Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

Hi Yu,

On Tue, Oct 20, 2015 at 01:44:20AM +, Chen, Yu C wrote:
> > -Original Message-
> > From: Javi Merino [mailto:javi.mer...@arm.com]
> > Sent: Thursday, October 15, 2015 10:05 PM
> > To: Chen, Yu C
> > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux- 
> > ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a 
> > cooling device registered
> > 
> > On Wed, Oct 14, 2015 at 07:23:55PM +, Chen, Yu C wrote:
> > > > -Original Message-
> > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > Sent: Thursday, October 15, 2015 1:08 AM
> > > > To: Chen, Yu C
> > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, 
> > > > Srinivas
> > > > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a 
> > > > cooling device registered
> > > >
> > > > On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > > > > Hi, Javi
> > > > > Sorry for my late response,
> > > > >
> > > > > > -Original Message-
> > > > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > > To: Chen, Yu C
> > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > > > > 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.mer...@arm.com]
> > > > > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > > > > To: Chen, Yu C
> > > > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, 
> > > > > > > > Rui;
> > > > > > > > linux- ker...@vger.kernel.org; sta...@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?
> > > > > >
> > > > > 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

Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

Hi Yu,

On Tue, Oct 20, 2015 at 01:44:20AM +, Chen, Yu C wrote:
> > -Original Message-
> > From: Javi Merino [mailto:javi.mer...@arm.com]
> > Sent: Thursday, October 15, 2015 10:05 PM
> > To: Chen, Yu C
> > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux- 
> > ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a 
> > cooling device registered
> > 
> > On Wed, Oct 14, 2015 at 07:23:55PM +, Chen, Yu C wrote:
> > > > -Original Message-
> > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > Sent: Thursday, October 15, 2015 1:08 AM
> > > > To: Chen, Yu C
> > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, 
> > > > Srinivas
> > > > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a 
> > > > cooling device registered
> > > >
> > > > On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > > > > Hi, Javi
> > > > > Sorry for my late response,
> > > > >
> > > > > > -Original Message-
> > > > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > > To: Chen, Yu C
> > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > > > > 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.mer...@arm.com]
> > > > > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > > > > To: Chen, Yu C
> > > > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, 
> > > > > > > > Rui;
> > > > > > > > linux- ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?
> > > > > >
> > > > > > 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,
> > >

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

[Chen, Yu C]

(resend for broken display)

Hi,
> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Thursday, October 15, 2015 10:05 PM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux- 
> ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a 
> cooling device registered
> 
> On Wed, Oct 14, 2015 at 07:23:55PM +, Chen, Yu C wrote:
> > > -Original Message-
> > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > Sent: Thursday, October 15, 2015 1:08 AM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, 
> > > Srinivas
> > > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a 
> > > cooling device registered
> > >
> > > On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > > > Hi, Javi
> > > > Sorry for my late response,
> > > >
> > > > > -Original Message-
> > > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > To: Chen, Yu C
> > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > > > 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.mer...@arm.com]
> > > > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > > > To: Chen, Yu C
> > > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, 
> > > > > > > Rui;
> > > > > > > linux- ker...@vger.kernel.org; sta...@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?
> > > > >
> > > > 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.
> > >
> > Before thermal_zone_bind_cooling_device is invoked, the 
> > thermal_list_lock will be firstly gripped:
> >
> > static void bind_cdev(struct thermal_cooling_device *cdev) { 
> > mutex_lock(_list_lock);
> > either tz->ops->bind:   thermal_zone_bind_co

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

[Chen, Yu C]

