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

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Date:   Wed, 26 Jun 2019 13:12:10 -0700
From:   Guenter Roeck <groeck@...gle.com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Paolo Valente <paolo.valente@...aro.org>,
        Jens Axboe <axboe@...nel.dk>,
        Guenter Roeck <groeck@...omium.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        linux-block@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block, bfq: Init saved_wr_start_at_switch_to_srt in
 unlikely case

On Wed, Jun 26, 2019 at 1:00 PM Douglas Anderson <dianders@...omium.org> wrote:
>
> 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>

Reviewed-by: Guenter Roeck <groeck@...omium.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
>