1 files changed, 178 insertions, 98 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f221446aa02d..c29831076e7a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -84,7 +84,7 @@ 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 */
@@ -148,8 +148,8 @@ 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
@@ -271,7 +271,7 @@ static void __put_css_set(struct css_set *cg, int taskexit)
 
         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)
@@ -384,6 +384,25 @@ static int allocate_cg_links(int count, struct list_head *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
@@ -399,7 +418,6 @@ static struct css_set *find_css_set(
         int i;
 
         struct list_head tmp_cg_links;
-        struct cg_cgroup_link *link;
 
         struct hlist_head *hhead;
 
@@ -444,26 +462,11 @@ 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));
 
@@ -586,11 +589,18 @@ static void cgroup_call_pre_destroy(struct cgroup *cgrp)
 {
         struct cgroup_subsys *ss;
         for_each_subsys(cgrp->root, ss)
-                if (ss->pre_destroy && cgrp->subsys[ss->subsys_id])
+                if (ss->pre_destroy)
                         ss->pre_destroy(ss, cgrp);
         return;
 }
 
+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 */
@@ -610,19 +620,19 @@ 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);
 }
@@ -712,23 +722,26 @@ 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]);
@@ -990,7 +1003,7 @@ 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;
 
@@ -1031,7 +1044,7 @@ 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
@@ -1042,29 +1055,18 @@ 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);
         }
@@ -1113,10 +1115,9 @@ static void cgroup_kill_sb(struct super_block *sb) {
         }
         write_unlock(&css_set_lock);
 
-        if (!list_empty(&root->root_list)) {
-                list_del(&root->root_list);
-                root_count--;
-        }
+        list_del(&root->root_list);
+        root_count--;
+
         mutex_unlock(&cgroup_mutex);
 
         kfree(root);
@@ -1145,14 +1146,16 @@ 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
@@ -1165,13 +1168,14 @@ 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)
@@ -1216,7 +1220,7 @@ 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;
@@ -1236,11 +1240,16 @@ 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;
 
@@ -1445,7 +1454,7 @@ 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);
@@ -1490,7 +1499,7 @@ static ssize_t cgroup_file_read(struct file *file, 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->read)
@@ -1554,10 +1563,8 @@ 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);
@@ -1671,7 +1678,7 @@ 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);
@@ -1812,6 +1819,7 @@ 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)
@@ -1819,7 +1827,8 @@ 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);
@@ -2013,14 +2022,16 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan)
  */
 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;
@@ -2052,7 +2063,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 
         ret = 0;
         cgrp = dentry->d_fsdata;
-        rcu_read_lock();
 
         cgroup_iter_start(cgrp, &it);
         while ((tsk = cgroup_iter_next(cgrp, &it))) {
@@ -2077,7 +2087,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
         }
         cgroup_iter_end(cgrp, &it);
 
-        rcu_read_unlock();
 err:
         return ret;
 }
@@ -2324,7 +2333,7 @@ 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;
         if (cgrp == dummytop)
                 set_bit(CSS_ROOT, &css->flags);
@@ -2332,6 +2341,29 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
         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_nested(&ss->hierarchy_mutex, i);
+        }
+}
+
+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
@@ -2380,7 +2412,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                 init_cgroup_css(css, ss, cgrp);
         }
 
+        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);
@@ -2431,7 +2465,7 @@ 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
@@ -2452,19 +2486,67 @@ static 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;
+                do {
+                        /* 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
+                         */
+                } while (atomic_cmpxchg(&css->refcnt, refcnt, 0) != refcnt);
+        }
+ 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;
 
         /* the vfs holds both inode->i_mutex already */
 
@@ -2487,12 +2569,10 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
 
         mutex_lock(&cgroup_mutex);
         parent = cgrp->parent;
-        root = cgrp->root;
-        sb = root->sb;
 
         if (atomic_read(&cgrp->count)
             || !list_empty(&cgrp->children)
-            || cgroup_has_css_refs(cgrp)) {
+            || !cgroup_clear_css_refs(cgrp)) {
                 mutex_unlock(&cgroup_mutex);
                 return -EBUSY;
         }
@@ -2502,8 +2582,12 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
         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);
         spin_unlock(&d->d_lock);
@@ -2525,6 +2609,7 @@ 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 */
@@ -2544,6 +2629,7 @@ 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);
         ss->active = 1;
 }
 
@@ -2562,7 +2648,6 @@ int __init cgroup_init_early(void)
         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;
 
@@ -2669,15 +2754,12 @@ 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);
@@ -2800,8 +2882,10 @@ 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);
         }
 }
@@ -2907,6 +2991,7 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
                 mutex_unlock(&cgroup_mutex);
                 return 0;
         }
+        task_lock(tsk);
         cg = tsk->cgroups;
         parent = task_cgroup(tsk, subsys->subsys_id);
 
@@ -2919,6 +3004,7 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
 
         /* Keep the cgroup alive */
         get_css_set(cg);
+        task_unlock(tsk);
         mutex_unlock(&cgroup_mutex);
 
         /* Now do the VFS work to create a cgroup */
@@ -2937,7 +3023,7 @@ 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) {
@@ -2947,13 +3033,6 @@ 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. */
@@ -3049,7 +3128,8 @@ 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)) {
+        if ((atomic_dec_return(&css->refcnt) == 1) &&
+            notify_on_release(cgrp)) {
                 set_bit(CGRP_RELEASABLE, &cgrp->flags);
                 check_for_release(cgrp);
         }