sched/deadline: Fix accounting after global limits change

JIRA: https://issues.redhat.com/browse/RHEL-105980

commit 440989c
Author: Juri Lelli <juri.lelli@redhat.com>
Date:   Fri Jun 27 13:51:16 2025 +0200

    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 <marcel.ziswiler@codethink.co.uk>
    Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Tested-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk> # nuc & rock5b
    Link: https://lore.kernel.org/r/20250627115118.438797-4-juri.lelli@redhat.com

Signed-off-by: Phil Auld <pauld@redhat.com>

Author: auldp

kernel/sched/deadline.c

@@ -3282,6 +3282,9 @@ void sched_dl_do_global(void)
 	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();
 
@@ -3297,7 +3300,6 @@ void sched_dl_do_global(void)
 		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

@@ -2938,6 +2938,12 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
 	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;
 }