blk-mq-sched: Allocate sched reserved tags as specified in the original queue tagset

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

Modified by me to also check at driver tag allocation time if the
original request was reserved, so we can be sure to allocate a
properly reserved tag at that point in time, too.
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-mq-sched.c

@@ -454,7 +454,8 @@ int blk_mq_sched_setup(struct request_queue *q)
 	 */
 	ret = 0;
 	queue_for_each_hw_ctx(q, hctx, i) {
-		hctx->sched_tags = blk_mq_alloc_rq_map(set, i, q->nr_requests, 0);
+		hctx->sched_tags = blk_mq_alloc_rq_map(set, i,
+				q->nr_requests, set->reserved_tags);
 		if (!hctx->sched_tags) {
 			ret = -ENOMEM;
 			break;

block/blk-mq-tag.c

@@ -181,7 +181,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, struct blk_mq_tags *tags,
 		    struct blk_mq_ctx *ctx, unsigned int tag)
 {
-	if (tag >= tags->nr_reserved_tags) {
+	if (!blk_mq_tag_is_reserved(tags, tag)) {
 		const int real_tag = tag - tags->nr_reserved_tags;
 
 		BUG_ON(real_tag >= tags->nr_tags);

block/blk-mq-tag.h

@@ -85,4 +85,10 @@ static inline void blk_mq_tag_set_rq(struct blk_mq_hw_ctx *hctx,
 	hctx->tags->rqs[tag] = rq;
 }
 
+static inline bool blk_mq_tag_is_reserved(struct blk_mq_tags *tags,
+					  unsigned int tag)
+{
+	return tag < tags->nr_reserved_tags;
+}
+
 #endif

block/blk-mq.c

@@ -852,6 +852,9 @@ bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
 		return true;
 	}
 
+	if (blk_mq_tag_is_reserved(data.hctx->sched_tags, rq->internal_tag))
+		data.flags |= BLK_MQ_REQ_RESERVED;
+
 	rq->tag = blk_mq_get_tag(&data);
 	if (rq->tag >= 0) {
 		if (blk_mq_tag_busy(data.hctx)) {