Merge tag 'sched-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:
 "Fix a cfs_rq->h_nr_runnable accounting bug that trips up a defensive
  SCHED_WARN_ON() on certain workloads. The bug is believed to be
  (accidentally) self-correcting, hence no behavioral side effects are
  expected.

  Also print se.slice in debug output, since this value can now be set
  via the syscall ABI and can be useful to track"

* tag 'sched-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/debug: Provide slice length for fair tasks
  sched/fair: Fix inaccurate h_nr_runnable accounting with delayed dequeue

Author: torvalds

kernel/sched/debug.c

@@ -1262,6 +1262,8 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
 	if (task_has_dl_policy(p)) {
 		P(dl.runtime);
 		P(dl.deadline);
+	} else if (fair_policy(p->policy)) {
+		P(se.slice);
 	}
 #ifdef CONFIG_SCHED_CLASS_EXT
 	__PS("ext.enabled", task_on_scx(p));

kernel/sched/fair.c

@@ -5385,6 +5385,15 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
 static void set_delayed(struct sched_entity *se)
 {
 	se->sched_delayed = 1;
+
+	/*
+	 * Delayed se of cfs_rq have no tasks queued on them.
+	 * Do not adjust h_nr_runnable since dequeue_entities()
+	 * will account it for blocked tasks.
+	 */
+	if (!entity_is_task(se))
+		return;
+
 	for_each_sched_entity(se) {
 		struct cfs_rq *cfs_rq = cfs_rq_of(se);
 
@@ -5397,6 +5406,16 @@ static void set_delayed(struct sched_entity *se)
 static void clear_delayed(struct sched_entity *se)
 {
 	se->sched_delayed = 0;
+
+	/*
+	 * Delayed se of cfs_rq have no tasks queued on them.
+	 * Do not adjust h_nr_runnable since a dequeue has
+	 * already accounted for it or an enqueue of a task
+	 * below it will account for it in enqueue_task_fair().
+	 */
+	if (!entity_is_task(se))
+		return;
+
 	for_each_sched_entity(se) {
 		struct cfs_rq *cfs_rq = cfs_rq_of(se);