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 0e456dba86 ("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: 0e456dba86 ("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>
73aeab3735