On 02/20/16 15:12, Mike Snitzer wrote:
> On Fri, Feb 19 2016 at 2:42pm -0500, Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
>> Have you been running with blk-mq?
>> Either by setting CONFIG_DM_MQ_DEFAULT or:
>> echo Y > /sys/module/dm_mod/parameters/use_blk_mq
>>
>> I'm seeing test_02_sdev_delete fail with blk-mq enabled.
>
> I only see failure if I stack dm-mq ontop of old non-mq scsi devices with:
>
> echo N > /sys/module/scsi_mod/parameters/use_blk_mq
> echo Y > /sys/module/dm_mod/parameters/use_blk_mq
Ah, I didn't test that combination. I can see the failure, too.
> But this makes me think the novelty of having dm-mq support stacking on
> non-blk-mq devices was misplaced. It is a senseless config. I'll
> probably remove support for such stacking soon (next week).
Looking at the failure, I suspect it could be a common issue of dm-mq
regardless of underlying device type.
When requeueing, following calls happen in dm-mq:
dm_requeue_original_request() {
..
blk_mq_requeue_request(rq);
blk_mq_kick_requeue_list(rq->q);
then from block workqueue:
blk_mq_requeue_work() {
..
blk_mq_start_hw_queue(q);
and blk_mq_start_hw_queue() re-starts the queue even if DM has
stopped it for suspending. As a result, dm-mq ends up repeating
submit-error-requeue forever and suspend never completes. Or,
suspend somehow proceeds to clear DMF_NOFLUSH_SUSPENDING and
I/O error may directly be returned to submitter.
Attached patch fixes the problem for DM. But given the code comment,
there should be call sites which depend on 'start-if-stopped' behavior
of blk_mq_requeue_work and we may need other solution.
--
Jun'ichi Nomura, NEC Corporation
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 56c0a72..bbfe936 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -481,11 +481,7 @@ static void blk_mq_requeue_work(struct work_struct *work)
blk_mq_insert_request(rq, false, false, false);
}
- /*
- * Use the start variant of queue running here, so that running
- * the requeue work will kick stopped queues.
- */
- blk_mq_start_hw_queues(q);
+ blk_mq_run_hw_queues(q, false);
}
void blk_mq_add_to_requeue_list(struct request *rq, bool at_head)
--
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