{
      css->cgroup = cgrp;
      atomic_set(&css->refcnt, 1);
      css->flags = 0;
      css->id = NULL;
      if (cgrp == dummytop)
            set_bit(CSS_ROOT, &css->flags);
      BUG_ON(cgrp->subsys[ss->subsys_id]);
      cgrp->subsys[ss->subsys_id] = css;
}

static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
{
      /* We need to take each hierarchy_mutex in a consistent order */
      int i;

      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup_subsys *ss = subsys[i];
            if (ss->root == root)
                  mutex_lock(&ss->hierarchy_mutex);
      }
}

static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
{
      int i;

      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup_subsys *ss = subsys[i];
            if (ss->root == root)
                  mutex_unlock(&ss->hierarchy_mutex);
      }
}

/*
 * cgroup_create - create a cgroup
 * @parent: cgroup that will be parent of the new cgroup
 * @dentry: dentry of the new cgroup
 * @mode: mode to set on new inode
 *
 * Must be called with the mutex on the parent inode held
 */
static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                       mode_t mode)
{
      struct cgroup *cgrp;
      struct cgroupfs_root *root = parent->root;
      int err = 0;
      struct cgroup_subsys *ss;
      struct super_block *sb = root->sb;

      cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
      if (!cgrp)
            return -ENOMEM;

      /* Grab a reference on the superblock so the hierarchy doesn't
       * get deleted on unmount if there are child cgroups.  This
       * can be done outside cgroup_mutex, since the sb can't
       * disappear while someone has an open control file on the
       * fs */
      atomic_inc(&sb->s_active);

      mutex_lock(&cgroup_mutex);

      init_cgroup_housekeeping(cgrp);

      cgrp->parent = parent;
      cgrp->root = parent->root;
      cgrp->top_cgroup = parent->top_cgroup;

      if (notify_on_release(parent))
            set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);

      for_each_subsys(root, ss) {
            struct cgroup_subsys_state *css = ss->create(ss, cgrp);
            if (IS_ERR(css)) {
                  err = PTR_ERR(css);
                  goto err_destroy;
            }
            init_cgroup_css(css, ss, cgrp);
            if (ss->use_id)
                  if (alloc_css_id(ss, parent, cgrp))
                        goto err_destroy;
            /* At error, ->destroy() callback has to free assigned ID. */
      }

      cgroup_lock_hierarchy(root);
      list_add(&cgrp->sibling, &cgrp->parent->children);
      cgroup_unlock_hierarchy(root);
      root->number_of_cgroups++;

      err = cgroup_create_dir(cgrp, dentry, mode);
      if (err < 0)
            goto err_remove;

      /* The cgroup directory was pre-locked for us */
      BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));

      err = cgroup_populate_dir(cgrp);
      /* If err < 0, we have a half-filled directory - oh well ;) */

      mutex_unlock(&cgroup_mutex);
      mutex_unlock(&cgrp->dentry->d_inode->i_mutex);

      return 0;

 err_remove:

      cgroup_lock_hierarchy(root);
      list_del(&cgrp->sibling);
      cgroup_unlock_hierarchy(root);
      root->number_of_cgroups--;

 err_destroy:

      for_each_subsys(root, ss) {
            if (cgrp->subsys[ss->subsys_id])
                  ss->destroy(ss, cgrp);
      }

      mutex_unlock(&cgroup_mutex);

      /* Release the reference count that we took on the superblock */
      deactivate_super(sb);

      kfree(cgrp);
      return err;
}

static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
      struct cgroup *c_parent = dentry->d_parent->d_fsdata;

      /* the vfs holds inode->i_mutex already */
      return cgroup_create(c_parent, dentry, mode | S_IFDIR);
}

static int cgroup_has_css_refs(struct cgroup *cgrp)
{
      /* Check the reference count on each subsystem. Since we
       * already established that there are no tasks in the
       * cgroup, if the css refcount is also 1, then there should
       * be no outstanding references, so the subsystem is safe to
       * destroy. We scan across all subsystems rather than using
       * the per-hierarchy linked list of mounted subsystems since
       * we can be called via check_for_release() with no
       * synchronization other than RCU, and the subsystem linked
       * list isn't RCU-safe */
      int i;
      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup_subsys *ss = subsys[i];
            struct cgroup_subsys_state *css;
            /* Skip subsystems not in this hierarchy */
            if (ss->root != cgrp->root)
                  continue;
            css = cgrp->subsys[ss->subsys_id];
            /* When called from check_for_release() it's possible
             * that by this point the cgroup has been removed
             * and the css deleted. But a false-positive doesn't
             * matter, since it can only happen if the cgroup
             * has been deleted and hence no longer needs the
             * release agent to be called anyway. */
            if (css && (atomic_read(&css->refcnt) > 1))
                  return 1;
      }
      return 0;
}

