Convert obvious places to deactivate_locked_super()
[linux-2.6.git] / kernel / cgroup.c
index abc4337..a7267bf 100644 (file)
@@ -45,6 +45,7 @@
 #include <linux/delayacct.h>
 #include <linux/cgroupstats.h>
 #include <linux/hash.h>
+#include <linux/namei.h>
 
 #include <asm/atomic.h>
 
@@ -83,21 +84,16 @@ struct cgroupfs_root {
        /* Tracks how many cgroups are currently defined in hierarchy.*/
        int number_of_cgroups;
 
-       /* A list running through the mounted hierarchies */
+       /* 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. No locking
-        * between setting and use - so if userspace updates this
-        * while child cgroups exist, you could miss a
-        * notification. We ensure that it's always a valid
-        * NUL-terminated string */
+       /* 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
@@ -105,6 +101,39 @@ struct cgroupfs_root {
  */
 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)
+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);
@@ -118,7 +147,7 @@ static int root_count;
  * extra work in the fork/exit path if none of the subsystems need to
  * be called.
  */
-static int need_forkexit_callback;
+static int need_forkexit_callback __read_mostly;
 
 /* convenient tests for these bits */
 inline int cgroup_is_removed(const struct cgroup *cgrp)
@@ -151,8 +180,8 @@ static int notify_on_release(const struct cgroup *cgrp)
 #define for_each_subsys(_root, _ss) \
 list_for_each_entry(_ss, &_root->subsys_list, sibling)
 
-/* for_each_root() allows you to iterate across the active hierarchies */
-#define for_each_root(_root) \
+/* 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
@@ -188,6 +217,8 @@ struct cg_cgroup_link {
 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() */
@@ -219,7 +250,7 @@ static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])
  * 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;
+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
@@ -240,30 +271,41 @@ static int use_task_css_set_links;
  */
 static void unlink_css_set(struct css_set *cg)
 {
-       write_lock(&css_set_lock);
+       struct cg_cgroup_link *link;
+       struct cg_cgroup_link *saved_link;
+
        hlist_del(&cg->hlist);
        css_set_count--;
-       while (!list_empty(&cg->cg_links)) {
-               struct cg_cgroup_link *link;
-               link = list_entry(cg->cg_links.next,
-                                 struct cg_cgroup_link, cg_link_list);
+
+       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);
        }
-       write_unlock(&css_set_lock);
 }
 
-static void __release_css_set(struct kref *k, int taskexit)
+static void __put_css_set(struct css_set *cg, int taskexit)
 {
        int i;
-       struct css_set *cg = container_of(k, struct css_set, ref);
-
+       /*
+        * 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 = cg->subsys[i]->cgroup;
+               struct cgroup *cgrp = rcu_dereference(cg->subsys[i]->cgroup);
                if (atomic_dec_and_test(&cgrp->count) &&
                    notify_on_release(cgrp)) {
                        if (taskexit)
@@ -275,32 +317,22 @@ static void __release_css_set(struct kref *k, int taskexit)
        kfree(cg);
 }
 
-static void release_css_set(struct kref *k)
-{
-       __release_css_set(k, 0);
-}
-
-static void release_css_set_taskexit(struct kref *k)
-{
-       __release_css_set(k, 1);
-}
-
 /*
  * refcounted get/put for css_set objects
  */
 static inline void get_css_set(struct css_set *cg)
 {
-       kref_get(&cg->ref);
+       atomic_inc(&cg->refcount);
 }
 
 static inline void put_css_set(struct css_set *cg)
 {
-       kref_put(&cg->ref, release_css_set);
+       __put_css_set(cg, 0);
 }
 
 static inline void put_css_set_taskexit(struct css_set *cg)
 {
-       kref_put(&cg->ref, release_css_set_taskexit);
+       __put_css_set(cg, 1);
 }
 
 /*
@@ -354,6 +386,17 @@ static struct css_set *find_existing_css_set(
        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
@@ -367,13 +410,7 @@ static int allocate_cg_links(int count, struct list_head *tmp)
        for (i = 0; i < count; i++) {
                link = kmalloc(sizeof(*link), GFP_KERNEL);
                if (!link) {
-                       while (!list_empty(tmp)) {
-                               link = list_entry(tmp->next,
-                                                 struct cg_cgroup_link,
-                                                 cgrp_link_list);
-                               list_del(&link->cgrp_link_list);
-                               kfree(link);
-                       }
+                       free_cg_links(tmp);
                        return -ENOMEM;
                }
                list_add(&link->cgrp_link_list, tmp);
@@ -381,16 +418,23 @@ static int allocate_cg_links(int count, struct list_head *tmp)
        return 0;
 }
 
-static void free_cg_links(struct list_head *tmp)
+/**
+ * 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)
 {
-       while (!list_empty(tmp)) {
-               struct cg_cgroup_link *link;
-               link = list_entry(tmp->next,
-                                 struct cg_cgroup_link,
-                                 cgrp_link_list);
-               list_del(&link->cgrp_link_list);
-               kfree(link);
-       }
+       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);
 }
 
 /*
@@ -408,17 +452,16 @@ static struct css_set *find_css_set(
        int i;
 
        struct list_head tmp_cg_links;
-       struct cg_cgroup_link *link;
 
        struct hlist_head *hhead;
 
