Re: [PATCH 12/24] sched/fair: Prepare exit/cleanup paths for delayed_dequeue

[Valentin Schneider]

On 27/07/24 12:27, Peter Zijlstra wrote:
> @@ -12817,10 +12830,26 @@ static void attach_task_cfs_rq(struct ta
>  static void switched_from_fair(struct rq *rq, struct task_struct *p)
>  {
>       detach_task_cfs_rq(p);
> +	/*
> +	 * Since this is called after changing class, this isn't quite right.
> +	 * Specifically, this causes the task to get queued in the target class
> +	 * and experience a 'spurious' wakeup.
> +	 *
> +	 * However, since 'spurious' wakeups are harmless, this shouldn't be a
> +	 * problem.
> +	 */
> +	p->se.sched_delayed = 0;
> +	/*
> +	 * While here, also clear the vlag, it makes little sense to carry that
> +	 * over the excursion into the new class.
> +	 */
> +	p->se.vlag = 0;

RQ lock is held, the task can't be current if it's ->sched_delayed; is a
dequeue_task() not possible at this point?  Or just not worth it?