On Thu, Jan 18 2018 at  3:58P -0500,
Bart Van Assche [off-list ref] wrote:

On Thu, 2018-01-18 at 15:48 -0500, Mike Snitzer wrote:

quoted

For Bart's test the underlying scsi-mq driver is what is regularly
hitting this case in __blk_mq_try_issue_directly():

        if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))

Hello Mike,

That code path is not the code path that triggered the lockups that I reported
during the past days.

If you're hitting blk_mq_sched_insert_request() then you most certainly
are hitting that code path.

If you aren't then what was your earlier email going on about?
https://www.redhat.com/archives/dm-devel/2018-January/msg00372.html

If you were just focusing on that as one possible reason, that isn't
very helpful.  By this point you really should _know_ what is triggering
the stall based on the code paths taken.  Please use ftrace's
function_graph tracer if need be.

These lockups were all triggered by incorrect handling of
.queue_rq() returning BLK_STS_RESOURCE.

Please be precise, dm_mq_queue_rq()'s return of BLK_STS_RESOURCE?
"Incorrect" because it no longer runs blk_mq_delay_run_hw_queue()?

Please try to do more work analyzing the test case that only you can
easily run (due to srp_test being a PITA).  And less time lobbying for
a change that you don't understand to _really_ be correct.

We have time to get this right, please stop hyperventilating about
"regressions".

Thanks,
Mike