Re: [PATCH v3] dell-rbtn: Ignore ACPI notifications if device is suspended

[Darren Hart]

On Thu, May 19, 2016 at 03:30:32PM +0200, Pali Rohár wrote:
> On Monday 25 April 2016 22:06:11 Gabriele Mazzotta wrote:
> > 2016-04-18 14:35 GMT+02:00 Pali Rohár <pali.rohar@xxxxxxxxx>:
> > > On Tuesday 29 March 2016 15:11:35 Rafael J. Wysocki wrote:
> > >> On Monday, March 28, 2016 10:33:09 AM Darren Hart wrote:
> > >> > On Thu, Mar 24, 2016 at 12:24:56PM +0100, Gabriele Mazzotta wrote:
> > >> > > 2016-03-24 10:39 GMT+01:00 Pali Rohár <pali.rohar@xxxxxxxxx>:
> > >> > > > On Monday 21 March 2016 16:13:34 Gabriele Mazzotta wrote:
> > >> > > >> 2016-03-21 13:17 GMT+01:00 Pali Rohár <pali.rohar@xxxxxxxxx>:
> > >> > > >> > On Friday 18 March 2016 23:44:23 Gabriele Mazzotta wrote:
> > >> > > >> >> +#ifdef CONFIG_PM_SLEEP
> > >> > > >> >> +static void ACPI_SYSTEM_XFACE rbtn_acpi_clear_flag(void *context)
> > >> > > >> >> +{
> > >> > > >> >> +     struct rbtn_data *rbtn_data = context;
> > >> > > >> >> +
> > >> > > >> >> +     rbtn_data->suspended = false;
> > >> > > >> >> +}
> > >> > > >> >> +
> > >> > > >> >> +static int rbtn_suspend(struct device *dev)
> > >> > > >> >> +{
> > >> > > >> >> +     struct acpi_device *device = to_acpi_device(dev);
> > >> > > >> >> +     struct rbtn_data *rbtn_data = acpi_driver_data(device);
> > >> > > >> >> +
> > >> > > >> >> +     rbtn_data->suspended = true;
> > >> > > >> >> +
> > >> > > >> >> +     return 0;
> > >> > > >> >> +}
> > >> > > >> >> +
> > >> > > >> >> +static int rbtn_resume(struct device *dev)
> > >> > > >> >> +{
> > >> > > >> >> +     struct acpi_device *device = to_acpi_device(dev);
> > >> > > >> >> +     struct rbtn_data *rbtn_data = acpi_driver_data(device);
> > >> > > >> >> +     acpi_status status;
> > >> > > >> >> +
> > >> > > >> >> +     /*
> > >> > > >> >> +      * Clear the flag only after we received the extra
> > >> > > >> >> +      * ACPI notification.
> > >> > > >> >> +      */
> > >> > > >> >> +     status = acpi_os_execute(OSL_NOTIFY_HANDLER,
> > >> > > >> >> +                      rbtn_acpi_clear_flag, rbtn_data);
> > >> > > >> >> +     if (ACPI_FAILURE(status))
> > >> > > >> >> +             rbtn_data->suspended = false;
> > >> > > >> >
> > >> > > >> > I case when acpi_os_execute success it calls rbtn_acpi_clear_flag,
> > >> > > >> > right? And that will set suspended to false. When acpi_os_execute fails,
> > >> > > >> > then it set suspended too to false... Then whole acpi_os_execute doing
> > >> > > >> > just "barrier" after which suspended flag can be set to false. So I
> > >> > > >> > think rbtn_acpi_clear_flag function is not needed here.
> > >> > > >> >
> > >> > > >> > Cannot you pass NULL or empty function pointer as callback? Or what was
> > >> > > >> > reason to do that flag clearing at "two places"?
> > >> > > >>
> > >> > > >> acpi_os_execute doesn't wait for the callback to be executed, so
> > >> > > >> I can't clear the flag from rbtn_resume.
> > >> > > >
> > >> > > > acpi_os_execute calls callback asynchronously later? Or what exactly do it?
> > >> > >
> > >> > > In this case, it adds the callback to the kacpi_notify_wq workqueue
> > >> > > for deferred execution.
> > >> >
> > >> > +Rafael for context/advice on the use of acpi_os_execute here.
> > >> >
> > >> > This is true, but a quick scan through that call path doesn't tell me why we
> > >> > would need to call it here instead of just setting rbtn_data->suspended = false.
> > >> > The comment suggests waiting for the event, but is that what this is doing? It
> > >> > appears to me to be immediately scheduling the function to a work queue, not
> > >> > waiting for the event notifier.
> > >>
> > >> I think this is supposed to work as a barrier.  That is, it will only run after
> > >> all events in the queue have been processed.
> > >>
> > >> I'm not sure if that's necessary, though.
> > >>
> > >> Thanks,
> > >> Rafael
> > >>
> > >
> > > Darren, Gabriele, what is state of this patch? Bug is not still fixed,
> > > right?
> > 
> > Yes, the bug is still there and this patch fixes it.
> > 
> > Just to make it clear, we need the barrier. Andrei could reproduce
> > the bug without it [1], but not with it, as he confirmed in this
> > thread [2].
> > 
> > [1] http://article.gmane.org/gmane.linux.drivers.platform.x86.devel/8001
> > [2] http://article.gmane.org/gmane.linux.drivers.platform.x86.devel/8937
> 
> Ok, so it means that somebody (who understand ACPI) should review code
> and accept it or show what is needed to fix. Plus maybe adds more
> comments how that "barrier" works as I was first confused...
> 
> Darren, Rafael, can you do review of this patch?
> 

Pali and Gabriele have responded to all questions raised. I have some
reservations that this solution is still a bit racy, but it does fix the problem
for the affected users.

I've queued this. Thanks for your patience.

-- 
Darren Hart
Intel Open Source Technology Center