FAILED: patch "[PATCH] dm: do not use waitqueue for request-based DM" failed to apply to 5.7-stable tree

The patch below does not apply to the 5.7-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 85067747cf9888249fa11fa49ef75af5192d3988 Mon Sep 17 00:00:00 2001
From: Ming Lei <[email protected]>
Date: Wed, 24 Jun 2020 16:00:58 -0400
Subject: [PATCH] dm: do not use waitqueue for request-based DM

Given request-based DM now uses blk-mq's blk_mq_queue_inflight() to determine if outstanding IO has completed (and DM has no control over the blk-mq state machine used to track outstanding IO) it is unsafe to wakeup waiter (dm_wait_for_completion) before blk-mq has cleared a request's state bits (e.g. MQ_RQ_IN_FLIGHT or MQ_RQ_COMPLETE). As such dm_wait_for_completion() could be left to wait indefinitely if no other requests complete.

Fix this by eliminating request-based DM's use of waitqueue to wait for blk-mq requests to complete in dm_wait_for_completion.

Depends-on: 3c94d83cb3526 ("blk-mq: change blk_mq_queue_busy() to blk_mq_queue_inflight()")

index f60c02512121..85e0daabad49 100644
@@ -146,10 +146,6 @@ static void rq_end_stats(struct mapped_device *md, struct request *orig)
  */
 static void rq_completed(struct mapped_device *md)
 {
-	/* nudge anyone waiting on suspend queue */
-	if (unlikely(wq_has_sleeper(&md->wait)))
-		wake_up(&md->wait);
-
 	/*
 	 * dm_put() must be at the end of this function. See the comment above
 	 */