sched/deadline: Fix accounting after global limits change

A global limits change (sched_rt_handler() logic) currently leaves stale
and/or incorrect values in variables related to accounting (e.g.
extra_bw).

Properly clean up per runqueue variables before implementing the change
and rebuild scheduling domains (so that accounting is also properly
restored) after such a change is complete.

Reported-by: Marcel Ziswiler <[e-mail]>
Signed-off-by: Juri Lelli <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Tested-by: Marcel Ziswiler <[e-mail]> # nuc & rock5b
Link: https://lore.kernel.org/r/[e-mail]

kernel/sched/deadline.c

···
 	if (global_rt_runtime() != RUNTIME_INF)
 		new_bw = to_ratio(global_rt_period(), global_rt_runtime());
 
+	for_each_possible_cpu(cpu)
+		init_dl_rq_bw_ratio(&cpu_rq(cpu)->dl);
+
 	for_each_possible_cpu(cpu) {
 		rcu_read_lock_sched();
 
···
 		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
 		rcu_read_unlock_sched();
-		init_dl_rq_bw_ratio(&cpu_rq(cpu)->dl);
 	}
 }
 

kernel/sched/rt.c

···
 	sched_domains_mutex_unlock();
 	mutex_unlock(&mutex);
 
+	/*
+	 * After changing maximum available bandwidth for DEADLINE, we need to
+	 * recompute per root domain and per cpus variables accordingly.
+	 */
+	rebuild_sched_domains();
+
 	return ret;
 }