[PATCH 7/8] blk-mq: use bd->last == true for list inserts

[axboe@kernel.dk (Jens Axboe)]

If we are issuing a list of requests, we know if we're at the last one.
If we fail issuing, ensure that we call ->commits_rqs() to flush any
potential previous requests.

Signed-off-by: Jens Axboe <axboe at kernel.dk>
---
 block/blk-core.c |  2 +-
 block/blk-mq.c   | 32 ++++++++++++++++++++++++--------
 block/blk-mq.h   |  2 +-
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index c9758d185357..808a65d23f1a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1334,7 +1334,7 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *
 	 * bypass a potential scheduler on the bottom device for
 	 * insert.
 	 */
-	return blk_mq_request_issue_directly(rq);
+	return blk_mq_request_issue_directly(rq, true);
 }
 EXPORT_SYMBOL_GPL(blk_insert_cloned_request);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 6a249bf6ed00..0a12cec0b426 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1260,6 +1260,14 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 	if (!list_empty(list)) {
 		bool needs_restart;
 
+		/*
+		 * If we didn't flush the entire list, we could have told
+		 * the driver there was more coming, but that turned out to
+		 * be a lie.
+		 */
+		if (q->mq_ops->commit_rqs)
+			q->mq_ops->commit_rqs(hctx);
+
 		spin_lock(&hctx->lock);
 		list_splice_init(list, &hctx->dispatch);
 		spin_unlock(&hctx->lock);
@@ -1736,12 +1744,12 @@ static blk_qc_t request_to_qc_t(struct blk_mq_hw_ctx *hctx, struct request *rq)
 
 static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 					    struct request *rq,
-					    blk_qc_t *cookie)
+					    blk_qc_t *cookie, bool last)
 {
 	struct request_queue *q = rq->q;
 	struct blk_mq_queue_data bd = {
 		.rq = rq,
-		.last = true,
+		.last = last,
 	};
 	blk_qc_t new_cookie;
 	blk_status_t ret;
@@ -1776,7 +1784,7 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 						struct request *rq,
 						blk_qc_t *cookie,
-						bool bypass_insert)
+						bool bypass_insert, bool last)
 {
 	struct request_queue *q = rq->q;
 	bool run_queue = true;
@@ -1805,7 +1813,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 		goto insert;
 	}
 
-	return __blk_mq_issue_directly(hctx, rq, cookie);
+	return __blk_mq_issue_directly(hctx, rq, cookie, last);
 insert:
 	if (bypass_insert)
 		return BLK_STS_RESOURCE;
@@ -1824,7 +1832,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 
 	hctx_lock(hctx, &srcu_idx);
 
-	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false);
+	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false, true);
 	if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
 		blk_mq_sched_insert_request(rq, false, true, false);
 	else if (ret != BLK_STS_OK)
@@ -1833,7 +1841,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 	hctx_unlock(hctx, srcu_idx);
 }
 
-blk_status_t blk_mq_request_issue_directly(struct request *rq)
+blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 {
 	blk_status_t ret;
 	int srcu_idx;
@@ -1841,7 +1849,7 @@ blk_status_t blk_mq_request_issue_directly(struct request *rq)
 	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
 	hctx_lock(hctx, &srcu_idx);
-	ret = __blk_mq_try_issue_directly(hctx, rq, &unused_cookie, true);
+	ret = __blk_mq_try_issue_directly(hctx, rq, &unused_cookie, true, last);
 	hctx_unlock(hctx, srcu_idx);
 
 	return ret;
@@ -1856,7 +1864,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 				queuelist);
 
 		list_del_init(&rq->queuelist);
-		ret = blk_mq_request_issue_directly(rq);
+		ret = blk_mq_request_issue_directly(rq, list_empty(list));
 		if (ret != BLK_STS_OK) {
 			if (ret == BLK_STS_RESOURCE ||
 					ret == BLK_STS_DEV_RESOURCE) {
@@ -1866,6 +1874,14 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 			blk_mq_end_request(rq, ret);
 		}
 	}
+
+	/*
+	 * If we didn't flush the entire list, we could have told
+	 * the driver there was more coming, but that turned out to
+	 * be a lie.
+	 */
+	if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs)
+		hctx->queue->mq_ops->commit_rqs(hctx);
 }
 
 static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 9ae8e9f8f8b1..7291e5379358 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -69,7 +69,7 @@ void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
 				struct list_head *list);
 
 /* Used by blk_insert_cloned_request() to issue request directly */
-blk_status_t blk_mq_request_issue_directly(struct request *rq);
+blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last);
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 				    struct list_head *list);
 
-- 
2.17.1