thermal: core/ACPI: Fix processor cooling device regression

From: Rafael J. Wysocki <[email protected]>

The cpufreq policy notifier in the ACPI processor driver may as well be registered before the driver itself, which causes acpi_processor_cpufreq_init to be true (unless the notifier registration fails, which is unlikely at that point) when the ACPI CPU thermal cooling devices are registered, so the processor_get_max_state() result does not change while acpi_processor_driver_init() is running.

Change the ordering in acpi_processor_driver_init() accordingly to prevent the max_state value from remaining 0 permanently for all ACPI CPU cooling devices.

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/acpi/processor_driver.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/acpi/processor_driver.c
===================================================================

drivers/acpi/processor_driver.c +6 -6

@@ -263,6 +263,12 @@ static int __init acpi_processor_driver_
 	if (acpi_disabled)
 		return 0;
 
+	if (!cpufreq_register_notifier(&acpi_processor_notifier_block,
+				       CPUFREQ_POLICY_NOTIFIER)) {
+		acpi_processor_cpufreq_init = true;
+		acpi_processor_ignore_ppc_init();
+	}
+
 	result = driver_register(&acpi_processor_driver);
 	if (result < 0)
 		return result;

@@ -276,12 +282,6 @@ static int __init acpi_processor_driver_
 	cpuhp_setup_state_nocalls(CPUHP_ACPI_CPUDRV_DEAD, "acpi/cpu-
 drv:dead",
 				  NULL, acpi_soft_cpu_dead);
 
-	if (!cpufreq_register_notifier(&acpi_processor_notifier_block,
-				       CPUFREQ_POLICY_NOTIFIER)) {
-		acpi_processor_cpufreq_init = true;
-		acpi_processor_ignore_ppc_init();
-	}
-
 	acpi_processor_throttling_init();
 	return 0;

err:

Quoted 45 lines · Rafael J. Wysocki

From: Rafael J. Wysocki <[email protected]>

The cpufreq policy notifier in the ACPI processor driver may as well be registered before the driver itself, which causes acpi_processor_cpufreq_init to be true (unless the notifier registration fails, which is unlikely at that point) when the ACPI CPU thermal cooling devices are registered, so the processor_get_max_state() result does not change while acpi_processor_driver_init() is running.

Change the ordering in acpi_processor_driver_init() accordingly to prevent the max_state value from remaining 0 permanently for all ACPI CPU cooling devices.

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/acpi/processor_driver.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/acpi/processor_driver.c
===================================================================

drivers/acpi/processor_driver.c +6 -0

@@ -263,6 +263,12 @@ static int __init acpi_processor_driver_
      if (acpi_disabled)
              return 0;
 
+     if (!cpufreq_register_notifier(&acpi_processor_notifier_block,
+                                    CPUFREQ_POLICY_NOTIFIER)) {
+             acpi_processor_cpufreq_init = true;
+             acpi_processor_ignore_ppc_init();
+     }
+
      result = driver_register(&acpi_processor_driver);
      if (result < 0)
              return result;

@@ -276,12 +282,6 @@ static int __init acpi_processor_driver_
      cpuhp_setup_state_nocalls(CPUHP_ACPI_CPUDRV_DEAD, "acpi/cpu-
 drv:dead",
                                NULL, acpi_soft_cpu_dead);
 

Quoted 10 lines

drivers/acpi/processor_driver.c +0 -6

-     if (!cpufreq_register_notifier(&acpi_processor_notifier_block,
-                                    CPUFREQ_POLICY_NOTIFIER)) {
-             acpi_processor_cpufreq_init = true;
-             acpi_processor_ignore_ppc_init();
-     }
-
      acpi_processor_throttling_init();
      return 0;

err:

Just FYI.
I need some time to ramp up on the ordering here to double confirm this does not break any dependency, too many things are involved here :p.

I will test the whole patch series later this week.

From: Rafael J. Wysocki <[email protected]>

The cpufreq policy notifier in the ACPI processor driver may as well be registered before the driver itself, which causes acpi_processor_cpufreq_init to be true (unless the notifier registration fails, which is unlikely at that point) when the ACPI CPU thermal cooling devices are registered, so the processor_get_max_state() result does not change while acpi_processor_driver_init() is running.

Change the ordering in acpi_processor_driver_init() accordingly to prevent the max_state value from remaining 0 permanently for all ACPI CPU cooling devices.

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/acpi/processor_driver.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/acpi/processor_driver.c
===================================================================

drivers/acpi/processor_driver.c +6 -6

@@ -263,6 +263,12 @@ static int __init acpi_processor_driver_
 	if (acpi_disabled)
 		return 0;
 
+	if (!cpufreq_register_notifier(&acpi_processor_notifier_block,
+				       CPUFREQ_POLICY_NOTIFIER)) {
+		acpi_processor_cpufreq_init = true;
+		acpi_processor_ignore_ppc_init();
+	}
+
 	result = driver_register(&acpi_processor_driver);
 	if (result < 0)
 		return result;

@@ -276,12 +282,6 @@ static int __init acpi_processor_driver_
 	cpuhp_setup_state_nocalls(CPUHP_ACPI_CPUDRV_DEAD, "acpi/cpu-
 drv:dead",
 				  NULL, acpi_soft_cpu_dead);
 
-	if (!cpufreq_register_notifier(&acpi_processor_notifier_block,
-				       CPUFREQ_POLICY_NOTIFIER)) {
-		acpi_processor_cpufreq_init = true;
-		acpi_processor_ignore_ppc_init();
-	}
-
 	acpi_processor_throttling_init();
 	return 0;

err:

Quoted 14 lines · Rafael J. Wysocki

From: Rafael J. Wysocki <[email protected]>

The cpufreq policy notifier in the ACPI processor driver may as well be registered before the driver itself, which causes acpi_processor_cpufreq_init to be true (unless the notifier registration fails, which is unlikely at that point) when the ACPI CPU thermal cooling devices are registered, so the processor_get_max_state() result does not change while acpi_processor_driver_init() is running.

