From ca125231dd29fc0678dd3622e9cdea80a51dffe4 Mon Sep 17 00:00:00 2001 From: xupengbo Date: Wed, 27 Aug 2025 10:22:07 +0800 Subject: [PATCH] sched/fair: Fix unfairness caused by stalled tg_load_avg_contrib when the last task migrates out When a task is migrated out, there is a probability that the tg->load_avg value will become abnormal. The reason is as follows: 1. Due to the 1ms update period limitation in update_tg_load_avg(), there is a possibility that the reduced load_avg is not updated to tg->load_avg when a task migrates out. 2. Even though __update_blocked_fair() traverses the leaf_cfs_rq_list and calls update_tg_load_avg() for cfs_rqs that are not fully decayed, the key function cfs_rq_is_decayed() does not check whether cfs->tg_load_avg_contrib is null. Consequently, in some cases, __update_blocked_fair() removes cfs_rqs whose avg.load_avg has not been updated to tg->load_avg. Add a check of cfs_rq->tg_load_avg_contrib in cfs_rq_is_decayed(), which fixes the case (2.) mentioned above. Fixes: 1528c661c24b ("sched/fair: Ratelimit update to tg->load_avg") Signed-off-by: xupengbo Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Aaron Lu Reviewed-by: Vincent Guittot Tested-by: Aaron Lu Link: https://patch.msgid.link/20250827022208.14487-1-xupengbo@oppo.com --- kernel/sched/fair.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 769d7b7990df..da46c3164537 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4034,6 +4034,9 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq) if (child_cfs_rq_on_list(cfs_rq)) return false; + if (cfs_rq->tg_load_avg_contrib) + return false; + return true; }