4.19-stable review patch. If anyone has any objections, please let me know.
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From: Yu Kuai yukuai3@huawei.com
[ 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@huawei.com Link: https://lore.kernel.org/r/20240902130329.3787024-3-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- 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 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