block: add a rq_list type

Replace the semi-open coded request list helpers with a proper rq_list
type that mirrors the bio_list and has head and tail pointers.  Besides
better type safety this actually allows to insert at the tail of the
list, which will be useful soon.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241113152050.157179-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 19 insertions, 21 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3c6cadba75e3..ff0b819e35fc 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -478,7 +478,7 @@ __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data)
 		prefetch(tags->static_rqs[tag]);
 		tag_mask &= ~(1UL << i);
 		rq = blk_mq_rq_ctx_init(data, tags, tag);
-		rq_list_add(data->cached_rq, rq);
+		rq_list_add_head(data->cached_rqs, rq);
 		nr++;
 	}
 	if (!(data->rq_flags & RQF_SCHED_TAGS))
@@ -487,7 +487,7 @@ __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data)
 	percpu_ref_get_many(&data->q->q_usage_counter, nr - 1);
 	data->nr_tags -= nr;
 
-	return rq_list_pop(data->cached_rq);
+	return rq_list_pop(data->cached_rqs);
 }
 
 static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
@@ -584,7 +584,7 @@ static struct request *blk_mq_rq_cache_fill(struct request_queue *q,
 		.flags		= flags,
 		.cmd_flags	= opf,
 		.nr_tags	= plug->nr_ios,
-		.cached_rq	= &plug->cached_rq,
+		.cached_rqs	= &plug->cached_rqs,
 	};
 	struct request *rq;
 
@@ -609,14 +609,14 @@ static struct request *blk_mq_alloc_cached_request(struct request_queue *q,
 	if (!plug)
 		return NULL;
 
-	if (rq_list_empty(plug->cached_rq)) {
+	if (rq_list_empty(&plug->cached_rqs)) {
 		if (plug->nr_ios == 1)
 			return NULL;
 		rq = blk_mq_rq_cache_fill(q, plug, opf, flags);
 		if (!rq)
 			return NULL;
 	} else {
-		rq = rq_list_peek(&plug->cached_rq);
+		rq = rq_list_peek(&plug->cached_rqs);
 		if (!rq || rq->q != q)
 			return NULL;
 
@@ -625,7 +625,7 @@ static struct request *blk_mq_alloc_cached_request(struct request_queue *q,
 		if (op_is_flush(rq->cmd_flags) != op_is_flush(opf))
 			return NULL;
 
-		plug->cached_rq = rq_list_next(rq);
+		rq_list_pop(&plug->cached_rqs);
 		blk_mq_rq_time_init(rq, blk_time_get_ns());
 	}
 
@@ -802,7 +802,7 @@ void blk_mq_free_plug_rqs(struct blk_plug *plug)
 {
 	struct request *rq;
 
-	while ((rq = rq_list_pop(&plug->cached_rq)) != NULL)
+	while ((rq = rq_list_pop(&plug->cached_rqs)) != NULL)
 		blk_mq_free_request(rq);
 }
 
@@ -1392,8 +1392,7 @@ static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
 	 */
 	if (!plug->has_elevator && (rq->rq_flags & RQF_SCHED_TAGS))
 		plug->has_elevator = true;
-	rq->rq_next = NULL;
-	rq_list_add(&plug->mq_list, rq);
+	rq_list_add_head(&plug->mq_list, rq);
 	plug->rq_count++;
 }
 
@@ -2785,7 +2784,7 @@ static void blk_mq_plug_issue_direct(struct blk_plug *plug)
 	blk_status_t ret = BLK_STS_OK;
 
 	while ((rq = rq_list_pop(&plug->mq_list))) {
-		bool last = rq_list_empty(plug->mq_list);
+		bool last = rq_list_empty(&plug->mq_list);
 
 		if (hctx != rq->mq_hctx) {
 			if (hctx) {
@@ -2828,8 +2827,7 @@ static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
 {
 	struct blk_mq_hw_ctx *this_hctx = NULL;
 	struct blk_mq_ctx *this_ctx = NULL;
-	struct request *requeue_list = NULL;
-	struct request **requeue_lastp = &requeue_list;
+	struct rq_list requeue_list = {};
 	unsigned int depth = 0;
 	bool is_passthrough = false;
 	LIST_HEAD(list);
@@ -2843,12 +2841,12 @@ static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
 			is_passthrough = blk_rq_is_passthrough(rq);
 		} else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx ||
 			   is_passthrough != blk_rq_is_passthrough(rq)) {
-			rq_list_add_tail(&requeue_lastp, rq);
+			rq_list_add_tail(&requeue_list, rq);
 			continue;
 		}
 		list_add(&rq->queuelist, &list);
 		depth++;
-	} while (!rq_list_empty(plug->mq_list));
+	} while (!rq_list_empty(&plug->mq_list));
 
 	plug->mq_list = requeue_list;
 	trace_block_unplug(this_hctx->queue, depth, !from_sched);
@@ -2903,19 +2901,19 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 		if (q->mq_ops->queue_rqs) {
 			blk_mq_run_dispatch_ops(q,
 				__blk_mq_flush_plug_list(q, plug));
-			if (rq_list_empty(plug->mq_list))
+			if (rq_list_empty(&plug->mq_list))
 				return;
 		}
 
 		blk_mq_run_dispatch_ops(q,
 				blk_mq_plug_issue_direct(plug));
-		if (rq_list_empty(plug->mq_list))
+		if (rq_list_empty(&plug->mq_list))
 			return;
 	}
 
 	do {
 		blk_mq_dispatch_plug_list(plug, from_schedule);
-	} while (!rq_list_empty(plug->mq_list));
+	} while (!rq_list_empty(&plug->mq_list));
 }
 
 static void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
@@ -2980,7 +2978,7 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q,
 	if (plug) {
 		data.nr_tags = plug->nr_ios;
 		plug->nr_ios = 1;
-		data.cached_rq = &plug->cached_rq;
+		data.cached_rqs = &plug->cached_rqs;
 	}
 
 	rq = __blk_mq_alloc_requests(&data);
@@ -3003,7 +3001,7 @@ static struct request *blk_mq_peek_cached_request(struct blk_plug *plug,
 
 	if (!plug)
 		return NULL;
-	rq = rq_list_peek(&plug->cached_rq);
+	rq = rq_list_peek(&plug->cached_rqs);
 	if (!rq || rq->q != q)
 		return NULL;
 	if (type != rq->mq_hctx->type &&
@@ -3017,14 +3015,14 @@ static struct request *blk_mq_peek_cached_request(struct blk_plug *plug,
 static void blk_mq_use_cached_rq(struct request *rq, struct blk_plug *plug,
 		struct bio *bio)
 {
-	WARN_ON_ONCE(rq_list_peek(&plug->cached_rq) != rq);
+	if (rq_list_pop(&plug->cached_rqs) != rq)
+		WARN_ON_ONCE(1);
 
 	/*
 	 * If any qos ->throttle() end up blocking, we will have flushed the
 	 * plug and hence killed the cached_rq list as well. Pop this entry
 	 * before we throttle.
 	 */
-	plug->cached_rq = rq_list_next(rq);
 	rq_qos_throttle(rq->q, bio);
 
 	blk_mq_rq_time_init(rq, blk_time_get_ns());