linux-kernel - Re: [patch] cgroups: disallow attaching kthreadd

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Message-ID: <20120403184901.GC27794@dhcp-172-17-108-109.mtv.corp.google.com>
Date:	Tue, 3 Apr 2012 11:49:01 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Mike Galbraith <mgalbraith@...e.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Li Zefan <lizf@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Paul Menage <paul@...lmenage.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] cgroups: disallow attaching kthreadd

On Tue, Apr 03, 2012 at 07:58:26PM +0200, Mike Galbraith wrote:
> @@ -1894,6 +1895,14 @@ int cgroup_attach_task(struct cgroup *cg
>  	if (tsk->flags & PF_EXITING)
>  		return -ESRCH;
>  
> +	/*
> +	 * Workqueue threads may acquire PF_THREAD_BOUND and become
> +	 * trapped in a cpuset, or RT worker may be born in a cgroup
> +	 * with no rt_runtime allocated.  Just say no.
> +	 */
> +	if (tsk == kthreadd_task)
> +		return -EINVAL;
> +
>  	/* Nothing to do if the task is already in that cgroup */
>  	oldcgrp = task_cgroup_from_root(tsk, root);
>  	if (cgrp == oldcgrp)
> @@ -2172,6 +2181,17 @@ static int attach_task_by_pid(struct cgr
>  
>  	if (threadgroup)
>  		tsk = tsk->group_leader;
> +
> +	/*
> +	 * Workqueue threads may acquire PF_THREAD_BOUND and become
> +	 * trapped in a cpuset, or RT worker may be born in a cgroup
> +	 * with no rt_runtime allocated.  Just say no.
> +	 */
> +	if (tsk == kthreadd_task) {
> +		ret = -EINVAL;
> +		goto out_unlock_cgroup;
> +	}

If we have this test here, do we need the same check in
cgroup_attach_task()/

Thanks.

-- 
tejun
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