linux-kernel - Re: [PATCH cgroup/for-3.10] cgroup: make cgroup_mutex outer to threadgroup

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Message-ID: <20130320150351.GW3042@htj.dyndns.org>
Date:	Wed, 20 Mar 2013 08:03:51 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	cgroups@...r.kernel.org
Subject: Re: [PATCH cgroup/for-3.10] cgroup: make cgroup_mutex outer to
 threadgroup_lock

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.

Thanks.

-- 
tejun
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