/*
 * Atomically mark all (or else none) of the cgroup's CSS objects as
 * CSS_REMOVED. Return true on success, or false if the cgroup has
 * busy subsystems. Call with cgroup_mutex held
 */

static int cgroup_clear_css_refs(struct cgroup *cgrp)
{
      struct cgroup_subsys *ss;
      unsigned long flags;
      bool failed = false;
      local_irq_save(flags);
      for_each_subsys(cgrp->root, ss) {
            struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
            int refcnt;
            while (1) {
                  /* We can only remove a CSS with a refcnt==1 */
                  refcnt = atomic_read(&css->refcnt);
                  if (refcnt > 1) {
                        failed = true;
                        goto done;
                  }
                  BUG_ON(!refcnt);
                  /*
                   * Drop the refcnt to 0 while we check other
                   * subsystems. This will cause any racing
                   * css_tryget() to spin until we set the
                   * CSS_REMOVED bits or abort
                   */
                  if (atomic_cmpxchg(&css->refcnt, refcnt, 0) == refcnt)
                        break;
                  cpu_relax();
            }
      }
 done:
      for_each_subsys(cgrp->root, ss) {
            struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
            if (failed) {
                  /*
                   * Restore old refcnt if we previously managed
                   * to clear it from 1 to 0
                   */
                  if (!atomic_read(&css->refcnt))
                        atomic_set(&css->refcnt, 1);
            } else {
                  /* Commit the fact that the CSS is removed */
                  set_bit(CSS_REMOVED, &css->flags);
            }
      }
      local_irq_restore(flags);
      return !failed;
}

static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
{
      struct cgroup *cgrp = dentry->d_fsdata;
      struct dentry *d;
      struct cgroup *parent;
      DEFINE_WAIT(wait);
      int ret;

      /* the vfs holds both inode->i_mutex already */
again:
      mutex_lock(&cgroup_mutex);
      if (atomic_read(&cgrp->count) != 0) {
            mutex_unlock(&cgroup_mutex);
            return -EBUSY;
      }
      if (!list_empty(&cgrp->children)) {
            mutex_unlock(&cgroup_mutex);
            return -EBUSY;
      }
      mutex_unlock(&cgroup_mutex);

      /*
       * In general, subsystem has no css->refcnt after pre_destroy(). But
       * in racy cases, subsystem may have to get css->refcnt after
       * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
       * make rmdir return -EBUSY too often. To avoid that, we use waitqueue
       * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
       * and subsystem's reference count handling. Please see css_get/put
       * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
       */
      set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);

      /*
       * Call pre_destroy handlers of subsys. Notify subsystems
       * that rmdir() request comes.
       */
      ret = cgroup_call_pre_destroy(cgrp);
      if (ret) {
            clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
            return ret;
      }

      mutex_lock(&cgroup_mutex);
      parent = cgrp->parent;
      if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
            clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
            mutex_unlock(&cgroup_mutex);
            return -EBUSY;
      }
      prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
      if (!cgroup_clear_css_refs(cgrp)) {
            mutex_unlock(&cgroup_mutex);
            /*
             * Because someone may call cgroup_wakeup_rmdir_waiter() before
             * prepare_to_wait(), we need to check this flag.
             */
            if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
                  schedule();
            finish_wait(&cgroup_rmdir_waitq, &wait);
            clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
            if (signal_pending(current))
                  return -EINTR;
            goto again;
      }
      /* NO css_tryget() can success after here. */
      finish_wait(&cgroup_rmdir_waitq, &wait);
      clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);

      spin_lock(&release_list_lock);
      set_bit(CGRP_REMOVED, &cgrp->flags);
      if (!list_empty(&cgrp->release_list))
            list_del(&cgrp->release_list);
      spin_unlock(&release_list_lock);

      cgroup_lock_hierarchy(cgrp->root);
      /* delete this cgroup from parent->children */
      list_del(&cgrp->sibling);
      cgroup_unlock_hierarchy(cgrp->root);

      spin_lock(&cgrp->dentry->d_lock);
      d = dget(cgrp->dentry);
      spin_unlock(&d->d_lock);

      cgroup_d_remove_dir(d);
      dput(d);

      set_bit(CGRP_RELEASABLE, &parent->flags);
      check_for_release(parent);

      mutex_unlock(&cgroup_mutex);
      return 0;
}

static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
{
      struct cgroup_subsys_state *css;

      printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);

