Re: [PATCH 1/1] thermal: core: call thermal_zone_device_update() after mode update

Keerthy
2016-06-23T12:38:45Z

On Thursday 23 June 2016 05:57 PM, Rafael J. Wysocki wrote:
> On Wed, Jun 22, 2016 at 7:06 AM, Eduardo Valentin <edubezval@gmail.com> wrote:
>> Because several drivers do the following pattern:
>> .set_mode()
>> ...
>> local_data->mode = new_mode;
>> thermal_zone_device_update(tz);
>>
>> makes sense to simply do the thermal_zone_device_update()
>> in thermal core, after setting the new mode.
>>
>> Also, this patch also remove deadlocks on drivers that
>> call thermal_zone_device_update() on .set_mode(),
>> as .set_mode() is now called always with tz->lock held.
>
> To me, this part of the patch is way more important than the
> optimization mentioned before.
>
> Apparently, the problem is that drivers deadlock, because the
> thermal_zone_device_update() invoked from ->set_mode() is called under
> tz->lock.
>
> So to address that problem you make the core call
> thermal_zone_device_update() after ->set_mode() outside of tz->lock
> and the drivers don't have to do it any more.
>
> Is that correct?

Rafael,

On my set up, mode_store locks tz->lock and eventually ends up calling
of_thermal_set_mode before releasing tz->lock which again tries to lock
tz->lock and ends up in a deadlock.

http://pastebin.ubuntu.com/17687601/

Regards,
Keerthy
>
> Thanks,
> Rafael
>