Hi,
> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Thursday, October 15, 2015 10:05 PM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> device registered
> 
> On Wed, Oct 14, 2015 at 07:23:55PM +, Chen, Yu C wrote:
> > > -Original Message-
> > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > Sent: Thursday, October 15, 2015 1:08 AM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada,
> > > Srinivas
> > > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a
> > > cooling device registered
> > >
> > > On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > > > Hi, Javi
> > > > Sorry for my late response,
> > > >
> > > > > -Original Message-
> > > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > To: Chen, Yu C
> > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > > > 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.mer...@arm.com]
> > > > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > > > To: Chen, Yu C
> > > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang,
> > > > > > > Rui;
> > > > > > > linux- ker...@vger.kernel.org; sta...@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?
> > > > >
> > > > 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.
> > >
> > Before thermal_zone_bind_cooling_device is invoked, the
> > thermal_list_lock will be firstly gripped:
> >
> > static void bind_cdev(struct thermal_cooling_device *cdev) {
> > mutex_lock(_list_lock);
> > either tz->ops->bind:   thermal_zone_bind_cooling_device
> > or __bind()  :   thermal_zone_bind_cooling_device
> &

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

[Chen, Yu C]

(resend for broken display)

Hi,
> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Thursday, October 15, 2015 10:05 PM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux- 
> ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a 
> cooling device registered
> 
> On Wed, Oct 14, 2015 at 07:23:55PM +, Chen, Yu C wrote:
> > > -Original Message-
> > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > Sent: Thursday, October 15, 2015 1:08 AM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, 
> > > Srinivas
> > > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a 
> > > cooling device registered
> > >
> > > On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > > > Hi, Javi
> > > > Sorry for my late response,
> > > >
> > > > > -Original Message-
> > > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > To: Chen, Yu C
> > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > > > 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.mer...@arm.com]
> > > > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > > > To: Chen, Yu C
> > > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, 
> > > > > > > Rui;
> > > > > > > linux- ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?
> > > > >
> > > > > 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.
> > >
> > Before thermal_zone_bind_cooling_device is invoked, the 
> > thermal_list_lock will be firstly gripped:
> >
> > static void bind_cdev(struct thermal_cooling_device *cdev) { 
> > mutex_lock(_list_lock);
> > either tz->ops->bind 

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

[Chen, Yu C]

Hi,
> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Thursday, October 15, 2015 10:05 PM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> device registered
> 
> On Wed, Oct 14, 2015 at 07:23:55PM +, Chen, Yu C wrote:
> > > -Original Message-
> > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > Sent: Thursday, October 15, 2015 1:08 AM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada,
> > > Srinivas
> > > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a
> > > cooling device registered
> > >
> > > On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > > > Hi, Javi
> > > > Sorry for my late response,
> > > >
> > > > > -Original Message-
> > > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > To: Chen, Yu C
> > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > > > 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.mer...@arm.com]
> > > > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > > > To: Chen, Yu C
> > > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang,
> > > > > > > Rui;
> > > > > > > linux- ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?
> > > > >
> > > > > 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.
> > >
> > Before thermal_zone_bind_cooling_device is invoked, the
> > thermal_list_lock will be firstly gripped:
> >
> > static void bind_cdev(struct thermal_cooling_device *cdev) {
> > mutex_lock(_list_lock);
> > either tz->ops->bind:   thermal_zone_bind_cooling_device
> > or __bind()  :   thermal_zone_bind

Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

On Wed, Oct 14, 2015 at 07:23:55PM +, Chen, Yu C wrote:
> > -Original Message-
> > From: Javi Merino [mailto:javi.mer...@arm.com]
> > Sent: Thursday, October 15, 2015 1:08 AM
> > To: Chen, Yu C
> > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> > ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> > device registered
> > 
> > On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > > Hi, Javi
> > > Sorry for my late response,
> > >
> > > > -Original Message-
> > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > To: Chen, Yu C
> > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > > 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.mer...@arm.com]
> > > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > > To: Chen, Yu C
> > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > > linux- ker...@vger.kernel.org; sta...@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?
> > > >
> > > 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.
> > 
> Before thermal_zone_bind_cooling_device is invoked,
> the thermal_list_lock will be firstly gripped:
> 
> static void bind_cdev(struct thermal_cooling_device *cdev)
> {
> mutex_lock(_list_lock);
> either tz->ops->bind:   thermal_zone_bind_cooling_device
> or __bind()  :   thermal_zone_bind_cooling_device
> mutex_unlock(_list_lock);
> }
> 
> And it is the same as in  passive_store.
> So when code is trying to add/delete thermal_instance of cdev,
> he has already hold thermal_list_lock IMO. Or do I miss anything?

thermal_zone_bind_cooling_device() is exported, so you can't really
rely on the static thermal_list_lock being acquired in every single
call.

thermal_list_lock and protects the lists thermal_tz_list and
thermal_cdev_list.  Making it implicitly protect the cooling device's
and thermal zone device's instances list because no sensible code
would call thermal_zone_bind_cooling_device() outside of a bind
function is just asking for trouble.

