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Date: Wed, 16 Apr 2008 22:16:02 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Linux Containers <containers@lists.linux-foundation.org>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Paul Jackson <pj@sgi.com>
Subject: Re: [PATCH] cgroup: fix a race condition in manipulating
 tsk->cg_list
Message-Id: <20080416221602.0a13b94b.akpm@linux-foundation.org>
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On Thu, 17 Apr 2008 13:10:33 +0800 Li Zefan <lizf@cn.fujitsu.com> wrote:

> Andrew Morton wrote:
> > On Wed, 16 Apr 2008 21:17:34 -0700 "Paul Menage" <menage@google.com> wrote:
> > 
> >> On Wed, Apr 16, 2008 at 9:11 PM, Andrew Morton
> >> <akpm@linux-foundation.org> wrote:
> >>>  I don't fully understand the race.  Both paths hold css_set_lock.
> >>>
> >>>  Can you describe it in more detail please?
> >> Task A starts exiting, passes the check for unlinking current->cg_list.
> > 
> > So cgroup_exit() sees !list_empty(tsk->cg_list)
> > 
> 
> cgroup_exit() sees list_empty(tsk->cg_list), then cgroup_enable_task_cg_list()
> links the task to the list, and then the task exited, so the list entry won't
> get deleted.

OK.