[PATCH] sched/core: Fix stale se.load when modifying nice value under sched_ext

[Wanwu Li]

From: Wanwu Li <liwanwu@xxxxxxxxxx>

When a task's nice value is modified while running under sched_ext
scheduling class, set_load_weight() calls reweight_task() which only
updates static_prio but leaves p->se.load unchanged because sched_ext
does not use it. After switching back to CFS, the stale se.load leads
to incorrect load weight calculation.

Fix this by explicitly refreshing p->se.load for sched_ext tasks after
calling reweight_task().

Fixes: d32960528702 ("sched/fair: set_load_weight() must also call reweight_task() for SCHED_IDLE tasks")
Signed-off-by: Wanwu Li <liwanwu@xxxxxxxxxx>
---
 kernel/sched/core.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 96226707c2f6..ebeadec41eb6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1538,10 +1538,21 @@ void set_load_weight(struct task_struct *p, bool update_load)
 	 * SCHED_OTHER tasks have to update their load when changing their
 	 * weight
 	 */
-	if (update_load && p->sched_class->reweight_task)
+	if (update_load && p->sched_class->reweight_task) {
 		p->sched_class->reweight_task(task_rq(p), p, &lw);
-	else
+
+		/*
+		 * If modify nice while task runs under ext class, only
+		 * static_prio updates, p->se.load stays stale and mismatches
+		 * the new nice value. After switching back to CFS, outdated
+		 * load leads to incorrect weight. Synchronously refresh
+		 * se.load to keep priority state consistent.
+		 */
+		if (task_on_scx(p))
+			p->se.load = lw;
+	} else {
 		p->se.load = lw;
+	}
 }
 
 #ifdef CONFIG_UCLAMP_TASK
-- 
2.25.1