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

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

[Chen Yu]

From: Zhang Rui <rui.zhang@intel.com>

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: <stable@vger.kernel.org> #3.18+
Reference:https://bugzilla.kernel.org/show_bug.cgi?id=92431
Tested-by: Manuel Krause <manuelkrause@netscape.net>
Tested-by: szegad <szegadlo@poczta.onet.pl>
Tested-by: prash <prash.n.rao@gmail.com>
Tested-by: amish <ammdispose-arch@yahoo.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 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, &cdev->thermal_instances, cdev_node) {
+			if (next->cdev_node.next == &cdev->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

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 <rui.zhang@intel.com>
> 
> 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: <stable@vger.kernel.org> #3.18+
> Reference:https://bugzilla.kernel.org/show_bug.cgi?id=92431
> Tested-by: Manuel Krause <manuelkrause@netscape.net>
> Tested-by: szegad <szegadlo@poczta.onet.pl>
> Tested-by: prash <prash.n.rao@gmail.com>
> Tested-by: amish <ammdispose-arch@yahoo.com>
> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> ---
>  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, &cdev->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 == &cdev->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, &cdev->thermal_instances, cdev_node)
        	thermal_zone_device_update(pos->tz);

Cheers,
Javi

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

[Chen, Yu C]

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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 <rui.zhang@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, &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.


Best Regards,
Yu
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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.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 <rui.zhang@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, &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

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

[Chen, Yu C]

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Hi, Javi
Sorry for my late response,

> -----Original Message-----
> From: Javi Merino [mailto:javi.merino@arm.com]
> Sent: Wednesday, September 30, 2015 12:02 AM
> 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
> 
> 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 <rui.zhang@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, &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
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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 +0000, Chen, Yu C wrote:
> Hi, Javi
> Sorry for my late response,
> 
> > -----Original Message-----
> > From: Javi Merino [mailto:javi.merino@arm.com]
> > Sent: Wednesday, September 30, 2015 12:02 AM
> > 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
> > 
> > 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 <rui.zhang@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

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

[Chen, Yu C]

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Hi Javi,


> -----Original Message-----
> From: Javi Merino [mailto:javi.merino@arm.com]
> Sent: Thursday, October 15, 2015 1:08 AM
> To: Chen, Yu C
> Cc: linux-pm@vger.kernel.org; edubezval@gmail.com; Zhang, Rui; linux-
> kernel@vger.kernel.org; stable@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 +0000, Chen, Yu C wrote:
> > Hi, Javi
> > Sorry for my late response,
> >
> > > -----Original Message-----
> > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > 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
> > >
> > > 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 <rui.zhang@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(&thermal_list_lock);

either tz->ops->bind    :   thermal_zone_bind_cooling_device

or __bind()  :   thermal_zone_bind_cooling_device
mutex_unlock(&thermal_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]

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Hi,Javi

> -----Original Message-----
> From: Javi Merino [mailto:javi.merino@arm.com]
> Sent: Thursday, October 15, 2015 1:08 AM
> To: Chen, Yu C
> Cc: linux-pm@vger.kernel.org; edubezval@gmail.com; Zhang, Rui; linux-
> kernel@vger.kernel.org; stable@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 +0000, Chen, Yu C wrote:
> > Hi, Javi
> > Sorry for my late response,
> >
> > > -----Original Message-----
> > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > 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
> > >
> > > 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 <rui.zhang@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(&thermal_list_lock);
either tz->ops->bind    :   thermal_zone_bind_cooling_device
or __bind()  :   thermal_zone_bind_cooling_device
mutex_unlock(&thermal_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
ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

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 +0000, Chen, Yu C wrote:
> > -----Original Message-----
> > From: Javi Merino [mailto:javi.merino@arm.com]
> > Sent: Thursday, October 15, 2015 1:08 AM
> > To: Chen, Yu C
> > Cc: linux-pm@vger.kernel.org; edubezval@gmail.com; Zhang, Rui; linux-
> > kernel@vger.kernel.org; stable@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 +0000, Chen, Yu C wrote:
> > > Hi, Javi
> > > Sorry for my late response,
> > >
> > > > -----Original Message-----
> > > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > 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
> > > >
> > > > 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 <rui.zhang@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(&thermal_list_lock);
> either tz->ops->bind    :   thermal_zone_bind_cooling_device
> or __bind()  :   thermal_zone_bind_cooling_device
> mutex_unlock(&thermal_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

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

[Chen, Yu C]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 5641 bytes --]

Hi,
> -----Original Message-----
> From: Javi Merino [mailto:javi.merino@arm.com]
> Sent: Thursday, October 15, 2015 10:05 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; 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 +0000, Chen, Yu C wrote:
> > > -----Original Message-----
> > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > Sent: Thursday, October 15, 2015 1:08 AM
> > > To: Chen, Yu C
> > > Cc: linux-pm@vger.kernel.org; edubezval@gmail.com; Zhang, Rui;
> > > linux- kernel@vger.kernel.org; stable@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 +0000, Chen, Yu C wrote:
> > > > Hi, Javi
> > > > Sorry for my late response,
> > > >
> > > > > -----Original Message-----
> > > > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > 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
> > > > >
> > > > > 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 <rui.zhang@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(&thermal_list_lock);
> > either tz->ops->bind    :   thermal_zone_bind_cooling_device
> > or __bind()  :   thermal_zone_bind_cooling_device
> > mutex_unlock(&thermal_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.
> 
Yes, from this point of view,it is true. 