Locking is hard to understand and easy to get wrong so let's keep it
simple.

Cheers,
Javi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

On Wed, Oct 14, 2015 at 07:23:55PM +, Chen, Yu C wrote:
> > -Original Message-
> > From: Javi Merino [mailto:javi.mer...@arm.com]
> > Sent: Thursday, October 15, 2015 1:08 AM
> > To: Chen, Yu C
> > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> > ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> > Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> > device registered
> > 
> > On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > > Hi, Javi
> > > Sorry for my late response,
> > >
> > > > -Original Message-
> > > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > To: Chen, Yu C
> > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > > 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.mer...@arm.com]
> > > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > > To: Chen, Yu C
> > > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > > linux- ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?
> > > >
> > > > 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.
> > 
> Before thermal_zone_bind_cooling_device is invoked,
> the thermal_list_lock will be firstly gripped:
> 
> static void bind_cdev(struct thermal_cooling_device *cdev)
> {
> mutex_lock(_list_lock);
> either tz->ops->bind:   thermal_zone_bind_cooling_device
> or __bind()  :   thermal_zone_bind_cooling_device
> mutex_unlock(_list_lock);
> }
> 
> And it is the same as in  passive_store.
> So when code is trying to add/delete thermal_instance of cdev,
> he has already hold thermal_list_lock IMO. Or do I miss anything?

thermal_zone_bind_cooling_device() is exported, so you can't really
rely on the static thermal_list_lock being acquired in every single
call.

thermal_list_lock and protects the lists thermal_tz_list and
thermal_cdev_list.  Making it implicitly protect the cooling device's
and thermal zone device's instances list because no sensible code
would call thermal_zone_bind_cooling_device() outside of a bind
function is just asking for trouble.

Locking is hard to understand and easy to get wrong so let's keep it
simple.

Cheers,
Javi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

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

[Chen, Yu C]

Hi,Javi

> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Thursday, October 15, 2015 1:08 AM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> device registered
> 
> On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > Hi, Javi
> > Sorry for my late response,
> >
> > > -Original Message-
> > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > 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.mer...@arm.com]
> > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > To: Chen, Yu C
> > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > linux- ker...@vger.kernel.org; sta...@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?
> > >
> > 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.
> 
Before thermal_zone_bind_cooling_device is invoked,
the thermal_list_lock will be firstly gripped:

static void bind_cdev(struct thermal_cooling_device *cdev)
{
mutex_lock(_list_lock);
either tz->ops->bind:   thermal_zone_bind_cooling_device
or __bind()  :   thermal_zone_bind_cooling_device
mutex_unlock(_list_lock);
}

And it is the same as in  passive_store.
So when code is trying to add/delete thermal_instance of cdev,
he has already hold thermal_list_lock IMO. Or do I miss anything?

Best Regards,
Yu

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

[Chen, Yu C]

Hi Javi,


> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Thursday, October 15, 2015 1:08 AM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> device registered
> 
> On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > Hi, Javi
> > Sorry for my late response,
> >
> > > -Original Message-
> > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > 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.mer...@arm.com]
> > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > To: Chen, Yu C
> > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > linux- ker...@vger.kernel.org; sta...@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?
> > >
> > 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.
> 

Before thermal_zone_bind_cooling_device is invoked, 
the thermal_list_lock will be firstly gripped:

static void bind_cdev(struct thermal_cooling_device *cdev)
{

mutex_lock(_list_lock);

either tz->ops->bind:   thermal_zone_bind_cooling_device

or __bind()  :   thermal_zone_bind_cooling_device
mutex_unlock(_list_lock);

}

And it is the same as in  passive_store.

So when code is trying to add/delete thermal_instance of cdev, he has
already hold thermal_list_lock IMO. Or do I miss anything?

