[dm-devel] dm-rq queue stalls

[Bart Van Assche]

On Wed, 2018-01-17 at 15:14 -0500, Mike Snitzer wrote:
> BUT my broader point stands: you aren't testing the dm-4.16 changes.  By
> just reverting that commit you're creating a self-fulfilling prophecy
> (that you'll see hangs without it).
> 
> Fact is you should pull all of dm-4.16 in, see:
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.16
> 
> But these dm-4.16 changes are particularly important:
> 050af08ffb1b dm mpath: return DM_MAPIO_REQUEUE on blk-mq rq allocation failure
> 459b54019cfe dm mpath: return DM_MAPIO_DELAY_REQUEUE if QUEUE_IO or PG_INIT_REQUIRED
> ec3eaf9a6731 dm mpath: don't call blk_mq_delay_run_hw_queue() in case of BLK_STS_RESOURCE
> 4dd6edd23e7e dm mpath: delay the retry of a request if the target responded as busy
> 
> This last one is the commit that _should_ serve as a proper replacement
> for the change you manually reverted in your branch.
> 
> Please re-test after pulling in dm-4.16 and let us know how things fair.

Hello Mike,

If I replace the patch I referred to in my previous e-mail with your dm-4.16
branch then I see the following:
* Without I/O scheduler: dm path removal at the end of the test fails. This
  succeeded reliably in the past so I think this is a regression:
  # srp-test/run_tests -c -d -r 10 -q 1 -t 02-mq
  [ ... ]
  Unmounting /root/mnt1 from /dev/mapper/mpathb
  SRP LUN /sys/class/scsi_device/4:0:0:0 / sdc: removing /dev/dm-1: done
  SRP LUN /sys/class/scsi_device/4:0:0:1 / sde: removing /dev/dm-2: done
  SRP LUN /sys/class/scsi_device/4:0:0:2 / sdd: removing /dev/dm-0: dm=$(dev_to_mpath "/dev/dm-0"): failed
  [ ... ]
* With the Kyber I/O scheduler: I/O hangs.
  # srp-test/run_tests -c -d -r 10 -q 1 -t 02-mq -e kyber
  [ ... ]
  Using /dev/disk/by-id/dm-uuid-mpath-3600140572616d6469736b31000000000 -> ../../dm-0
  (hangs)

I have attached a queue state dump for the last test case to this e-mail.

Bart.

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