This is a note to let you know that I've just added the patch titled
block, bfq: choose the last bfqq from merge chain in bfq_setup_cooperator()
to the 4.19-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:
block-bfq-choose-the-last-bfqq-from-merge-chain-in-b.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit dfeaff9dc45d96e758ed7780fc616cc29246b442
Author: Yu Kuai <yukuai3@xxxxxxxxxx>
Date: Mon Sep 2 21:03:27 2024 +0800
block, bfq: choose the last bfqq from merge chain in bfq_setup_cooperator()
[ Upstream commit 0e456dba86c7f9a19792204a044835f1ca2c8dbb ]
Consider the following merge chain:
Process 1 Process 2 Process 3 Process 4
(BIC1) (BIC2) (BIC3) (BIC4)
Λ | | |
\--------------\ \-------------\ \-------------\|
V V V
bfqq1--------->bfqq2---------->bfqq3----------->bfqq4
IO from Process 1 will get bfqf2 from BIC1 first, then
bfq_setup_cooperator() will found bfqq2 already merged to bfqq3 and then
handle this IO from bfqq3. However, the merge chain can be much deeper
and bfqq3 can be merged to other bfqq as well.
Fix this problem by iterating to the last bfqq in
bfq_setup_cooperator().
Fixes: 36eca8948323 ("block, bfq: add Early Queue Merge (EQM)")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240902130329.3787024-3-yukuai1@xxxxxxxxxxxxxxx
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 1479e8d6fede2..3ed6584496f34 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2226,8 +2226,12 @@ 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;
+ new_bfqq = bfqq->new_bfqq;
+ if (new_bfqq) {
+ while (new_bfqq->new_bfqq)
+ new_bfqq = new_bfqq->new_bfqq;
+ return new_bfqq;
+ }
/*
* Prevent bfqq from being merged if it has been created too
