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

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Message-ID: <54D8ECEF.5040609@kernel.dk>
Date:	Mon, 09 Feb 2015 10:22:55 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	linux-kernel@...r.kernel.org
CC:	Tejun Heo <tj@...nel.org>, Vivek Goyal <vgoyal@...hat.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH] cfq-iosched: handle failure of cfq group allocation

On 02/09/2015 06:42 AM, 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.

Thanks, added and marked for stable as well.

-- 
Jens Axboe

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