Best Regards,
Yu


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Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> Hi, Javi
> Sorry for my late response,
> 
> > -Original Message-
> > From: Javi Merino [mailto:javi.mer...@arm.com]
> > Sent: Wednesday, September 30, 2015 12:02 AM
> > To: Chen, Yu C
> > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> > ker...@vger.kernel.org; sta...@vger.kernel.org
> > 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.mer...@arm.com]
> > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > To: Chen, Yu C
> > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > linux- ker...@vger.kernel.org; sta...@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?
> > 
> 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 linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> Hi, Javi
> Sorry for my late response,
> 
> > -Original Message-
> > From: Javi Merino [mailto:javi.mer...@arm.com]
> > Sent: Wednesday, September 30, 2015 12:02 AM
> > To: Chen, Yu C
> > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> > ker...@vger.kernel.org; sta...@vger.kernel.org
> > 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.mer...@arm.com]
> > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > To: Chen, Yu C
> > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > linux- ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?
> > 
> > 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


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

[Chen, Yu C]

Hi Javi,


> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Thursday, October 15, 2015 1:08 AM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> device registered
> 
> On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > Hi, Javi
> > Sorry for my late response,
> >
> > > -Original Message-
> > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > 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.mer...@arm.com]
> > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > To: Chen, Yu C
> > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > linux- ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?
> > >
> > > 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.
> 

Before thermal_zone_bind_cooling_device is invoked, 
the thermal_list_lock will be firstly gripped:

static void bind_cdev(struct thermal_cooling_device *cdev)
{

mutex_lock(_list_lock);

either tz->ops->bind:   thermal_zone_bind_cooling_device

or __bind()  :   thermal_zone_bind_cooling_device
mutex_unlock(_list_lock);

}

And it is the same as in  passive_store.

So when code is trying to add/delete thermal_instance of cdev, he has
already hold thermal_list_lock IMO. Or do I miss anything?

Best Regards,
Yu


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

[Chen, Yu C]

Hi,Javi

> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Thursday, October 15, 2015 1:08 AM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@vger.kernel.org; Pandruvada, Srinivas
> Subject: Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling
> device registered
> 
> On Mon, Oct 12, 2015 at 09:23:28AM +, Chen, Yu C wrote:
> > Hi, Javi
> > Sorry for my late response,
> >
> > > -Original Message-
> > > From: Javi Merino [mailto:javi.mer...@arm.com]
> > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@vger.kernel.org
> > > 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.mer...@arm.com]
> > > > > Sent: Monday, September 28, 2015 10:29 PM
> > > > > To: Chen, Yu C
> > > > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > > > linux- ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?
> > >
> > > 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.
> 
Before thermal_zone_bind_cooling_device is invoked,
the thermal_list_lock will be firstly gripped:

static void bind_cdev(struct thermal_cooling_device *cdev)
{
mutex_lock(_list_lock);
either tz->ops->bind:   thermal_zone_bind_cooling_device
or __bind()  :   thermal_zone_bind_cooling_device
mutex_unlock(_list_lock);
}

And it is the same as in  passive_store.
So when code is trying to add/delete thermal_instance of cdev,
he has already hold thermal_list_lock IMO. Or do I miss anything?

Best Regards,
Yu

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

[Chen, Yu C]

Hi, Javi
Sorry for my late response,

> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Wednesday, September 30, 2015 12:02 AM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@vger.kernel.org
> 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.mer...@arm.com]
> > > Sent: Monday, September 28, 2015 10:29 PM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@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?
> 
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, >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(>cdev_node, 
> >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

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

[Chen, Yu C]

Hi, Javi
Sorry for my late response,

> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Wednesday, September 30, 2015 12:02 AM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@vger.kernel.org
> 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.mer...@arm.com]
> > > Sent: Monday, September 28, 2015 10:29 PM
> > > To: Chen, Yu C
> > > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui;
> > > linux- ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?
> 
> 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, >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(>cdev_node, 
> >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

Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

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.mer...@arm.com]
> > Sent: Monday, September 28, 2015 10:29 PM
> > To: Chen, Yu C
> > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> > ker...@vger.kernel.org; sta...@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, >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(>cdev_node, >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 linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

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.mer...@arm.com]
> > Sent: Monday, September 28, 2015 10:29 PM
> > To: Chen, Yu C
> > Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> > ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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?

