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workqueue: annotate racy sum_exec_runtime reads for CPU-intensive detection

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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 ecf5aad9a4 ("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 <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Breno Leitao 2026-07-03 08:52:50 -07:00 committed by Tejun Heo
parent ecf5aad9a4
commit 5eaadebf10
1 changed files with 3 additions and 3 deletions
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6
kernel/workqueue.c
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@ -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);