linux-kernel - Re: [PATCH] sched, autogroup: fix crash on reboot when autogroup is disabled

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Date:	Sun, 28 Oct 2012 06:33:21 -0700
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Xiaotian Feng <xtfeng@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Xiaotian Feng <dannyfeng@...cent.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] sched, autogroup: fix crash on reboot when autogroup is
 disabled

On Sun, 2012-10-28 at 14:19 +0100, Ingo Molnar wrote: 
> * Mike Galbraith <efault@....de> wrote:
> 
> > On Sun, 2012-10-28 at 11:25 +0100, Ingo Molnar wrote: 
> > > * Mike Galbraith <efault@....de> wrote:
> > > 
> > 
> > > > 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.
> > 
> > The Kconfig option is still there.  The noautogroup -> 
> > autogroup arg change just makes it off by default (since an 
> > on/off switch would have to be a full move everybody thing 
> > post 8323f26ce race fix), so distros can make it available in 
> > their swiss army knife config, but it'll be out of the way 
> > unless specifically asked for by the user at boot.
> > 
> > I can make it default 'on' by removing that arg change if you 
> > think that's the better way to go, but opt in at boot sounded 
> > better to me given there is no runtime on/off switch at all 
> > now.
> 
> If I got your patch right then adding a command line option to 
> turn it on will disable it in essence for pretty much everyone 
> who has CONFIG_SCHED_AUTOGROUP=y in their .config today.

With no user intervention, yes.

> The patch should not change the defaults for existing .config's. 
> 
> I.e. if autogroups was off, it should stay off, but if 
> autogroups was enabled in the .config and the kernel booted with 
> it enabled, then it should continue to do so in the future as 
> well.
> 
> Adding a boot tweak and removing the runtime knobs is OK - 
> changing the current default functionality is not.

Ok, I'll whack the arg change and respin.

-Mike

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