        /* First see if we already have a cgroup group that matches
         * the desired set */
-       write_lock(&css_set_lock);
+       read_lock(&css_set_lock);
        res = find_existing_css_set(oldcg, cgrp, template);
        if (res)
                get_css_set(res);
-       write_unlock(&css_set_lock);
+       read_unlock(&css_set_lock);
 
        if (res)
                return res;
@@ -433,7 +476,7 @@ static struct css_set *find_css_set(
                return NULL;
        }
 
-       kref_init(&res->ref);
+       atomic_set(&res->refcount, 1);
        INIT_LIST_HEAD(&res->cg_links);
        INIT_LIST_HEAD(&res->tasks);
        INIT_HLIST_NODE(&res->hlist);
@@ -453,26 +496,11 @@ static struct css_set *find_css_set(
                 * only do it for the first subsystem in each
                 * hierarchy
                 */
-               if (ss->root->subsys_list.next == &ss->sibling) {
-                       BUG_ON(list_empty(&tmp_cg_links));
-                       link = list_entry(tmp_cg_links.next,
-                                         struct cg_cgroup_link,
-                                         cgrp_link_list);
-                       list_del(&link->cgrp_link_list);
-                       list_add(&link->cgrp_link_list, &cgrp->css_sets);
-                       link->cg = res;
-                       list_add(&link->cg_link_list, &res->cg_links);
-               }
-       }
-       if (list_empty(&rootnode.subsys_list)) {
-               link = list_entry(tmp_cg_links.next,
-                                 struct cg_cgroup_link,
-                                 cgrp_link_list);
-               list_del(&link->cgrp_link_list);
-               list_add(&link->cgrp_link_list, &dummytop->css_sets);
-               link->cg = res;
-               list_add(&link->cg_link_list, &res->cg_links);
+               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));
 
@@ -506,10 +534,6 @@ static struct css_set *find_css_set(
  * knows that the cgroup won't be removed, as cgroup_rmdir()
  * needs that mutex.
  *
- * The cgroup_common_file_write handler for operations that modify
- * the cgroup hierarchy holds cgroup_mutex across the entire operation,
- * single threading all such cgroup modifications across the system.
- *
  * 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(),
@@ -574,18 +598,20 @@ 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_DIRTY | BDI_CAP_NO_WRITEBACK,
+       .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_blocks = 0;
+               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;
        }
@@ -596,13 +622,25 @@ static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
  * Call subsys's pre_destroy handler.
  * This is called before css refcnt check.
  */
-static void cgroup_call_pre_destroy(struct cgroup *cgrp)
+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 && cgrp->subsys[ss->subsys_id])
-                       ss->pre_destroy(ss, cgrp);
-       return;
+               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)
@@ -624,19 +662,19 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
                /*
                 * Release the subsystem state objects.
                 */
-               for_each_subsys(cgrp->root, ss) {
-                       if (cgrp->subsys[ss->subsys_id])
-                               ss->destroy(ss, cgrp);
-               }
+               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 */
+               /*
+                * Drop the active superblock reference that we took when we
+                * created the cgroup
+                */
                deactivate_super(cgrp->root->sb);
 
-               kfree(cgrp);
+               call_rcu(&cgrp->rcu_head, free_cgroup_rcu);
        }
        iput(inode);
 }
@@ -689,6 +727,22 @@ static void cgroup_d_remove_dir(struct dentry *dentry)
        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 modified under cgroup's inode->i_mutex;
+ */
+DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
+
+static void cgroup_wakeup_rmdir_waiters(const struct cgroup *cgrp)
+{
+       if (unlikely(test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
+               wake_up_all(&cgroup_rmdir_waitq);
+}
+
 static int rebind_subsystems(struct cgroupfs_root *root,
                              unsigned long final_bits)
 {
@@ -714,7 +768,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
         * any child cgroups exist. This is theoretically supportable
         * but involves complex error handling, so it's being left until
         * later */
-       if (!list_empty(&cgrp->children))
+       if (root->number_of_cgroups > 1)
                return -EBUSY;
 
        /* Process each subsystem */
@@ -726,23 +780,26 @@ static int rebind_subsystems(struct cgroupfs_root *root,
                        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_add(&ss->sibling, &root->subsys_list);
-                       rcu_assign_pointer(ss->root, root);
+                       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;
-                       rcu_assign_pointer(subsys[i]->root, &rootnode);
-                       list_del(&ss->sibling);
+                       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]);
@@ -858,16 +915,16 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
        }
 
        ret = rebind_subsystems(root, opts.subsys_bits);
+       if (ret)
+               goto out_unlock;
 
        /* (re)populate subsystem files */
-       if (!ret)
-               cgroup_populate_dir(cgrp);
+       cgroup_populate_dir(cgrp);
 
        if (opts.release_agent)
                strcpy(root->release_agent_path, opts.release_agent);
  out_unlock:
-       if (opts.release_agent)
-               kfree(opts.release_agent);
+       kfree(opts.release_agent);
        mutex_unlock(&cgroup_mutex);
        mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
        return ret;
@@ -880,6 +937,14 @@ static struct super_operations cgroup_ops = {
        .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_rwsem(&cgrp->pids_mutex);
+}
 static void init_cgroup_root(struct cgroupfs_root *root)
 {
        struct cgroup *cgrp = &root->top_cgroup;
@@ -888,10 +953,7 @@ static void init_cgroup_root(struct cgroupfs_root *root)
        root->number_of_cgroups = 1;
        cgrp->root = root;
        cgrp->top_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_cgroup_housekeeping(cgrp);
 }
 
 static int cgroup_test_super(struct super_block *sb, void *data)
@@ -961,20 +1023,17 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
        struct super_block *sb;
        struct cgroupfs_root *root;
        struct list_head tmp_cg_links;
-       INIT_LIST_HEAD(&tmp_cg_links);
 