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, >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(>cdev_node, >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 linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

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

[Chen, Yu C]

Hi, Javi,

> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Monday, September 28, 2015 10:29 PM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@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?

> 
> 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, >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

Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

On Sun, Sep 27, 2015 at 06:48:44AM +0100, Chen Yu wrote:
> From: Zhang Rui 
> 
> When a new cooling device is registered, we need to update the
> thermal zone to set the new registered cooling device to a proper
> state.
> 
> This fixes a problem that the system is cool, while the fan devices
> are left running on full speed after boot, if fan device is registered
> after thermal zone device.
> 
> CC:  #3.18+
> Reference:https://bugzilla.kernel.org/show_bug.cgi?id=92431
> Tested-by: Manuel Krause 
> Tested-by: szegad 
> Tested-by: prash 
> Tested-by: amish 
> Signed-off-by: Zhang Rui 
> Signed-off-by: Chen Yu 
> ---
>  drivers/thermal/thermal_core.c | 10 ++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index c3bdb48..09c78a4 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -1450,6 +1450,7 @@ __thermal_cooling_device_register(struct device_node 
> *np,
> const struct thermal_cooling_device_ops *ops)
>  {
>   struct thermal_cooling_device *cdev;
> + struct thermal_instance *pos, *next;
>   int result;
>  
>   if (type && strlen(type) >= THERMAL_NAME_LENGTH)
> @@ -1494,6 +1495,15 @@ __thermal_cooling_device_register(struct device_node 
> *np,
>   /* Update binding information for 'this' new cdev */
>   bind_cdev(cdev);
>  

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.

> + list_for_each_entry_safe(pos, next, >thermal_instances, 
> cdev_node) {

Why list_for_each_entry_safe() ?  You are not going to remove any
entry, so you can just use list_for_each_entry()

> + if (next->cdev_node.next == >thermal_instances) {
> + thermal_zone_device_update(next->tz);
> + break;
> + }
> + if (pos->tz != next->tz)
> + thermal_zone_device_update(pos->tz);
> + }

Why is this so complicated?  Can't you just do:

list_for_each_entry(pos, >thermal_instances, cdev_node)
thermal_zone_device_update(pos->tz);

Cheers,
Javi
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RE: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Chen, Yu C]

Hi, Javi,

> -Original Message-
> From: Javi Merino [mailto:javi.mer...@arm.com]
> Sent: Monday, September 28, 2015 10:29 PM
> To: Chen, Yu C
> Cc: linux...@vger.kernel.org; edubez...@gmail.com; Zhang, Rui; linux-
> ker...@vger.kernel.org; sta...@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 <rui.zh...@intel.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, >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

Re: [PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Javi Merino]

On Sun, Sep 27, 2015 at 06:48:44AM +0100, Chen Yu wrote:
> From: Zhang Rui 
> 
> When a new cooling device is registered, we need to update the
> thermal zone to set the new registered cooling device to a proper
> state.
> 
> This fixes a problem that the system is cool, while the fan devices
> are left running on full speed after boot, if fan device is registered
> after thermal zone device.
> 
> CC:  #3.18+
> Reference:https://bugzilla.kernel.org/show_bug.cgi?id=92431
> Tested-by: Manuel Krause 
> Tested-by: szegad 
> Tested-by: prash 
> Tested-by: amish 
> Signed-off-by: Zhang Rui 
> Signed-off-by: Chen Yu 
> ---
>  drivers/thermal/thermal_core.c | 10 ++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index c3bdb48..09c78a4 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -1450,6 +1450,7 @@ __thermal_cooling_device_register(struct device_node 
> *np,
> const struct thermal_cooling_device_ops *ops)
>  {
>   struct thermal_cooling_device *cdev;
> + struct thermal_instance *pos, *next;
>   int result;
>  
>   if (type && strlen(type) >= THERMAL_NAME_LENGTH)
> @@ -1494,6 +1495,15 @@ __thermal_cooling_device_register(struct device_node 
> *np,
>   /* Update binding information for 'this' new cdev */
>   bind_cdev(cdev);
>  

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.

