linux-kernel - [PATCH AUTOSEL 5.12 061/134] block, bfq: fix weight-raising resume with !low

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Message-Id: <20210503163513.2851510-61-sashal@kernel.org>
Date:   Mon,  3 May 2021 12:34:00 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Paolo Valente <paolo.valente@...aro.org>, Jan Kara <jack@...e.cz>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 5.12 061/134] block, bfq: fix weight-raising resume with !low_latency

From: Paolo Valente <paolo.valente@...aro.org>

[ Upstream commit 8c544770092a3d7532d01903b75721e537d87001 ]

When the io_latency heuristic is off, bfq_queues must not start to be
weight-raised. Unfortunately, by mistake, this may happen when the
state of a previously weight-raised bfq_queue is resumed after a queue
split. This commit fixes this error.

Tested-by: Jan Kara <jack@...e.cz>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
Tested-by: Oleksandr Natalenko <oleksandr@...alenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-5-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/bfq-iosched.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 95586137194e..20ba5db0f61c 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -1012,7 +1012,7 @@ static void
 bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
 		      struct bfq_io_cq *bic, bool bfq_already_existing)
 {
-	unsigned int old_wr_coeff = bfqq->wr_coeff;
+	unsigned int old_wr_coeff = 1;
 	bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
 
 	if (bic->saved_has_short_ttime)
@@ -1033,7 +1033,13 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
 	bfqq->ttime = bic->saved_ttime;
 	bfqq->io_start_time = bic->saved_io_start_time;
 	bfqq->tot_idle_time = bic->saved_tot_idle_time;
-	bfqq->wr_coeff = bic->saved_wr_coeff;
+	/*
+	 * Restore weight coefficient only if low_latency is on
+	 */
+	if (bfqd->low_latency) {
+		old_wr_coeff = bfqq->wr_coeff;
+		bfqq->wr_coeff = bic->saved_wr_coeff;
+	}
 	bfqq->service_from_wr = bic->saved_service_from_wr;
 	bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
 	bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
-- 
2.30.2