[tip: sched/core] sched/deadline: Ignore special tasks when rebuilding domains

["tip-bot2 for Juri Lelli" <tip-bot2@linutronix.de>]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     f6147af176eaa4027b692fdbb1a0a60dfaa1e9b6
Gitweb:        https://git.kernel.org/tip/f6147af176eaa4027b692fdbb1a0a60dfaa1e9b6
Author:        Juri Lelli <juri.lelli@redhat.com>
AuthorDate:    Thu, 13 Mar 2025 18:00:04 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 17 Mar 2025 11:23:41 +01:00

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: 53916d5fd3c0 ("sched/deadline: Check bandwidth overflow earlier for hotplug")
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Waiman Long <longman@redhat.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20250313170011.357208-2-juri.lelli@redhat.com
---
 kernel/sched/deadline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index ff4df16..1a041c1 100644
--- a/kernel/sched/deadline.c
+++ b/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;
 	}