      /* Create the top cgroup state for this subsystem */
      list_add(&ss->sibling, &rootnode.subsys_list);
      ss->root = &rootnode;
      css = ss->create(ss, dummytop);
      /* We don't handle early failures gracefully */
      BUG_ON(IS_ERR(css));
      init_cgroup_css(css, ss, dummytop);

      /* Update the init_css_set to contain a subsys
       * pointer to this state - since the subsystem is
       * newly registered, all tasks and hence the
       * init_css_set is in the subsystem's top cgroup. */
      init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];

      need_forkexit_callback |= ss->fork || ss->exit;

      /* At system boot, before all subsystems have been
       * registered, no tasks have been forked, so we don't
       * need to invoke fork callbacks here. */
      BUG_ON(!list_empty(&init_task.tasks));

      mutex_init(&ss->hierarchy_mutex);
      lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
      ss->active = 1;
}

/**
 * cgroup_init_early - cgroup initialization at system boot
 *
 * Initialize cgroups at system boot, and initialize any
 * subsystems that request early init.
 */
int __init cgroup_init_early(void)
{
      int i;
      atomic_set(&init_css_set.refcount, 1);
      INIT_LIST_HEAD(&init_css_set.cg_links);
      INIT_LIST_HEAD(&init_css_set.tasks);
      INIT_HLIST_NODE(&init_css_set.hlist);
      css_set_count = 1;
      init_cgroup_root(&rootnode);
      root_count = 1;
      init_task.cgroups = &init_css_set;

      init_css_set_link.cg = &init_css_set;
      list_add(&init_css_set_link.cgrp_link_list,
             &rootnode.top_cgroup.css_sets);
      list_add(&init_css_set_link.cg_link_list,
             &init_css_set.cg_links);

      for (i = 0; i < CSS_SET_TABLE_SIZE; i++)
            INIT_HLIST_HEAD(&css_set_table[i]);

      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup_subsys *ss = subsys[i];

            BUG_ON(!ss->name);
            BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
            BUG_ON(!ss->create);
            BUG_ON(!ss->destroy);
            if (ss->subsys_id != i) {
                  printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
                         ss->name, ss->subsys_id);
                  BUG();
            }

            if (ss->early_init)
                  cgroup_init_subsys(ss);
      }
      return 0;
}

/**
 * cgroup_init - cgroup initialization
 *
 * Register cgroup filesystem and /proc file, and initialize
 * any subsystems that didn't request early init.
 */
int __init cgroup_init(void)
{
      int err;
      int i;
      struct hlist_head *hhead;

      err = bdi_init(&cgroup_backing_dev_info);
      if (err)
            return err;

      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup_subsys *ss = subsys[i];
            if (!ss->early_init)
                  cgroup_init_subsys(ss);
            if (ss->use_id)
                  cgroup_subsys_init_idr(ss);
      }

      /* Add init_css_set to the hash table */
      hhead = css_set_hash(init_css_set.subsys);
      hlist_add_head(&init_css_set.hlist, hhead);

      err = register_filesystem(&cgroup_fs_type);
      if (err < 0)
            goto out;

      proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations);

out:
      if (err)
            bdi_destroy(&cgroup_backing_dev_info);

      return err;
}

/*
 * proc_cgroup_show()
 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
 *  - Used for /proc/<pid>/cgroup.
 *  - No need to task_lock(tsk) on this tsk->cgroup reference, as it
 *    doesn't really matter if tsk->cgroup changes after we read it,
 *    and we take cgroup_mutex, keeping cgroup_attach_task() from changing it
 *    anyway.  No need to check that tsk->cgroup != NULL, thanks to
 *    the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
 *    cgroup to top_cgroup.
 */

