linux-kernel - Re: [PATCH] cfq-iosched: handle failure of cfq group allocation

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Message-ID: <20150209134537.GG3220@htj.duckdns.org>
Date:	Mon, 9 Feb 2015 08:45:37 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	Vivek Goyal <vgoyal@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH] cfq-iosched: handle failure of cfq group allocation

On Mon, Feb 09, 2015 at 04:42:49PM +0300, Konstantin Khlebnikov wrote:
> Cfq_lookup_create_cfqg() allocates struct blkcg_gq using GFP_ATOMIC.
> In cfq_find_alloc_queue() possible allocation failure is not handled.
> As a result kernel oopses on NULL pointer dereference when
> cfq_link_cfqq_cfqg() calls cfqg_get() for NULL pointer.
> 
> Bug was introduced in v3.5 in commit cd1604fab4f9 ("blkcg: factor
> out blkio_group creation"). Prior to that commit cfq group lookup
> had returned pointer to root group as fallback.
> 
> This patch handles this error using existing fallback oom_cfqq.
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

Oops,

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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