From: Ming Lei <ming.lei@redhat.com>
Date: Thu, 14 Oct 2021 16:17:10 +0800
Subject: blk-mq: support concurrent queue quiesce/unquiesce
Patch-mainline: v5.16-rc1
Git-commit: e70feb8b3e6886c525c88943b5f1508d02f5a683
References: bsc#1201651

blk_mq_quiesce_queue() has been used a bit wide now, so far we don't support
concurrent/nested quiesce. One biggest issue is that unquiesce can happen
unexpectedly in case that quiesce/unquiesce are run concurrently from
more than one context.

This patch introduces q->mq_quiesce_depth to deal concurrent quiesce,
and we only unquiesce queue when it is the last/outer-most one of all
contexts.

Several kernel panic issue has been reported[1][2][3] when running stress
quiesce test. And this patch has been verified in these reports.

[1] https://lore.kernel.org/linux-block/9b21c797-e505-3821-4f5b-df7bf9380328@huawei.com/T/#m1fc52431fad7f33b1ffc3f12c4450e4238540787
[2] https://lore.kernel.org/linux-block/9b21c797-e505-3821-4f5b-df7bf9380328@huawei.com/T/#m10ad90afeb9c8cc318334190a7c24c8b5c5e0722
[3] https://listman.redhat.com/archives/dm-devel/2021-September/msg00189.html

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211014081710.1871747-7-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 block/blk-mq.c         |   22 +++++++++++++++++++---
 include/linux/blkdev.h |    2 ++
 2 files changed, 21 insertions(+), 3 deletions(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -207,7 +207,12 @@ EXPORT_SYMBOL_GPL(blk_mq_unfreeze_queue)
  */
 void blk_mq_quiesce_queue_nowait(struct request_queue *q)
 {
-	blk_queue_flag_set(QUEUE_FLAG_QUIESCED, q);
+	unsigned long flags;
+
+	spin_lock_irqsave(&q->queue_lock, flags);
+	if (!q->quiesce_depth++)
+		blk_queue_flag_set(QUEUE_FLAG_QUIESCED, q);
+	spin_unlock_irqrestore(&q->queue_lock, flags);
 }
 EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
 
@@ -248,10 +253,21 @@ EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue);
  */
 void blk_mq_unquiesce_queue(struct request_queue *q)
 {
-	blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
+	unsigned long flags;
+	bool run_queue = false;
+
+	spin_lock_irqsave(&q->queue_lock, flags);
+	if (WARN_ON_ONCE(q->quiesce_depth <= 0)) {
+		;
+	} else if (!--q->quiesce_depth) {
+		blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
+		run_queue = true;
+	}
+	spin_unlock_irqrestore(&q->queue_lock, flags);
 
 	/* dispatch requests which are inserted during quiescing */
-	blk_mq_run_hw_queues(q, true);
+	if (run_queue)
+		blk_mq_run_hw_queues(q, true);
 }
 EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue);
 
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -553,6 +553,8 @@ struct request_queue {
 	 */
 	struct mutex		mq_freeze_lock;
 
+	int			quiesce_depth;
+
 	struct blk_mq_tag_set	*tag_set;
 	struct list_head	tag_set_list;
 	struct bio_set		bio_split;