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Date:	Mon, 16 May 2016 09:55:31 -0600
From:	Jens Axboe <>
To:	Bartlomiej Zolnierkiewicz <>,
	Meelis Roos <>
Cc:	Linux Kernel list <>,,,
	Tejun Heo <>
Subject: Re: UBSAN: Undefined behaviour in block/blk-mq.c:1459:27 with

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