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

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Message-ID: <1319010659.29774.3.camel@twins>
Date:	Wed, 19 Oct 2011 09:50:59 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Mike Galbraith <efault@....de>,
	LKML <linux-kernel@...r.kernel.org>,
	Tejun Heo <htejun@...il.com>, Li Zefan <lizf@...fujitsu.com>,
	Paul Menage <paul@...lmenage.org>
Subject: Re: patch] cpusets, cgroups: disallow attaching kthreadd

On Tue, 2011-10-18 at 13:38 -0700, David Rientjes wrote:
> 
> Eek, this seems like complete overkill, there may be cgroups now or in the 
> future that it would be perfectly acceptable to move kthreadd into without 
> any negative effects.  There's no reason to restrict it this broadly, 
> that's why I thought your change to cpusets was fine and acked it.  It's 
> the perfect candidate for what the ->can_attach() pointer for a cgroup can 
> identify is problematic for _that_ cgroup. 

My thinking is that kthreadd is the mother of all kernel threads and the
kernel assumes it can spawn kthreads without constraints, a valid
assumption IMO.

Therefore the kthreadd thread should live in the root cgroup at all
times, irrespective of whatever controllers are or aren't actually safe.


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