Turns out that blk_mq_freeze_queue() isn't stronger[1] than blk_mq_quiesce_queue() because dispatch may still be in-progress after queue is frozen, and in several cases, such as switching io scheduler, updating nr_requests & wbt latency, we still need to quiesce queue as a supplement of freezing queue. As we need to extend uses of blk_mq_quiesce_queue(), it is inevitable for us to need support nested quiesce, especially we can't let unquiesce happen when there is quiesce originated from other contexts. 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. One kernel panic issue has been reported[2] when running stress test on dm-mpath's updating nr_requests and suspending queue, and the similar issue should exist on almost all drivers which use quiesce/unquiesce. [1] https://marc.info/?l=linux-block&m=150993988115872&w=2 [2] https://listman.redhat.com/archives/dm-devel/2021-September/msg00189.html Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> --- block/blk-mq.c | 20 +++++++++++++++++--- include/linux/blkdev.h | 2 ++ 2 files changed, 19 insertions(+), 3 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 21bf4c3f0825..10f8a3d4e3a1 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -209,7 +209,12 @@ 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); @@ -250,10 +255,19 @@ 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 (q->quiesce_depth > 0 && !--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); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 0e960d74615e..74c60e2d61f9 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -315,6 +315,8 @@ 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; -- 2.31.1