Change the ordering in acpi_processor_driver_init() accordingly to prevent the max_state value from remaining 0 permanently for all ACPI CPU cooling devices.

Quoted 5 lines

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

The full patch series fixes the problem but this one does not.

This is because,

static int cpu_has_cpufreq(unsigned int cpu)
{
struct
cpufreq_policy *policy;

        if (!acpi_processor_cpufreq_init)
                return 0;

        policy = cpufreq_cpu_get(cpu);
        if (policy) {
                cpufreq_cpu_put(policy);
                return 1;
        }
        return 0;
}

Although acpi_processor_cpufreq_init is set to true with patch 1/4, but we don't have cpufreq driver registered, thus cpufreq_cpu_get() return NULL.
so acpi_processor_cpufreq_init is not the only dependency here. :(

Quoted 38 lines

---
 drivers/acpi/processor_driver.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/acpi/processor_driver.c
===================================================================

drivers/acpi/processor_driver.c +6 -6

@@ -263,6 +263,12 @@ static int __init acpi_processor_driver_
      if (acpi_disabled)
              return 0;
 
+     if (!cpufreq_register_notifier(&acpi_processor_notifier_block,
+                                    CPUFREQ_POLICY_NOTIFIER)) {
+             acpi_processor_cpufreq_init = true;
+             acpi_processor_ignore_ppc_init();
+     }
+
      result = driver_register(&acpi_processor_driver);
      if (result < 0)
              return result;

@@ -276,12 +282,6 @@ static int __init acpi_processor_driver_
      cpuhp_setup_state_nocalls(CPUHP_ACPI_CPUDRV_DEAD, "acpi/cpu-
 drv:dead",
                                NULL, acpi_soft_cpu_dead);
 
-     if (!cpufreq_register_notifier(&acpi_processor_notifier_block,
-                                    CPUFREQ_POLICY_NOTIFIER)) {
-             acpi_processor_cpufreq_init = true;
-             acpi_processor_ignore_ppc_init();
-     }
-
      acpi_processor_throttling_init();
      return 0;

err:

Quoted 22 lines · Rui

Quoted 20 lines · Rafael J. Wysocki

From: Rafael J. Wysocki <[email protected]>

The cpufreq policy notifier in the ACPI processor driver may as well be registered before the driver itself, which causes acpi_processor_cpufreq_init to be true (unless the notifier registration fails, which is unlikely at that point) when the ACPI CPU thermal cooling devices are registered, so the processor_get_max_state() result does not change while acpi_processor_driver_init() is running.

Change the ordering in acpi_processor_driver_init() accordingly to prevent the max_state value from remaining 0 permanently for all
ACPI CPU cooling devices.

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

Quoted 1 line

The full patch series fixes the problem but this one does not.

That is a correct observation, but the $subject patch fixes part of the problem (which is not addressed by the rest of the series AFAICS) and so it deserves a Fixes tag of its own IMO.

I guess I should clarify that in the changelog.

Quoted 18 lines

This is because,

static int cpu_has_cpufreq(unsigned int cpu)
{
struct
cpufreq_policy *policy;

        if (!acpi_processor_cpufreq_init)
                return 0;

        policy = cpufreq_cpu_get(cpu);
        if (policy) {
                cpufreq_cpu_put(policy);
                return 1;
        }
        return 0;
}

Quoted 6 lines

Although acpi_processor_cpufreq_init is set to true with patch 1/4, but
we don't have cpufreq driver registered, thus cpufreq_cpu_get() return
NULL.
so acpi_processor_cpufreq_init is not the only dependency here. :(

Right. That's why the other patches in the series are needed too.

Quoted 42 lines

Quoted 42 lines

---
 drivers/acpi/processor_driver.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/acpi/processor_driver.c
=================================================================
==

drivers/acpi/processor_driver.c +6 -0

@@ -263,6 +263,12 @@ static int __init acpi_processor_driver_
      if (acpi_disabled)
              return 0;
 
+     if
 (!cpufreq_register_notifier(&acpi_processor_notifier_block,
+                                    CPUFREQ_POLICY_NOTIFIER)) {
+             acpi_processor_cpufreq_init = true;
+             acpi_processor_ignore_ppc_init();
+     }
+
      result = driver_register(&acpi_processor_driver);
      if (result < 0)

              return result;

drivers/acpi/processor_driver.c +0 -0

@@ -276,12 +282,6 @@ static int __init acpi_processor_driver_
      cpuhp_setup_state_nocalls(CPUHP_ACPI_CPUDRV_DEAD,

"acpi/cpu-
drv:dead",

                                NULL, acpi_soft_cpu_dead);

- if
(!cpufreq_register_notifier(&acpi_processor_notifier_block,

drivers/acpi/processor_driver.c +0 -5

-                                    CPUFREQ_POLICY_NOTIFIER)) {
-             acpi_processor_cpufreq_init = true;
-             acpi_processor_ignore_ppc_init();
-     }
-
      acpi_processor_throttling_init();
      return 0;
 err:

Quoted 24 lines · Rafael J. Wysocki

Quoted 22 lines · Rui

Quoted 20 lines · Rafael J. Wysocki

From: Rafael J. Wysocki <[email protected]>

The cpufreq policy notifier in the ACPI processor driver may as well be registered before the driver itself, which causes acpi_processor_cpufreq_init to be true (unless the notifier registration fails, which is unlikely at that point) when the ACPI CPU thermal cooling devices are registered, so the processor_get_max_state() result does not change while acpi_processor_driver_init() is running.

Change the ordering in acpi_processor_driver_init() accordingly to prevent the max_state value from remaining 0 permanently for all
ACPI CPU cooling devices.

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

Quoted 5 lines

Quoted 1 line

The full patch series fixes the problem but this one does not.

