From 5eaadebf10e77b190f01ecb211c110c69275b7bd Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Fri, 3 Jul 2026 08:52:50 -0700 Subject: workqueue: annotate racy sum_exec_runtime reads for CPU-intensive detection The automatic CPU-intensive work item detection reads the worker task's se.sum_exec_runtime without a lock in wq_worker_running(), wq_worker_tick() and process_one_work(). The scheduler updates that field under the rq lock (from the tick via update_curr(), or cross-CPU via task_sched_runtime()), raising: BUG: KCSAN: data-race in wq_worker_running+0xa8/0xe8 race at unknown origin, with read to 0xffff0009a11d1df8 of 8 bytes by task 238535 on cpu 68: wq_worker_running schedule schedule_preempt_disabled __mutex_lock mutex_lock_nested cgroup_bpf_release process_one_work worker_thread kthread ret_from_fork value changed: 0x0000000088482ba0 -> 0x00000000884893c0 The value only feeds a heuristic, so the race is benign-ish. Unlike commit ecf5aad9a441 ("workqueue: annotate racy PWQ_STAT_CPU_TIME update in wq_worker_tick()") that only needs data_race(), these are plain reads whose result drives a subtraction and comparison, so use READ_ONCE() for a single, non-torn load, which also silences KCSAN. Signed-off-by: Breno Leitao Signed-off-by: Tejun Heo --- kernel/workqueue.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'kernel/workqueue.c') diff --git a/kernel/workqueue.c b/kernel/workqueue.c index f8b5598f7272..4ec3db31493d 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1468,7 +1468,7 @@ void wq_worker_running(struct task_struct *task) * CPU intensive auto-detection cares about how long a work item hogged * CPU without sleeping. Reset the starting timestamp on wakeup. */ - worker->current_at = worker->task->se.sum_exec_runtime; + worker->current_at = READ_ONCE(worker->task->se.sum_exec_runtime); WRITE_ONCE(worker->sleeping, 0); } @@ -1557,7 +1557,7 @@ void wq_worker_tick(struct task_struct *task) * We probably want to make this prettier in the future. */ if ((worker->flags & WORKER_NOT_RUNNING) || READ_ONCE(worker->sleeping) || - worker->task->se.sum_exec_runtime - worker->current_at < + READ_ONCE(worker->task->se.sum_exec_runtime) - worker->current_at < wq_cpu_intensive_thresh_us * NSEC_PER_USEC) return; @@ -3294,7 +3294,7 @@ __acquires(&pool->lock) worker->current_func = work->func; worker->current_pwq = pwq; if (worker->task) - worker->current_at = worker->task->se.sum_exec_runtime; + worker->current_at = READ_ONCE(worker->task->se.sum_exec_runtime); worker->current_start = jiffies; work_data = *work_data_bits(work); worker->current_color = get_work_color(work_data); -- cgit v1.2.3