[PATCH -next v4] blk-mq: fix tag_get wait task can't be awakened

[Laibin Qiu]

In case of shared tags, there might be more than one hctx which
allocates from the same tags, and each hctx is limited to allocate at
most:
        hctx_max_depth = max((bt->sb.depth + users - 1) / users, 4U);

tag idle detection is lazy, and may be delayed for 30sec, so there
could be just one real active hctx(queue) but all others are actually
idle and still accounted as active because of the lazy idle detection.
Then if wake_batch is > hctx_max_depth, driver tag allocation may wait
forever on this real active hctx.

Fix this by recalculating wake_batch when inc or dec active_queues.

Fixes: 0d2602ca30e41 ("blk-mq: improve support for shared tags maps")
Suggested-by: Ming Lei <ming.lei@xxxxxxxxxx>
Suggested-by: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Laibin Qiu <qiulaibin@xxxxxxxxxx>
---
 block/blk-mq-tag.c      | 39 ++++++++++++++++++++++++++++++++-------
 include/linux/sbitmap.h | 11 +++++++++++
 lib/sbitmap.c           | 22 +++++++++++++++++++---
 3 files changed, 62 insertions(+), 10 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index e55a6834c9a6..48b00d56141a 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -16,6 +16,21 @@
 #include "blk-mq-sched.h"
 #include "blk-mq-tag.h"
 
+/*
+ * Recalculate wakeup batch when tag is shared by hctx.
+ */
+static void blk_mq_update_wake_batch(struct blk_mq_tags *tags,
+		unsigned int users)
+{
+	if (!users)
+		return;
+
+	sbitmap_queue_recalculate_wake_batch(&tags->bitmap_tags,
+			users);
+	sbitmap_queue_recalculate_wake_batch(&tags->breserved_tags,
+			users);
+}
+
 /*
  * If a previously inactive queue goes active, bump the active user count.
  * We need to do this before try to allocate driver tag, then even if fail
@@ -24,18 +39,25 @@
  */
 bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 {
+	unsigned int users;
 	if (blk_mq_is_shared_tags(hctx->flags)) {
 		struct request_queue *q = hctx->queue;
 
-		if (!test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) &&
-		    !test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
-			atomic_inc(&hctx->tags->active_queues);
+		if (test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) ||
+		    test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags)) {
+			return true;
+		}
 	} else {
-		if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
-		    !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
-			atomic_inc(&hctx->tags->active_queues);
+		if (test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) ||
+		    test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state)) {
+			return true;
+		}
 	}
 
+	users = atomic_inc_return(&hctx->tags->active_queues);
+
+	blk_mq_update_wake_batch(hctx->tags, users);
+
 	return true;
 }
 
@@ -56,6 +78,7 @@ void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
 void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 {
 	struct blk_mq_tags *tags = hctx->tags;
+	unsigned int users;
 
 	if (blk_mq_is_shared_tags(hctx->flags)) {
 		struct request_queue *q = hctx->queue;
@@ -68,7 +91,9 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 			return;
 	}
 
-	atomic_dec(&tags->active_queues);
+	users = atomic_dec_return(&tags->active_queues);
+
+	blk_mq_update_wake_batch(tags, users);
 
 	blk_mq_tag_wakeup_all(tags, false);
 }
diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index fc0357a6e19b..95df357ec009 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -415,6 +415,17 @@ static inline void sbitmap_queue_free(struct sbitmap_queue *sbq)
 	sbitmap_free(&sbq->sb);
 }
 
+/**
+ * sbitmap_queue_recalculate_wake_batch() - Recalculate wake batch
+ * @sbq: Bitmap queue to recalculate wake batch.
+ * @users: Number of shares.
+ *
+ * Like sbitmap_queue_update_wake_batch(), this will calculate wake batch
+ * by depth. This interface is for HCTX shared tags or queue shared tags.
+ */
+void sbitmap_queue_recalculate_wake_batch(struct sbitmap_queue *sbq,
+					    unsigned int users);
+
 /**
  * sbitmap_queue_resize() - Resize a &struct sbitmap_queue.
  * @sbq: Bitmap queue to resize.
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 2709ab825499..94b3272effd8 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -457,10 +457,9 @@ int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 }
 EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
 
-static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
-					    unsigned int depth)
+static inline void __sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
+					    unsigned int wake_batch)
 {
-	unsigned int wake_batch = sbq_calc_wake_batch(sbq, depth);
 	int i;
 
 	if (sbq->wake_batch != wake_batch) {
@@ -476,6 +475,23 @@ static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
 	}
 }
 
+static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
+					    unsigned int depth)
+{
+	unsigned int wake_batch = sbq_calc_wake_batch(sbq, depth);
+
+	__sbitmap_queue_update_wake_batch(sbq, wake_batch);
+}
+
+void sbitmap_queue_recalculate_wake_batch(struct sbitmap_queue *sbq,
+					    unsigned int users)
+{
+	unsigned int wake_batch = clamp_t(unsigned int,
+			(sbq->sb.depth + users - 1) / users, 4U, SBQ_WAKE_BATCH);
+	__sbitmap_queue_update_wake_batch(sbq, wake_batch);
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_recalculate_wake_batch);
+
 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
 {
 	sbitmap_queue_update_wake_batch(sbq, depth);
-- 
2.22.0