That is a correct observation, but the $subject patch fixes part of the problem (which is not addressed by the rest of the series AFAICS) and so it deserves a Fixes tag of its own IMO.

Am I understanding this correctly that this patch helps in below case?

cpufreq driver like intel_pstate is registered before we register the notifier callback in processor_driver. In this case, we are not able to catch the CPUFREQ_CREATE_POLICY notification and cpufreq should be counted as part of cooling states when registering the ACPI CPU cooling device. (acpi_processor_cpufreq_init must be set at this time)

Or else, in normal case, the ACPI CPU cdev->max_state always return 0 (when t-state not available) until we receive the CPUFREQ_CREATE_POLICY notification and call thermal_cooling_device_update(), both with and without this patch.

Patch 2,3,4 works on my test platform, without applying patch 1/4.

Quoted 71 lines

I guess I should clarify that in the changelog.

Quoted 18 lines

This is because,

static int cpu_has_cpufreq(unsigned int cpu)
{
struct
cpufreq_policy *policy;

        if (!acpi_processor_cpufreq_init)
                return 0;

        policy = cpufreq_cpu_get(cpu);
        if (policy) {
                cpufreq_cpu_put(policy);
                return 1;
        }
        return 0;
}

Quoted 6 lines

Although acpi_processor_cpufreq_init is set to true with patch 1/4, but
we don't have cpufreq driver registered, thus cpufreq_cpu_get() return
NULL.
so acpi_processor_cpufreq_init is not the only dependency here. :(

Right. That's why the other patches in the series are needed too.

Quoted 42 lines

Quoted 42 lines

---
 drivers/acpi/processor_driver.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/acpi/processor_driver.c
=================================================================
==

drivers/acpi/processor_driver.c +6 -0

@@ -263,6 +263,12 @@ static int __init acpi_processor_driver_
      if (acpi_disabled)
              return 0;
 
+     if
 (!cpufreq_register_notifier(&acpi_processor_notifier_block,
+                                    CPUFREQ_POLICY_NOTIFIER)) {
+             acpi_processor_cpufreq_init = true;
+             acpi_processor_ignore_ppc_init();
+     }
+
      result = driver_register(&acpi_processor_driver);
      if (result < 0)

              return result;

drivers/acpi/processor_driver.c +0 -0

@@ -276,12 +282,6 @@ static int __init acpi_processor_driver_
      cpuhp_setup_state_nocalls(CPUHP_ACPI_CPUDRV_DEAD,

"acpi/cpu-
drv:dead",

                                NULL, acpi_soft_cpu_dead);

- if
(!cpufreq_register_notifier(&acpi_processor_notifier_block,

drivers/acpi/processor_driver.c +0 -5

-                                    CPUFREQ_POLICY_NOTIFIER)) {
-             acpi_processor_cpufreq_init = true;
-             acpi_processor_ignore_ppc_init();
-     }
-
      acpi_processor_throttling_init();
      return 0;
 err:

From: Rafael J. Wysocki <[email protected]>

Introduce a core thermal API function, thermal_cooling_device_update(),
for updating the max_state value for a cooling device and rearranging its statistics in sysfs after a possible change of its ->get_max_state()
callback return value.

That callback is now invoked only once, during cooling device registration, to populate the max_state field in the cooling device object, so if its return value changes, it needs to be invoked again and the new return value needs to be stored as max_state. Moreover, the statistics presented in sysfs need to be rearranged in general, because there may not be enough room in them to store data for all of the possible states (in the case when max_state grows).

The new function takes care of that (and some other minor things related to it), but some extra locking and lockdep annotations are added in several places too to protect against crashes in the cases when the statistics are not present or when a stale max_state value might be used by sysfs attributes.

Note that the actual user of the new function will be added separately.

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/thermal/thermal_core.c  |   47 ++++++++++++++++++++++++++
 drivers/thermal/thermal_core.h  |    1 
 drivers/thermal/thermal_sysfs.c |   72
+++++++++++++++++++++++++++++++++++-----
 include/linux/thermal.h         |    1 
 4 files changed, 113 insertions(+), 8 deletions(-)

Index: linux-pm/drivers/thermal/thermal_core.c
===================================================================

drivers/thermal/thermal_core.c +9 -0

@@ -1057,6 +1057,53 @@ static bool thermal_cooling_device_prese
 	return false;
 }
 
+void thermal_cooling_device_update(struct thermal_cooling_device
 *cdev)
+{
+	unsigned long state;
+
+	if (!cdev)
+		return;
+
+	/*
+	 * Hold thermal_list_lock throughout the update to prevent the

device

drivers/thermal/thermal_core.c +9 -0

+	 * from going away while being updated.
+	 */
+	mutex_lock(&thermal_list_lock);
+
+	if (!thermal_cooling_device_present(cdev))
+		goto unlock_list;
+
+	/*
+	 * Update under the cdev lock to prevent the state from being

set beyond

drivers/thermal/thermal_core.c +5 -0

+	 * the new limit concurrently.
+	 */
+	mutex_lock(&cdev->lock);
+
+	if (cdev->ops->get_max_state(cdev, &cdev->max_state))

drivers/thermal/thermal_core.c +12 -0

+
+update_stats:
+	thermal_cooling_device_stats_update(cdev, state);
+
+unlock:
+	mutex_unlock(&cdev->lock);
+
+unlock_list:
+	mutex_unlock(&thermal_list_lock);
+}
+EXPORT_SYMBOL_GPL(thermal_cooling_device_update);
+
 static void __unbind(struct thermal_zone_device *tz, int mask,
 		     struct thermal_cooling_device *cdev)
 {

Index: linux-pm/drivers/thermal/thermal_sysfs.c
===================================================================

drivers/thermal/thermal_sysfs.c +45 -5

@@ -685,6 +685,8 @@ void thermal_cooling_device_stats_update
 {
 	struct cooling_dev_stats *stats = cdev->stats;
 