        /* First find the desired set of subsystems */
        ret = parse_cgroupfs_options(data, &opts);
        if (ret) {
-               if (opts.release_agent)
-                       kfree(opts.release_agent);
+               kfree(opts.release_agent);
                return ret;
        }
 
        root = kzalloc(sizeof(*root), GFP_KERNEL);
        if (!root) {
-               if (opts.release_agent)
-                       kfree(opts.release_agent);
+               kfree(opts.release_agent);
                return -ENOMEM;
        }
 
@@ -1000,7 +1059,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                root = NULL;
        } else {
                /* New superblock */
-               struct cgroup *cgrp = &root->top_cgroup;
+               struct cgroup *root_cgrp = &root->top_cgroup;
                struct inode *inode;
                int i;
 
@@ -1032,7 +1091,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                if (ret == -EBUSY) {
                        mutex_unlock(&cgroup_mutex);
                        mutex_unlock(&inode->i_mutex);
-                       goto drop_new_super;
+                       goto free_cg_links;
                }
 
                /* EBUSY should be the only error here */
@@ -1041,7 +1100,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                list_add(&root->root_list, &roots);
                root_count++;
 
-               sb->s_root->d_fsdata = &root->top_cgroup;
+               sb->s_root->d_fsdata = root_cgrp;
                root->top_cgroup.dentry = sb->s_root;
 
                /* Link the top cgroup in this hierarchy into all
@@ -1052,39 +1111,29 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                        struct hlist_node *node;
                        struct css_set *cg;
 
-                       hlist_for_each_entry(cg, node, hhead, hlist) {
-                               struct cg_cgroup_link *link;
-
-                               BUG_ON(list_empty(&tmp_cg_links));
-                               link = list_entry(tmp_cg_links.next,
-                                                 struct cg_cgroup_link,
-                                                 cgrp_link_list);
-                               list_del(&link->cgrp_link_list);
-                               link->cg = cg;
-                               list_add(&link->cgrp_link_list,
-                                        &root->top_cgroup.css_sets);
-                               list_add(&link->cg_link_list, &cg->cg_links);
-                       }
+                       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(&cgrp->sibling));
-               BUG_ON(!list_empty(&cgrp->children));
+               BUG_ON(!list_empty(&root_cgrp->sibling));
+               BUG_ON(!list_empty(&root_cgrp->children));
                BUG_ON(root->number_of_cgroups != 1);
 
-               cgroup_populate_dir(cgrp);
+               cgroup_populate_dir(root_cgrp);
                mutex_unlock(&inode->i_mutex);
                mutex_unlock(&cgroup_mutex);
        }
 
-       return simple_set_mnt(mnt, sb);
+       simple_set_mnt(mnt, sb);
+       return 0;
 
- drop_new_super:
-       up_write(&sb->s_umount);
-       deactivate_super(sb);
+ free_cg_links:
        free_cg_links(&tmp_cg_links);
+ drop_new_super:
+       deactivate_locked_super(sb);
        return ret;
 }
 
@@ -1092,6 +1141,8 @@ 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);
 
@@ -1111,10 +1162,9 @@ static void cgroup_kill_sb(struct super_block *sb) {
         * root cgroup
         */
        write_lock(&css_set_lock);
-       while (!list_empty(&cgrp->css_sets)) {
-               struct cg_cgroup_link *link;
-               link = list_entry(cgrp->css_sets.next,
-                                 struct cg_cgroup_link, cgrp_link_list);
+
+       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);
@@ -1125,10 +1175,11 @@ static void cgroup_kill_sb(struct super_block *sb) {
                list_del(&root->root_list);
                root_count--;
        }
+
        mutex_unlock(&cgroup_mutex);
 
-       kfree(root);
        kill_litter_super(sb);
+       kfree(root);
 }
 
 static struct file_system_type cgroup_fs_type = {
@@ -1153,14 +1204,16 @@ static inline struct cftype *__d_cft(struct dentry *dentry)
  * @buf: the buffer to write the path into
  * @buflen: the length of the buffer
  *
- * Called with cgroup_mutex held. Writes path of cgroup into buf.
- * Returns 0 on success, -errno on error.
+ * 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 (cgrp == dummytop) {
+       if (!dentry || cgrp == dummytop) {
                /*
                 * Inactive subsystems have no dentry for their root
                 * cgroup
@@ -1173,13 +1226,14 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
 
        *--start = '\0';
        for (;;) {
-               int len = cgrp->dentry->d_name.len;
+               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)
@@ -1224,7 +1278,7 @@ 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 = tsk->cgroups;
+       struct css_set *cg;
        struct css_set *newcg;
        struct cgroupfs_root *root = cgrp->root;
        int subsys_id;
@@ -1244,11 +1298,16 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
                }
        }
 
+       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;
 
@@ -1276,22 +1335,25 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *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_waiters(cgrp);
        return 0;
 }
 
 /*
- * Attach task with pid 'pid' to cgroup 'cgrp'. Call with
- * cgroup_mutex, may take task_lock of task
+ * 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, char *pidbuf)
+static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
 {
-       pid_t pid;
        struct task_struct *tsk;
+       const struct cred *cred = current_cred(), *tcred;
        int ret;
 
