scsi: core: Only start the request just before dispatching

This has no change in behavior, but improves the accounting a bit.

Link: https://lore.kernel.org/r/20201005084130.143273-11-hch@lst.deReviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -1557,8 +1557,6 @@ static blk_status_t scsi_prepare_cmd(struct request *req)
 			(struct scatterlist *)(cmd->prot_sdb + 1);
 	}
 
-	blk_mq_start_request(req);
-
 	/*
 	 * Special handling for passthrough commands, which don't go to the ULP
 	 * at all:
@@ -1659,7 +1657,6 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 		req->rq_flags |= RQF_DONTPREP;
 	} else {
 		clear_bit(SCMD_STATE_COMPLETE, &cmd->state);
-		blk_mq_start_request(req);
 	}
 
 	cmd->flags &= SCMD_PRESERVED_FLAGS;
@@ -1672,6 +1669,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 	memset(cmd->sense_buffer, 0, SCSI_SENSE_BUFFERSIZE);
 	cmd->scsi_done = scsi_mq_done;
 
+	blk_mq_start_request(req);
 	reason = scsi_dispatch_cmd(cmd);
 	if (reason) {
 		scsi_set_blocked(cmd, reason);