linux-kernel - Re: BUG: cgroup_task_counter subsys may crash with whole-threadgroup move

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Message-ID: <4E9BD73B.7060405@cn.fujitsu.com>
Date:	Mon, 17 Oct 2011 15:20:27 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Ben Blum <bblum@...rew.cmu.edu>
CC:	Frederic Weisbecker <fweisbec@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Paul Menage <paul@...lmenage.org>, linux-kernel@...r.kernel.org
Subject: Re: BUG: cgroup_task_counter subsys may crash with whole-threadgroup
 move

08:09, Ben Blum wrote:
> I was testing some patches for cgroup_attach_proc and managed to cause a
> crash with the following usage pattern:
> 
>     mount -t cgroup none -o tasks /dev/cgroup
>     cd /dev/cgroup
>     mkdir foo
>     echo $PID > foo/cgroup.procs
>     echo $PID > tasks
>     echo $PID > foo/cgroup.procs
> 
> Where $PID is the thread ID of a member of a multithreaded process (my
> test program just does CLONE_THREAD 8 times and then all threads sleep).
> (It doesn't matter if the thread is the group leader or not, but a
> single-threaded process doesn't crash.)
> 
> And get the following kernel panic:
> http://maximegalon.andrew.cmu.edu/cgroup-taskstats/panic.txt
> 
> It's deterministic, and happens only when the "tasks" subsystem is
> mounted.
> 
> I'm using user-mode linux to test, with the following config:
> http://maximegalon.andrew.cmu.edu/cgroup-taskstats/config.txt
> 
> and I ran it in GDB to get the following backtrace:
> http://maximegalon.andrew.cmu.edu/cgroup-taskstats/bt.txt
> 

I've figured out what's wrong. Patch will be sent out soon.

Thanks for reporting this!

--
Li Zefan
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