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SubjectRe: [PATCH] sched, autogroup: fix crash on reboot when autogroup is disabled

* Mike Galbraith <efault@gmx.de> wrote:

> On Sun, 2012-10-28 at 14:19 +0100, Ingo Molnar wrote:
> > * Mike Galbraith <efault@gmx.de> wrote:
> >
> > > On Sun, 2012-10-28 at 11:25 +0100, Ingo Molnar wrote:
> > > > * Mike Galbraith <efault@gmx.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.

'No user intervention' is what happens with new kernel
commandline options, in 99.9999% of the cases.

> > 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.

Thanks!

I'd also suggest to still expose the state of autosched in
/proc/sys, read-only, so that its status can be checked.

Ingo


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