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

[Meelis Roos]

> 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.
> 
> Reported-by: Meelis Roos <mroos@xxxxxxxx>
> Fixes: 320ae51feed5 ("blk-mq: new multi-queue block IO queueing mechanism")
> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>

It fixes the warning independently of the pata driver - ata_piix 
pata_via pata_serverworks pata_macio 3ware were fixed too.

-- 
Meelis Roos (mroos@xxxxxxxx)