linux-kernel - Re: [PATCH] sched/fair: add !se->on

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Date:   Thu, 20 Feb 2020 10:38:02 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     qiwuchen55@...il.com
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        chenqiwu <chenqiwu@...omi.com>
Subject: Re: [PATCH] sched/fair: add !se->on_rq check before dequeue entity

On Thu, 20 Feb 2020 at 08:29, <qiwuchen55@...il.com> wrote:
>
> From: chenqiwu <chenqiwu@...omi.com>
>
> We igonre checking for !se->on_rq condition before dequeue one
> entity from cfs rq. It must be required in case the entity has
> been dequeued.

Do you have a use case that triggers this situation ?

This is the only way to reach this situation seems to be dequeuing a
task on a throttled cfs_rq

>
> Signed-off-by: chenqiwu <chenqiwu@...omi.com>
> ---
>  kernel/sched/fair.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 3c8a379..945dcaf 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5341,6 +5341,8 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>         bool was_sched_idle = sched_idle_rq(rq);
>
>         for_each_sched_entity(se) {
> +               if (!se->on_rq)
> +                       break;
>                 cfs_rq = cfs_rq_of(se);
>                 dequeue_entity(cfs_rq, se, flags);
>
> --
> 1.9.1
>