From ecf5aad9a4417fece80890f27a9899db90c9c457 Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Thu, 2 Jul 2026 09:28:00 -0700 Subject: [PATCH] workqueue: annotate racy PWQ_STAT_CPU_TIME update in wq_worker_tick() wq_worker_tick() bumps pwq->stats[PWQ_STAT_CPU_TIME] on every scheduler tick before pool->lock is taken. For unbound workqueues the pool_workqueue is shared by all workers of the pool across CPUs, so concurrent ticks on different CPUs perform an unsynchronized 64-bit read-modify-write on the same counter. KCSAN reports this as a data-race: BUG: KCSAN: data-race in wq_worker_tick / wq_worker_tick read-write to 0xffff0004d6989500 of 8 bytes by interrupt on cpu 29: wq_worker_tick+0x70/0x418 sched_tick+0x248/0x3a0 update_process_times+0x200/0x260 tick_nohz_handler+0x230/0x2f8 __hrtimer_run_queues+0x1ec/0x6c8 hrtimer_interrupt+0x174/0x4b8 ... read-write to 0xffff0004d6989500 of 8 bytes by interrupt on cpu 24: wq_worker_tick+0x70/0x418 sched_tick+0x248/0x3a0 ... value changed: 0x000000000010a1d0 -> 0x000000000010a9a0 The counter is purely advisory, so an occasional lost update is harmless, and every other stats[] update already runs under pool->lock. Annotate the update with data_race(). Signed-off-by: Breno Leitao Signed-off-by: Tejun Heo --- kernel/workqueue.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 86b6e43d41b5..f8b5598f7272 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1535,7 +1535,11 @@ void wq_worker_tick(struct task_struct *task) if (!pwq) return; - pwq->stats[PWQ_STAT_CPU_TIME] += TICK_USEC; + /* + * @pwq is shared across CPUs for unbound wqs and this advisory stat is + * bumped outside pool->lock, so the update is intentionally racy. + */ + data_race(pwq->stats[PWQ_STAT_CPU_TIME] += TICK_USEC); if (!wq_cpu_intensive_thresh_us) return;