-       if (sscanf(pidbuf, "%d", &pid) != 1)
-               return -EIO;
-
        if (pid) {
                rcu_read_lock();
                tsk = find_task_by_vpid(pid);
@@ -1299,14 +1361,16 @@ static int attach_task_by_pid(struct cgroup *cgrp, char *pidbuf)
                        rcu_read_unlock();
                        return -ESRCH;
                }
-               get_task_struct(tsk);
-               rcu_read_unlock();
 
-               if ((current->euid) && (current->euid != tsk->uid)
-                   && (current->euid != tsk->suid)) {
-                       put_task_struct(tsk);
+               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);
@@ -1317,6 +1381,16 @@ static int attach_task_by_pid(struct cgroup *cgrp, char *pidbuf)
        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,
@@ -1326,12 +1400,54 @@ enum cgroup_filetype {
        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[64];
+       char buffer[CGROUP_LOCAL_BUFFER_SIZE];
        int retval = 0;
        char *end;
 
@@ -1360,68 +1476,39 @@ static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
        return retval;
 }
 
-static ssize_t cgroup_common_file_write(struct cgroup *cgrp,
-                                          struct cftype *cft,
-                                          struct file *file,
-                                          const char __user *userbuf,
-                                          size_t nbytes, loff_t *unused_ppos)
+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)
 {
-       enum cgroup_filetype type = cft->private;
-       char *buffer;
+       char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
        int retval = 0;
+       size_t max_bytes = cft->max_write_len;
+       char *buffer = local_buffer;
 
-       if (nbytes >= PATH_MAX)
+       if (!max_bytes)
+               max_bytes = sizeof(local_buffer) - 1;
+       if (nbytes >= max_bytes)
                return -E2BIG;
-
-       /* +1 for nul-terminator */
-       buffer = kmalloc(nbytes + 1, GFP_KERNEL);
-       if (buffer == NULL)
-               return -ENOMEM;
-
-       if (copy_from_user(buffer, userbuf, nbytes)) {
+       /* 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 out1;
+               goto out;
        }
-       buffer[nbytes] = 0;     /* nul-terminate */
-       strstrip(buffer);       /* strip -just- trailing whitespace */
-
-       mutex_lock(&cgroup_mutex);
 
-       /*
-        * This was already checked for in cgroup_file_write(), but
-        * check again now we're holding cgroup_mutex.
-        */
-       if (cgroup_is_removed(cgrp)) {
-               retval = -ENODEV;
-               goto out2;
-       }
-
-       switch (type) {
-       case FILE_TASKLIST:
-               retval = attach_task_by_pid(cgrp, buffer);
-               break;
-       case FILE_NOTIFY_ON_RELEASE:
-               clear_bit(CGRP_RELEASABLE, &cgrp->flags);
-               if (simple_strtoul(buffer, NULL, 10) != 0)
-                       set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
-               else
-                       clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
-               break;
-       case FILE_RELEASE_AGENT:
-               BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
-               strcpy(cgrp->root->release_agent_path, buffer);
-               break;
-       default:
-               retval = -EINVAL;
-               goto out2;
-       }
-
-       if (retval == 0)
+       buffer[nbytes] = 0;     /* nul-terminate */
+       strstrip(buffer);
+       retval = cft->write_string(cgrp, cft, buffer);
+       if (!retval)
                retval = nbytes;
-out2:
-       mutex_unlock(&cgroup_mutex);
-out1:
-       kfree(buffer);
+out:
+       if (buffer != local_buffer)
+               kfree(buffer);
        return retval;
 }
 
@@ -1431,12 +1518,14 @@ static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
        struct cftype *cft = __d_cft(file->f_dentry);
        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
 
-       if (!cft || cgroup_is_removed(cgrp))
+       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;
@@ -1449,7 +1538,7 @@ static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
                               char __user *buf, size_t nbytes,
                               loff_t *ppos)
 {
-       char tmp[64];
+       char tmp[CGROUP_LOCAL_BUFFER_SIZE];
        u64 val = cft->read_u64(cgrp, cft);
        int len = sprintf(tmp, "%llu\n", (unsigned long long) val);
 
@@ -1461,63 +1550,20 @@ static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
                               char __user *buf, size_t nbytes,
                               loff_t *ppos)
 {
-       char tmp[64];
+       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_common_file_read(struct cgroup *cgrp,
-                                         struct cftype *cft,
-                                         struct file *file,
-                                         char __user *buf,
-                                         size_t nbytes, loff_t *ppos)
-{
-       enum cgroup_filetype type = cft->private;
-       char *page;
-       ssize_t retval = 0;
-       char *s;
-
-       if (!(page = (char *)__get_free_page(GFP_KERNEL)))
-               return -ENOMEM;
-
-       s = page;
-
-       switch (type) {
-       case FILE_RELEASE_AGENT:
-       {
-               struct cgroupfs_root *root;
-               size_t n;
-               mutex_lock(&cgroup_mutex);
-               root = cgrp->root;
-               n = strnlen(root->release_agent_path,
-                           sizeof(root->release_agent_path));
-               n = min(n, (size_t) PAGE_SIZE);
-               strncpy(s, root->release_agent_path, n);
-               mutex_unlock(&cgroup_mutex);
-               s += n;
-               break;
-       }
-       default:
-               retval = -EINVAL;
-               goto out;
-       }
-       *s++ = '\n';
-
-       retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);
-out:
-       free_page((unsigned long)page);
-       return retval;
-}
-
 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 (!cft || cgroup_is_removed(cgrp))
+       if (cgroup_is_removed(cgrp))
                return -ENODEV;
 
        if (cft->read)
@@ -1559,7 +1605,7 @@ static int cgroup_seqfile_show(struct seq_file *m, void *arg)
        return cft->read_seq_string(state->cgroup, cft, m);
 }
 
