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Date: Fri, 23 Apr 2010 15:05:30 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Li Zefan <lizf@cn.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
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On Fri, 23 Apr 2010 14:10:32 +0800
Li Zefan <lizf@cn.fujitsu.com> wrote:

> > 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>
> 
Thank you!.

-Kame

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