> Locking is hard to understand and easy to get wrong so let's keep it simple.
> 
How about the following 2 methods:
1. avoid accessing device's thermal_instance,but
access all thermal_zone_device directly, although there might be some redundancy,
some thermal zones do not need to be updated, but we can avoid gripping dev->lock:

	mutex_lock(&thermal_list_lock);
	list_for_each_entry(pos, &thermal_tz_list, node)
		thermal_zone_device_update(tz);
	mutex_unlock(&thermal_list_lock); 

or, 
2. Once we bind the new device with the thermal_zone_device, we can record that
thermal_zone_device, and update that thermal_zone_device alone.

BTW, since thermal_zone_device_update is not atomic, we might need another patch
to make it into atomic or something like that, but for now, I think these three patches are 
just for fixing the regressions.


Thanks

Best Regards,
Yu

ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

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

[Chen, Yu C]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 5920 bytes --]

(resend for broken display)

Hi,
> -----Original Message-----
> From: Javi Merino [mailto:javi.merino@arm.com]
> Sent: Thursday, October 15, 2015 10:05 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; 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 +0000, Chen, Yu C wrote:
> > > -----Original Message-----
> > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > Sent: Thursday, October 15, 2015 1:08 AM
> > > To: Chen, Yu C
> > > Cc: linux-pm@vger.kernel.org; edubezval@gmail.com; Zhang, Rui;
> > > linux- kernel@vger.kernel.org; stable@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 +0000, Chen, Yu C wrote:
> > > > Hi, Javi
> > > > Sorry for my late response,
> > > >
> > > > > -----Original Message-----
> > > > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > 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
> > > > >
> > > > > 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 <rui.zhang@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(&thermal_list_lock);
> > either tz->ops->bind    :   thermal_zone_bind_cooling_device
> > or __bind()  :   thermal_zone_bind_cooling_device
> > mutex_unlock(&thermal_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.
> 
Yes, from this point of view,it is true. 

> Locking is hard to understand and easy to get wrong so let's keep it simple.
> 
How about the following 2 methods:
1. avoid accessing device's thermal_instance,
but access all thermal_zone_device directly,
 although there might be some redundancy,
 some thermal zones do not need to be updated, 
but we can avoid gripping dev->lock:

	mutex_lock(&thermal_list_lock);
	list_for_each_entry(pos, &thermal_tz_list, node)
		thermal_zone_device_update(tz);
	mutex_unlock(&thermal_list_lock); 

or,
2. Once we bind the new device with the thermal_zone_device,
 we can record that thermal_zone_device, 
and update that thermal_zone_device alone,the the code would be:
	
	mutex_lock(&thermal_list_lock);
	list_for_each_entry(pos, &thermal_tz_list, node){
		if (tz->need_update)
			thermal_zone_device_update(tz);
	}
	mutex_unlock(&thermal_list_lock);


BTW, since thermal_zone_device_update is not atomic, 
we might need another patch to make it into atomic or 
something like that, but for now, I think these three patches 
are just for fixing the regressions.


Thanks

Best Regards,
Yu

ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

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 +0000, Chen, Yu C wrote:
> > -----Original Message-----
> > From: Javi Merino [mailto:javi.merino@arm.com]
> > Sent: Thursday, October 15, 2015 10:05 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; 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 +0000, Chen, Yu C wrote:
> > > > -----Original Message-----
> > > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > > Sent: Thursday, October 15, 2015 1:08 AM
> > > > To: Chen, Yu C
> > > > Cc: linux-pm@vger.kernel.org; edubezval@gmail.com; Zhang, Rui;
> > > > linux- kernel@vger.kernel.org; stable@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 +0000, Chen, Yu C wrote:
> > > > > Hi, Javi
> > > > > Sorry for my late response,
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Javi Merino [mailto:javi.merino@arm.com]
> > > > > > Sent: Wednesday, September 30, 2015 12:02 AM
> > > > > > 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
> > > > > >
> > > > > > 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 <rui.zhang@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(&thermal_list_lock);
> > > either tz->ops->bind    :   thermal_zone_bind_cooling_device
> > > or __bind()  :   thermal_zone_bind_cooling_device
> > > mutex_unlock(&thermal_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.
> > 
> Yes, from this point of view,it is true. 
> 
> > Locking is hard to understand and easy to get wrong so let's keep it simple.
> > 
> How about the following 2 methods:
> 1. avoid accessing device's thermal_instance,
> but access all thermal_zone_device directly,
>  although there might be some redundancy,
>  some thermal zones do not need to be updated, 
> but we can avoid gripping dev->lock:
> 
> 	mutex_lock(&thermal_list_lock);
> 	list_for_each_entry(pos, &thermal_tz_list, node)
> 		thermal_zone_device_update(tz);
> 	mutex_unlock(&thermal_list_lock); 
> 
> or,
> 2. Once we bind the new device with the thermal_zone_device,
>  we can record that thermal_zone_device, 
> and update that thermal_zone_device alone,the the code would be:
> 	
> 	mutex_lock(&thermal_list_lock);
> 	list_for_each_entry(pos, &thermal_tz_list, node){
> 		if (tz->need_update)
> 			thermal_zone_device_update(tz);
> 	}
> 	mutex_unlock(&thermal_list_lock);

This sounds like a better alternative to me.  I was thinking whether
we could add the thremal_zone_device_update() directly in bind_cdev()
to avoid the need_update field but I don't think it's any better: you
would have to put it in two places (for the bind() and tbp.match()
paths).

With the solution you propose above you only have to put it in
__thermal_cooling_device_register(), which is simpler.  I vote for
your solution (2) above.

> BTW, since thermal_zone_device_update is not atomic, 
> we might need another patch to make it into atomic or 
> something like that, but for now, I think these three patches 
> are just for fixing the regressions.

Yeah, we can fix that in another series.

Cheers,
Javi