Commit 493afbd1 authored by K Prateek Nayak's avatar K Prateek Nayak Committed by Peter Zijlstra
Browse files

sched/fair: Fix NEXT_BUDDY 



Adam reports that enabling NEXT_BUDDY insta triggers a WARN in
pick_next_entity().

Moving clear_buddies() up before the delayed dequeue bits ensures
no ->next buddy becomes delayed. Further ensure no new ->next buddy
ever starts as delayed.

Fixes: 152e11f6 ("sched/fair: Implement delayed dequeue")
Reported-by: default avatarAdam Li <adamli@os.amperecomputing.com>
Signed-off-by: default avatarK Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarAdam Li <adamli@os.amperecomputing.com>
Link: https://lkml.kernel.org/r/670a0d54-e398-4b1f-8a6e-90784e2fdf89@amd.com
parent 82f9cc09

kernel/sched/fair.c

+2 −5
Original line number Diff line number Diff line
@@ -5478,6 +5478,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) 
	bool sleep = flags & DEQUEUE_SLEEP;



	update_curr(cfs_rq);

	clear_buddies(cfs_rq, se);



	if (flags & DEQUEUE_DELAYED) {

		SCHED_WARN_ON(!se->sched_delayed);
@@ -5494,8 +5495,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) 


		if (sched_feat(DELAY_DEQUEUE) && delay &&

		    !entity_eligible(cfs_rq, se)) {

			if (cfs_rq->next == se)

				cfs_rq->next = NULL;

			update_load_avg(cfs_rq, se, 0);

			se->sched_delayed = 1;

			return false;
@@ -5520,8 +5519,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) 


	update_stats_dequeue_fair(cfs_rq, se, flags);



	clear_buddies(cfs_rq, se);



	update_entity_lag(cfs_rq, se);

	if (sched_feat(PLACE_REL_DEADLINE) && !sleep) {

		se->deadline -= se->vruntime;
@@ -8774,7 +8771,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int 
	if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))

		return;



	if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK)) {

	if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK) && !pse->sched_delayed) {

		set_next_buddy(pse);

	}