linux-kernel - [PATCH] block, bfq: Init saved_wr_start_at_switch_to

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Message-Id: <20190626195919.107425-1-dianders@chromium.org>
Date:   Wed, 26 Jun 2019 12:59:19 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Paolo Valente <paolo.valente@...aro.org>,
        Jens Axboe <axboe@...nel.dk>
Cc:     groeck@...omium.org, drinkcat@...omium.org,
        Douglas Anderson <dianders@...omium.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] block, bfq: Init saved_wr_start_at_switch_to_srt in unlikely case

Some debug code suggested by Paolo was tripping when I did reboot
stress tests.  Specifically in bfq_bfqq_resume_state()
"bic->saved_wr_start_at_switch_to_srt" was later than the current
value of "jiffies".  A bit of debugging showed that
"bic->saved_wr_start_at_switch_to_srt" was actually 0 and a bit more
debugging showed that was because we had run through the "unlikely"
case in the bfq_bfqq_save_state() function.

Let's init "saved_wr_start_at_switch_to_srt" in the unlikely case to
something sane.

NOTE: this fixes no known real-world errors.

Signed-off-by: Douglas Anderson <dianders@...omium.org>
Reviewed-by: Paolo Valente <paolo.valente@...aro.org>
---
Paolo said to add his Reviewed-by in https://crrev.com/c/1678756.

 block/bfq-iosched.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 72840ebf953e..008c93d6b8d7 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2678,6 +2678,7 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
 		 * to enjoy weight raising if split soon.
 		 */
 		bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
+		bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now();
 		bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
 		bic->saved_last_wr_start_finish = jiffies;
 	} else {
-- 
2.22.0.410.gd8fdbe21b5-goog