The patch titled
Subject: kernel: workqueue: clarify wq_worker_last_func() caller requirements
has been added to the -mm tree. Its filename is
kernel-workqueue-clarify-wq_worker_last_func-caller-requirements.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kernel-workqueue-clarify-wq_worker_last_func-caller-requirements.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kernel-workqueue-clarify-wq_worker_last_func-caller-requirements.patch
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------------------------------------------------------
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
@@ -918,6 +918,16 @@ 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.
_
Patches currently in -mm which might be from hannes@xxxxxxxxxxx are
fs-kernfs-add-poll-file-operation.patch
kernel-cgroup-add-poll-file-operation.patch
kernel-workqueue-clarify-wq_worker_last_func-caller-requirements.patch
