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Fix a cfs_rq->h_nr_runnable accounting bug that trips up a

Browse source 
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.
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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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
This commit is contained in:
Linus Torvalds 2025-02-08 11:16:22 -08:00
commit c7b92e8969
2 changed files with 21 additions and 0 deletions
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2
kernel/sched/debug.c
View file

@ -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));

19
kernel/sched/fair.c
View file

@ -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);