From 0927780c90ce551869fb692279d66387a4b66af5 Mon Sep 17 00:00:00 2001 From: zhidao su Date: Thu, 5 Mar 2026 14:18:56 +0800 Subject: [PATCH] sched_ext: Use READ_ONCE() for lock-free reads of module param variables bypass_lb_cpu() reads scx_bypass_lb_intv_us and scx_slice_bypass_us without holding any lock, in timer callback context where module parameter writes via sysfs can happen concurrently: min_delta_us = scx_bypass_lb_intv_us / SCX_BYPASS_LB_MIN_DELTA_DIV; ^^^^^^^^^^^^^^^^^^^^ plain read -- KCSAN data race if (delta < DIV_ROUND_UP(min_delta_us, scx_slice_bypass_us)) ^^^^^^^^^^^^^^^^^ plain read -- KCSAN data race scx_bypass_lb_intv_us already uses READ_ONCE() in scx_bypass_lb_timerfn() and scx_bypass() for its other lock-free read sites, leaving bypass_lb_cpu() inconsistent. scx_slice_bypass_us has the same lock-free access pattern in the same function. Fix both plain reads by using READ_ONCE() to complete the concurrent access annotation and make the code KCSAN-clean. Signed-off-by: zhidao su Signed-off-by: Tejun Heo --- kernel/sched/ext.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index c56de568ed94..10866bfb88bf 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -3908,8 +3908,8 @@ static u32 bypass_lb_cpu(struct scx_sched *sch, struct rq *rq, * consider offloading iff the total queued duration is over the * threshold. */ - min_delta_us = scx_bypass_lb_intv_us / SCX_BYPASS_LB_MIN_DELTA_DIV; - if (delta < DIV_ROUND_UP(min_delta_us, scx_slice_bypass_us)) + min_delta_us = READ_ONCE(scx_bypass_lb_intv_us) / SCX_BYPASS_LB_MIN_DELTA_DIV; + if (delta < DIV_ROUND_UP(min_delta_us, READ_ONCE(scx_slice_bypass_us))) return 0; raw_spin_rq_lock_irq(rq); -- 2.47.3