Patch "Revert "block, bfq: honor already-setup queue merges"" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     revert-block-bfq-honor-already-setup-queue-merges.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit afc79690dd3b80153a630fc3ed9550564f8e1cb7
Author: Jens Axboe <axboe@xxxxxxxxx>
Date:   Tue Sep 28 06:33:15 2021 -0600

    Revert "block, bfq: honor already-setup queue merges"
    
    [ Upstream commit ebc69e897e17373fbe1daaff1debaa77583a5284 ]
    
    This reverts commit 2d52c58b9c9bdae0ca3df6a1eab5745ab3f7d80b.
    
    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: 2d52c58b9c9b ("block, bfq: honor already-setup queue merges")
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 8dee243e639f..73bffd7af15c 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2523,15 +2523,6 @@ 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;
 }
@@ -2591,10 +2582,6 @@ 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;
-
 	/*
 	 * Do not perform queue merging if the device is non
 	 * rotational and performs internal queueing. In fact, such a
@@ -2649,6 +2636,9 @@ 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;