/* TODO: Use a proper seq_file iterator */
static int proc_cgroup_show(struct seq_file *m, void *v)
{
      struct pid *pid;
      struct task_struct *tsk;
      char *buf;
      int retval;
      struct cgroupfs_root *root;

      retval = -ENOMEM;
      buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
      if (!buf)
            goto out;

      retval = -ESRCH;
      pid = m->private;
      tsk = get_pid_task(pid, PIDTYPE_PID);
      if (!tsk)
            goto out_free;

      retval = 0;

      mutex_lock(&cgroup_mutex);

      for_each_active_root(root) {
            struct cgroup_subsys *ss;
            struct cgroup *cgrp;
            int subsys_id;
            int count = 0;

            seq_printf(m, "%lu:", root->subsys_bits);
            for_each_subsys(root, ss)
                  seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
            seq_putc(m, ':');
            get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
            cgrp = task_cgroup(tsk, subsys_id);
            retval = cgroup_path(cgrp, buf, PAGE_SIZE);
            if (retval < 0)
                  goto out_unlock;
            seq_puts(m, buf);
            seq_putc(m, '\n');
      }

out_unlock:
      mutex_unlock(&cgroup_mutex);
      put_task_struct(tsk);
out_free:
      kfree(buf);
out:
      return retval;
}

static int cgroup_open(struct inode *inode, struct file *file)
{
      struct pid *pid = PROC_I(inode)->pid;
      return single_open(file, proc_cgroup_show, pid);
}

struct file_operations proc_cgroup_operations = {
      .open       = cgroup_open,
      .read       = seq_read,
      .llseek           = seq_lseek,
      .release    = single_release,
};

/* Display information about each subsystem and each hierarchy */
static int proc_cgroupstats_show(struct seq_file *m, void *v)
{
      int i;

      seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
      mutex_lock(&cgroup_mutex);
      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
            struct cgroup_subsys *ss = subsys[i];
            seq_printf(m, "%s\t%lu\t%d\t%d\n",
                     ss->name, ss->root->subsys_bits,
                     ss->root->number_of_cgroups, !ss->disabled);
      }
      mutex_unlock(&cgroup_mutex);
      return 0;
}

static int cgroupstats_open(struct inode *inode, struct file *file)
{
      return single_open(file, proc_cgroupstats_show, NULL);
}

static struct file_operations proc_cgroupstats_operations = {
      .open = cgroupstats_open,
      .read = seq_read,
      .llseek = seq_lseek,
      .release = single_release,
};

/**
 * cgroup_fork - attach newly forked task to its parents cgroup.
 * @child: pointer to task_struct of forking parent process.
 *
 * Description: A task inherits its parent's cgroup at fork().
 *
 * A pointer to the shared css_set was automatically copied in
 * fork.c by dup_task_struct().  However, we ignore that copy, since
 * it was not made under the protection of RCU or cgroup_mutex, so
 * might no longer be a valid cgroup pointer.  cgroup_attach_task() might
 * have already changed current->cgroups, allowing the previously
 * referenced cgroup group to be removed and freed.
 *
 * At the point that cgroup_fork() is called, 'current' is the parent
 * task, and the passed argument 'child' points to the child task.
 */
void cgroup_fork(struct task_struct *child)
{
      task_lock(current);
      child->cgroups = current->cgroups;
      get_css_set(child->cgroups);
      task_unlock(current);
      INIT_LIST_HEAD(&child->cg_list);
}

/**
 * cgroup_fork_callbacks - run fork callbacks
 * @child: the new task
 *
 * Called on a new task very soon before adding it to the
 * tasklist. No need to take any locks since no-one can
 * be operating on this task.
 */
void cgroup_fork_callbacks(struct task_struct *child)
{
      if (need_forkexit_callback) {
            int i;
            for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                  struct cgroup_subsys *ss = subsys[i];
                  if (ss->fork)
                        ss->fork(ss, child);
            }
      }
}

