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 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@huawei.com Link: https://lore.kernel.org/r/20240902130329.3787024-4-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/bfq-iosched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 3ed6584496f34..afc30a200fe82 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -5037,7 +5037,7 @@ 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);