From: Johannes Weiner <hannes@xxxxxxxxxxx> Subject: kernel: workqueue: clarify wq_worker_last_func() caller requirements This function can only be called safely from very specific scheduler contexts. Document those. Link: http://lkml.kernel.org/r/20190206150528.31198-1-hannes@xxxxxxxxxxx Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/kernel/workqueue.c~kernel-workqueue-clarify-wq_worker_last_func-caller-requirements +++ a/kernel/workqueue.c @@ -920,6 +920,16 @@ struct task_struct *wq_worker_sleeping(s * CONTEXT: * spin_lock_irq(rq->lock) * + * This function is called during schedule() when a kworker is going + * to sleep. It's used by psi to identify aggregation workers during + * dequeuing, to allow periodic aggregation to shut-off when that + * worker is the last task in the system or cgroup to go to sleep. + * + * As this function doesn't involve any workqueue-related locking, it + * only returns stable values when called from inside the scheduler's + * queuing and dequeuing paths, when @task, which must be a kworker, + * is guaranteed to not be processing any works. + * * Return: * The last work function %current executed as a worker, NULL if it * hasn't executed any work yet. _
