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

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Message-ID: <20160701205329.GB7814@localhost.localdomain>
Date:	Fri, 1 Jul 2016 13:53:31 -0700
From:	Eduardo Valentin <edubezval@...il.com>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
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 Thu, Jun 23, 2016 at 02:27:12PM +0200, 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?

Yes this is correct. The optimization is simply a consequence of the bug
fix, as reported by Keerthy.

> 
> Thanks,
> Rafael