[RFC 1/6] sched: Add nice value change notifier

[Peter Zijlstra]

On Thu, Sep 30, 2021 at 06:15:47PM +0100, Tvrtko Ursulin wrote:
>  void set_user_nice(struct task_struct *p, long nice)
>  {
>  	bool queued, running;
> -	int old_prio;
> +	int old_prio, ret;
>  	struct rq_flags rf;
>  	struct rq *rq;
>  
> @@ -6913,6 +6945,9 @@ void set_user_nice(struct task_struct *p, long nice)
>  	 */
>  	p->sched_class->prio_changed(rq, p, old_prio);
>  
> +	ret = atomic_notifier_call_chain(&user_nice_notifier_list, nice, p);
> +	WARN_ON_ONCE(ret != NOTIFY_DONE);
> +
>  out_unlock:
>  	task_rq_unlock(rq, p, &rf);
>  }

No, we're not going to call out to exported, and potentially unbounded,
functions under scheduler locks.