From 4b0470027528ba98f9617f4ceba328de71d2fe49 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Thu, 7 Mar 2019 16:29:30 -0800 Subject: [PATCH] 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@cmpxchg.org Signed-off-by: Johannes Weiner Suggested-by: Andrew Morton Acked-by: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/workqueue.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 56814902bc56..d51c37dd9422 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -920,6 +920,16 @@ struct task_struct *wq_worker_sleeping(struct task_struct *task) * 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.