linux-kernel - [PATCH FIXES/IMPROVEMENTS 2/7] block, bfq: fix delayed stable merge check

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Message-Id: <20210619140948.98712-3-paolo.valente@linaro.org>
Date:   Sat, 19 Jun 2021 16:09:43 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        mariottiluca1@...mail.it, holger@...lied-asynchrony.com,
        pedroni.pietro.96@...il.com,
        Paolo Valente <paolo.valente@...more.it>
Subject: [PATCH FIXES/IMPROVEMENTS 2/7] block, bfq: fix delayed stable merge check

From: Luca Mariotti <mariottiluca1@...mail.it>

When attempting to schedule a merge of a given bfq_queue with the currently
in-service bfq_queue or with a cooperating bfq_queue among the scheduled
bfq_queues, delayed stable merge is checked for rotational or non-queueing
devs. For this stable merge to be performed, some conditions must be met.
If the current bfq_queue underwent some split from some merged bfq_queue,
one of these conditions is that two hundred milliseconds must elapse from
split, otherwise this condition is always met.

Unfortunately, by mistake, time_is_after_jiffies() was written instead of
time_is_before_jiffies() for this check, verifying that less than two
hundred milliseconds have elapsed instead of verifying that at least two
hundred milliseconds have elapsed.

Fix this issue by replacing time_is_after_jiffies() with
time_is_before_jiffies().

Signed-off-by: Luca Mariotti <mariottiluca1@...mail.it>
Signed-off-by: Paolo Valente <paolo.valente@...more.it>
Signed-off-by: Pietro Pedroni <pedroni.pietro.96@...il.com>
---
 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 da2363f12e53..c5c0e74977d4 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2710,7 +2710,7 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	if (unlikely(!bfqd->nonrot_with_queueing)) {
 		if (bic->stable_merge_bfqq &&
 		    !bfq_bfqq_just_created(bfqq) &&
-		    time_is_after_jiffies(bfqq->split_time +
+		    time_is_before_jiffies(bfqq->split_time +
 					  msecs_to_jiffies(200))) {
 			struct bfq_queue *stable_merge_bfqq =
 				bic->stable_merge_bfqq;
-- 
2.20.1