-int cgroup_seqfile_release(struct inode *inode, struct file *file)
+static int cgroup_seqfile_release(struct inode *inode, struct file *file)
 {
        struct seq_file *seq = file->private_data;
        kfree(seq->private);
@@ -1568,6 +1614,7 @@ int cgroup_seqfile_release(struct inode *inode, struct file *file)
 
 static struct file_operations cgroup_seqfile_operations = {
        .read = seq_read,
+       .write = cgroup_file_write,
        .llseek = seq_lseek,
        .release = cgroup_seqfile_release,
 };
@@ -1580,10 +1627,8 @@ static int cgroup_file_open(struct inode *inode, struct file *file)
        err = generic_file_open(inode, file);
        if (err)
                return err;
-
        cft = __d_cft(file->f_dentry);
-       if (!cft)
-               return -ENODEV;
+
        if (cft->read_map || cft->read_seq_string) {
                struct cgroup_seqfile_state *state =
                        kzalloc(sizeof(*state), GFP_USER);
@@ -1641,10 +1686,10 @@ static struct inode_operations cgroup_dir_inode_operations = {
        .rename = cgroup_rename,
 };
 
-static int cgroup_create_file(struct dentry *dentry, int mode,
+static int cgroup_create_file(struct dentry *dentry, mode_t mode,
                                struct super_block *sb)
 {
-       static struct dentry_operations cgroup_dops = {
+       static const struct dentry_operations cgroup_dops = {
                .d_iput = cgroup_diput,
        };
 
@@ -1687,7 +1732,7 @@ static int cgroup_create_file(struct dentry *dentry, int mode,
  * @mode: mode to set on new directory.
  */
 static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
-                               int mode)
+                               mode_t mode)
 {
        struct dentry *parent;
        int error = 0;
@@ -1697,7 +1742,7 @@ static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
        if (!error) {
                dentry->d_fsdata = cgrp;
                inc_nlink(parent->d_inode);
-               cgrp->dentry = dentry;
+               rcu_assign_pointer(cgrp->dentry, dentry);
                dget(dentry);
        }
        dput(dentry);
@@ -1705,6 +1750,33 @@ static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *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)
@@ -1712,6 +1784,7 @@ int cgroup_add_file(struct cgroup *cgrp,
        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)) {
@@ -1722,7 +1795,8 @@ int cgroup_add_file(struct cgroup *cgrp,
        BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
        dentry = lookup_one_len(name, dir, strlen(name));
        if (!IS_ERR(dentry)) {
-               error = cgroup_create_file(dentry, 0644 | S_IFREG,
+               mode = cgroup_file_mode(cft);
+               error = cgroup_create_file(dentry, mode | S_IFREG,
                                                cgrp->root->sb);
                if (!error)
                        dentry->d_fsdata = (void *)cft;
@@ -1755,15 +1829,11 @@ int cgroup_add_files(struct cgroup *cgrp,
 int cgroup_task_count(const struct cgroup *cgrp)
 {
        int count = 0;
-       struct list_head *l;
+       struct cg_cgroup_link *link;
 
        read_lock(&css_set_lock);
-       l = cgrp->css_sets.next;
-       while (l != &cgrp->css_sets) {
-               struct cg_cgroup_link *link =
-                       list_entry(l, struct cg_cgroup_link, cgrp_link_list);
-               count += atomic_read(&link->cg->ref.refcount);
-               l = l->next;
+       list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
+               count += atomic_read(&link->cg->refcount);
        }
        read_unlock(&css_set_lock);
        return count;
@@ -1842,6 +1912,7 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
 {
        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)
@@ -1849,7 +1920,8 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
        res = list_entry(l, struct task_struct, cg_list);
        /* Advance iterator to find next entry */
        l = l->next;
-       if (l == &res->cgroups->tasks) {
+       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);
@@ -2032,16 +2104,7 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan)
  * but we cannot guarantee that the information we produce is correct
  * unless we produce it entirely atomically.
  *
- * Upon tasks file open(), a struct ctr_struct is allocated, that
- * will have a pointer to an array (also allocated here).  The struct
- * ctr_struct * is stored in file->private_data.  Its resources will
- * be freed by release() when the file is closed.  The array is used
- * to sprintf the PIDs and then used by read().
  */
-struct ctr_struct {
-       char *buf;
-       int bufsz;
-};
 
 /*
  * Load into 'pidarray' up to 'npids' of the tasks using cgroup
@@ -2052,14 +2115,16 @@ struct ctr_struct {
  */
 static int pid_array_load(pid_t *pidarray, int npids, struct cgroup *cgrp)
 {
-       int n = 0;
+       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;
-               pidarray[n++] = task_pid_vnr(tsk);
+               pid = task_pid_vnr(tsk);
+               if (pid > 0)
+                       pidarray[n++] = pid;
        }
        cgroup_iter_end(cgrp, &it);
        return n;
@@ -2080,15 +2145,17 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
        struct cgroup *cgrp;
        struct cgroup_iter it;
        struct task_struct *tsk;
+
        /*
-        * Validate dentry by checking the superblock operations
+        * Validate dentry by checking the superblock operations,
+        * and make sure it's a directory.
         */
-       if (dentry->d_sb->s_op != &cgroup_ops)
+       if (dentry->d_sb->s_op != &cgroup_ops ||
+           !S_ISDIR(dentry->d_inode->i_mode))
                 goto err;
 
        ret = 0;
        cgrp = dentry->d_fsdata;
-       rcu_read_lock();
 
        cgroup_iter_start(cgrp, &it);
        while ((tsk = cgroup_iter_next(cgrp, &it))) {
@@ -2113,7 +2180,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
        }
        cgroup_iter_end(cgrp, &it);
 
