dm: requeue from blk-mq dm_mq_queue_rq() using BLK_MQ_RQ_QUEUE_BUSY

Use BLK_MQ_RQ_QUEUE_BUSY to requeue a blk-mq request directly from the
DM blk-mq device's .queue_rq.  This cleans up the previous convoluted
handling of request requeueing that would return BLK_MQ_RQ_QUEUE_OK
(even though it wasn't) and then run blk_mq_requeue_request() followed
by blk_mq_kick_requeue_list().

Also, document that DM blk-mq ontop of old request_fn devices cannot
fail in clone_rq() since the clone request is preallocated as part of
the pdu.

Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 1c62ed8d09f41e13a3e8ca97d669309fe9a66721..1badfb250a182cfeafe685f7626145792d27a0ed 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2754,13 +2754,15 @@ static int dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
        if (dm_table_get_type(map) == DM_TYPE_REQUEST_BASED) {
                /* clone request is allocated at the end of the pdu */
                tio->clone = (void *)blk_mq_rq_to_pdu(rq) + sizeof(struct dm_rq_target_io);
-               if (!clone_rq(rq, md, tio, GFP_ATOMIC))
-                       return BLK_MQ_RQ_QUEUE_BUSY;
+               (void) clone_rq(rq, md, tio, GFP_ATOMIC);
                queue_kthread_work(&md->kworker, &tio->work);
        } else {
                /* Direct call is fine since .queue_rq allows allocations */
-               if (map_request(tio, rq, md) == DM_MAPIO_REQUEUE)
-                       dm_requeue_unmapped_original_request(md, rq);
+               if (map_request(tio, rq, md) == DM_MAPIO_REQUEUE) {
+                       /* Undo dm_start_request() before requeuing */
+                       rq_completed(md, rq_data_dir(rq), false);
+                       return BLK_MQ_RQ_QUEUE_BUSY;
+               }
        }
 
        return BLK_MQ_RQ_QUEUE_OK;