From: Tejun Heo Date: Mon, 29 Jun 2026 22:55:48 +0000 (-1000) Subject: sched_ext: Don't warn on core-sched forced idle in put_prev_task_scx() X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=b7d9c359e5cf867f7eb23df3bb1c6b9e58af24da;p=thirdparty%2Fkernel%2Flinux.git sched_ext: Don't warn on core-sched forced idle in put_prev_task_scx() put_prev_task_scx() warns when a runnable task drops to a lower sched_class without SCX_OPS_ENQ_LAST, on the assumption that balance_one() would have kept it running. Core scheduling breaks that: a forced-idle SMT sibling reschedules through the core_pick fast path in pick_next_task(), which skips pick_task_scx() and thus balance_one(), so a runnable task can drop to idle with ENQ_LAST unset. Gate the warning on sched_cpu_cookie_match(): a cookie mismatch means core scheduling forced the idle, while a match (or core scheduling off) still catches a genuine missing-ENQ_LAST drop. Fixes: 7c65ae81ea86 ("sched_ext: Don't call put_prev_task_scx() before picking the next task") Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c index 3b2e13bc924b..e75e2fd5ab7e 100644 --- a/kernel/sched/ext/ext.c +++ b/kernel/sched/ext/ext.c @@ -3090,9 +3090,14 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p, * sched_class, %SCX_OPS_ENQ_LAST must be set. Tell * ops.enqueue() that @p is the only one available for this cpu, * which should trigger an explicit follow-up scheduling event. + * + * Core scheduling can force this CPU idle while @p stays + * runnable. @p's cookie then won't match the core's, so skip + * the warning in that case. */ if (next && sched_class_above(&ext_sched_class, next->sched_class)) { - WARN_ON_ONCE(!(sch->ops.flags & SCX_OPS_ENQ_LAST)); + WARN_ON_ONCE(sched_cpu_cookie_match(rq, p) && + !(sch->ops.flags & SCX_OPS_ENQ_LAST)); do_enqueue_task(rq, p, SCX_ENQ_LAST, -1); } else { do_enqueue_task(rq, p, 0, -1);