From 1e0216aad2ca6877a0652b59d8f82cd371cd13db Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@cmpxchg.org>
Date: Tue, 29 May 2012 15:06:24 -0700
Subject: [PATCH] --- yaml --- r: 308839 b: refs/heads/master c:
 91c63734f6908425903aed69c04035592f18d398 h: refs/heads/master i:   308837:
 ac26583c0bf54598789b408e07dda2d91df0c9cc   308835:
 8d3107683c2799241303916db0cb2a9b7091daa6   308831:
 30911fa6897d65a6ead1a9bf075a5ec31fbcb624 v: v3

---
 [refs]                |  2 +-
 trunk/kernel/cgroup.c | 20 ++++++++++----------
 trunk/mm/memcontrol.c | 14 +++++++++-----
 3 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/[refs] b/[refs]
index 72b9cb92d2b2..c103ea20182a 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 0ce72d4f7333248efbef1f3309770c7edb1b2625
+refs/heads/master: 91c63734f6908425903aed69c04035592f18d398
diff --git a/trunk/kernel/cgroup.c b/trunk/kernel/cgroup.c
index a0c6af34d500..0f3527d6184a 100644
--- a/trunk/kernel/cgroup.c
+++ b/trunk/kernel/cgroup.c
@@ -5132,7 +5132,7 @@ EXPORT_SYMBOL_GPL(css_depth);
  * @root: the css supporsed to be an ancestor of the child.
  *
  * Returns true if "root" is an ancestor of "child" in its hierarchy. Because
- * this function reads css->id, this use rcu_dereference() and rcu_read_lock().
+ * this function reads css->id, the caller must hold rcu_read_lock().
  * But, considering usual usage, the csses should be valid objects after test.
  * Assuming that the caller will do some action to the child if this returns
  * returns true, the caller must take "child";s reference count.
@@ -5144,18 +5144,18 @@ bool css_is_ancestor(struct cgroup_subsys_state *child,
 {
 	struct css_id *child_id;
 	struct css_id *root_id;
-	bool ret = true;
 
-	rcu_read_lock();
 	child_id  = rcu_dereference(child->id);
+	if (!child_id)
+		return false;
 	root_id = rcu_dereference(root->id);
-	if (!child_id
-	    || !root_id
-	    || (child_id->depth < root_id->depth)
-	    || (child_id->stack[root_id->depth] != root_id->id))
-		ret = false;
-	rcu_read_unlock();
-	return ret;
+	if (!root_id)
+		return false;
+	if (child_id->depth < root_id->depth)
+		return false;
+	if (child_id->stack[root_id->depth] != root_id->id)
+		return false;
+	return true;
 }
 
 void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
diff --git a/trunk/mm/memcontrol.c b/trunk/mm/memcontrol.c
index 92675fe8a2ef..faad98e6d17d 100644
--- a/trunk/mm/memcontrol.c
+++ b/trunk/mm/memcontrol.c
@@ -1152,12 +1152,16 @@ struct lruvec *mem_cgroup_lru_move_lists(struct zone *zone,
 static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
 		struct mem_cgroup *memcg)
 {
-	if (root_memcg != memcg) {
-		return (root_memcg->use_hierarchy &&
-			css_is_ancestor(&memcg->css, &root_memcg->css));
-	}
+	bool ret;
 
-	return true;
+	if (root_memcg == memcg)
+		return true;
+	if (!root_memcg->use_hierarchy)
+		return false;
+	rcu_read_lock();
+	ret = css_is_ancestor(&memcg->css, &root_memcg->css);
+	rcu_read_unlock();
+	return ret;
 }
 
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)