Re: [PATCH cgroup/for-3.10] cgroup: make cgroup_mutex outer tothreadgroup_lock

From: Tejun Heo
Date: Wed Mar 20 2013 - 11:04:11 EST

On Wed, Mar 20, 2013 at 08:58:08AM +0800, Li Zefan wrote:
> On 2013/3/20 6:02, Tejun Heo wrote:
> > It doesn't make sense to nest cgroup_mutex inside threadgroup_lock
> > when it should be outer to most all locks used by all cgroup
> > controllers. It was nested inside threadgroup_lock only because some
> > controllers were abusing cgroup_mutex inside controllers leading to
> > locking order inversion.
> >
> > cgroup_mutex is no longer abused by controllers and can be put outer
> > to threadgroup_lock. Reverse the locking order in
> > attach_task_by_pid().
> >
> But the code contrast to the changelog. ;)
> cgroup_mutex is currently outside of threadgroup_lock, and you're making
> it nested inside threadgroup_lock in the code.

Heh heh, thanks for spotting my idiocy. Yeah, the locking order
between the two has been swapped a couple times while writing up the
original threadgroup_lock patch and I misremembered how it was at the
end and got totally confused when writing this patch. Sorry about
that. So, let's leave the locking in cgroup alone. I like
cgroup_mutex to be the outer one.


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