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

From: Jens Axboe
Date: Tue Aug 25 2015 - 16:37:04 EST

On 08/05/2015 02:44 PM, Jeff Moyer wrote:
Jens Axboe <axboe@xxxxxxxxx> writes:

On 07/29/2015 08:22 AM, Jeff Moyer wrote:

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

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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