X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=kernel%2Fcgroup.c;h=9edb5c4b79b4f1a88a0487f588c36fc6207f54a9;hb=0c2a498fa6d33d8ca9c8a0c29039c41e1734cb9e;hp=657f8f8d93a5fa947e79d0b8567a9c5288f425d9;hpb=3f8206d496e9e9495afb1d4e70d29712b4d403c9;p=safe%2Fjmp%2Flinux-2.6

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 657f8f8..9edb5c4 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 */
@@ -116,7 +116,6 @@ static int root_count;
  * be called.
  */
 static int need_forkexit_callback __read_mostly;
-static int need_mm_owner_callback __read_mostly;
 
 /* convenient tests for these bits */
 inline int cgroup_is_removed(const struct cgroup *cgrp)
@@ -149,8 +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
@@ -241,7 +240,6 @@ static void unlink_css_set(struct css_set *cg)
 	struct cg_cgroup_link *link;
 	struct cg_cgroup_link *saved_link;
 
-	write_lock(&css_set_lock);
 	hlist_del(&cg->hlist);
 	css_set_count--;
 
@@ -251,20 +249,29 @@ static void unlink_css_set(struct css_set *cg)
 		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)
@@ -276,32 +283,22 @@ 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);
 }
 
 /*
@@ -355,6 +352,17 @@ 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
@@ -363,17 +371,12 @@ static struct css_set *find_existing_css_set(
 static int allocate_cg_links(int count, struct list_head *tmp)
 {
 	struct cg_cgroup_link *link;
-	struct cg_cgroup_link *saved_link;
 	int i;
 	INIT_LIST_HEAD(tmp);
 	for (i = 0; i < count; i++) {
 		link = kmalloc(sizeof(*link), GFP_KERNEL);
 		if (!link) {
-			list_for_each_entry_safe(link, saved_link, tmp,
-						 cgrp_link_list) {
-				list_del(&link->cgrp_link_list);
-				kfree(link);
-			}
+			free_cg_links(tmp);
 			return -ENOMEM;
 		}
 		list_add(&link->cgrp_link_list, tmp);
@@ -381,15 +384,23 @@ 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)
 {
 	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);
-	}
+	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);
 }
 
 /*
@@ -407,7 +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;
 
@@ -432,7 +442,7 @@ 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);
@@ -452,26 +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));
 
@@ -578,9 +573,8 @@ static struct inode *cgroup_new_inode(mode_t mode, struct super_block *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;
 	}
@@ -595,11 +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 */
@@ -619,19 +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);
 }
@@ -709,7 +710,7 @@ 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 */
@@ -721,23 +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]);
@@ -875,6 +879,14 @@ 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;
@@ -883,10 +895,7 @@ 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)
@@ -956,7 +965,6 @@ 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);
@@ -995,7 +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;
 
@@ -1027,7 +1035,7 @@ 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 */
@@ -1036,7 +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
@@ -1047,39 +1055,29 @@ 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);
 
+ free_cg_links:
+	free_cg_links(&tmp_cg_links);
  drop_new_super:
 	up_write(&sb->s_umount);
 	deactivate_super(sb);
-	free_cg_links(&tmp_cg_links);
 	return ret;
 }
 
@@ -1121,10 +1119,11 @@ 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 = {
@@ -1149,14 +1148,16 @@ 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
@@ -1169,13 +1170,14 @@ 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)
@@ -1220,7 +1222,7 @@ 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;
@@ -1240,11 +1242,16 @@ 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;
 
@@ -1282,6 +1289,7 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
 {
 	struct task_struct *tsk;
+	const struct cred *cred = current_cred(), *tcred;
 	int ret;
 
 	if (pid) {
@@ -1291,14 +1299,16 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
 			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);
@@ -1424,14 +1434,17 @@ static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
 		if (buffer == NULL)
 			return -ENOMEM;
 	}
-	if (nbytes && copy_from_user(buffer, userbuf, nbytes))
-		return -EFAULT;
+	if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
+		retval = -EFAULT;
+		goto out;
+	}
 
 	buffer[nbytes] = 0;     /* nul-terminate */
 	strstrip(buffer);
 	retval = cft->write_string(cgrp, cft, buffer);
 	if (!retval)
 		retval = nbytes;
+out:
 	if (buffer != local_buffer)
 		kfree(buffer);
 	return retval;
@@ -1443,7 +1456,7 @@ 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);
@@ -1488,7 +1501,7 @@ 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)
@@ -1552,10 +1565,8 @@ 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);
@@ -1669,7 +1680,7 @@ 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);
@@ -1731,7 +1742,7 @@ int cgroup_task_count(const struct cgroup *cgrp)
 
 	read_lock(&css_set_lock);
 	list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
-		count += atomic_read(&link->cg->ref.refcount);
+		count += atomic_read(&link->cg->refcount);
 	}
 	read_unlock(&css_set_lock);
 	return count;
@@ -1810,6 +1821,7 @@ 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)
@@ -1817,7 +1829,8 @@ 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);
@@ -2000,16 +2013,7 @@ 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
@@ -2020,14 +2024,16 @@ 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;
@@ -2048,15 +2054,17 @@ 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))) {
@@ -2081,7 +2089,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 	}
 	cgroup_iter_end(cgrp, &it);
 