+	lockdep_assert_held(&cdev->lock);
+
 	if (!stats)
 		return;
 

@@ -706,13 +708,22 @@ static ssize_t total_trans_show(struct d
 				struct device_attribute *attr, char
 *buf)
 {
 	struct thermal_cooling_device *cdev = to_cooling_device(dev);
-	struct cooling_dev_stats *stats = cdev->stats;
+	struct cooling_dev_stats *stats;
 	int ret;
 
+	mutex_lock(&cdev->lock);
+
+	stats = cdev->stats;
+	if (!stats)
+		goto unlock;
+
 	spin_lock(&stats->lock);
 	ret = sprintf(buf, "%u\n", stats->total_trans);
 	spin_unlock(&stats->lock);
 
+unlock:
+	mutex_unlock(&cdev->lock);
+
 	return ret;
 }

@@ -721,11 +732,18 @@ time_in_state_ms_show(struct device *dev
 		      char *buf)
 {
 	struct thermal_cooling_device *cdev = to_cooling_device(dev);
-	struct cooling_dev_stats *stats = cdev->stats;
+	struct cooling_dev_stats *stats;
 	ssize_t len = 0;
 	int i;
 
+	mutex_lock(&cdev->lock);
+
+	stats = cdev->stats;
+	if (!stats)
+		goto unlock;
+
 	spin_lock(&stats->lock);
+
 	update_time_in_state(stats);
 
 	for (i = 0; i <= cdev->max_state; i++) {

@@ -734,6 +752,9 @@ time_in_state_ms_show(struct device *dev
 	}
 	spin_unlock(&stats->lock);
 
+unlock:
+	mutex_unlock(&cdev->lock);
+
 	return len;
 }
 

@@ -742,8 +763,16 @@ reset_store(struct device *dev, struct d
 	    size_t count)
 {
 	struct thermal_cooling_device *cdev = to_cooling_device(dev);
-	struct cooling_dev_stats *stats = cdev->stats;
-	int i, states = cdev->max_state + 1;
+	struct cooling_dev_stats *stats;
+	int i, states;
+
+	mutex_lock(&cdev->lock);
+
+	stats = cdev->stats;
+	if (!stats)
+		goto unlock;
+
+	states = cdev->max_state + 1;
 
 	spin_lock(&stats->lock);
 

@@ -757,6 +786,9 @@ reset_store(struct device *dev, struct d
 
 	spin_unlock(&stats->lock);
 
+unlock:
+	mutex_unlock(&cdev->lock);
+
 	return count;
 }
 

@@ -764,10 +796,18 @@ static ssize_t trans_table_show(struct d
 				struct device_attribute *attr, char
 *buf)
 {
 	struct thermal_cooling_device *cdev = to_cooling_device(dev);
-	struct cooling_dev_stats *stats = cdev->stats;
+	struct cooling_dev_stats *stats;
 	ssize_t len = 0;
 	int i, j;
 
+	mutex_lock(&cdev->lock);
+
+	stats = cdev->stats;
+	if (!stats) {
+		len = -ENODATA;
+		goto unlock;
+	}
+
 	len += snprintf(buf + len, PAGE_SIZE - len, "
 From  :    To\n");

drivers/thermal/thermal_sysfs.c +13 -3

 	len += snprintf(buf + len, PAGE_SIZE - len, "       : ");
 	for (i = 0; i <= cdev->max_state; i++) {

@@ -775,8 +815,10 @@ static ssize_t trans_table_show(struct d
 			break;
 		len += snprintf(buf + len, PAGE_SIZE - len,
 "state%2u  ", i);
 	}
-	if (len >= PAGE_SIZE)
-		return PAGE_SIZE;
+	if (len >= PAGE_SIZE) {
+		len = PAGE_SIZE;
+		goto unlock;
+	}
 
 	len += snprintf(buf + len, PAGE_SIZE - len, "\n");

@@ -799,8 +841,12 @@ static ssize_t trans_table_show(struct d
 
 	if (len >= PAGE_SIZE) {
 		pr_warn_once("Thermal transition table exceeds
 PAGE_SIZE. Disabling\n");
-		return -EFBIG;
+		len = -EFBIG;
 	}
+
+unlock:
+	mutex_unlock(&cdev->lock);
+
 	return len;
 }

@@ -830,6 +876,8 @@ static void cooling_device_stats_setup(s
 	unsigned long states = cdev->max_state + 1;
 	int var;
 
+	lockdep_assert_held(&cdev->lock);
+
 	var = sizeof(*stats);
 	var += sizeof(*stats->time_in_state) * states;
 	var += sizeof(*stats->trans_table) * states * states;

@@ -855,6 +903,8 @@ out:
 
 static void cooling_device_stats_destroy(struct
 thermal_cooling_device *cdev)
 {
+	lockdep_assert_held(&cdev->lock);
+
 	kfree(cdev->stats);
 	cdev->stats = NULL;

}

drivers/thermal/thermal_sysfs.c +6 -0

@@ -879,6 +929,12 @@ void thermal_cooling_device_destroy_sysf
 	cooling_device_stats_destroy(cdev);
 }
 