/**
 * cgroup_post_fork - called on a new task after adding it to the task list
 * @child: the task in question
 *
 * Adds the task to the list running through its css_set if necessary.
 * Has to be after the task is visible on the task list in case we race
 * with the first call to cgroup_iter_start() - to guarantee that the
 * new task ends up on its list.
 */
void cgroup_post_fork(struct task_struct *child)
{
      if (use_task_css_set_links) {
            write_lock(&css_set_lock);
            task_lock(child);
            if (list_empty(&child->cg_list))
                  list_add(&child->cg_list, &child->cgroups->tasks);
            task_unlock(child);
            write_unlock(&css_set_lock);
      }
}
/**
 * cgroup_exit - detach cgroup from exiting task
 * @tsk: pointer to task_struct of exiting process
 * @run_callback: run exit callbacks?
 *
 * Description: Detach cgroup from @tsk and release it.
 *
 * Note that cgroups marked notify_on_release force every task in
 * them to take the global cgroup_mutex mutex when exiting.
 * This could impact scaling on very large systems.  Be reluctant to
 * use notify_on_release cgroups where very high task exit scaling
 * is required on large systems.
 *
 * the_top_cgroup_hack:
 *
 *    Set the exiting tasks cgroup to the root cgroup (top_cgroup).
 *
 *    We call cgroup_exit() while the task is still competent to
 *    handle notify_on_release(), then leave the task attached to the
 *    root cgroup in each hierarchy for the remainder of its exit.
 *
 *    To do this properly, we would increment the reference count on
 *    top_cgroup, and near the very end of the kernel/exit.c do_exit()
 *    code we would add a second cgroup function call, to drop that
 *    reference.  This would just create an unnecessary hot spot on
 *    the top_cgroup reference count, to no avail.
 *
 *    Normally, holding a reference to a cgroup without bumping its
 *    count is unsafe.   The cgroup could go away, or someone could
 *    attach us to a different cgroup, decrementing the count on
 *    the first cgroup that we never incremented.  But in this case,
 *    top_cgroup isn't going away, and either task has PF_EXITING set,
 *    which wards off any cgroup_attach_task() attempts, or task is a failed
 *    fork, never visible to cgroup_attach_task.
 */
void cgroup_exit(struct task_struct *tsk, int run_callbacks)
{
      int i;
      struct css_set *cg;

      if (run_callbacks && need_forkexit_callback) {
            for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                  struct cgroup_subsys *ss = subsys[i];
                  if (ss->exit)
                        ss->exit(ss, tsk);
            }
      }

      /*
       * Unlink from the css_set task list if necessary.
       * Optimistically check cg_list before taking
       * css_set_lock
       */
      if (!list_empty(&tsk->cg_list)) {
            write_lock(&css_set_lock);
            if (!list_empty(&tsk->cg_list))
                  list_del(&tsk->cg_list);
            write_unlock(&css_set_lock);
      }

      /* Reassign the task to the init_css_set. */
      task_lock(tsk);
      cg = tsk->cgroups;
      tsk->cgroups = &init_css_set;
      task_unlock(tsk);
      if (cg)
            put_css_set_taskexit(cg);
}

/**
 * cgroup_clone - clone the cgroup the given subsystem is attached to
 * @tsk: the task to be moved
 * @subsys: the given subsystem
 * @nodename: the name for the new cgroup
 *
 * Duplicate the current cgroup in the hierarchy that the given
 * subsystem is attached to, and move this task into the new
 * child.
 */
int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
                                          char *nodename)
{
      struct dentry *dentry;
      int ret = 0;
      struct cgroup *parent, *child;
      struct inode *inode;
      struct css_set *cg;
      struct cgroupfs_root *root;
      struct cgroup_subsys *ss;

      /* We shouldn't be called by an unregistered subsystem */
      BUG_ON(!subsys->active);

      /* First figure out what hierarchy and cgroup we're dealing
       * with, and pin them so we can drop cgroup_mutex */
      mutex_lock(&cgroup_mutex);
 again:
      root = subsys->root;
      if (root == &rootnode) {
            mutex_unlock(&cgroup_mutex);
            return 0;
      }

      /* Pin the hierarchy */
      if (!atomic_inc_not_zero(&root->sb->s_active)) {
            /* We race with the final deactivate_super() */
            mutex_unlock(&cgroup_mutex);
            return 0;
      }

      /* Keep the cgroup alive */
      task_lock(tsk);
      parent = task_cgroup(tsk, subsys->subsys_id);
      cg = tsk->cgroups;
      get_css_set(cg);
      task_unlock(tsk);

      mutex_unlock(&cgroup_mutex);

      /* Now do the VFS work to create a cgroup */
      inode = parent->dentry->d_inode;

