linux-kernel - Re: [PATCH block/for-linus] blkcg: fix use-after-free in __blkg_release_rcu() by making blkcg_gq refcnt an atomic

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Date:	Fri, 20 Jun 2014 12:50:53 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Vivek Goyal <vgoyal@...hat.com>, Tejun Heo <tj@...nel.org>
CC:	Joe Lawrence <joe.lawrence@...atus.com>,
	linux-kernel@...r.kernel.org, Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH block/for-linus] blkcg: fix use-after-free in __blkg_release_rcu()
 by making blkcg_gq refcnt an atomic_t

On 06/20/2014 08:39 AM, Vivek Goyal wrote:
> On Thu, Jun 19, 2014 at 05:42:57PM -0400, Tejun Heo wrote:
>> Hello,
>>
>> So, this patch should do.  Joe, Vivek, can one of you guys please
>> verify that the oops goes away with this patch?
> 
> Hi Tejun,
> 
> This patch seems to fix the issue for me. Tried 10 times and no crash.
> 
> So now one need to hold queue lock for getting refernce on the group
> only if caller does not already have a reference and if group has been
> looked up from some tree/queue etc. I guess only such usage seems to
> be in blkg_create() where we take a reference on parent after looking
> it up.
> 
> This patch looks good to me.
> 
> Acked-by: Vivek Goyal <vgoyal@...hat.com>

Thanks. Tejun, I'll queue this up for this cycle.

-- 
Jens Axboe

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