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

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Message-ID: <20121028131950.GA15159@gmail.com>
Date:	Sun, 28 Oct 2012 14:19:50 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Galbraith <efault@....de>
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


* 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.

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.

Thanks,

	Ingo
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