It doesn't matter. Because the reentry of quiesce&unquiesce queue is not
safe, must be avoided by other mechanism. otherwise, exceptions may
occur. Introduce mq_quiesce_lock looks saving possible synchronization
waits, but it should not happen. If really happen, we need fix it.
On 2020/8/25 22:17, Ming Lei wrote:
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.
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Johannes Thumshirn <Johannes.Thumshirn@xxxxxxx>
Cc: Chao Leng <lengchao@xxxxxxxxxx>
---
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 d9d632639bd1..ffc57df70064 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -561,6 +561,8 @@ 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 b3d2785eefe9..817e016ef886 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 d8dba550ecac..5ed03066b33e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -569,6 +569,8 @@ 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;
