Revert "block, bfq: honor already-setup queue merges"

This reverts commit 2d52c58.

We have had several folks complain that this causes hangs for them, which
is especially problematic as the commit has also hit stable already.

As no resolution seems to be forthcoming right now, revert the patch.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=214503
Fixes: 2d52c58 ("block, bfq: honor already-setup queue merges")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-iosched.c

@@ -2662,15 +2662,6 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
 	 * are likely to increase the throughput.
 	 */
 	bfqq->new_bfqq = new_bfqq;
-	/*
-	 * The above assignment schedules the following redirections:
-	 * each time some I/O for bfqq arrives, the process that
-	 * generated that I/O is disassociated from bfqq and
-	 * associated with new_bfqq. Here we increases new_bfqq->ref
-	 * in advance, adding the number of processes that are
-	 * expected to be associated with new_bfqq as they happen to
-	 * issue I/O.
-	 */
 	new_bfqq->ref += process_refs;
 	return new_bfqq;
 }
@@ -2733,10 +2724,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 {
 	struct bfq_queue *in_service_bfqq, *new_bfqq;
 
-	/* if a merge has already been setup, then proceed with that first */
-	if (bfqq->new_bfqq)
-		return bfqq->new_bfqq;
-
 	/*
 	 * Check delayed stable merge for rotational or non-queueing
 	 * devs. For this branch to be executed, bfqq must not be
@@ -2838,6 +2825,9 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	if (bfq_too_late_for_merging(bfqq))
 		return NULL;
 
+	if (bfqq->new_bfqq)
+		return bfqq->new_bfqq;
+
 	if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
 		return NULL;