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

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Date:	Tue, 6 Dec 2011 14:47:21 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Mike Galbraith <efault@....de>, Paul Menage <paul@...lmenage.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Tejun Heo <htejun@...il.com>, Li Zefan <lizf@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch-final] Re: patch] cpusets, cgroups: disallow attaching
 kthreadd

On Tue, 6 Dec 2011 12:13:10 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> On Thu, 10 Nov 2011, David Rientjes wrote:
> 
> > On Wed, 26 Oct 2011, David Rientjes wrote:
> > 
> > > On Wed, 19 Oct 2011, Mike Galbraith wrote:
> > > 
> > > > 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>
> > > > Acked-by: Paul Menage <paul@...lmenage.org>
> > > > 
> > > 
> > > Let's add Andrew to the cc so we can get it in -mm, I haven't seen it hit 
> > > linux-next yet.
> > > 
> > 
> > Ping?  Still missing from -mm and linux-next.
> > 
> 
> Ping #2?
> 

Why am I being pinged about scheduler patches?  My sole contribution
to this one is to point out that "its"->possessive and "it's"->"it is".

Also, Peter has said

: I really think that if we want to restrain userspace from doing
: something stupid we might as well do something that makes sense, and
: that is mandate kthreadd stays in the root group at all times for
: everybody.

which appears to be what the patch already did, so I'm confused again.

It's time for a fresh resend, IMO.
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