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| author | Vincent Guittot <vincent.guittot@linaro.org> | 2026-05-03 13:45:03 +0300 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-05-06 18:41:18 +0300 |
| commit | 9f6d929ee2c6f0266edb564bcd2bd47fd6e884a8 (patch) | |
| tree | 8d2c487fb8e4a993c470836a58701a7708d65d2c | |
| parent | b6eee96843e8d088200f01b035da98e72067c5fe (diff) | |
| download | linux-9f6d929ee2c6f0266edb564bcd2bd47fd6e884a8.tar.xz | |
sched/fair: Fix wakeup_preempt_fair() for not waking up task
Make sure to only call pick_next_entity() on an non-empty cfs_rq.
The assumption that p is always enqueued and not delayed, is only true for
wakeup. If p was moved while delayed, pick_next_entity() will dequeue it and
the cfs might become empty. Test if there are still queued tasks before trying
again to determine if p could be the next one to be picked.
There are at least 2 cases:
When cfs becomes idle, it tries to pull tasks but if those pulled tasks are
delayed, they will be dequeued when attached to cfs. attach_tasks() ->
attach_task() -> wakeup_preempt(rq, p, 0);
A misfit task running on cfs A triggers a load balance to be pulled on a better
cpu, the load balance on cfs B starts an active load balance to pulled the
running misfit task. If there is a delayed dequeue task on cfs A, it can be
pulled instead of the previously running misfit task. attach_one_task() ->
attach_task() -> wakeup_preempt(rq, p, 0);
Fixes: ac8e69e69363 ("sched/fair: Fix wakeup_preempt_fair() vs delayed dequeue")
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260503104503.1732682-1-vincent.guittot@linaro.org
| -rw-r--r-- | kernel/sched/fair.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index b91c8b294229..3ebec186f982 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9174,9 +9174,10 @@ pick: /* * Because p is enqueued, nse being null can only mean that we - * dequeued a delayed task. + * dequeued a delayed task. If there are still entities queued in + * cfs, check if the next one will be p. */ - if (!nse) + if (!nse && cfs_rq->nr_queued) goto pick; if (sched_feat(RUN_TO_PARITY)) |