-       rcu_read_unlock();
 err:
        return ret;
 }
@@ -2123,42 +2189,132 @@ static int cmppid(const void *a, const void *b)
        return *(pid_t *)a - *(pid_t *)b;
 }
 
+
 /*
- * Convert array 'a' of 'npids' pid_t's to a string of newline separated
- * decimal pids in 'buf'.  Don't write more than 'sz' chars, but return
- * count 'cnt' of how many chars would be written if buf were large enough.
+ * 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 int pid_array_to_buf(char *buf, int sz, pid_t *a, int npids)
+
+static void *cgroup_tasks_start(struct seq_file *s, loff_t *pos)
 {
-       int cnt = 0;
-       int i;
+       /*
+        * 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 *cgrp = s->private;
+       int index = 0, pid = *pos;
+       int *iter;
+
+       down_read(&cgrp->pids_mutex);
+       if (pid) {
+               int end = cgrp->pids_length;
+
+               while (index < end) {
+                       int mid = (index + end) / 2;
+                       if (cgrp->tasks_pids[mid] == pid) {
+                               index = mid;
+                               break;
+                       } else if (cgrp->tasks_pids[mid] <= pid)
+                               index = mid + 1;
+                       else
+                               end = mid;
+               }
+       }
+       /* If we're off the end of the array, we're done */
+       if (index >= cgrp->pids_length)
+               return NULL;
+       /* Update the abstract position to be the actual pid that we found */
+       iter = cgrp->tasks_pids + index;
+       *pos = *iter;
+       return iter;
+}
+
+static void cgroup_tasks_stop(struct seq_file *s, void *v)
+{
+       struct cgroup *cgrp = s->private;
+       up_read(&cgrp->pids_mutex);
+}
+
+static void *cgroup_tasks_next(struct seq_file *s, void *v, loff_t *pos)
+{
+       struct cgroup *cgrp = s->private;
+       int *p = v;
+       int *end = cgrp->tasks_pids + cgrp->pids_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;
+       }
+}
 
-       for (i = 0; i < npids; i++)
-               cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]);
-       return cnt;
+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 *cgrp)
+{
+       down_write(&cgrp->pids_mutex);
+       BUG_ON(!cgrp->pids_use_count);
+       if (!--cgrp->pids_use_count) {
+               kfree(cgrp->tasks_pids);
+               cgrp->tasks_pids = NULL;
+               cgrp->pids_length = 0;
+       }
+       up_write(&cgrp->pids_mutex);
 }
 
+static int cgroup_tasks_release(struct inode *inode, struct file *file)
+{
+       struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
+
+       if (!(file->f_mode & FMODE_READ))
+               return 0;
+
+       release_cgroup_pid_array(cgrp);
+       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 a buffer listing the
+ * Handle an open on 'tasks' file.  Prepare an array containing the
  * process id's of tasks currently attached to the cgroup being opened.
- *
- * Does not require any specific cgroup mutexes, and does not take any.
  */
+
 static int cgroup_tasks_open(struct inode *unused, struct file *file)
 {
        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
-       struct ctr_struct *ctr;
        pid_t *pidarray;
        int npids;
-       char c;
+       int retval;
 
+       /* Nothing to do for write-only files */
        if (!(file->f_mode & FMODE_READ))
                return 0;
 
-       ctr = kmalloc(sizeof(*ctr), GFP_KERNEL);
-       if (!ctr)
-               goto err0;
-
        /*
         * If cgroup gets more users after we read count, we won't have
         * enough space - tough.  This race is indistinguishable to the
@@ -2166,57 +2322,31 @@ static int cgroup_tasks_open(struct inode *unused, struct file *file)
         * show up until sometime later on.
         */
        npids = cgroup_task_count(cgrp);
-       if (npids) {
-               pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
-               if (!pidarray)
-                       goto err1;
-
-               npids = pid_array_load(pidarray, npids, cgrp);
-               sort(pidarray, npids, sizeof(pid_t), cmppid, NULL);
-
-               /* Call pid_array_to_buf() twice, first just to get bufsz */
-               ctr->bufsz = pid_array_to_buf(&c, sizeof(c), pidarray, npids) + 1;
-               ctr->buf = kmalloc(ctr->bufsz, GFP_KERNEL);
-               if (!ctr->buf)
-                       goto err2;
-               ctr->bufsz = pid_array_to_buf(ctr->buf, ctr->bufsz, pidarray, npids);
-
-               kfree(pidarray);
-       } else {
-               ctr->buf = NULL;
-               ctr->bufsz = 0;
-       }
-       file->private_data = ctr;
-       return 0;
-
-err2:
-       kfree(pidarray);
-err1:
-       kfree(ctr);
-err0:
-       return -ENOMEM;
-}
-
-static ssize_t cgroup_tasks_read(struct cgroup *cgrp,
-                                   struct cftype *cft,
-                                   struct file *file, char __user *buf,
-                                   size_t nbytes, loff_t *ppos)
-{
-       struct ctr_struct *ctr = file->private_data;
+       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);
 
