Hi, Javi Sorry for my late response, > -----Original Message----- > From: Javi Merino [mailto:javi.merino@xxxxxxx] > Sent: Wednesday, September 30, 2015 12:02 AM > To: Chen, Yu C > Cc: linux-pm@xxxxxxxxxxxxxxx; edubezval@xxxxxxxxx; Zhang, Rui; linux- > kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling > device registered > > 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@xxxxxxx] > > > Sent: Monday, September 28, 2015 10:29 PM > > > To: Chen, Yu C > > > Cc: linux-pm@xxxxxxxxxxxxxxx; edubezval@xxxxxxxxx; Zhang, Rui; > > > linux- kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx > > > 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@xxxxxxxxx> > > > > > > > > > > > > > > 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? > RCU would need extra spinlocks to protect the list, and need to sync_rcu after we delete one instance from thermal_instance list, I think it is too complicated for me to rewrite: ( How about using thermal_list_lock instead of cdev ->lock? This guy should be big enough to protect the device.thermal_instance list. > > > > 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); > Sure, ok > 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. > OK Best Regards, Yu ��.n��������+%������w��{.n�����������ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f