+void thermal_cooling_device_stats_reinit(struct
 thermal_cooling_device *cdev)
+{
+	cooling_device_stats_destroy(cdev);
+	cooling_device_stats_setup(cdev);
+}
+
 /* these helper will be used only at the time of bindig */
 ssize_t

trip_point_show(struct device *dev, struct device_attribute *attr,
char *buf)
Index: linux-pm/drivers/thermal/thermal_core.h
===================================================================

drivers/thermal/thermal_core.h +1 -0

@@ -127,6 +127,7 @@ int thermal_zone_create_device_groups(st
 void thermal_zone_destroy_device_groups(struct thermal_zone_device
 *);
 void thermal_cooling_device_setup_sysfs(struct
 thermal_cooling_device *);
 void thermal_cooling_device_destroy_sysfs(struct
 thermal_cooling_device *cdev);
+void thermal_cooling_device_stats_reinit(struct

thermal_cooling_device *cdev);
/* used only at binding time */
ssize_t trip_point_show(struct device *, struct device_attribute *,
char *);
ssize_t weight_show(struct device *, struct device_attribute *, char
*);
Index: linux-pm/include/linux/thermal.h
===================================================================

include/linux/thermal.h +1 -0

@@ -384,6 +384,7 @@ devm_thermal_of_cooling_device_register(
 				struct device_node *np,
 				char *type, void *devdata,
 				const struct thermal_cooling_device_ops
 *ops);
+void thermal_cooling_device_update(struct thermal_cooling_device *);
 void thermal_cooling_device_unregister(struct thermal_cooling_device
 *);

struct thermal_zone_device *thermal_zone_get_zone_by_name(const char
*name);
int thermal_zone_get_temp(struct thermal_zone_device *tz, int
*temp);

Quoted 75 lines · Rafael J. Wysocki

From: Rafael J. Wysocki <[email protected]>

Introduce a core thermal API function, thermal_cooling_device_update(),
for updating the max_state value for a cooling device and rearranging its statistics in sysfs after a possible change of its ->get_max_state()
callback return value.

That callback is now invoked only once, during cooling device registration, to populate the max_state field in the cooling device object, so if its return value changes, it needs to be invoked again and the new return value needs to be stored as max_state. Moreover, the statistics presented in sysfs need to be rearranged in general, because there may not be enough room in them to store data for all of the possible states (in the case when max_state grows).

The new function takes care of that (and some other minor things related to it), but some extra locking and lockdep annotations are added in several places too to protect against crashes in the cases when the statistics are not present or when a stale max_state value might be used by sysfs attributes.

Note that the actual user of the new function will be added separately.

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/thermal/thermal_core.c  |   47 ++++++++++++++++++++++++++
 drivers/thermal/thermal_core.h  |    1
 drivers/thermal/thermal_sysfs.c |   72
+++++++++++++++++++++++++++++++++++-----
 include/linux/thermal.h         |    1
 4 files changed, 113 insertions(+), 8 deletions(-)

Index: linux-pm/drivers/thermal/thermal_core.c
===================================================================

drivers/thermal/thermal_core.c +9 -0

@@ -1057,6 +1057,53 @@ static bool thermal_cooling_device_prese
      return false;
 }
 
+void thermal_cooling_device_update(struct thermal_cooling_device
 *cdev)
+{
+     unsigned long state;
+
+     if (!cdev)
+             return;
+
+     /*
+      * Hold thermal_list_lock throughout the update to prevent the

device

drivers/thermal/thermal_core.c +9 -0

+      * from going away while being updated.
+      */
+     mutex_lock(&thermal_list_lock);
+
+     if (!thermal_cooling_device_present(cdev))
+             goto unlock_list;
+
+     /*
+      * Update under the cdev lock to prevent the state from being

set beyond

drivers/thermal/thermal_core.c +9 -0

+      * the new limit concurrently.
+      */
+     mutex_lock(&cdev->lock);
+
+     if (cdev->ops->get_max_state(cdev, &cdev->max_state))
+             goto unlock;
+
+     thermal_cooling_device_stats_reinit(cdev);
+

drivers/thermal/thermal_core.c static bool thermal_cooling_device_prese · line 1092

Quoted 6 lines

drivers/thermal/thermal_core.c +6 -0

+     if (cdev->ops->get_cur_state(cdev, &state))
+             goto unlock;
+
+     if (state <= cdev->max_state)
+             goto update_stats;
+

how could the .get_cur_state() callback returns a value higher than .get_max_state()? Isn't this a driver problem?

drivers/thermal/thermal_core.c static bool thermal_cooling_device_prese · line 1094

Quoted 2 lines

drivers/thermal/thermal_core.c +2 -0

+     if (cdev->ops->set_cur_state(cdev, state))
+             goto unlock;

even if we don't error out, should we reevaluate .get_max_state() and update cdev->max_state?

Quoted 234 lines

drivers/thermal/thermal_core.c +12 -0

+
+update_stats:
+     thermal_cooling_device_stats_update(cdev, state);
+
+unlock:
+     mutex_unlock(&cdev->lock);
+
+unlock_list:
+     mutex_unlock(&thermal_list_lock);
+}
+EXPORT_SYMBOL_GPL(thermal_cooling_device_update);
+
 static void __unbind(struct thermal_zone_device *tz, int mask,
                   struct thermal_cooling_device *cdev)
 {

Index: linux-pm/drivers/thermal/thermal_sysfs.c
===================================================================

drivers/thermal/thermal_sysfs.c +45 -5

@@ -685,6 +685,8 @@ void thermal_cooling_device_stats_update
 {
      struct cooling_dev_stats *stats = cdev->stats;
 
+     lockdep_assert_held(&cdev->lock);
+
      if (!stats)
              return;
 

@@ -706,13 +708,22 @@ static ssize_t total_trans_show(struct d
                              struct device_attribute *attr, char
 *buf)
 {
      struct thermal_cooling_device *cdev = to_cooling_device(dev);
-     struct cooling_dev_stats *stats = cdev->stats;
+     struct cooling_dev_stats *stats;
      int ret;
 
+     mutex_lock(&cdev->lock);
+
+     stats = cdev->stats;
+     if (!stats)
+             goto unlock;
+
      spin_lock(&stats->lock);
      ret = sprintf(buf, "%u\n", stats->total_trans);
      spin_unlock(&stats->lock);
 
+unlock:
+     mutex_unlock(&cdev->lock);
+
      return ret;
 }

@@ -721,11 +732,18 @@ time_in_state_ms_show(struct device *dev
                    char *buf)
 {
      struct thermal_cooling_device *cdev = to_cooling_device(dev);
-     struct cooling_dev_stats *stats = cdev->stats;
+     struct cooling_dev_stats *stats;
      ssize_t len = 0;
      int i;
 
