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? > > 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html