Re: [QUESTION] blk_mq_freeze_queue in elevator_init_mq

[Bart Van Assche <bvanassche@acm.org>]

On 11/16/21 19:37, yangerkun wrote:
> This commit add blk_mq_freeze_queue in elevator_init_mq which try to
> make sure no in-flight request while we go through blk_mq_init_sched.
> But does there any drivers can leave IO alive while we go through
> elevator_init_mq？ And if no, maybe we can just remove this logical to
> fix the regression...

Does this untested patch help? Please note that I'm not recommending to
integrate this patch in the upstream kernel but if it helps it can be a
building block of a solution.

Thanks,

Bart.

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3ab34c4f20da..b85dcb72a579 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -167,6 +167,7 @@ void blk_freeze_queue_start(struct request_queue *q)
  		mutex_unlock(&q->mq_freeze_lock);
  		if (queue_is_mq(q))
  			blk_mq_run_hw_queues(q, false);
+		synchronize_rcu_expedited();
  	} else {
  		mutex_unlock(&q->mq_freeze_lock);
  	}