[PATCH 5.15 531/667] bfq: Avoid false marking of bic as stably merged

[Greg Kroah-Hartman]

From: Jan Kara <jack@xxxxxxx>

commit 70456e5210f40ffdb8f6d905acfdcec5bd5fad9e upstream.

bfq_setup_cooperator() can mark bic as stably merged even though it
decides to not merge its bfqqs (when bfq_setup_merge() returns NULL).
Make sure to mark bic as stably merged only if we are really going to
merge bfqqs.

CC: stable@xxxxxxxxxxxxxxx
Tested-by: "yukuai (C)" <yukuai3@xxxxxxxxxx>
Fixes: 430a67f9d616 ("block, bfq: merge bursts of newly-created queues")
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Link: https://lore.kernel.org/r/20220401102752.8599-1-jack@xxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 block/bfq-iosched.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2773,9 +2773,12 @@ bfq_setup_cooperator(struct bfq_data *bf
 				struct bfq_queue *new_bfqq =
 					bfq_setup_merge(bfqq, stable_merge_bfqq);
 
-				bic->stably_merged = true;
-				if (new_bfqq && new_bfqq->bic)
-					new_bfqq->bic->stably_merged = true;
+				if (new_bfqq) {
+					bic->stably_merged = true;
+					if (new_bfqq->bic)
+						new_bfqq->bic->stably_merged =
+									true;
+				}
 				return new_bfqq;
 			} else
 				return NULL;