Date: Wed, 20 Mar 2013 08:03:51 -0700
From: Tejun Heo <tj@kernel.org>
To: Li Zefan <lizefan@huawei.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Dave Jones <davej@redhat.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>, cgroups@vger.kernel.org
Subject: Re: [PATCH cgroup/for-3.10] cgroup: make cgroup_mutex outer to
 threadgroup_lock
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 <513A9A67.60909@huawei.com>
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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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