[tip: sched/urgent] sched/deadline: Use ENQUEUE_MOVE to allow priority change

["tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>]

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

Commit-ID:     627cc25f84466d557d86e5dc67b43a4eea604c80
Gitweb:        https://git.kernel.org/tip/627cc25f84466d557d86e5dc67b43a4eea604c80
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Thu, 15 Jan 2026 09:27:22 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 15 Jan 2026 21:57:53 +01:00

sched/deadline: Use ENQUEUE_MOVE to allow priority change

Pierre reported hitting balance callback warnings for deadline tasks
after commit 6455ad5346c9 ("sched: Move sched_class::prio_changed()
into the change pattern").

It turns out that DEQUEUE_SAVE+ENQUEUE_RESTORE does not preserve DL
priority and subsequently trips a balance pass -- where one was not
expected.

>From discussion with Juri and Luca, the purpose of this clause was to
deal with tasks new to DL and all those sites will have MOVE set (as
well as CLASS, but MOVE is move conservative at this point).

Per the previous patches MOVE is audited to always run the balance
callbacks, so switch enqueue_dl_entity() to use MOVE for this case.

Fixes: 6455ad5346c9 ("sched: Move sched_class::prio_changed() into the change pattern")
Reported-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://patch.msgid.link/20260114130528.GB831285@noisy.programming.kicks-ass.net
---
 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 5d6f3cc..c509f2e 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2214,7 +2214,7 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se, int flags)
 		update_dl_entity(dl_se);
 	} else if (flags & ENQUEUE_REPLENISH) {
 		replenish_dl_entity(dl_se);
-	} else if ((flags & ENQUEUE_RESTORE) &&
+	} else if ((flags & ENQUEUE_MOVE) &&
 		   !is_dl_boosted(dl_se) &&
 		   dl_time_before(dl_se->deadline, rq_clock(rq_of_dl_se(dl_se)))) {
 		setup_new_dl_entity(dl_se);