linux-kernel - Re: [PATCH 1/1] thermal: core: call thermal_zone_device

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Message-ID: <576BD826.6030007@ti.com>
Date:	Thu, 23 Jun 2016 18:07:58 +0530
From:	Keerthy <a0393675@...com>
To:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Eduardo Valentin <edubezval@...il.com>
CC:	Rui Zhang <rui.zhang@...el.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"Lee, Chun-Yi" <jlee@...e.com>, Darren Hart <dvhart@...radead.org>,
	Keerthy <j-keerthy@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	<platform-driver-x86@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 1/1] thermal: core: call thermal_zone_device_update()
 after mode update



On Thursday 23 June 2016 05:57 PM, Rafael J. Wysocki wrote:
> On Wed, Jun 22, 2016 at 7:06 AM, Eduardo Valentin <edubezval@...il.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
>