On Mon, Oct 12, 2015 at 09:23:28AM +0000, Chen, Yu C wrote: > 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. thermal_list_lock protects thermal_tz_list and thermal_cdev_list, but it doesn't protect the thermal_instances list. For example, thermal_zone_bind_cooling_device() adds a cooling device to the cdev->thermal_instances list without taking thermal_tz_list. To sum up, you have to protect accessing the cdev->thermal_instances list but with the current locking scheme, you would create an AB-BA deadlock. As I see it you would have to change the locking scheme to either RCU or add a new mutex that protects the cdev->thermal_instances and tz->thermal_instances lists and change all accesses to them to make sure they comply with the new locking scheme. Is there a better way of solving this? 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