linux-kernel - Re: [PATCH block/for-3.4/core] cfq: fix cfqg ref handling when BLK_CGROUP && !CFQ_GROUP

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Date:	Fri, 16 Mar 2012 12:20:36 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <axboe@...nel.dk>, Vivek Goyal <vgoyal@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH block/for-3.4/core] cfq: fix cfqg ref handling when
 BLK_CGROUP && !CFQ_GROUP_IOSCHED

On Thu, Mar 15, 2012 at 09:35:46AM -0700, Tejun Heo wrote:
> When BLK_CGROUP is enabled but CFQ_GROUP_IOSCHED is, cfq ends up
> calling blkg_get/put() on dummy cfqg leading to the following crash.
> 
>   BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0
>   IP: [<ffffffff813d44d8>] cfq_init_queue+0x258/0x430

> Reported-by: Fengguang Wu <fengguang.wu@...el.com>
> Signed-off-by: Tejun Heo <tj@...nel.org>

Tested-by: Fengguang Wu <fengguang.wu@...el.com>

Thanks for the quick fix!

> ---
> Yeap, forgot to test that config combination.  Fengguang, can you
> please test this patch?  Jens, once Fengguang confirms the fix, can
> you please apply this on top of for-3.4/core along with the pending
> stats updates?
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