-	rcu_read_unlock();
 err:
 	return ret;
 }
@@ -2091,42 +2098,132 @@ 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;
 
-	for (i = 0; i < npids; i++)
-		cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]);
-	return cnt;
+		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;
+	}
 }
 
+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
@@ -2134,57 +2231,31 @@ 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;
 }
 
@@ -2213,7 +2284,6 @@ static struct cftype files[] = {
 	{
 		.name = "tasks",
 		.open = cgroup_tasks_open,
-		.read = cgroup_tasks_read,
 		.write_u64 = cgroup_tasks_write,
 		.release = cgroup_tasks_release,
 		.private = FILE_TASKLIST,
@@ -2265,7 +2335,7 @@ 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);
@@ -2273,6 +2343,29 @@ 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(&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
@@ -2303,10 +2396,7 @@ 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;
@@ -2324,7 +2414,9 @@ 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);
@@ -2344,7 +2436,9 @@ 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:
@@ -2371,11 +2465,11 @@ 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
@@ -2396,19 +2490,70 @@ 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;
 
 	/* the vfs holds both inode->i_mutex already */
 
@@ -2421,10 +2566,7 @@ 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
@@ -2432,7 +2574,12 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
 	 */
 	cgroup_call_pre_destroy(cgrp);
 
-	if (cgroup_has_css_refs(cgrp)) {
+	mutex_lock(&cgroup_mutex);
+	parent = cgrp->parent;
+
+	if (atomic_read(&cgrp->count)
+	    || !list_empty(&cgrp->children)
+	    || !cgroup_clear_css_refs(cgrp)) {
 		mutex_unlock(&cgroup_mutex);
 		return -EBUSY;
 	}
@@ -2442,11 +2589,14 @@ 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);
-	cgrp->dentry = NULL;
 	spin_unlock(&d->d_lock);
 
 	cgroup_d_remove_dir(d);
@@ -2466,6 +2616,7 @@ 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 */
@@ -2479,13 +2630,14 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 	init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
 
 	need_forkexit_callback |= ss->fork || ss->exit;
-	need_mm_owner_callback |= !!ss->mm_owner_changed;
 
 	/* At system boot, before all subsystems have been
 	 * registered, no tasks have been forked, so we don't
 	 * need to invoke fork callbacks here. */
 	BUG_ON(!list_empty(&init_task.tasks));
 
+	mutex_init(&ss->hierarchy_mutex);
+	lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
 	ss->active = 1;
 }
 
@@ -2498,14 +2650,12 @@ 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;
 
@@ -2612,15 +2762,12 @@ 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);
@@ -2730,34 +2877,6 @@ void cgroup_fork_callbacks(struct task_struct *child)
 	}
 }
 
-#ifdef CONFIG_MM_OWNER
-/**
- * cgroup_mm_owner_callbacks - run callbacks when the mm->owner changes
- * @p: the new owner
- *
- * Called on every change to mm->owner. mm_init_owner() does not
- * invoke this routine, since it assigns the mm->owner the first time
- * and does not change it.
- */
-void cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new)
-{
-	struct cgroup *oldcgrp, *newcgrp;
-
-	if (need_mm_owner_callback) {
-		int i;
-		for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-			struct cgroup_subsys *ss = subsys[i];
-			oldcgrp = task_cgroup(old, ss->subsys_id);
-			newcgrp = task_cgroup(new, ss->subsys_id);
-			if (oldcgrp == newcgrp)
-				continue;
-			if (ss->mm_owner_changed)
-				ss->mm_owner_changed(ss, oldcgrp, newcgrp);
-		}
-	}
-}
-#endif /* CONFIG_MM_OWNER */
-
 /**
  * cgroup_post_fork - called on a new task after adding it to the task list
  * @child: the task in question
@@ -2771,8 +2890,10 @@ 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);
 	}
 }
@@ -2875,20 +2996,24 @@ 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);
 
 	/* 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 */
@@ -2907,7 +3032,7 @@ 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) {
@@ -2917,13 +3042,6 @@ 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. */
@@ -2934,7 +3052,7 @@ 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. */
@@ -2960,7 +3078,7 @@ 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;
 }
 
@@ -3019,7 +3137,8 @@ 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);
 	}