Re: Revert "dm mpath: remove unnecessary NVMe branching in favor of scsi_dh checks"

[Mike Snitzer <snitzer@redhat.com>]

On Tue, Mar 13 2018 at  1:02pm -0400,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Tue, Mar 13 2018 at 12:43pm -0400,
> Bart Van Assche <Bart.VanAssche@wdc.com> wrote:
> 
> > On Mon, 2018-03-12 at 21:23 -0400, Mike Snitzer wrote:
> > > Anyway, I'm hopeful I fixed the issue you reported.  Please feel free to
> > > test the 2 topmost commits I've staged in linux-next, via dm-4.16:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.16
> > 
> > So far I haven't seen the crash I reported yesterday in my tests with dm-4.16
> > of this morning. But I see hanging dm requests. I did not see any such issue
> > yesterday with the revert I posted applied on top of dm-4.16. What I see today
> > in the logs is the following:
> > 
> > INFO: task kworker/3:150:1681 blocked for more than 120 seconds
> > 
> > and in debugfs:
> > # (cd /sys/kernel/debug/block/ && grep -r op= .)
> > ./dm-2/requeue_list:00000000df366fff {.op=READ, .cmd_flags=, .rq_flags=SORTED|STARTED|SOFTBARRIER|ELVPRIV|IO_STAT, .state=idle, .tag=-1, .internal_tag=45}
> > ./dm-0/requeue_list:000000008302ea45 {.op=READ, .cmd_flags=, .rq_flags=SORTED|STARTED|SOFTBARRIER|ELVPRIV|IO_STAT, .state=idle, .tag=-1, .internal_tag=211}
> > ./dm-1/requeue_list:000000007ea8ad0e {.op=READ, .cmd_flags=, .rq_flags=SOFTBARRIER|IO_STAT, .state=idle, .tag=428, .internal_tag=-1}
> > ./dm-1/requeue_list:00000000e93ecaa8 {.op=READ, .cmd_flags=, .rq_flags=SOFTBARRIER|IO_STAT, .state=idle, .tag=429, .internal_tag=-1}
> 
> Strange.. but I'll review closer.  Clearly requests aren't getting
> pulled off the request_list

Just a thought: Maybe dm-4.16 (rc4 based) is missing a blk-mq fix?

Might be worth cherry-picking the 2 topmost commits from dm-4.16 into
the linus-based (rc5) tree you reported the original issue against?

(looking at jens' rc5 block pull request, it seems unlikely but...)