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Miscellaneous scheduler fixes:

Browse Source 
- Fix the delayed dequeue negative lag increase fix in the
    fair scheduler (Peter Zijlstra)
 
  - Fix wakeup_preempt_fair() to do proper delayed dequeue
    (Vincent Guittot)
 
  - Clear sched_entity::rel_deadline when initializing
    forked entities, which bug can cause all tasks to be
    EEVDF-ineligible, causing a NULL pointer dereference
    crash in pick_next_entity() (Zicheng Qu)
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-urgent-2026-05-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:

 - Fix the delayed dequeue negative lag increase fix in the
   fair scheduler (Peter Zijlstra)

 - Fix wakeup_preempt_fair() to do proper delayed dequeue
   (Vincent Guittot)

 - Clear sched_entity::rel_deadline when initializing
   forked entities, which bug can cause all tasks to be
   EEVDF-ineligible, causing a NULL pointer dereference
   crash in pick_next_entity() (Zicheng Qu)

* tag 'sched-urgent-2026-05-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Clear rel_deadline when initializing forked entities
  sched/fair: Fix wakeup_preempt_fair() vs delayed dequeue
  sched/fair: Fix the negative lag increase fix
This commit is contained in:
Linus Torvalds 2026-05-03 08:05:23 -07:00
commit c3cba36b39
2 changed files with 26 additions and 19 deletions
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1
kernel/sched/core.c
View File

@ -4458,6 +4458,7 @@ static void __sched_fork(u64 clone_flags, struct task_struct *p)
p->se.nr_migrations = 0;
p->se.vruntime = 0;
p->se.vlag = 0;
p->se.rel_deadline = 0;
INIT_LIST_HEAD(&p->se.group_node);
/* A delayed task cannot be in clone(). */

44
kernel/sched/fair.c
View File

@ -847,13 +847,19 @@ static s64 entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se, u64 avrunt
* Similarly, check that the entity didn't gain positive lag when DELAY_ZERO
* is set.
*
* Return true if the lag has been adjusted.
* Return true if the vlag has been modified. Specifically:
*
* se->vlag != avg_vruntime() - se->vruntime
*
* This can be due to clamping in entity_lag() or clamping due to
* sched_delayed. Either way, when vlag is modified and the entity is
* retained, the tree needs to be adjusted.
*/
static __always_inline
bool update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
s64 vlag = entity_lag(cfs_rq, se, avg_vruntime(cfs_rq));
bool ret;
u64 avruntime = avg_vruntime(cfs_rq);
s64 vlag = entity_lag(cfs_rq, se, avruntime);
WARN_ON_ONCE(!se->on_rq);
@ -863,10 +869,9 @@ bool update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
if (sched_feat(DELAY_ZERO))
vlag = min(vlag, 0);
}
ret = (vlag == se->vlag);
se->vlag = vlag;
return ret;
return avruntime - vlag != se->vruntime;
}
/*
@ -1099,7 +1104,7 @@ static inline void cancel_protect_slice(struct sched_entity *se)
*
* Which allows tree pruning through eligibility.
*/
static struct sched_entity *__pick_eevdf(struct cfs_rq *cfs_rq, bool protect)
static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq, bool protect)
{
struct rb_node *node = cfs_rq->tasks_timeline.rb_root.rb_node;
struct sched_entity *se = __pick_first_entity(cfs_rq);
@ -1170,11 +1175,6 @@ static struct sched_entity *__pick_eevdf(struct cfs_rq *cfs_rq, bool protect)
return best;
}
static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq)
{
return __pick_eevdf(cfs_rq, true);
}
struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
{
struct rb_node *last = rb_last(&cfs_rq->tasks_timeline.rb_root);
@ -5749,11 +5749,11 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags);
* 4) do not run the "skip" process, if something else is available
*/
static struct sched_entity *
pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq, bool protect)
{
struct sched_entity *se;
se = pick_eevdf(cfs_rq);
se = pick_eevdf(cfs_rq, protect);
if (se->sched_delayed) {
dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
/*
@ -9027,7 +9027,7 @@ static void wakeup_preempt_fair(struct rq *rq, struct task_struct *p, int wake_f
{
enum preempt_wakeup_action preempt_action = PREEMPT_WAKEUP_PICK;
struct task_struct *donor = rq->donor;
struct sched_entity *se = &donor->se, *pse = &p->se;
struct sched_entity *nse, *se = &donor->se, *pse = &p->se;
struct cfs_rq *cfs_rq = task_cfs_rq(donor);
int cse_is_idle, pse_is_idle;
@ -9138,12 +9138,18 @@ static void wakeup_preempt_fair(struct rq *rq, struct task_struct *p, int wake_f
}
pick:
/*
* If @p has become the most eligible task, force preemption.
*/
if (__pick_eevdf(cfs_rq, preempt_action != PREEMPT_WAKEUP_SHORT) == pse)
nse = pick_next_entity(rq, cfs_rq, preempt_action != PREEMPT_WAKEUP_SHORT);
/* If @p has become the most eligible task, force preemption */
if (nse == pse)
goto preempt;
/*
* Because p is enqueued, nse being null can only mean that we
* dequeued a delayed task.
*/
if (!nse)
goto pick;
if (sched_feat(RUN_TO_PARITY))
update_protect_slice(cfs_rq, se);
@ -9179,7 +9185,7 @@ static struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
throttled |= check_cfs_rq_runtime(cfs_rq);
se = pick_next_entity(rq, cfs_rq);
se = pick_next_entity(rq, cfs_rq, true);
if (!se)
goto again;
cfs_rq = group_cfs_rq(se);