[PATCH V3] block: drain queue before waiting for q_usage_counter becoming zero

[Ming Lei <ming.lei@redhat.com>]

Now we track legacy requests with .q_usage_counter in commit 055f6e18e08f
("block: Make q_usage_counter also track legacy requests"), but that
commit never runs and drains legacy queue before waiting for this counter
becoming zero, then IO hang is caused in the test of pulling disk during IO.

This patch fixes the issue by draining requests before waiting for
q_usage_counter becoming zero, both Mauricio and chenxiang reported this
issue, and observed that it can be fixed by this patch.

Link: https://marc.info/?l=linux-block&m=151192424731797&w=2
Fixes: 055f6e18e08f("block: Make q_usage_counter also track legacy requests")
Cc: Wen Xiong <wenxiong@us.ibm.com>
Tested-by: "chenxiang (M)" <chenxiang66@hisilicon.com>
Tested-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
V3:
	- V2 can't cover chenxiang's issue, so we have to drain queue via
	blk_drain_queue(), and fallback to original post(V1)


 block/blk-core.c | 9 +++++++--
 block/blk-mq.c   | 2 ++
 block/blk.h      | 2 ++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index e5a623b45a1d..01329367e51c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -562,6 +562,13 @@ static void __blk_drain_queue(struct request_queue *q, bool drain_all)
 	}
 }
 
+void blk_drain_queue(struct request_queue *q)
+{
+	spin_lock_irq(q->queue_lock);
+	__blk_drain_queue(q, true);
+	spin_unlock_irq(q->queue_lock);
+}
+
 /**
  * blk_queue_bypass_start - enter queue bypass mode
  * @q: queue of interest
@@ -689,8 +696,6 @@ void blk_cleanup_queue(struct request_queue *q)
 	 */
 	blk_freeze_queue(q);
 	spin_lock_irq(lock);
-	if (!q->mq_ops)
-		__blk_drain_queue(q, true);
 	queue_flag_set(QUEUE_FLAG_DEAD, q);
 	spin_unlock_irq(lock);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index c94a8d225b63..e4c2e5c17343 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -161,6 +161,8 @@ void blk_freeze_queue(struct request_queue *q)
 	 * exported to drivers as the only user for unfreeze is blk_mq.
 	 */
 	blk_freeze_queue_start(q);
+	if (!q->mq_ops)
+		blk_drain_queue(q);
 	blk_mq_freeze_queue_wait(q);
 }
 
diff --git a/block/blk.h b/block/blk.h
index 3f1446937aec..442098aa9463 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -330,4 +330,6 @@ static inline void blk_queue_bounce(struct request_queue *q, struct bio **bio)
 }
 #endif /* CONFIG_BOUNCE */
 
+extern void blk_drain_queue(struct request_queue *q);
+
 #endif /* BLK_INTERNAL_H */
-- 
2.9.5