linux-kernel - Re: patch] cpusets, cgroups: disallow attaching kthreadd

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Date:	Tue, 18 Oct 2011 01:16:07 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Mike Galbraith <efault@....de>
cc:	LKML <linux-kernel@...r.kernel.org>, Tejun Heo <htejun@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Paul Menage <paul@...lmenage.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: patch] cpusets, cgroups: disallow attaching kthreadd

On Tue, 18 Oct 2011, Mike Galbraith wrote:

> Ahem, the buildable copy..
> 
> I've been asked to add this toe saver to the trees I work on at least
> until something better comes along.  ACK/NACK equally understandable
> given the infrequency of the toe shooting, and user's right to do so.
> 
> Off you go, fly or die little patchlet.
> 

Heh.

> cpusets, cgroups: disallow attaching kthreadd
> 
> Allowing kthreadd to be moved to a non-root group makes no sense, it being
> a global resource, and needlessly leads unsuspecting users toward trouble.
> 
> 1. An RT workqueue worker thread spawned in a task group with no rt_runtime
> allocated is not schedulable.  Simple user error, but harmful to the box.
> 
> 2. A worker thread which acquires PF_THREAD_BOUND can never leave a cpuset,
> rendering the cpuset immortal.
> 
> Save the user some unexpected trouble, just say no.
> 
> Signed-off-by: Mike Galbraith <efault@....de>

Acked-by: David Rientjes <rientjes@...gle.com>
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