linux-kernel - Re: [PATCH] sched, cgroup: Use exit hook to avoid use-after-free crash

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Message-ID: <1293211491.15747.3.camel@marge.simson.net>
Date:	Fri, 24 Dec 2010 18:24:51 +0100
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Miklos Vajna <vmiklos@...galware.org>,
	shenghui <crosslonelyover@...il.com>,
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, Greg KH <greg@...ah.com>,
	Paul Turner <pjt@...gle.com>,
	Yong Zhang <yong.zhang0@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Paul Menage <menage@...gle.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>
Subject: Re: [PATCH] sched, cgroup: Use exit hook to avoid use-after-free
 crash

On Fri, 2010-12-24 at 18:07 +0100, Peter Zijlstra wrote:
> On Fri, 2010-12-24 at 17:48 +0100, Mike Galbraith wrote:
> > On Fri, 2010-12-24 at 16:59 +0100, Peter Zijlstra wrote:
> > 
> > > So cgroup moves a task without calling cgroup_subsys::attach() which is
> > > odd, but it does have an ::exit method, sadly it calls that _before_
> > > re-assigning the task, which means we have to jump through some hoops.
> > 
> > Could you do the move in cgroup_exit() in the CONFIG_PREEMPT case?
> 
> I'm not really comfortable relying on that.. voluntary might just grow a
> cond_resched() somewhere in the exit path and lead us down the same
> path, also I think that !preempt smp might have the same race.

Yeah, good point.

	-Mike


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