linux-kernel - bfq io scheduler fifo_expire

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Date:   Wed, 19 Jul 2023 21:35:47 +0800 (CST)
From:   "Zhang Bo" <zbsdta@....com>
To:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Cc:     paolo.valente@...more.it, axboe@...nel.dk
Subject: bfq io scheduler fifo_expire_sync have no function

In bfq_check_fifo(...) function,  bfq_bfqq_fifo_expire(bfqq) is checked at first, and then  bfq_mark_bfqq_fifo_expire(bfqq) later. 
I think bfq_check_fifo return NULL because of bfq_bfqq_fifo_expire(bfqq) return true. So expired request is not dispatch.
Could any one explain this problem?

static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
				      struct request *last)
{
	struct request *rq;

	if (bfq_bfqq_fifo_expire(bfqq)) {
		return NULL;
	}

	bfq_mark_bfqq_fifo_expire(bfqq);

	...................
}