+     mutex_lock(&cdev->lock);
+
+     stats = cdev->stats;
+     if (!stats)
+             goto unlock;
+
      spin_lock(&stats->lock);
+
      update_time_in_state(stats);
 
      for (i = 0; i <= cdev->max_state; i++) {

@@ -734,6 +752,9 @@ time_in_state_ms_show(struct device *dev
      }
      spin_unlock(&stats->lock);
 
+unlock:
+     mutex_unlock(&cdev->lock);
+
      return len;
 }
 

@@ -742,8 +763,16 @@ reset_store(struct device *dev, struct d
          size_t count)
 {
      struct thermal_cooling_device *cdev = to_cooling_device(dev);
-     struct cooling_dev_stats *stats = cdev->stats;
-     int i, states = cdev->max_state + 1;
+     struct cooling_dev_stats *stats;
+     int i, states;
+
+     mutex_lock(&cdev->lock);
+
+     stats = cdev->stats;
+     if (!stats)
+             goto unlock;
+
+     states = cdev->max_state + 1;
 
      spin_lock(&stats->lock);
 

@@ -757,6 +786,9 @@ reset_store(struct device *dev, struct d
 
      spin_unlock(&stats->lock);
 
+unlock:
+     mutex_unlock(&cdev->lock);
+
      return count;
 }
 

@@ -764,10 +796,18 @@ static ssize_t trans_table_show(struct d
                              struct device_attribute *attr, char
 *buf)
 {
      struct thermal_cooling_device *cdev = to_cooling_device(dev);
-     struct cooling_dev_stats *stats = cdev->stats;
+     struct cooling_dev_stats *stats;
      ssize_t len = 0;
      int i, j;
 
+     mutex_lock(&cdev->lock);
+
+     stats = cdev->stats;
+     if (!stats) {
+             len = -ENODATA;
+             goto unlock;
+     }
+
      len += snprintf(buf + len, PAGE_SIZE - len, "
 From  :    To\n");

      len += snprintf(buf + len, PAGE_SIZE - len, "       : ");
      for (i = 0; i <= cdev->max_state; i++) {

drivers/thermal/thermal_sysfs.c +13 -3

@@ -775,8 +815,10 @@ static ssize_t trans_table_show(struct d
                      break;
              len += snprintf(buf + len, PAGE_SIZE - len,
 "state%2u  ", i);
      }
-     if (len >= PAGE_SIZE)
-             return PAGE_SIZE;
+     if (len >= PAGE_SIZE) {
+             len = PAGE_SIZE;
+             goto unlock;
+     }
 
      len += snprintf(buf + len, PAGE_SIZE - len, "\n");

@@ -799,8 +841,12 @@ static ssize_t trans_table_show(struct d
 
      if (len >= PAGE_SIZE) {
              pr_warn_once("Thermal transition table exceeds
 PAGE_SIZE. Disabling\n");
-             return -EFBIG;
+             len = -EFBIG;
      }
+
+unlock:
+     mutex_unlock(&cdev->lock);
+
      return len;
 }

@@ -830,6 +876,8 @@ static void cooling_device_stats_setup(s
      unsigned long states = cdev->max_state + 1;
      int var;
 
+     lockdep_assert_held(&cdev->lock);
+
      var = sizeof(*stats);
      var += sizeof(*stats->time_in_state) * states;
      var += sizeof(*stats->trans_table) * states * states;

@@ -855,6 +903,8 @@ out:
 
 static void cooling_device_stats_destroy(struct
 thermal_cooling_device *cdev)
 {
+     lockdep_assert_held(&cdev->lock);
+
      kfree(cdev->stats);
      cdev->stats = NULL;

}

drivers/thermal/thermal_sysfs.c +6 -0

@@ -879,6 +929,12 @@ void thermal_cooling_device_destroy_sysf
      cooling_device_stats_destroy(cdev);
 }
 
+void thermal_cooling_device_stats_reinit(struct
 thermal_cooling_device *cdev)
+{
+     cooling_device_stats_destroy(cdev);
+     cooling_device_stats_setup(cdev);
+}
+
 /* these helper will be used only at the time of bindig */
 ssize_t

trip_point_show(struct device *dev, struct device_attribute *attr,
char *buf)
Index: linux-pm/drivers/thermal/thermal_core.h
===================================================================

drivers/thermal/thermal_core.h +1 -0

@@ -127,6 +127,7 @@ int thermal_zone_create_device_groups(st
 void thermal_zone_destroy_device_groups(struct thermal_zone_device
 *);
 void thermal_cooling_device_setup_sysfs(struct
 thermal_cooling_device *);
 void thermal_cooling_device_destroy_sysfs(struct
 thermal_cooling_device *cdev);
+void thermal_cooling_device_stats_reinit(struct

thermal_cooling_device *cdev);
/* used only at binding time */
ssize_t trip_point_show(struct device *, struct device_attribute *,
char *);
ssize_t weight_show(struct device *, struct device_attribute *, char
*);
Index: linux-pm/include/linux/thermal.h
===================================================================

include/linux/thermal.h +1 -0

@@ -384,6 +384,7 @@ devm_thermal_of_cooling_device_register(
                              struct device_node *np,
                              char *type, void *devdata,
                              const struct thermal_cooling_device_ops
 *ops);
+void thermal_cooling_device_update(struct thermal_cooling_device *);
 void thermal_cooling_device_unregister(struct thermal_cooling_device
 *);

struct thermal_zone_device *thermal_zone_get_zone_by_name(const char
*name);
int thermal_zone_get_temp(struct thermal_zone_device *tz, int
*temp);

Hi,

this leads to the stacktrace below triggered by lockdep_assert_held(&cdev->lock) in cooling_device_stats_setup(),

and

drivers/thermal/thermal_core.c +2 -0

index 566df4522b885..132175b14814f 100644
@@ -918,7 +918,9 @@ __thermal_cooling_device_register(struct device_node *np,
        if (ret)
                goto out_cdev_type;
 
+       mutex_lock(&cdev->lock);
        thermal_cooling_device_setup_sysfs(cdev);
+       mutex_unlock(&cdev->lock);
 
        ret = dev_set_name(&cdev->device, "cooling_device%d", cdev->id);
        if (ret)

fixed it up for me, but not sure if it's the correct fix.

