Subject: Re: [PATCH] sched, cgroup: Use exit hook to avoid use-after-free
 crash
From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <efault@gmx.de>
Cc: Miklos Vajna <vmiklos@frugalware.org>,
        shenghui <crosslonelyover@gmail.com>, kernel-janitors@vger.kernel.org,
        linux-kernel@vger.kernel.org, mingo@elte.hu, Greg KH <greg@kroah.com>,
        Paul Turner <pjt@google.com>, Yong Zhang <yong.zhang0@gmail.com>,
        Li Zefan <lizf@cn.fujitsu.com>, Paul Menage <menage@google.com>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Srivatsa Vaddagiri <vatsa@in.ibm.com>
In-Reply-To: <1293209297.14433.4.camel@marge.simson.net>
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Date: Fri, 24 Dec 2010 18:07:37 +0100
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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.


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