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Subject: Re: [patch] cpusets: allow PF_THREAD_BOUND kworkers to escape from
 a cpuset
From: Mike Galbraith <efault@gmx.de>
To: David Rientjes <rientjes@google.com>
Cc: Tejun Heo <htejun@gmail.com>, Li Zefan <lizf@cn.fujitsu.com>,
        LKML <linux-kernel@vger.kernel.org>, Paul Menage <paul@paulmenage.org>
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Date: Fri, 23 Sep 2011 20:16:47 +0200
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On Fri, 2011-09-23 at 16:33 +0200, Mike Galbraith wrote:

> @@ -1382,9 +1383,10 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
>  	 * set of allowed nodes is unnecessary.  Thus, cpusets are not
>  	 * applicable for such threads.  This prevents checking for success of
>  	 * set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
> -	 * be changed.
> +	 * be changed.  We also disallow attaching kthreadd, to prevent it's
> +	 * child from becoming trapped should it then acquire PF_THREAD_BOUND.
>  	 */
> -	if (tsk->flags & PF_THREAD_BOUND)
> +	if (tsk->flags & PF_THREAD_BOUND || tsk == kthreadd_task)
>  		return -EINVAL;
>  
>  	return 0;

And maybe || is_container_init(tsk) for symmetry.

	-Mike