Re: [PATCH 1/2] PM / sleep: ensure deferred probe workqueue is finished in wait_for_device_probe

[Grygorii Strashko]

On 10/10/2015 12:16 AM, Rafael J. Wysocki wrote:
> On Friday, October 09, 2015 09:38:13 AM Grygorii Strashko wrote:
> > 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.
>
> Well, in that case why don't you make it part of the second patch after all
> instead of making a false impression of fixing a more general problem?

ok.


--
regards,
-grygorii
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