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

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Message-ID: <alpine.DEB.2.00.1204050055180.13439@chino.kir.corp.google.com>
Date:	Thu, 5 Apr 2012 01:00:20 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Mike Galbraith <mgalbraith@...e.de>
cc:	Tejun Heo <tj@...nel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Menage <paul@...lmenage.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [patch] cgroups: disallow attaching kthreadd

On Thu, 5 Apr 2012, Mike Galbraith wrote:

> That question made perfect sense to me.  Putting a global resource in
> any bin of any sort makes little if any sense.
> 

This has nothing to do with global resources, it has to do with 
PF_THREAD_BOUND since those threads cannot move amongst these cgroups.

For cgroups that do not have anything to do with cpu affinity, 
PF_THREAD_BOUND means nothing to their attachment rules.  This patch is 
addressing kthreadd since it, as the changelog says, has the ability to 
spawn threads that become PF_THREAD_BOUND.  By logic, we then can't allow 
kthreadd to be attached to cgroups where PF_THREAD_BOUND matters either.

I know we've been through several iterations on this over the past several 
months and the patch getting dropped a couple times along the way, but I 
really do appreciate your time and effort spent in developing this fix, 
it's very helpful.
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