[PATCH 3/3] blk-mq: update hctx->nr_active in blk_mq_end_request_batch()

[Ming Lei <ming.lei@xxxxxxxxxx>]

In case of shared tags and none io sched, batched completion still may
be run into, and hctx->nr_active is accounted when getting driver tag,
so it has to be updated in blk_mq_end_request_batch().

Otherwise, hctx->nr_active may become same with queue depth, then
hctx_may_queue() always return false, then io hang is caused.

Fixes the issue by updating the counter in batched way.

Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
Fixes: f794f3351f26 ("block: add support for blk_mq_end_request_batch()")
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 block/blk-mq.c | 15 +++++++++++++--
 block/blk-mq.h | 12 +++++++++---
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 07eb1412760b..0dbe75034f61 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -825,6 +825,7 @@ void blk_mq_end_request_batch(struct io_comp_batch *iob)
 	struct blk_mq_hw_ctx *cur_hctx = NULL;
 	struct request *rq;
 	u64 now = 0;
+	int active = 0;
 
 	if (iob->need_ts)
 		now = ktime_get_ns();
@@ -846,16 +847,26 @@ void blk_mq_end_request_batch(struct io_comp_batch *iob)
 		rq_qos_done(rq->q, rq);
 
 		if (nr_tags == TAG_COMP_BATCH || cur_hctx != rq->mq_hctx) {
-			if (cur_hctx)
+			if (cur_hctx) {
+				if (active)
+					__blk_mq_sub_active_requests(cur_hctx,
+							active);
 				blk_mq_flush_tag_batch(cur_hctx, tags, nr_tags);
+			}
 			nr_tags = 0;
+			active = 0;
 			cur_hctx = rq->mq_hctx;
 		}
 		tags[nr_tags++] = rq->tag;
+		if (rq->rq_flags & RQF_MQ_INFLIGHT)
+			active++;
 	}
 
-	if (nr_tags)
+	if (nr_tags) {
+		if (active)
+			__blk_mq_sub_active_requests(cur_hctx, active);
 		blk_mq_flush_tag_batch(cur_hctx, tags, nr_tags);
+	}
 }
 EXPORT_SYMBOL_GPL(blk_mq_end_request_batch);
 
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 28859fc5faee..cb0b5482ca5e 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -225,12 +225,18 @@ static inline void __blk_mq_inc_active_requests(struct blk_mq_hw_ctx *hctx)
 		atomic_inc(&hctx->nr_active);
 }
 
-static inline void __blk_mq_dec_active_requests(struct blk_mq_hw_ctx *hctx)
+static inline void __blk_mq_sub_active_requests(struct blk_mq_hw_ctx *hctx,
+		int val)
 {
 	if (blk_mq_is_shared_tags(hctx->flags))
-		atomic_dec(&hctx->queue->nr_active_requests_shared_tags);
+		atomic_sub(val, &hctx->queue->nr_active_requests_shared_tags);
 	else
-		atomic_dec(&hctx->nr_active);
+		atomic_sub(val, &hctx->nr_active);
+}
+
+static inline void __blk_mq_dec_active_requests(struct blk_mq_hw_ctx *hctx)
+{
+	__blk_mq_sub_active_requests(hctx, 1);
 }
 
 static inline int __blk_mq_active_requests(struct blk_mq_hw_ctx *hctx)
-- 
2.31.1