From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH] cgroup: make sure that decisions in __css_put are atomic
Date: Thu, 7 Jun 2012 10:54:30 +0900
Message-ID: <20120607015430.GG21357@google.com>
References: <20120605215019.4722.31817.stgit@dungbeetle.mtv.corp.google.com>
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To: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Cc: Salman Qazi <sqazi-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

On Wed, Jun 06, 2012 at 03:31:19PM +0800, Li Zefan wrote:
> Salman Qazi wrote:
> 
> > __css_put is using atomic_dec on the ref count, and then
> > looking at the ref count to make decisions.  This is prone
> > to races, as someone else may decrement ref count between
> > our decrement and our decision.  Instead, we should base our
> > decisions on the value that we decremented the ref count to.
> > 
> > (This results in an actual race on Google's kernel which I
> > haven't been able to reproduce on the upstream kernel.  Having
> > said that, it's still incorrect by inspection).
> > 
> > Signed-off-by: Salman Qazi <sqazi-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> 
> 
> Acked-by: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
> 
> Good catch! This patch should be backported for 3.4.

Applied to for-3.5-fixes w/ stable@ added.

Thanks.

-- 
tejun