      /* Hold the parent directory mutex across this operation to
       * stop anyone else deleting the new cgroup */
      mutex_lock(&inode->i_mutex);
      dentry = lookup_one_len(nodename, parent->dentry, strlen(nodename));
      if (IS_ERR(dentry)) {
            printk(KERN_INFO
                   "cgroup: Couldn't allocate dentry for %s: %ld\n", nodename,
                   PTR_ERR(dentry));
            ret = PTR_ERR(dentry);
            goto out_release;
      }

      /* Create the cgroup directory, which also creates the cgroup */
      ret = vfs_mkdir(inode, dentry, 0755);
      child = __d_cgrp(dentry);
      dput(dentry);
      if (ret) {
            printk(KERN_INFO
                   "Failed to create cgroup %s: %d\n", nodename,
                   ret);
            goto out_release;
      }

      /* The cgroup now exists. Retake cgroup_mutex and check
       * that we're still in the same state that we thought we
       * were. */
      mutex_lock(&cgroup_mutex);
      if ((root != subsys->root) ||
          (parent != task_cgroup(tsk, subsys->subsys_id))) {
            /* Aargh, we raced ... */
            mutex_unlock(&inode->i_mutex);
            put_css_set(cg);

            deactivate_super(root->sb);
            /* The cgroup is still accessible in the VFS, but
             * we're not going to try to rmdir() it at this
             * point. */
            printk(KERN_INFO
                   "Race in cgroup_clone() - leaking cgroup %s\n",
                   nodename);
            goto again;
      }

      /* do any required auto-setup */
      for_each_subsys(root, ss) {
            if (ss->post_clone)
                  ss->post_clone(ss, child);
      }

      /* All seems fine. Finish by moving the task into the new cgroup */
      ret = cgroup_attach_task(child, tsk);
      mutex_unlock(&cgroup_mutex);

 out_release:
      mutex_unlock(&inode->i_mutex);

      mutex_lock(&cgroup_mutex);
      put_css_set(cg);
      mutex_unlock(&cgroup_mutex);
      deactivate_super(root->sb);
      return ret;
}

/**
 * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp
 * @cgrp: the cgroup in question
 * @task: the task in question
 *
 * See if @cgrp is a descendant of @task's cgroup in the appropriate
 * hierarchy.
 *
 * If we are sending in dummytop, then presumably we are creating
 * the top cgroup in the subsystem.
 *
 * Called only by the ns (nsproxy) cgroup.
 */
int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
{
      int ret;
      struct cgroup *target;
      int subsys_id;

      if (cgrp == dummytop)
            return 1;

      get_first_subsys(cgrp, NULL, &subsys_id);
      target = task_cgroup(task, subsys_id);
      while (cgrp != target && cgrp!= cgrp->top_cgroup)
            cgrp = cgrp->parent;
      ret = (cgrp == target);
      return ret;
}

static void check_for_release(struct cgroup *cgrp)
{
      /* All of these checks rely on RCU to keep the cgroup
       * structure alive */
      if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count)
          && list_empty(&cgrp->children) && !cgroup_has_css_refs(cgrp)) {
            /* Control Group is currently removeable. If it's not
             * already queued for a userspace notification, queue
             * it now */
            int need_schedule_work = 0;
            spin_lock(&release_list_lock);
            if (!cgroup_is_removed(cgrp) &&
                list_empty(&cgrp->release_list)) {
                  list_add(&cgrp->release_list, &release_list);
                  need_schedule_work = 1;
            }
            spin_unlock(&release_list_lock);
            if (need_schedule_work)
                  schedule_work(&release_agent_work);
      }
}

void __css_put(struct cgroup_subsys_state *css)
{
      struct cgroup *cgrp = css->cgroup;
      rcu_read_lock();
      if (atomic_dec_return(&css->refcnt) == 1) {
            if (notify_on_release(cgrp)) {
                  set_bit(CGRP_RELEASABLE, &cgrp->flags);
                  check_for_release(cgrp);
            }
            cgroup_wakeup_rmdir_waiter(cgrp);
      }
      rcu_read_unlock();
}