[    4.662358] ------------[ cut here ]------------
[    4.662361] WARNING: CPU: 3 PID: 1 at drivers/thermal/thermal_sysfs.c:879 cooling_device_stats_setup+0xb4/0xc0
[    4.662370] Modules linked in:
[    4.662375] CPU: 3 PID: 1 Comm: swapper/0 Tainted: G          I        6.3.0-rc4-imre+ #771
[    4.662379] Hardware name: Intel Corporation Shark Bay Client platform/Flathead Creek Crb, BIOS HSWLPTU1.86C.0109.R03.1301282055 01/28/2013
[    4.662382] RIP: 0010:cooling_device_stats_setup+0xb4/0xc0
[    4.662387] Code: 89 1d 58 52 36 01 5b 41 5c 41 5d 5d c3 cc cc cc cc 48 8d bf 18 05 00 00 be ff ff ff ff e8 f4 d2 3e 00 85 c0 0f 85 6f ff ff ff <0f> 0b e9 68 ff ff ff 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90
[    4.662390] RSP: 0000:ffff9f48c0057b30 EFLAGS: 00010246
[    4.662395] RAX: 0000000000000000 RBX: ffff8fc381ca9800 RCX: 0000000000000000
[    4.662398] RDX: 0000000000000000 RSI: ffffffff94ad1d28 RDI: ffffffff94b58cc6
[    4.662401] RBP: ffff9f48c0057b48 R08: 0000000000000004 R09: 0000000000000000
[    4.662404] R10: ffff8fc381c77cd0 R11: 0000000000000000 R12: 0000000000000002
[    4.662406] R13: ffff8fc381ca9800 R14: ffff8fc381b0a000 R15: 0000000000000000
[    4.662409] FS:  0000000000000000(0000) GS:ffff8fc6b5580000(0000) knlGS:0000000000000000
[    4.662412] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    4.662415] CR2: 0000000000000000 CR3: 0000000283856001 CR4: 00000000001706e0
[    4.662418] Call Trace:
[    4.662421]  <TASK>
[    4.662427]  thermal_cooling_device_setup_sysfs+0x12/0x30
[    4.662433]  __thermal_cooling_device_register+0x195/0x410
[    4.662442]  thermal_cooling_device_register+0x19/0x20
[    4.662446]  acpi_fan_probe+0xd7/0x5a0
[    4.662458]  ? acpi_match_device_ids+0x12/0x20
[    4.662464]  ? acpi_dev_pm_attach+0x41/0x110
[    4.662473]  platform_probe+0x48/0xc0
[    4.662481]  really_probe+0x1be/0x420
[    4.662487]  __driver_probe_device+0x8c/0x190
[    4.662493]  driver_probe_device+0x24/0x90
[    4.662498]  __driver_attach+0xf7/0x200
[    4.662503]  ? __pfx___driver_attach+0x10/0x10
[    4.662507]  bus_for_each_dev+0x80/0xd0
[    4.662516]  driver_attach+0x1e/0x30
[    4.662522]  bus_add_driver+0x11f/0x230
[    4.662530]  driver_register+0x5e/0x120
[    4.662534]  ? __pfx_acpi_fan_driver_init+0x10/0x10
[    4.662540]  __platform_driver_register+0x1e/0x30
[    4.662545]  acpi_fan_driver_init+0x17/0x20
[    4.662549]  do_one_initcall+0x61/0x280
[    4.662559]  ? debug_smp_processor_id+0x17/0x20
[    4.662568]  kernel_init_freeable+0x411/0x640
[    4.662582]  ? __pfx_kernel_init+0x10/0x10
[    4.662589]  kernel_init+0x1b/0x1f0
[    4.662594]  ? __pfx_kernel_init+0x10/0x10
[    4.662599]  ret_from_fork+0x2c/0x50
[    4.662615]  </TASK>
[    4.662618] irq event stamp: 506869
[    4.662620] hardirqs last  enabled at (506875): [<ffffffff9338e2d8>] __up_console_sem+0x68/0x80
[    4.662625] hardirqs last disabled at (506880): [<ffffffff9338e2bd>] __up_console_sem+0x4d/0x80
[    4.662628] softirqs last  enabled at (504698): [<ffffffff932de49f>] __irq_exit_rcu+0xbf/0x140
[    4.662633] softirqs last disabled at (504689): [<ffffffff932de49f>] __irq_exit_rcu+0xbf/0x140
[    4.662636] ---[ end trace 0000000000000000 ]---
[    4.662779] ------------[ cut here ]------------

From: Rafael J. Wysocki <[email protected]>

When a cpufreq policy appears or goes away, the CPU cooling devices for
the CPUs covered by that policy need to be updated so that the new processor_get_max_state() value is stored as max_state and the statistics in sysfs are rearranged for each of them.

Do that accordingly in acpi_thermal_cpufreq_init() and acpi_thermal_cpufreq_exit().

