This is a note to let you know that I've just added the patch titled
block, bfq: don't break merge chain in bfq_split_bfqq()
to the 5.10-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-don-t-break-merge-chain-in-bfq_split_bfqq.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 70be68fe1da91b0a082d0f6bb3e2def53263e71c
Author: Yu Kuai <yukuai3@xxxxxxxxxx>
Date: Mon Sep 2 21:03:28 2024 +0800
block, bfq: don't break merge chain in bfq_split_bfqq()
[ Upstream commit 42c306ed723321af4003b2a41bb73728cab54f85 ]
Consider the following scenario:
Process 1 Process 2 Process 3 Process 4
(BIC1) (BIC2) (BIC3) (BIC4)
Λ | | |
\-------------\ \-------------\ \--------------\|
V V V
bfqq1--------->bfqq2---------->bfqq3----------->bfqq4
ref 0 1 2 4
If Process 1 issue a new IO and bfqq2 is found, and then bfq_init_rq()
decide to spilt bfqq2 by bfq_split_bfqq(). Howerver, procress reference
of bfqq2 is 1 and bfq_split_bfqq() just clear the coop flag, which will
break the merge chain.
Expected result: caller will allocate a new bfqq for BIC1
Process 1 Process 2 Process 3 Process 4
(BIC1) (BIC2) (BIC3) (BIC4)
| | |
\-------------\ \--------------\|
V V
bfqq1--------->bfqq2---------->bfqq3----------->bfqq4
ref 0 0 1 3
Since the condition is only used for the last bfqq4 when the previous
bfqq2 and bfqq3 are already splited. Fix the problem by checking if
bfqq is the last one in the merge chain as well.
Fixes: 36eca8948323 ("block, bfq: add Early Queue Merge (EQM)")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240902130329.3787024-4-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 e68881f71ff13..515e3c1a54759 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -6013,7 +6013,7 @@ bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
{
bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
- if (bfqq_process_refs(bfqq) == 1) {
+ if (bfqq_process_refs(bfqq) == 1 && !bfqq->new_bfqq) {
bfqq->pid = current->pid;
bfq_clear_bfqq_coop(bfqq);
bfq_clear_bfqq_split_coop(bfqq);
