linux-kernel - Re: [PATCH] cgroup: fix a race condition in manipulating tsk->cg

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Date:	Wed, 16 Apr 2008 22:16:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Paul Menage <menage@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Paul Jackson <pj@....com>
Subject: Re: [PATCH] cgroup: fix a race condition in manipulating
 tsk->cg_list

On Thu, 17 Apr 2008 13:04:47 +0800 Li Zefan <lizf@...fujitsu.com> wrote:

> > 
> > Yes, that looks like it could be the same one - great. But this
> > corruption can only be triggered the first time you cat a tasks file
> > after a reboot, right? That would partly explain why it was hard to
> > reproduce (at least, I had trouble).
> > 
> 
> Right. I was lucky to trigger this and thus knew how to reproduce.
> 
> > My only thought about the downside of this is that an exiting task
> > that gets stuck somewhere  between setting PF_EXITING and calling
> > cgroup_exit() won't show up in its cgroup's tasks file, since we'll
> > enable cgroup links but skip it. I guess that's not a big deal.
> > 
> 
> Agree. I think it won't be a problem.
> 
> > Maybe it would be better to not do a cgroup_exit() until we're
> > unhashed, so that cgroup_enable_task_cg_list() can't find the exiting
> > task?

So we won't be doing what Paul suggested?
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