linux-kernel - RE: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

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Date:	Mon, 28 Sep 2015 17:52:00 +0000
From:	"Chen, Yu C" <yu.c.chen@...el.com>
To:	Javi Merino <javi.merino@....com>
CC:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"edubezval@...il.com" <edubezval@...il.com>,
	"Zhang, Rui" <rui.zhang@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH 3/3] Thermal: do thermal zone update after a cooling
 device registered

Hi, Javi,

> -----Original Message-----
> From: Javi Merino [mailto:javi.merino@....com]
> Sent: Monday, September 28, 2015 10:29 PM
> To: Chen, Yu C
> Cc: linux-pm@...r.kernel.org; edubezval@...il.com; Zhang, Rui; linux-
> kernel@...r.kernel.org; stable@...r.kernel.org
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> device registered
> 
> On Sun, Sep 27, 2015 at 06:48:44AM +0100, Chen Yu wrote:
> > From: Zhang Rui <rui.zhang@...el.com>
> >
> >
> 
> I think you need to hold cdev->lock here, to make sure that no thermal zone
> is added or removed from cdev->thermal_instances while you are looping.
> 
Ah right, will add. If I add the cdev ->lock here, will there be a AB-BA lock with 
thermal_zone_unbind_cooling_device?

> 
> Why list_for_each_entry_safe() ?  You are not going to remove any entry, so
> you can just use list_for_each_entry()
> 
> 
> Why is this so complicated?  Can't you just do:
> 
> 	list_for_each_entry(pos, &cdev->thermal_instances, cdev_node)
>         	thermal_zone_device_update(pos->tz);
> 

This is an optimization here:
Ignore thermal instance that refers to the same thermal zone in this loop,
this works because bind_cdev() always binds the cooling device to one 
thermal zone first, and then binds to the next thermal zone.


Best Regards,
Yu