linux-kernel - Re: [PATCH] cgroups: fix a css_set not found bug in cgroup_attach

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Message-ID: <20111215212329.GH32002@google.com>
Date:	Thu, 15 Dec 2011 13:23:29 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Mandeep Singh Baines <msb@...omium.org>
Cc:	Li Zefan <lizf@...fujitsu.com>, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	stable@...nel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <paul@...lmenage.org>,
	Olof Johansson <olofj@...omium.org>
Subject: Re: [PATCH] cgroups: fix a css_set not found bug in
 cgroup_attach_proc

On Thu, Dec 15, 2011 at 11:36:43AM -0800, Mandeep Singh Baines wrote:
> There is a BUG when migrating a PF_EXITING proc. Since css_set_prefetch()
> is not called for the PF_EXITING case, find_existing_css_set() will return
> NULL inside cgroup_task_migrate() causing a BUG.
> 
> This bug is easy to reproduce. Create a zombie and echo its pid to
> cgroup.procs.
> 
> $ cat zombie.c
> \#include <unistd.h>
> 
> int main()
> {
>   if (fork())
>       pause();
>   return 0;
> }
> $
> 
> We are hitting this bug pretty regularly on ChromeOS.
> 
> This bug is already fixed by Tejun Heo's cgroup patchset which is
> targetted for the next merge window:
> 
> https://lkml.org/lkml/2011/11/1/356
> 
> I've create a smaller patch here which just fixes this bug so that a
> fix can be merged into the current release and stable.

Looks safe to me.  Li?

Thanks.

-- 
tejun
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