On 10/08/2015 03:53 PM, Alan Stern wrote:
> On Thu, 8 Oct 2015, Rafael J. Wysocki wrote:
>
>>> @@ -391,6 +391,10 @@ int driver_probe_done(void)
>>> */
>>> void wait_for_device_probe(void)
>>> {
>>> + /* wait for the deferred probe workqueue to finish */
>>> + if (driver_deferred_probe_enable)
>>> + flush_workqueue(deferred_wq);
>>> +
>>> /* wait for the known devices to complete their probing */
>>> wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
>>> async_synchronize_full();
>>
>> I'm not sure if this is sufficient.
>>
>> Something may be added to the workqueue right after you've flushed it and
>> then be reporobed after the wait_event() in theory. Or am I missing
>> anything?
>
> Maybe I'm missing part of this, but I think the point is to make sure
> that every probe which began or was queued before this function got
> called, has finished before the function returns.
>
> Thus, in the case at hand we want to defer all probes starting from
> some point in the system sleep transition. Grygorii sets his
> defer_all_probes variable and then calls this function. It waits for
> any probes that were initiated before the function call. Any probe
> that was initiated after the function call (for example, the ones
> you're concerned about between the flush_workqueue and wait_event) will
> see that defer_all_probes is set and so will defer itself.
Yes. It will work as expected with the next patch.
For all other case, where this API is used alone -
it will make things more safe, but there is no way to completely block
scheduling of new probes.
>
> Now, I'm not sure what happens when a probe that was deferred tries to
> defer itself again. Do we end up in an infinite probing loop?
No. handling of defered probes will be re triggered only if
some probe was finished successfully.
> Is the deferred_wq workqueue freezable?
seems WQ_FREEZABLE is not set for this WQ.
--
regards,
-grygorii
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