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Date: Fri, 23 Apr 2010 14:10:32 +0800
From: Li Zefan <lizf@cn.fujitsu.com>
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To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
CC: Balbir Singh <balbir@linux.vnet.ibm.com>,
       Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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       LKML <linux-kernel@vger.kernel.org>,
       "akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [BUGFIX][PATCH] memcg rcu lock fix v3
References: <4BD10D59.9090504@cn.fujitsu.com>	<20100423121424.ae47efcb.kamezawa.hiroyu@jp.fujitsu.com>	<4BD118E2.7080307@cn.fujitsu.com>	<4BD11A24.2070500@cn.fujitsu.com>	<20100423125814.01e95bce.kamezawa.hiroyu@jp.fujitsu.com> <20100423130349.f320d0be.kamezawa.hiroyu@jp.fujitsu.com>
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> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> css_id() should be called under rcu_read_lock().
> Following is a report from Li Zefan.
> ==
> ===================================================
> [ INFO: suspicious rcu_dereference_check() usage. ]
> ---------------------------------------------------
> kernel/cgroup.c:4438 invoked rcu_dereference_check() without protection!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 1, debug_locks = 1
> 1 lock held by kswapd0/31:
>  #0:  (swap_lock){+.+.-.}, at: [<c05058bb>] swap_info_get+0x4b/0xd0
> 
> stack backtrace:
...
> 
> And css_is_ancestor() should be called under rcu_read_lock().
> 
> 
> Reported-by: Li Zefan <lizf@cn.fujitsu.com>
> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

With this patch applied, I did some more test, and no warning was triggered.

Tested-by: Li Zefan <lizf@cn.fujitsu.com>

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