/*
 * Notify userspace when a cgroup is released, by running the
 * configured release agent with the name of the cgroup (path
 * relative to the root of cgroup file system) as the argument.
 *
 * Most likely, this user command will try to rmdir this cgroup.
 *
 * This races with the possibility that some other task will be
 * attached to this cgroup before it is removed, or that some other
 * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
 * The presumed 'rmdir' will fail quietly if this cgroup is no longer
 * unused, and this cgroup will be reprieved from its death sentence,
 * to continue to serve a useful existence.  Next time it's released,
 * we will get notified again, if it still has 'notify_on_release' set.
 *
 * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
 * means only wait until the task is successfully execve()'d.  The
 * separate release agent task is forked by call_usermodehelper(),
 * then control in this thread returns here, without waiting for the
 * release agent task.  We don't bother to wait because the caller of
 * this routine has no use for the exit status of the release agent
 * task, so no sense holding our caller up for that.
 */
static void cgroup_release_agent(struct work_struct *work)
{
      BUG_ON(work != &release_agent_work);
      mutex_lock(&cgroup_mutex);
      spin_lock(&release_list_lock);
      while (!list_empty(&release_list)) {
            char *argv[3], *envp[3];
            int i;
            char *pathbuf = NULL, *agentbuf = NULL;
            struct cgroup *cgrp = list_entry(release_list.next,
                                        struct cgroup,
                                        release_list);
            list_del_init(&cgrp->release_list);
            spin_unlock(&release_list_lock);
            pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
            if (!pathbuf)
                  goto continue_free;
            if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
                  goto continue_free;
            agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
            if (!agentbuf)
                  goto continue_free;

            i = 0;
            argv[i++] = agentbuf;
            argv[i++] = pathbuf;
            argv[i] = NULL;

            i = 0;
            /* minimal command environment */
            envp[i++] = "HOME=/";
            envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
            envp[i] = NULL;

            /* Drop the lock while we invoke the usermode helper,
             * since the exec could involve hitting disk and hence
             * be a slow process */
            mutex_unlock(&cgroup_mutex);
            call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
            mutex_lock(&cgroup_mutex);
 continue_free:
            kfree(pathbuf);
            kfree(agentbuf);
            spin_lock(&release_list_lock);
      }
      spin_unlock(&release_list_lock);
      mutex_unlock(&cgroup_mutex);
}

static int __init cgroup_disable(char *str)
{
      int i;
      char *token;

      while ((token = strsep(&str, ",")) != NULL) {
            if (!*token)
                  continue;

            for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                  struct cgroup_subsys *ss = subsys[i];

                  if (!strcmp(token, ss->name)) {
                        ss->disabled = 1;
                        printk(KERN_INFO "Disabling %s control group"
                              " subsystem\n", ss->name);
                        break;
                  }
            }
      }
      return 1;
}
__setup("cgroup_disable=", cgroup_disable);

/*
 * Functons for CSS ID.
 */

/*
 *To get ID other than 0, this should be called when !cgroup_is_removed().
 */
unsigned short css_id(struct cgroup_subsys_state *css)
{
      struct css_id *cssid = rcu_dereference(css->id);

      if (cssid)
            return cssid->id;
      return 0;
}

unsigned short css_depth(struct cgroup_subsys_state *css)
{
      struct css_id *cssid = rcu_dereference(css->id);

      if (cssid)
            return cssid->depth;
      return 0;
}

bool css_is_ancestor(struct cgroup_subsys_state *child,
                const struct cgroup_subsys_state *root)
{
      struct css_id *child_id = rcu_dereference(child->id);
      struct css_id *root_id = rcu_dereference(root->id);

      if (!child_id || !root_id || (child_id->depth < root_id->depth))
            return false;
      return child_id->stack[root_id->depth] == root_id->id;
}

static void __free_css_id_cb(struct rcu_head *head)
{
      struct css_id *id;

      id = container_of(head, struct css_id, rcu_head);
      kfree(id);
}

void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
{
      struct css_id *id = css->id;
      /* When this is called before css_id initialization, id can be NULL */
      if (!id)
            return;

      BUG_ON(!ss->use_id);

      rcu_assign_pointer(id->css, NULL);
      rcu_assign_pointer(css->id, NULL);
      spin_lock(&ss->id_lock);
      idr_remove(&ss->idr, id->id);
      spin_unlock(&ss->id_lock);
      call_rcu(&id->rcu_head, __free_css_id_cb);
}

/*
 * This is called by init or create(). Then, calls to this function are
 * always serialized (By cgroup_mutex() at create()).
 */

static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
{
      struct css_id *newid;
      int myid, error, size;

