sched/deadline: Ignore special tasks when rebuilding domains

SCHED_DEADLINE special tasks get a fake bandwidth that is only used to
make sure sleeping and priority inheritance 'work', but it is ignored
for runtime enforcement and admission control.

Be consistent with it also when rebuilding root domains.

Fixes: 53916d5 ("sched/deadline: Check bandwidth overflow earlier for hotplug")
Reported-by: Jon Hunter <[email protected]>
Signed-off-by: Juri Lelli <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Reviewed-by: Dietmar Eggemann <[email protected]>
Tested-by: Waiman Long <[email protected]>
Tested-by: Jon Hunter <[email protected]>
Tested-by: Dietmar Eggemann <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: jlelli

kernel/sched/deadline.c

@@ -2956,7 +2956,7 @@ void dl_add_task_root_domain(struct task_struct *p)
 	struct dl_bw *dl_b;
 
 	raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
-	if (!dl_task(p)) {
+	if (!dl_task(p) || dl_entity_is_special(&p->dl)) {
 		raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
 		return;
 	}