From ec170e255cc146668e4e355cee6bc2ad1ede0b02 Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Mon, 2 Sep 2024 21:03:27 +0800 Subject: [PATCH] block, bfq: choose the last bfqq from merge chain in bfq_setup_cooperator() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [ 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 Link: https://lore.kernel.org/r/20240902130329.3787024-3-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- block/bfq-iosched.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 30045b28ad63..7684df94fcc6 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2889,8 +2889,12 @@ 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; + } /* * Check delayed stable merge for rotational or non-queueing