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

Ming Lei
2020-09-08T08:16:14Z

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