From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sha Zhengju <handai.szj@gmail.com>
Subject: [PATCH 2/4] memcg: check for proper lock held in mem_cgroup_update_page_stat
Date: Thu, 22 Aug 2013 17:52:11 +0800
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Cc: mhocko@suse.cz,
	kamezawa.hiroyu@jp.fujitsu.com,
	gthelen@google.com,
	linux-mm@kvack.org,
	cgroups@vger.kernel.org,
	linux-fsdevel@vger.kernel.org,
	Sha Zhengju <handai.szj@taobao.com>
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From: Sha Zhengju <handai.szj@taobao.com>

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>
---
 mm/memcontrol.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 24d6d02..0a50871 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2249,6 +2249,7 @@ 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;
-- 
1.7.9.5

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