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

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Message-ID: <55B8E6D6.7090809@kernel.dk>
Date:	Wed, 29 Jul 2015 08:44:38 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Jeff Moyer <jmoyer@...hat.com>, Ming Lei <ming.lei@...onical.com>,
	Sam Bradshaw <sbradshaw@...ron.com>,
	Asai Thambi SP <asamymuthupa@...ron.com>
CC:	linux-kernel@...r.kernel.org, dmilburn@...hat.com
Subject: Re: [patch|rfc] mtip32x: fix regression introduced by blk-mq per-hctx
 flush

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.

-- 
Jens Axboe

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