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Re: [RFC PATCH 01/11] workqueue: Add a decrement-after-return and wake if 0 facility

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Hello, David.

On Fri, Sep 01, 2017 at 04:40:53PM +0100, David Howells wrote:
> Add a facility to the workqueue subsystem whereby an atomic_t can be
> registered by a work function such that the work function dispatcher will
> decrement the atomic after the work function has returned and then call
> wake_up_atomic() on it if it reached 0.
> 
> This is analogous to complete_and_exit() for kernel threads and is used to
> avoid a race between notifying that a work item is about to finish and the
> .text segment from a module being discarded.
> 
> The way this is used is that the work function calls:
> 
> 	dec_after_work(atomic_t *counter);
> 
> to register the counter and then process_one_work() calls it, potentially
> wakes it and clears the registration.
> 
> The reason I've used an atomic_t rather than a completion is that (1) it
> takes up less space and (2) it can monitor multiple objects.

Given how work items are used, I think this is too inviting to abuses
where people build complex event chains through these counters and
those chains would be completely opaque.  If the goal is protecting
.text of a work item, can't we just do that?  Can you please describe
your use case in more detail?  Why can't it be done via the usual
"flush from exit"?

Thanks.

-- 
tejun

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[RFC PATCH 01/11] workqueue: Add a decrement-after-return and wake  if 0 facility David Howells <dhowells@redhat.com> - 2017-09-01 17:50 +0200
  [RFC PATCH 00/11] AFS: Namespacing part 1 David Howells <dhowells@redhat.com> - 2017-09-01 18:00 +0200
  Re: [RFC PATCH 01/11] workqueue: Add a decrement-after-return and  wake if 0 facility Tejun Heo <tj@kernel.org> - 2017-09-05 15:40 +0200
    Re: [RFC PATCH 01/11] workqueue: Add a decrement-after-return and wake if 0 facility David Howells <dhowells@redhat.com> - 2017-09-05 17:00 +0200
      Re: [RFC PATCH 01/11] workqueue: Add a decrement-after-return and  wake if 0 facility Tejun Heo <tj@kernel.org> - 2017-09-06 17:00 +0200

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