Re: UBSAN: Undefined behaviour in block/blk-mq.c:1459:27 with pata_amd

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On 05/13/2016 09:31 AM, Bartlomiej Zolnierkiewicz wrote:
Does the patch below help?

From: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Subject: [PATCH] blk-mq: fix undefined behaviour in order_to_size()

When this_order variable in blk_mq_init_rq_map() becomes zero
the code incorrectly decrements the variable and passes the result
to order_to_size() helper causing undefined behaviour:

  UBSAN: Undefined behaviour in block/blk-mq.c:1459:27
  shift exponent 4294967295 is too large for 32-bit type 'unsigned int'
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.6.0-rc6-00072-g33656a1 #22

Fix the code by checking this_order variable for not having the zero
value first.

Thanks Bart, added for 4.7.

--
Jens Axboe

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