[PATCH 1/7] block: use legacy path for flush requests for MQ with a scheduler

[Jens Axboe <axboe@fb.com>]

No functional changes with this patch, it's just in preparation for
supporting legacy schedulers on blk-mq.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 block/blk-core.c  |  2 +-
 block/blk-exec.c  |  2 +-
 block/blk-flush.c | 26 ++++++++++++++------------
 block/blk.h       | 12 +++++++++++-
 4 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 4b7ec5958055..813c448453bf 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1310,7 +1310,7 @@ static struct request *blk_old_get_request(struct request_queue *q, int rw,
 
 struct request *blk_get_request(struct request_queue *q, int rw, gfp_t gfp_mask)
 {
-	if (q->mq_ops)
+	if (!blk_use_sched_path(q))
 		return blk_mq_alloc_request(q, rw,
 			(gfp_mask & __GFP_DIRECT_RECLAIM) ?
 				0 : BLK_MQ_REQ_NOWAIT);
diff --git a/block/blk-exec.c b/block/blk-exec.c
index 3ecb00a6cf45..3356dff5508c 100644
--- a/block/blk-exec.c
+++ b/block/blk-exec.c
@@ -64,7 +64,7 @@ void blk_execute_rq_nowait(struct request_queue *q, struct gendisk *bd_disk,
 	 * don't check dying flag for MQ because the request won't
 	 * be reused after dying flag is set
 	 */
-	if (q->mq_ops) {
+	if (!blk_use_sched_path(q)) {
 		blk_mq_insert_request(rq, at_head, true, false);
 		return;
 	}
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 1bdbb3d3e5f5..040c36b83ef7 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -133,14 +133,16 @@ static void blk_flush_restore_request(struct request *rq)
 
 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
 {
-	if (rq->q->mq_ops) {
+	struct request_queue *q = rq->q;
+
+	if (!blk_use_sched_path(q)) {
 		blk_mq_add_to_requeue_list(rq, add_front, true);
 		return false;
 	} else {
 		if (add_front)
-			list_add(&rq->queuelist, &rq->q->queue_head);
+			list_add(&rq->queuelist, &q->queue_head);
 		else
-			list_add_tail(&rq->queuelist, &rq->q->queue_head);
+			list_add_tail(&rq->queuelist, &q->queue_head);
 		return true;
 	}
 }
@@ -201,7 +203,7 @@ static bool blk_flush_complete_seq(struct request *rq,
 		BUG_ON(!list_empty(&rq->queuelist));
 		list_del_init(&rq->flush.list);
 		blk_flush_restore_request(rq);
-		if (q->mq_ops)
+		if (!blk_use_sched_path(q))
 			blk_mq_end_request(rq, error);
 		else
 			__blk_end_request_all(rq, error);
@@ -224,7 +226,7 @@ static void flush_end_io(struct request *flush_rq, int error)
 	unsigned long flags = 0;
 	struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
 
-	if (q->mq_ops) {
+	if (!blk_use_sched_path(q)) {
 		struct blk_mq_hw_ctx *hctx;
 
 		/* release the tag's ownership to the req cloned from */
@@ -240,7 +242,7 @@ static void flush_end_io(struct request *flush_rq, int error)
 	/* account completion of the flush request */
 	fq->flush_running_idx ^= 1;
 
-	if (!q->mq_ops)
+	if (blk_use_sched_path(q))
 		elv_completed_request(q, flush_rq);
 
 	/* and push the waiting requests to the next stage */
@@ -267,7 +269,7 @@ static void flush_end_io(struct request *flush_rq, int error)
 		blk_run_queue_async(q);
 	}
 	fq->flush_queue_delayed = 0;
-	if (q->mq_ops)
+	if (!blk_use_sched_path(q))
 		spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 }
 
@@ -315,7 +317,7 @@ static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
 	 * be in flight at the same time. And acquire the tag's
 	 * ownership for flush req.
 	 */
-	if (q->mq_ops) {
+	if (!blk_use_sched_path(q)) {
 		struct blk_mq_hw_ctx *hctx;
 
 		flush_rq->mq_ctx = first_rq->mq_ctx;
@@ -409,7 +411,7 @@ void blk_insert_flush(struct request *rq)
 	 * complete the request.
 	 */
 	if (!policy) {
-		if (q->mq_ops)
+		if (!blk_use_sched_path(q))
 			blk_mq_end_request(rq, 0);
 		else
 			__blk_end_bidi_request(rq, 0, 0, 0);
@@ -425,9 +427,9 @@ void blk_insert_flush(struct request *rq)
 	 */
 	if ((policy & REQ_FSEQ_DATA) &&
 	    !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
-		if (q->mq_ops) {
+		if (!blk_use_sched_path(q))
 			blk_mq_insert_request(rq, false, false, true);
-		} else
+		else
 			list_add_tail(&rq->queuelist, &q->queue_head);
 		return;
 	}
@@ -440,7 +442,7 @@ void blk_insert_flush(struct request *rq)
 	INIT_LIST_HEAD(&rq->flush.list);
 	rq->rq_flags |= RQF_FLUSH_SEQ;
 	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
-	if (q->mq_ops) {
+	if (!blk_use_sched_path(q)) {
 		rq->end_io = mq_flush_data_end_io;
 
 		spin_lock_irq(&fq->mq_flush_lock);
diff --git a/block/blk.h b/block/blk.h
index 041185e5f129..600e22ea62e9 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -36,10 +36,20 @@ extern struct kmem_cache *request_cachep;
 extern struct kobj_type blk_queue_ktype;
 extern struct ida blk_queue_ida;
 
+/*
+ * Use the MQ path if we have mq_ops, but not if we are using an IO
+ * scheduler. For the scheduler, we should use the legacy path. Only
+ * for internal use in the block layer.
+ */
+static inline bool blk_use_sched_path(struct request_queue *q)
+{
+	return !q->mq_ops || q->elevator;
+}
+
 static inline struct blk_flush_queue *blk_get_flush_queue(
 		struct request_queue *q, struct blk_mq_ctx *ctx)
 {
-	if (q->mq_ops)
+	if (!blk_use_sched_path(q))
 		return blk_mq_map_queue(q, ctx->cpu)->fq;
 	return q->fq;
 }
-- 
2.7.4