6 files changed, 49 insertions, 15 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 68929bad9a6a..7e5303820452 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -680,6 +680,8 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
         struct request_queue *q = hctx->queue;
         struct request *rq;
         LIST_HEAD(rq_list);
+        LIST_HEAD(driver_list);
+        struct list_head *dptr;
         int queued;
 
         WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask));
@@ -706,16 +708,27 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
         }
 
         /*
+         * Start off with dptr being NULL, so we start the first request
+         * immediately, even if we have more pending.
+         */
+        dptr = NULL;
+
+        /*
          * Now process all the entries, sending them to the driver.
          */
         queued = 0;
         while (!list_empty(&rq_list)) {
+                struct blk_mq_queue_data bd;
                 int ret;
 
                 rq = list_first_entry(&rq_list, struct request, queuelist);
                 list_del_init(&rq->queuelist);
 
-                ret = q->mq_ops->queue_rq(hctx, rq, list_empty(&rq_list));
+                bd.rq = rq;
+                bd.list = dptr;
+                bd.last = list_empty(&rq_list);
+
+                ret = q->mq_ops->queue_rq(hctx, &bd);
                 switch (ret) {
                 case BLK_MQ_RQ_QUEUE_OK:
                         queued++;
@@ -734,6 +747,13 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 
                 if (ret == BLK_MQ_RQ_QUEUE_BUSY)
                         break;
+
+                /*
+                 * We've done the first request. If we have more than 1
+                 * left in the list, set dptr to defer issue.
+                 */
+                if (!dptr && rq_list.next != rq_list.prev)
+                        dptr = &driver_list;
         }
 
         if (!queued)
@@ -1153,6 +1173,11 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
         }
 
         if (is_sync) {
+                struct blk_mq_queue_data bd = {
+                        .rq = rq,
+                        .list = NULL,
+                        .last = 1
+                };
                 int ret;
 
                 blk_mq_bio_to_request(rq, bio);
@@ -1162,7 +1187,7 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
                  * error (busy), just add it to our list as we previously
                  * would have done
                  */
-                ret = q->mq_ops->queue_rq(data.hctx, rq, true);
+                ret = q->mq_ops->queue_rq(data.hctx, &bd);
                 if (ret == BLK_MQ_RQ_QUEUE_OK)
                         goto done;
                 else {
diff --git a/drivers/block/mtip32xx/mtip32xx.c b/drivers/block/mtip32xx/mtip32xx.c
index 1bd5f523f8fd..3bd7ca9853a8 100644
--- a/drivers/block/mtip32xx/mtip32xx.c
+++ b/drivers/block/mtip32xx/mtip32xx.c
@@ -3775,9 +3775,10 @@ static bool mtip_check_unal_depth(struct blk_mq_hw_ctx *hctx,
         return false;
 }
 
-static int mtip_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *rq,
-                bool last)
+static int mtip_queue_rq(struct blk_mq_hw_ctx *hctx,
+                         const struct blk_mq_queue_data *bd)
 {
+        struct request *rq = bd->rq;
         int ret;
 
         if (unlikely(mtip_check_unal_depth(hctx, rq)))
diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 2671a3f02f0c..8433bc8ead3d 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -313,15 +313,15 @@ static void null_request_fn(struct request_queue *q)
         }
 }
 
-static int null_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *rq,
-                bool last)
+static int null_queue_rq(struct blk_mq_hw_ctx *hctx,
+                         const struct blk_mq_queue_data *bd)
 {
-        struct nullb_cmd *cmd = blk_mq_rq_to_pdu(rq);
+        struct nullb_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
 
-        cmd->rq = rq;
+        cmd->rq = bd->rq;
         cmd->nq = hctx->driver_data;
 
-        blk_mq_start_request(rq);
+        blk_mq_start_request(bd->rq);
 
         null_handle_cmd(cmd);
         return BLK_MQ_RQ_QUEUE_OK;
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index c6a27d54ad62..cecd3f983e49 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -158,10 +158,11 @@ static void virtblk_done(struct virtqueue *vq)
         spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);
 }
 
-static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req,
-                bool last)
+static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
+                           const struct blk_mq_queue_data *bd)
 {
         struct virtio_blk *vblk = hctx->queue->queuedata;
+        struct request *req = bd->rq;
         struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
         unsigned long flags;
         unsigned int num;
@@ -222,7 +223,7 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req,
                 return BLK_MQ_RQ_QUEUE_ERROR;
         }
 
-        if (last && virtqueue_kick_prepare(vblk->vqs[qid].vq))
+        if (bd->last && virtqueue_kick_prepare(vblk->vqs[qid].vq))
                 notify = true;
         spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9eff8a375132..161dcc93ac75 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1858,9 +1858,10 @@ static void scsi_mq_done(struct scsi_cmnd *cmd)
         blk_mq_complete_request(cmd->request);
 }
 
-static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req,
-                bool last)
+static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
+                         const struct blk_mq_queue_data *bd)
 {
+        struct request *req = bd->rq;
         struct request_queue *q = req->q;
         struct scsi_device *sdev = q->queuedata;
         struct Scsi_Host *shost = sdev->host;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index c9be1589415a..be01d7a687d4 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -79,7 +79,13 @@ struct blk_mq_tag_set {
         struct list_head        tag_list;
 };
 
-typedef int (queue_rq_fn)(struct blk_mq_hw_ctx *, struct request *, bool);
+struct blk_mq_queue_data {
+        struct request *rq;
+        struct list_head *list;
+        bool last;
+};
+
+typedef int (queue_rq_fn)(struct blk_mq_hw_ctx *, const struct blk_mq_queue_data *);
 typedef struct blk_mq_hw_ctx *(map_queue_fn)(struct request_queue *, const int);
 typedef enum blk_eh_timer_return (timeout_fn)(struct request *, bool);
 typedef int (init_hctx_fn)(struct blk_mq_hw_ctx *, void *, unsigned int);