-       return simple_read_from_buffer(buf, nbytes, ppos, ctr->buf, ctr->bufsz);
-}
+       /*
+        * Store the array in the cgroup, freeing the old
+        * array if necessary
+        */
+       down_write(&cgrp->pids_mutex);
+       kfree(cgrp->tasks_pids);
+       cgrp->tasks_pids = pidarray;
+       cgrp->pids_length = npids;
+       cgrp->pids_use_count++;
+       up_write(&cgrp->pids_mutex);
 
-static int cgroup_tasks_release(struct inode *unused_inode,
-                                       struct file *file)
-{
-       struct ctr_struct *ctr;
+       file->f_op = &cgroup_tasks_operations;
 
-       if (file->f_mode & FMODE_READ) {
-               ctr = file->private_data;
-               kfree(ctr->buf);
-               kfree(ctr);
+       retval = seq_open(file, &cgroup_tasks_seq_operations);
+       if (retval) {
+               release_cgroup_pid_array(cgrp);
+               return retval;
        }
+       ((struct seq_file *)file->private_data)->private = cgrp;
        return 0;
 }
 
@@ -2226,6 +2356,18 @@ static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
        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
  */
@@ -2233,24 +2375,25 @@ static struct cftype files[] = {
        {
                .name = "tasks",
                .open = cgroup_tasks_open,
-               .read = cgroup_tasks_read,
-               .write = cgroup_common_file_write,
+               .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 = cgroup_common_file_write,
+               .write_u64 = cgroup_write_notify_on_release,
                .private = FILE_NOTIFY_ON_RELEASE,
        },
 };
 
 static struct cftype cft_release_agent = {
        .name = "release_agent",
-       .read = cgroup_common_file_read,
-       .write = cgroup_common_file_write,
+       .read_seq_string = cgroup_release_agent_show,
+       .write_string = cgroup_release_agent_write,
+       .max_write_len = PATH_MAX,
        .private = FILE_RELEASE_AGENT,
 };
 
@@ -2275,6 +2418,17 @@ static int cgroup_populate_dir(struct cgroup *cgrp)
                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;
 }
@@ -2284,14 +2438,38 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
                               struct cgroup *cgrp)
 {
        css->cgroup = cgrp;
-       atomic_set(&css->refcnt, 0);
+       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
@@ -2301,7 +2479,7 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
  * Must be called with the mutex on the parent inode held
  */
 static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
-                            int mode)
+                            mode_t mode)
 {
        struct cgroup *cgrp;
        struct cgroupfs_root *root = parent->root;
@@ -2322,10 +2500,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 
        mutex_lock(&cgroup_mutex);
 
-       INIT_LIST_HEAD(&cgrp->sibling);
-       INIT_LIST_HEAD(&cgrp->children);
-       INIT_LIST_HEAD(&cgrp->css_sets);
-       INIT_LIST_HEAD(&cgrp->release_list);
+       init_cgroup_housekeeping(cgrp);
 
        cgrp->parent = parent;
        cgrp->root = parent->root;
@@ -2341,9 +2516,15 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                        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);
@@ -2363,7 +2544,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 
  err_remove:
 
+       cgroup_lock_hierarchy(root);
        list_del(&cgrp->sibling);
+       cgroup_unlock_hierarchy(root);
        root->number_of_cgroups--;
 
  err_destroy:
@@ -2390,11 +2573,11 @@ static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)
        return cgroup_create(c_parent, dentry, mode | S_IFDIR);
 }
 
-static inline int cgroup_has_css_refs(struct cgroup *cgrp)
+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 0, then there should
+        * 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
@@ -2415,22 +2598,75 @@ static inline int cgroup_has_css_refs(struct cgroup *cgrp)
                 * 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))
+               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;
-       struct super_block *sb;
-       struct cgroupfs_root *root;
+       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);
@@ -2440,32 +2676,59 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
                mutex_unlock(&cgroup_mutex);
                return -EBUSY;
        }
-
-       parent = cgrp->parent;
-       root = cgrp->root;
-       sb = root->sb;
+       mutex_unlock(&cgroup_mutex);
 
        /*
         * Call pre_destroy handlers of subsys. Notify subsystems
         * that rmdir() request comes.
         */
-       cgroup_call_pre_destroy(cgrp);
+       ret = cgroup_call_pre_destroy(cgrp);
+       if (ret)
+               return ret;
 
-       if (cgroup_has_css_refs(cgrp)) {
+       mutex_lock(&cgroup_mutex);
+       parent = cgrp->parent;
+       if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
                mutex_unlock(&cgroup_mutex);
                return -EBUSY;
        }
+       /*
+        * css_put/get is provided for subsys to grab refcnt to css. In typical
+        * case, subsystem has no reference after pre_destroy(). But, under
+        * hierarchy management, some *temporal* refcnt can be hold.
+        * To avoid returning -EBUSY to a user, waitqueue is used. If subsys
+        * is really busy, it should return -EBUSY at pre_destroy(). wake_up
+        * is called when css_put() is called and refcnt goes down to 0.
+        */
+       set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
+       prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
+
+       if (!cgroup_clear_css_refs(cgrp)) {
+               mutex_unlock(&cgroup_mutex);
+               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);
-       /* delete my sibling from parent->children */
+
+       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);
-       cgrp->dentry = NULL;
        spin_unlock(&d->d_lock);
 
        cgroup_d_remove_dir(d);
@@ -2485,6 +2748,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
        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 */
@@ -2504,6 +2768,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
         * 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;
 }
 
