From: Yu Kuai yukuai3@huawei.com

[ Upstream commit 73aeab373557fa6ee4ae0b742c6211ccd9859280 ]

Original state:

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

After commit 0e456dba86c7 ("block, bfq: choose the last bfqq from merge chain in bfq_setup_cooperator()"), if P1 issues a new IO:

Without the patch:

Process 1 Process 2 Process 3 Process 4 (BIC1) (BIC2) (BIC3) (BIC4) Λ | | | ------------------------------\ -------------| V V bfqq1--------->bfqq2---------->bfqq3----------->bfqq4 ref 0 0 2 4

bfqq3 will be used to handle IO from P1, this is not expected, IO should be redirected to bfqq4;

With the patch:

------------------------------------------- | | Process 1 Process 2 Process 3 | Process 4 (BIC1) (BIC2) (BIC3) | (BIC4) | | | | -------------\ -------------| V V bfqq1--------->bfqq2---------->bfqq3----------->bfqq4 ref 0 0 2 4

IO is redirected to bfqq4, however, procress reference of bfqq3 is still 2, while there is only P2 using it.

Fix the problem by calling bfq_merge_bfqqs() for each bfqq in the merge chain. Also change bfqq_merge_bfqqs() to return new_bfqq to simplify code.

Fixes: 0e456dba86c7 ("block, bfq: choose the last bfqq from merge chain in bfq_setup_cooperator()") Signed-off-by: Yu Kuai yukuai3@huawei.com Link: https://lore.kernel.org/r/20240909134154.954924-3-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe axboe@kernel.dk --- block/bfq-iosched.c | 33 ++++++++++++++++----------------- 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 515e3c1a5475..c1600e3ac333 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2774,10 +2774,12 @@ void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq) bfq_put_queue(bfqq); }

-static void -bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic, - struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) +static struct bfq_queue *bfq_merge_bfqqs(struct bfq_data *bfqd, + struct bfq_io_cq *bic, + struct bfq_queue *bfqq) { + struct bfq_queue *new_bfqq = bfqq->new_bfqq; + bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu", (unsigned long)new_bfqq->pid); /* Save weight raising and idle window of the merged queues */ @@ -2845,6 +2847,8 @@ bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic, new_bfqq->pid = -1; bfqq->bic = NULL; bfq_release_process_ref(bfqd, bfqq); + + return new_bfqq; }

static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq, @@ -2880,14 +2884,8 @@ static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq, * fulfilled, i.e., bic can be redirected to new_bfqq * and bfqq can be put. */ - bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq, - new_bfqq); - /* - * If we get here, bio will be queued into new_queue, - * so use new_bfqq to decide whether bio and rq can be - * merged. - */ - bfqq = new_bfqq; + while (bfqq != new_bfqq) + bfqq = bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq);

/* * Change also bqfd->bio_bfqq, as @@ -5444,6 +5442,7 @@ static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq) bool waiting, idle_timer_disabled = false;

if (new_bfqq) { + struct bfq_queue *old_bfqq = bfqq; /* * Release the request's reference to the old bfqq * and make sure one is taken to the shared queue. @@ -5459,18 +5458,18 @@ static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq) * then complete the merge and redirect it to * new_bfqq. */ - if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq) - bfq_merge_bfqqs(bfqd, RQ_BIC(rq), - bfqq, new_bfqq); + if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq) { + while (bfqq != new_bfqq) + bfqq = bfq_merge_bfqqs(bfqd, RQ_BIC(rq), bfqq); + }

- bfq_clear_bfqq_just_created(bfqq); + bfq_clear_bfqq_just_created(old_bfqq); /* * rq is about to be enqueued into new_bfqq, * release rq reference on bfqq */ - bfq_put_queue(bfqq); + bfq_put_queue(old_bfqq); rq->elv.priv[1] = new_bfqq; - bfqq = new_bfqq; }

bfq_update_io_thinktime(bfqd, bfqq);