Re: [PATCH] sched/deadline: Fix missing ENQUEUE_REPLENISH during PI de-boosting

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Feb 09, 2026 at 10:46:18AM +0100, Juri Lelli wrote:

> > (afaict nothing clears dl_se::pi_se except rt_mutex_setprio() so that
> > should still be valid here -- so we don't need to go find it again)
> 
> But, maybe with something like this? I believe we need to make things
> right at this point "promoting" the now becoming lower prio class task
> to DEADLINE (inheriting from the task it didn't inherit from in the
> past). Maybe we can avoid checking pi_task since dl_prio(newprio). And
> also move everything in an helper to remove ifdeffery.
> 
> ---
> diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
> index 6f10db3646e7f..856df1a22e3ca 100644
> --- a/kernel/sched/syscalls.c
> +++ b/kernel/sched/syscalls.c
> @@ -655,6 +655,16 @@ int __sched_setscheduler(struct task_struct *p,
>  			__setscheduler_params(p, attr);
>  			p->sched_class = next_class;
>  			p->prio = newprio;
> +#ifdef CONFIG_RT_MUTEXES
> +			if (dl_prio(newprio) && !dl_policy(policy)) {
> +				struct task_struct *pi_task = rt_mutex_get_top_task(p);
> +
> +				if (pi_task) {
> +					p->dl.pi_se = pi_task->dl.pi_se;
> +					scope->flags |= ENQUEUE_REPLENISH;
> +				}
> +			}
> +#endif
>  		}
>  		__setscheduler_uclamp(p, attr);

I'm still a bit confused on the pi_se thing; if this was a dl task, then
rt_mutex_setprio() would've already set this to pi_task->dl.pi_se, no?

Anyway, yes something like that, possibly with a helper sounds fine.