Re: [PATCH] Revert "scsi-mq: Always unprepare before requeuing a request"

Damien Le Moal
2017-08-17T00:42:10Z

Martin,

On 8/17/17 09:11, Martin K. Petersen wrote:
>
> Bart,
>
>> For an unknown reason this patch causes the boot process to hang on
>> PowerPC systems:
>
> OK, dropped it from fixes for now.
>
> Thanks!

It means that commit 70e42fd02c46e2aa9ab07b766d418637e3a51de7 "scsi:
sd_zbc: Write unlock zone from sd_uninit_cmnd()" will need to be
reverted too as it will not solve the potential deadlock anymore. Bart's
patch was needed for it to work.

So we are back to the initial patch I sent that Chirstoph nacked, that
is, not write locking zones with scsi-mq to avoid deadlocking (blk-mq
does not dispatch write requests in order anyway, so SMR does not work
with mq for now).

Other solutions would be:
1) Do not change the zone locking and add a big fat warning for scanned
zoned block devices that things can get nasty
2) Fail initialization of zoned block devices with scsi-mq (do not
create the block devices)

(2) may actually be the better solution for now until I get a fix for
blk-mq.

Thoughts ?

Best regards.

--
Damien Le Moal,
Western Digital