@@ -2516,14 +2782,12 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 int __init cgroup_init_early(void)
 {
        int i;
-       kref_init(&init_css_set.ref);
-       kref_get(&init_css_set.ref);
+       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);
-       list_add(&rootnode.root_list, &roots);
        root_count = 1;
        init_task.cgroups = &init_css_set;
 
@@ -2575,6 +2839,8 @@ int __init cgroup_init(void)
                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 */
@@ -2630,15 +2896,12 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
 
        mutex_lock(&cgroup_mutex);
 
-       for_each_root(root) {
+       for_each_active_root(root) {
                struct cgroup_subsys *ss;
                struct cgroup *cgrp;
                int subsys_id;
                int count = 0;
 
-               /* Skip this hierarchy if it has no active subsystems */
-               if (!root->actual_subsys_bits)
-                       continue;
                seq_printf(m, "%lu:", root->subsys_bits);
                for_each_subsys(root, ss)
                        seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
@@ -2761,8 +3024,10 @@ 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);
        }
 }
@@ -2839,16 +3104,17 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
  * 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)
+int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
+                                                       char *nodename)
 {
        struct dentry *dentry;
        int ret = 0;
-       char nodename[MAX_CGROUP_TYPE_NAMELEN];
        struct cgroup *parent, *child;
        struct inode *inode;
        struct css_set *cg;
@@ -2864,22 +3130,24 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys)
  again:
        root = subsys->root;
        if (root == &rootnode) {
-               printk(KERN_INFO
-                      "Not cloning cgroup for unused subsystem %s\n",
-                      subsys->name);
                mutex_unlock(&cgroup_mutex);
                return 0;
        }
-       cg = tsk->cgroups;
-       parent = task_cgroup(tsk, subsys->subsys_id);
-
-       snprintf(nodename, MAX_CGROUP_TYPE_NAMELEN, "node_%d", tsk->pid);
 
        /* Pin the hierarchy */
-       atomic_inc(&parent->root->sb->s_active);
+       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 */
@@ -2898,7 +3166,7 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys)
        }
 
        /* Create the cgroup directory, which also creates the cgroup */
-       ret = vfs_mkdir(inode, dentry, S_IFDIR | 0755);
+       ret = vfs_mkdir(inode, dentry, 0755);
        child = __d_cgrp(dentry);
        dput(dentry);
        if (ret) {
@@ -2908,13 +3176,6 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys)
                goto out_release;
        }
 
-       if (!child) {
-               printk(KERN_INFO
-                      "Couldn't find new cgroup %s\n", nodename);
-               ret = -ENOMEM;
-               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. */
@@ -2925,7 +3186,7 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys)
                mutex_unlock(&inode->i_mutex);
                put_css_set(cg);
 
-               deactivate_super(parent->root->sb);
+               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. */
@@ -2951,23 +3212,24 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys)
        mutex_lock(&cgroup_mutex);
        put_css_set(cg);
        mutex_unlock(&cgroup_mutex);
-       deactivate_super(parent->root->sb);
+       deactivate_super(root->sb);
        return ret;
 }
 
 /**
- * cgroup_is_descendant - see if @cgrp is a descendant of current task's cgrp
+ * 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 the current task's cgroup in
- * the appropriate hierarchy.
+ * 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)
+int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
 {
        int ret;
        struct cgroup *target;
@@ -2977,7 +3239,7 @@ int cgroup_is_descendant(const struct cgroup *cgrp)
                return 1;
 
        get_first_subsys(cgrp, NULL, &subsys_id);
-       target = task_cgroup(current, subsys_id);
+       target = task_cgroup(task, subsys_id);
        while (cgrp != target && cgrp!= cgrp->top_cgroup)
                cgrp = cgrp->parent;
        ret = (cgrp == target);
@@ -3010,9 +3272,12 @@ void __css_put(struct cgroup_subsys_state *css)
 {
        struct cgroup *cgrp = css->cgroup;
        rcu_read_lock();
-       if (atomic_dec_and_test(&css->refcnt) && notify_on_release(cgrp)) {
-               set_bit(CGRP_RELEASABLE, &cgrp->flags);
-               check_for_release(cgrp);
+       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_waiters(cgrp);
        }
        rcu_read_unlock();
 }
@@ -3048,27 +3313,24 @@ static void cgroup_release_agent(struct work_struct *work)
        while (!list_empty(&release_list)) {
                char *argv[3], *envp[3];
                int i;
-               char *pathbuf;
+               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) {
-                       spin_lock(&release_list_lock);
-                       continue;
-               }
-
-               if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0) {
-                       kfree(pathbuf);
-                       spin_lock(&release_list_lock);
-                       continue;
-               }
+               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++] = cgrp->root->release_agent_path;
-               argv[i++] = (char *)pathbuf;
+               argv[i++] = agentbuf;
+               argv[i++] = pathbuf;
                argv[i] = NULL;
 
                i = 0;
@@ -3082,8 +3344,10 @@ static void cgroup_release_agent(struct work_struct *work)
                 * be a slow process */
                mutex_unlock(&cgroup_mutex);
                call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
-               kfree(pathbuf);
                mutex_lock(&cgroup_mutex);
+ continue_free:
+               kfree(pathbuf);
+               kfree(agentbuf);
                spin_lock(&release_list_lock);
        }
        spin_unlock(&release_list_lock);
@@ -3113,3 +3377,232 @@ static int __init cgroup_disable(char *str)
        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;
+}
+