From 658b72c5a7a033f0dde61b15dff86bf423ce425e Mon Sep 17 00:00:00 2001
From: Sha Zhengju <handai.szj@taobao.com>
Date: Thu, 12 Sep 2013 15:13:52 -0700
Subject: [PATCH] memcg: check for proper lock held in
 mem_cgroup_update_page_stat

We should call mem_cgroup_begin_update_page_stat() before
mem_cgroup_update_page_stat() to get proper locks, however the latter
doesn't do any checking that we use proper locking, which would be hard.
Suggested by Michal Hock we could at least test for rcu_read_lock_held()
because RCU is held if !mem_cgroup_disabled().

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Greg Thelen <gthelen@google.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/memcontrol.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f3803462a7e6..0093bc36c5fc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2225,6 +2225,7 @@ void mem_cgroup_update_page_stat(struct page *page,
 	if (mem_cgroup_disabled())
 		return;
 
+	VM_BUG_ON(!rcu_read_lock_held());
 	memcg = pc->mem_cgroup;
 	if (unlikely(!memcg || !PageCgroupUsed(pc)))
 		return;
-- 
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