Re: [PATCH 2/2] sched/fair: Refill bandwidth before scaling

From: bsegall
Date: Mon Apr 20 2020 - 13:55:00 EST


Huaixin Chang <changhuaixin@xxxxxxxxxxxxxxxxx> writes:

> In order to prevent possible hardlockup of sched_cfs_period_timer()
> loop, loop count is introduced to denote whether to scale quota and
> period or not. However, scale is done between forwarding period timer
> and refilling cfs bandwidth runtime, which means that period timer is
> forwarded with old "period" while runtime is refilled with scaled
> "quota".
>
> Move do_sched_cfs_period_timer() before scaling to solve this.

Reviewed-by: Ben Segall <bsegall@xxxxxxxxxx>

>
> Fixes: 2e8e19226398 ("sched/fair: Limit sched_cfs_period_timer() loop to avoid hard lockup")
> Signed-off-by: Huaixin Chang <changhuaixin@xxxxxxxxxxxxxxxxx>
> ---
> kernel/sched/fair.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 02f323b85b6d..9ace1c5c73a5 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5152,6 +5152,8 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
> if (!overrun)
> break;
>
> + idle = do_sched_cfs_period_timer(cfs_b, overrun, flags);
> +
> if (++count > 3) {
> u64 new, old = ktime_to_ns(cfs_b->period);
>
> @@ -5181,8 +5183,6 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
> /* reset count so we don't come right back in here */
> count = 0;
> }
> -
> - idle = do_sched_cfs_period_timer(cfs_b, overrun, flags);
> }
> if (idle)
> cfs_b->period_active = 0;