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/acpi/processor_thermal.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/acpi/processor_thermal.c
===================================================================

drivers/acpi/processor_thermal.c +0 -0

@@ -140,9 +140,14 @@ void acpi_thermal_cpufreq_init(struct cp
 		ret = freq_qos_add_request(&policy->constraints,
 					   &pr->thermal_req,
 					   FREQ_QOS_MAX, INT_MAX);

drivers/acpi/processor_thermal.c +7 -2

 	}
 }

@@ -153,8 +158,13 @@ void acpi_thermal_cpufreq_exit(struct cp
 	for_each_cpu(cpu, policy->related_cpus) {
 		struct acpi_processor *pr = per_cpu(processors, cpu);
 
-		if (pr)
-			freq_qos_remove_request(&pr->thermal_req);
+		if (!pr)
+			continue;
+
+		freq_qos_remove_request(&pr->thermal_req);
+
+		if (!IS_ERR(pr->cdev))
+			thermal_cooling_device_update(pr->cdev);
 	}
 }
 #else				/* ! CONFIG_CPU_FREQ */

Quoted 33 lines · Rafael J. Wysocki

From: Rafael J. Wysocki <[email protected]>

When a cpufreq policy appears or goes away, the CPU cooling devices for
the CPUs covered by that policy need to be updated so that the new processor_get_max_state() value is stored as max_state and the statistics in sysfs are rearranged for each of them.

Do that accordingly in acpi_thermal_cpufreq_init() and acpi_thermal_cpufreq_exit().

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/acpi/processor_thermal.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/acpi/processor_thermal.c
===================================================================

drivers/acpi/processor_thermal.c +1 -1

@@ -140,9 +140,14 @@ void acpi_thermal_cpufreq_init(struct cp
              ret = freq_qos_add_request(&policy->constraints,
                                         &pr->thermal_req,
                                         FREQ_QOS_MAX, INT_MAX);
-             if (ret < 0)
+             if (ret < 0) {
                      pr_err("Failed to add freq constraint for CPU%d
 (%d)\n",
                             cpu, ret);

drivers/acpi/processor_thermal.c void acpi_thermal_cpufreq_init(struct cp · line 150

Quoted 5 lines

drivers/acpi/processor_thermal.c +5 -0

+                     continue;
+             }
+
+             if (!IS_ERR(pr->cdev))
+                     thermal_cooling_device_update(pr->cdev);

Although thermal_cooling_device_update() handles "pr->cdev == NULL" case, I think it is better to use !IS_ERR_OR_NULL() here.

Quoted 38 lines · Rui

Quoted 37 lines · Rafael J. Wysocki

From: Rafael J. Wysocki <[email protected]>

When a cpufreq policy appears or goes away, the CPU cooling devices
for
the CPUs covered by that policy need to be updated so that the new
processor_get_max_state() value is stored as max_state and the statistics in sysfs are rearranged for each of them.

Do that accordingly in acpi_thermal_cpufreq_init() and acpi_thermal_cpufreq_exit().

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/acpi/processor_thermal.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/acpi/processor_thermal.c
=================================================================
==

drivers/acpi/processor_thermal.c +1 -1

@@ -140,9 +140,14 @@ void acpi_thermal_cpufreq_init(struct cp
              ret = freq_qos_add_request(&policy->constraints,
                                         &pr->thermal_req,
                                         FREQ_QOS_MAX, INT_MAX);
-             if (ret < 0)
+             if (ret < 0) {
                      pr_err("Failed to add freq constraint for

CPU%d
(%d)\n",

                             cpu, ret);

Quoted 8 lines

drivers/acpi/processor_thermal.c void acpi_thermal_cpufreq_init(struct cp · line 150

Quoted 5 lines

drivers/acpi/processor_thermal.c +5 -0

+                     continue;
+             }
+
+             if (!IS_ERR(pr->cdev))
+                     thermal_cooling_device_update(pr->cdev);

Although thermal_cooling_device_update() handles "pr->cdev == NULL" case, I think it is better to use !IS_ERR_OR_NULL() here.

Why is it?

I was thinking about doing that, but then I realized that the NULL case had been covered and that's why I went for the change above. If there is a particular reason to check for NULL here, I can do that, but I'm not sure what it is.

Quoted 49 lines · Rafael J. Wysocki

Quoted 38 lines · Rui

Quoted 37 lines · Rafael J. Wysocki

From: Rafael J. Wysocki <[email protected]>

When a cpufreq policy appears or goes away, the CPU cooling devices
for
the CPUs covered by that policy need to be updated so that the new
processor_get_max_state() value is stored as max_state and the statistics in sysfs are rearranged for each of them.

Do that accordingly in acpi_thermal_cpufreq_init() and acpi_thermal_cpufreq_exit().

Fixes a365105c685c("thermal: sysfs: Reuse cdev->max_state")

Reported-by Wang, Quanxian <[email protected]>

Link:
https://lore.kernel.org/linux-pm/[email protected]/

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/acpi/processor_thermal.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/acpi/processor_thermal.c
=================================================================
==

drivers/acpi/processor_thermal.c +1 -1

@@ -140,9 +140,14 @@ void acpi_thermal_cpufreq_init(struct cp
              ret = freq_qos_add_request(&policy->constraints,
                                         &pr->thermal_req,
                                         FREQ_QOS_MAX, INT_MAX);
-             if (ret < 0)
+             if (ret < 0) {
                      pr_err("Failed to add freq constraint for

CPU%d
(%d)\n",

                             cpu, ret);

Quoted 8 lines

drivers/acpi/processor_thermal.c void acpi_thermal_cpufreq_init(struct cp · line 150

Quoted 5 lines

drivers/acpi/processor_thermal.c +5 -0

+                     continue;
+             }
+
+             if (!IS_ERR(pr->cdev))
+                     thermal_cooling_device_update(pr->cdev);

Although thermal_cooling_device_update() handles "pr->cdev == NULL" case, I think it is better to use !IS_ERR_OR_NULL() here.

Quoted 6 lines

Why is it?

I was thinking about doing that, but then I realized that the NULL case had been covered and that's why I went for the change above. If there is a particular reason to check for NULL here, I can do that, but I'm not sure what it is.

I don't have a strong objection here.

I thought this was a code bug at first glance, until I double checked t hermal_cooling_device_update().

So I think the latter would be more straight forward without introducing code complexity.