      BUG_ON(!ss->use_id);

      size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
      newid = kzalloc(size, GFP_KERNEL);
      if (!newid)
            return ERR_PTR(-ENOMEM);
      /* get id */
      if (unlikely(!idr_pre_get(&ss->idr, GFP_KERNEL))) {
            error = -ENOMEM;
            goto err_out;
      }
      spin_lock(&ss->id_lock);
      /* Don't use 0. allocates an ID of 1-65535 */
      error = idr_get_new_above(&ss->idr, newid, 1, &myid);
      spin_unlock(&ss->id_lock);

      /* Returns error when there are no free spaces for new ID.*/
      if (error) {
            error = -ENOSPC;
            goto err_out;
      }
      if (myid > CSS_ID_MAX)
            goto remove_idr;

      newid->id = myid;
      newid->depth = depth;
      return newid;
remove_idr:
      error = -ENOSPC;
      spin_lock(&ss->id_lock);
      idr_remove(&ss->idr, myid);
      spin_unlock(&ss->id_lock);
err_out:
      kfree(newid);
      return ERR_PTR(error);

}

static int __init cgroup_subsys_init_idr(struct cgroup_subsys *ss)
{
      struct css_id *newid;
      struct cgroup_subsys_state *rootcss;

      spin_lock_init(&ss->id_lock);
      idr_init(&ss->idr);

      rootcss = init_css_set.subsys[ss->subsys_id];
      newid = get_new_cssid(ss, 0);
      if (IS_ERR(newid))
            return PTR_ERR(newid);

      newid->stack[0] = newid->id;
      newid->css = rootcss;
      rootcss->id = newid;
      return 0;
}

static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
                  struct cgroup *child)
{
      int subsys_id, i, depth = 0;
      struct cgroup_subsys_state *parent_css, *child_css;
      struct css_id *child_id, *parent_id = NULL;

      subsys_id = ss->subsys_id;
      parent_css = parent->subsys[subsys_id];
      child_css = child->subsys[subsys_id];
      depth = css_depth(parent_css) + 1;
      parent_id = parent_css->id;

      child_id = get_new_cssid(ss, depth);
      if (IS_ERR(child_id))
            return PTR_ERR(child_id);

      for (i = 0; i < depth; i++)
            child_id->stack[i] = parent_id->stack[i];
      child_id->stack[depth] = child_id->id;
      /*
       * child_id->css pointer will be set after this cgroup is available
       * see cgroup_populate_dir()
       */
      rcu_assign_pointer(child_css->id, child_id);

      return 0;
}

/**
 * css_lookup - lookup css by id
 * @ss: cgroup subsys to be looked into.
 * @id: the id
 *
 * Returns pointer to cgroup_subsys_state if there is valid one with id.
 * NULL if not. Should be called under rcu_read_lock()
 */
struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
{
      struct css_id *cssid = NULL;

      BUG_ON(!ss->use_id);
      cssid = idr_find(&ss->idr, id);

      if (unlikely(!cssid))
            return NULL;

      return rcu_dereference(cssid->css);
}

/**
 * css_get_next - lookup next cgroup under specified hierarchy.
 * @ss: pointer to subsystem
 * @id: current position of iteration.
 * @root: pointer to css. search tree under this.
 * @foundid: position of found object.
 *
 * Search next css under the specified hierarchy of rootid. Calling under
 * rcu_read_lock() is necessary. Returns NULL if it reaches the end.
 */
struct cgroup_subsys_state *
css_get_next(struct cgroup_subsys *ss, int id,
           struct cgroup_subsys_state *root, int *foundid)
{
      struct cgroup_subsys_state *ret = NULL;
      struct css_id *tmp;
      int tmpid;
      int rootid = css_id(root);
      int depth = css_depth(root);

      if (!rootid)
            return NULL;

      BUG_ON(!ss->use_id);
      /* fill start point for scan */
      tmpid = id;
      while (1) {
            /*
             * scan next entry from bitmap(tree), tmpid is updated after
             * idr_get_next().
             */
            spin_lock(&ss->id_lock);
            tmp = idr_get_next(&ss->idr, &tmpid);
            spin_unlock(&ss->id_lock);

            if (!tmp)
                  break;
            if (tmp->depth >= depth && tmp->stack[depth] == rootid) {
                  ret = rcu_dereference(tmp->css);
                  if (ret) {
                        *foundid = tmpid;
                        break;
                  }
            }
            /* continue to scan from next id */
            tmpid = tmpid + 1;
      }
      return ret;
}


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