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authorkuyo chang <kuyo.chang@mediatek.com>2022-04-14 17:02:20 +0800
committerPeter Zijlstra <peterz@infradead.org>2022-04-19 21:15:41 +0200
commit40f5aa4c5eaebfeaca4566217cb9c468e28ed682 (patch)
tree030ff237ce759d040bdb01ebe5420bc2ed330516 /kernel
parentb2d229d4ddb17db541098b83524d901257e93845 (diff)
sched/pelt: Fix attach_entity_load_avg() corner case
The warning in cfs_rq_is_decayed() triggered: SCHED_WARN_ON(cfs_rq->avg.load_avg || cfs_rq->avg.util_avg || cfs_rq->avg.runnable_avg) There exists a corner case in attach_entity_load_avg() which will cause load_sum to be zero while load_avg will not be. Consider se_weight is 88761 as per the sched_prio_to_weight[] table. Further assume the get_pelt_divider() is 47742, this gives: se->avg.load_avg is 1. However, calculating load_sum: se->avg.load_sum = div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se)); se->avg.load_sum = 1*47742/88761 = 0. Then enqueue_load_avg() adds this to the cfs_rq totals: cfs_rq->avg.load_avg += se->avg.load_avg; cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum; Resulting in load_avg being 1 with load_sum is 0, which will trigger the WARN. Fixes: f207934fb79d ("sched/fair: Align PELT windows between cfs_rq and its se") Signed-off-by: kuyo chang <kuyo.chang@mediatek.com> [peterz: massage changelog] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Link: https://lkml.kernel.org/r/20220414090229.342-1-kuyo.chang@mediatek.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/fair.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d4bd299d67ab..a68482d66535 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3829,11 +3829,11 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
se->avg.runnable_sum = se->avg.runnable_avg * divider;
- se->avg.load_sum = divider;
- if (se_weight(se)) {
- se->avg.load_sum =
- div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se));
- }
+ se->avg.load_sum = se->avg.load_avg * divider;
+ if (se_weight(se) < se->avg.load_sum)
+ se->avg.load_sum = div_u64(se->avg.load_sum, se_weight(se));
+ else
+ se->avg.load_sum = 1;
enqueue_load_avg(cfs_rq, se);
cfs_rq->avg.util_avg += se->avg.util_avg;