[PATCH V3 1/4] blk-mq: serialize queue quiesce and unquiesce by mutex

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

Add .mq_quiesce_mutext to request queue, so that queue quiesce and
unquiesce can be serialized. Meantime we can avoid unnecessary
synchronize_rcu() in case that queue has been quiesced already.

Prepare for replace SRCU with percpu-refcount, so that we can avoid
warning in percpu_ref_kill_and_confirm() in case that blk_mq_quiesce_queue()
is run on already-quiesced request queue.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Cc: Chao Leng <lengchao@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-core.c       |  2 ++
 block/blk-mq.c         | 11 +++++++++++
 include/linux/blkdev.h |  2 ++
 3 files changed, 15 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 093649bd252e..e7e787ea77be 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -564,6 +564,8 @@ struct request_queue *blk_alloc_queue(int node_id)
 	init_waitqueue_head(&q->mq_freeze_wq);
 	mutex_init(&q->mq_freeze_lock);
 
+	mutex_init(&q->mq_quiesce_lock);
+
 	/*
 	 * Init percpu_ref in atomic mode so that it's faster to shutdown.
 	 * See blk_register_queue() for details.
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4abb71459f94..13cc10b89629 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -224,6 +224,11 @@ void blk_mq_quiesce_queue(struct request_queue *q)
 	unsigned int i;
 	bool rcu = false;
 
+	mutex_lock(&q->mq_quiesce_lock);
+
+	if (blk_queue_quiesced(q))
+		goto exit;
+
 	blk_mq_quiesce_queue_nowait(q);
 
 	queue_for_each_hw_ctx(q, hctx, i) {
@@ -234,6 +239,8 @@ void blk_mq_quiesce_queue(struct request_queue *q)
 	}
 	if (rcu)
 		synchronize_rcu();
+ exit:
+	mutex_unlock(&q->mq_quiesce_lock);
 }
 EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue);
 
@@ -246,10 +253,14 @@ EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue);
  */
 void blk_mq_unquiesce_queue(struct request_queue *q)
 {
+	mutex_lock(&q->mq_quiesce_lock);
+
 	blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
 
 	/* dispatch requests which are inserted during quiescing */
 	blk_mq_run_hw_queues(q, true);
+
+	mutex_unlock(&q->mq_quiesce_lock);
 }
 EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue);
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 7b1e53084799..cc6fb4d0d078 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -572,6 +572,8 @@ struct request_queue {
 	 */
 	struct mutex		mq_freeze_lock;
 
+	struct mutex		mq_quiesce_lock;
+
 	struct blk_mq_tag_set	*tag_set;
 	struct list_head	tag_set_list;
 	struct bio_set		bio_split;
-- 
2.25.2