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kernel: workqueue: clarify wq_worker_last_func() caller requirements

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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 <hannes@cmpxchg.org>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change-Id: Iba9616c0193affb09f04daa59efb5a76f8d8f637
Git-commit: 4b0470027528ba98f9617f4ceba328de71d2fe49
Git-repo: https://source.codeaurora.org/quic/la/kernel/msm
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
This commit is contained in:
Johannes Weiner
2019-03-07 16:29:30 -08:00
committed by Patrick Daly
parent ab214458fb
commit 680e58e76f
1 changed files with 10 additions and 0 deletions
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10
kernel/workqueue.c
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@@ -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.