scsi: move blk_mq_start_request call earlier

Some ATA drivers need the dma drain size workaround, and thus need to
call blk_mq_start_request before the S/G mapping.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 86b1156edb82b9d682df2d59b6964eb41065c9d6..5c5617ec834f005f6253d5327a6661fab79c48ef 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1846,6 +1846,8 @@ static int scsi_mq_prep_fn(struct request *req)
                next_rq->special = bidi_sdb;
        }
 
+       blk_mq_start_request(req);
+
        return scsi_setup_cmnd(sdev, req);
 }
 
@@ -1880,17 +1882,19 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req,
        if (!scsi_host_queue_ready(q, shost, sdev))
                goto out_dec_target_busy;
 
+
        if (!(req->cmd_flags & REQ_DONTPREP)) {
                ret = prep_to_mq(scsi_mq_prep_fn(req));
                if (ret)
                        goto out_dec_host_busy;
                req->cmd_flags |= REQ_DONTPREP;
+       } else {
+               blk_mq_start_request(req);
        }
 
        scsi_init_cmd_errh(cmd);
        cmd->scsi_done = scsi_mq_done;
 
-       blk_mq_start_request(req);
        reason = scsi_dispatch_cmd(cmd);
        if (reason) {
                scsi_set_blocked(cmd, reason);