diff --git a/[refs] b/[refs]
index fa71bc1c8063..a478264abaa1 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 9f7de8275b46d9d11b1505adbfe6c2bb48df4741
+refs/heads/master: 42aee6c495e07dba7410b863a360db6bb9ec6d66
diff --git a/trunk/include/linux/cgroup.h b/trunk/include/linux/cgroup.h
index 501adb1b2f43..5a85b3415c1b 100644
--- a/trunk/include/linux/cgroup.h
+++ b/trunk/include/linux/cgroup.h
@@ -498,7 +498,7 @@ struct cgroup_subsys {
 	struct list_head sibling;
 	/* used when use_id == true */
 	struct idr idr;
-	rwlock_t id_lock;
+	spinlock_t id_lock;
 
 	/* should be defined only by modular subsystems */
 	struct module *module;
diff --git a/trunk/kernel/cgroup.c b/trunk/kernel/cgroup.c
index c6877fe9a831..8eb90f25bd7b 100644
--- a/trunk/kernel/cgroup.c
+++ b/trunk/kernel/cgroup.c
@@ -4885,9 +4885,9 @@ void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
 
 	rcu_assign_pointer(id->css, NULL);
 	rcu_assign_pointer(css->id, NULL);
-	write_lock(&ss->id_lock);
+	spin_lock(&ss->id_lock);
 	idr_remove(&ss->idr, id->id);
-	write_unlock(&ss->id_lock);
+	spin_unlock(&ss->id_lock);
 	kfree_rcu(id, rcu_head);
 }
 EXPORT_SYMBOL_GPL(free_css_id);
@@ -4913,10 +4913,10 @@ static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
 		error = -ENOMEM;
 		goto err_out;
 	}
-	write_lock(&ss->id_lock);
+	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);
-	write_unlock(&ss->id_lock);
+	spin_unlock(&ss->id_lock);
 
 	/* Returns error when there are no free spaces for new ID.*/
 	if (error) {
@@ -4931,9 +4931,9 @@ static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
 	return newid;
 remove_idr:
 	error = -ENOSPC;
-	write_lock(&ss->id_lock);
+	spin_lock(&ss->id_lock);
 	idr_remove(&ss->idr, myid);
-	write_unlock(&ss->id_lock);
+	spin_unlock(&ss->id_lock);
 err_out:
 	kfree(newid);
 	return ERR_PTR(error);
@@ -4945,7 +4945,7 @@ static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
 {
 	struct css_id *newid;
 
-	rwlock_init(&ss->id_lock);
+	spin_lock_init(&ss->id_lock);
 	idr_init(&ss->idr);
 
 	newid = get_new_cssid(ss, 0);
@@ -5040,9 +5040,9 @@ css_get_next(struct cgroup_subsys *ss, int id,
 		 * scan next entry from bitmap(tree), tmpid is updated after
 		 * idr_get_next().
 		 */
-		read_lock(&ss->id_lock);
+		spin_lock(&ss->id_lock);
 		tmp = idr_get_next(&ss->idr, &tmpid);
-		read_unlock(&ss->id_lock);
+		spin_unlock(&ss->id_lock);
 
 		if (!tmp)
 			break;