Re: [PATCH v2 1/3] sched/fair: Fix warning if NEXT_BUDDY enabled

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Nov 28, 2024 at 12:59:54PM +0530, K Prateek Nayak wrote:

> Can you please try the following diff instead of the first two patches
> and see if you still hit these warnings, stalls, and pick_eevdf()
> returning NULL?
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ff7cae9274c5..61e74eb5af22 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5478,6 +5478,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	bool sleep = flags & DEQUEUE_SLEEP;
>  	update_curr(cfs_rq);
> +	clear_buddies(cfs_rq, se);
>  	if (flags & DEQUEUE_DELAYED) {
>  		SCHED_WARN_ON(!se->sched_delayed);
> @@ -5520,8 +5521,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  	update_stats_dequeue_fair(cfs_rq, se, flags);
> -	clear_buddies(cfs_rq, se);
> -
>  	update_entity_lag(cfs_rq, se);
>  	if (sched_feat(PLACE_REL_DEADLINE) && !sleep) {
>  		se->deadline -= se->vruntime;
> @@ -8767,7 +8766,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
>  	if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
>  		return;
> -	if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK)) {
> +	if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK) && !pse->sched_delayed) {
>  		set_next_buddy(pse);
>  	}


Prateek, I've presumed your SoB on this change:

  https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=sched/urgent&id=d1139307fe97ffefcf90212772f7516732a11034

Holler if you want it modified.

Thanks!