Date: Sun, 28 Oct 2012 11:25:20 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Mike Galbraith <efault@gmx.de>
Cc: Xiaotian Feng <xtfeng@gmail.com>, Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, Xiaotian Feng <dannyfeng@tencent.com>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH] sched, autogroup: fix crash on reboot when autogroup is
 disabled
Message-ID: <20121028102520.GA7711@gmail.com>
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* Mike Galbraith <efault@gmx.de> wrote:

> On Fri, 2012-10-26 at 13:29 -0700, Mike Galbraith wrote: 
> > On Sat, 2012-10-20 at 08:38 -0400, Mike Galbraith wrote:
> > 
> > > So what I would do is either let the user decide once at boot, in which
> > > case if off, creating groups would be stupid), or, just rip autogroup
> > > completely out, since systemd is taking over the known universe anyway.
> > 
> > I'm traveling, but have somewhat functional connectivity ATM, so..
> > 
> > Peter: which would prefer.  Simple noautogroup -> autogroup one time
> > only boottime enable, and autogroup lives on (I like it for my laptop)
> > with backport for stable.
> 
> Like so, with bonus points for extra minus signs.
> 
> sched, autogroup: fix crash on reboot when autogroup is disabled
> 
> Between 8323f26ce and 800d4d30, autogroup is a wreck.  With both
> applied, all you have to do to crash a box is disable autogroup
> during boot up, then reboot.. boom, NULL pointer dereference due
> to 800d4d30 not allowing autogroup to move things, and 8323f26ce
> making that the only way to switch runqueues.
> 
> Remove all of the knobs, and make autogroup only go active if the
> user provides 'autogroup' on the command line.  This allows distros
> to offer it, once the user asks for it, it's on.  If the user then
> fiddles with cgroups, tough, once tasks are moved, autogroup won't
> mess with them again unless they call setsid().
> 
> No knobs, no glitz, nada, just a cute little thing folks can turn
> on if they don't want to muck about with cgroups and/or systemd.

Please also keep the Kconfig switch and reuse it to turn on the 
'autogroups' knob.

That way people with existing .config's don't have to change a 
thing to get this functionality.

Thanks,

	Ingo
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