> + list_for_each_entry_safe(pos, next, >thermal_instances, 
> cdev_node) {

Why list_for_each_entry_safe() ?  You are not going to remove any
entry, so you can just use list_for_each_entry()

> + if (next->cdev_node.next == >thermal_instances) {
> + thermal_zone_device_update(next->tz);
> + break;
> + }
> + if (pos->tz != next->tz)
> + thermal_zone_device_update(pos->tz);
> + }

Why is this so complicated?  Can't you just do:

list_for_each_entry(pos, >thermal_instances, cdev_node)
thermal_zone_device_update(pos->tz);

Cheers,
Javi
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[PATCH 3/3] Thermal: do thermal zone update after a cooling device registered

[Chen Yu]

From: Zhang Rui 

When a new cooling device is registered, we need to update the
thermal zone to set the new registered cooling device to a proper
state.

This fixes a problem that the system is cool, while the fan devices
are left running on full speed after boot, if fan device is registered
after thermal zone device.

CC:  #3.18+
Reference:https://bugzilla.kernel.org/show_bug.cgi?id=92431
Tested-by: Manuel Krause 
Tested-by: szegad 
Tested-by: prash 
Tested-by: amish 
Signed-off-by: Zhang Rui 
Signed-off-by: Chen Yu 
---
 drivers/thermal/thermal_core.c | 10 ++
 1 file changed, 10 insertions(+)

diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index c3bdb48..09c78a4 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -1450,6 +1450,7 @@ __thermal_cooling_device_register(struct device_node *np,
  const struct thermal_cooling_device_ops *ops)
 {
struct thermal_cooling_device *cdev;
+   struct thermal_instance *pos, *next;
int result;
 
if (type && strlen(type) >= THERMAL_NAME_LENGTH)
@@ -1494,6 +1495,15 @@ __thermal_cooling_device_register(struct device_node *np,
/* Update binding information for 'this' new cdev */
bind_cdev(cdev);
 
+   list_for_each_entry_safe(pos, next, >thermal_instances, 
cdev_node) {
+   if (next->cdev_node.next == >thermal_instances) {
+   thermal_zone_device_update(next->tz);
+   break;
+   }
+   if (pos->tz != next->tz)
+   thermal_zone_device_update(pos->tz);
+   }
+
return cdev;
 }
 
-- 
1.8.4.2

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

[Chen Yu]

From: Zhang Rui 

When a new cooling device is registered, we need to update the
thermal zone to set the new registered cooling device to a proper
state.

This fixes a problem that the system is cool, while the fan devices
are left running on full speed after boot, if fan device is registered
after thermal zone device.

CC:  #3.18+
Reference:https://bugzilla.kernel.org/show_bug.cgi?id=92431
Tested-by: Manuel Krause 
Tested-by: szegad 
Tested-by: prash 
Tested-by: amish 
Signed-off-by: Zhang Rui 
Signed-off-by: Chen Yu 
---
 drivers/thermal/thermal_core.c | 10 ++
 1 file changed, 10 insertions(+)

diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index c3bdb48..09c78a4 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -1450,6 +1450,7 @@ __thermal_cooling_device_register(struct device_node *np,
  const struct thermal_cooling_device_ops *ops)
 {
struct thermal_cooling_device *cdev;
+   struct thermal_instance *pos, *next;
int result;
 
if (type && strlen(type) >= THERMAL_NAME_LENGTH)
@@ -1494,6 +1495,15 @@ __thermal_cooling_device_register(struct device_node *np,
/* Update binding information for 'this' new cdev */
bind_cdev(cdev);
 
+   list_for_each_entry_safe(pos, next, >thermal_instances, 
cdev_node) {
+   if (next->cdev_node.next == >thermal_instances) {
+   thermal_zone_device_update(next->tz);
+   break;
+   }
+   if (pos->tz != next->tz)
+   thermal_zone_device_update(pos->tz);
+   }
+
return cdev;
 }
 
-- 
1.8.4.2

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