From mboxrd@z Thu Jan 1 00:00:00 1970 From: Javi Merino Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered Date: Tue, 29 Sep 2015 17:01:34 +0100 Message-ID: <20150929160133.GA11588@e104805> References: <1443332924-14028-1-git-send-email-yu.c.chen@intel.com> <20150928142902.GA9175@e104805> <36DF59CE26D8EE47B0655C516E9CE64026F22641@SHSMSX101.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <36DF59CE26D8EE47B0655C516E9CE64026F22641@SHSMSX101.ccr.corp.intel.com> Sender: stable-owner@vger.kernel.org To: "Chen, Yu C" Cc: "linux-pm@vger.kernel.org" , "edubezval@gmail.com" , "Zhang, Rui" , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" List-Id: linux-pm@vger.kernel.org Hi Yu, On Mon, Sep 28, 2015 at 06:52:00PM +0100, Chen, Yu C wrote: > Hi, Javi, > > > -----Original Message----- > > From: Javi Merino [mailto:javi.merino@arm.com] > > Sent: Monday, September 28, 2015 10:29 PM > > To: Chen, Yu C > > Cc: linux-pm@vger.kernel.org; edubezval@gmail.com; Zhang, Rui; linux- > > kernel@vger.kernel.org; stable@vger.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 > > > > > > > > > > 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? You're right, it could lead to a deadlock. The locks can't be swapped because that won't work in step_wise. The best way that I can think of accessing thermal_instances atomically is by making it RCU protected instead of with mutexes. What do you think? > > 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. It has taken me a while to understand this optimization. Please document both "if"s in the code. For the first "if" maybe you can use list_is_last() to make it easier to understand that you're looking for the last element in the list: if (list_is_last(&pos->cdev_node, &cdev->thermal_instances)) { thermal_zone_device_update(pos->tz); For the second "if" you can say that you only need to run thermal_zone_device_update() once per thermal zone, even though multiple thermal instances may refer to the same thermal zone. Cheers, Javi