linux-kernel - Re: [patch|rfc] mtip32x: fix regression introduced by blk-mq per-hctx flush

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Message-ID: <55DCD1E7.8090006@kernel.dk>
Date:	Tue, 25 Aug 2015 14:36:55 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Ming Lei <ming.lei@...onical.com>,
	Sam Bradshaw <sbradshaw@...ron.com>,
	Asai Thambi SP <asamymuthupa@...ron.com>,
	linux-kernel@...r.kernel.org, dmilburn@...hat.com
Subject: Re: [patch|rfc] mtip32x: fix regression introduced by blk-mq per-hctx
 flush

On 08/05/2015 02:44 PM, Jeff Moyer wrote:
> Jens Axboe <axboe@...nel.dk> writes:
>
>> On 07/29/2015 08:22 AM, Jeff Moyer wrote:
>>> Hi,
>>>
>>> After commit f70ced091707 (blk-mq: support per-distpatch_queue flush
>>> machinery), the mtip32xx driver may oops upon module load due to walking
>>> off the end of an array in mtip_init_cmd.  On initialization of the
>>> flush_rq, init_request is called with request_index >= the maximum queue
>>> depth the driver supports.  For mtip32xx, this value is used to index
>>> into an array.  What this means is that the driver will walk off the end
>>> of the array, and either oops or cause random memory corruption.
>>>
>>> The problem is easily reproduced by doing modprobe/rmmod of the mtip32xx
>>> driver in a loop.  I can typically reproduce the problem in about 30
>>> seconds.
>>>
>>> Now, in the case of mtip32xx, it actually doesn't support flush/fua, so
>>> I think we can simply return without doing anything.  In addition, no
>>> other mq-enabled driver does anything with the request_index passed into
>>> init_request(), so no other driver is affected.  However, I'm not really
>>> sure what is expected of drivers.  Ming, what did you envision drivers
>>> would do when initializing the flush requests?
>>
>> This is really a bug in the core, we should not have to work around
>> this in the driver. I'll take a look at this.
>
> Hi, Jens,
>
> Any update on this?

To avoid stalling further on this, I'll apply the simple fix for 4.2 so 
we can move forward. It's a memory corruption issue and should get 
fixed, we can argue details later.

-- 
Jens Axboe

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