Merge tag 'sched-urgent-2026-03-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fix from Ingo Molnar:
 "Fix a DL scheduler bug that may corrupt internal metrics during PI and
  setscheduler() syscalls, resulting in kernel warnings and misbehavior.

  Found during stress-testing"

* tag 'sched-urgent-2026-03-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/deadline: Fix missing ENQUEUE_REPLENISH during PI de-boosting

1 files changed, 30 insertions, 0 deletions

diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index 6f10db3646e7..cadb0e9fe19b 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -284,6 +284,35 @@ static bool check_same_owner(struct task_struct *p)
 		uid_eq(cred->euid, pcred->uid));
 }
 
+#ifdef CONFIG_RT_MUTEXES
+static inline void __setscheduler_dl_pi(int newprio, int policy,
+			      struct task_struct *p,
+			      struct sched_change_ctx *scope)
+{
+	/*
+	 * In case a DEADLINE task (either proper or boosted) gets
+	 * setscheduled to a lower priority class, check if it neeeds to
+	 * inherit parameters from a potential pi_task. In that case make
+	 * sure replenishment happens with the next enqueue.
+	 */
+
+	if (dl_prio(newprio) && !dl_policy(policy)) {
+		struct task_struct *pi_task = rt_mutex_get_top_task(p);
+
+		if (pi_task) {
+			p->dl.pi_se = pi_task->dl.pi_se;
+			scope->flags |= ENQUEUE_REPLENISH;
+		}
+	}
+}
+#else /* !CONFIG_RT_MUTEXES */
+static inline void __setscheduler_dl_pi(int newprio, int policy,
+			      struct task_struct *p,
+			      struct sched_change_ctx *scope)
+{
+}
+#endif /* !CONFIG_RT_MUTEXES */
+
 #ifdef CONFIG_UCLAMP_TASK
 
 static int uclamp_validate(struct task_struct *p,
@@ -655,6 +684,7 @@ change:
 			__setscheduler_params(p, attr);
 			p->sched_class = next_class;
 			p->prio = newprio;
+			__setscheduler_dl_pi(newprio, policy, p, scope);
 		}
 		__setscheduler_uclamp(p, attr);