The user-space can change thermal instance weight value while the
throtte() callback is running for a governor. The IPA governor uses the
'weight' value for power calculation and also keeps it in 'total_weight'.
Therefore, the 'weight' value must not change during the throttle()
callback. Use 'tz->lock' mutex which also guards the throttle() to make
the update value safe.
Signed-off-by: Lukasz Luba <[email protected]>
---
drivers/thermal/thermal_sysfs.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index eef40d4f3063..df85df7d4a88 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -961,6 +961,7 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
{
struct thermal_instance *instance;
+ struct thermal_zone_device *tz;
int ret, weight;
ret = kstrtoint(buf, 0, &weight);
@@ -968,7 +969,12 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
return ret;
instance = container_of(attr, struct thermal_instance, weight_attr);
+ tz = instance->tz;
+
+ /* Don't race with governors using the 'weight' value */
+ mutex_lock(&tz->lock);
instance->weight = weight;
+ mutex_unlock(&tz->lock);
return count;
}
--
2.25.1
On Tue, Dec 12, 2023 at 2:48 PM Lukasz Luba <[email protected]> wrote:
>
> The user-space can change thermal instance weight value while the
> throtte() callback is running for a governor.
This needs to be more precise IMV. Something like
"User space can change the weight of a thermal instance via sysfs
while the .throttle() callback is running for a governor, because
weight_store() does not use the zone lock."
> The IPA governor uses the
> 'weight' value for power calculation and also keeps it in 'total_weight'.
> Therefore, the 'weight' value must not change during the throttle()
> callback. Use 'tz->lock' mutex which also guards the throttle() to make
> the update value safe.
"The IPA governor uses instance weight values for power calculations
and caches the sum of them as total_weight, so it gets confused when
one of them changes while its .throttle() callback is running.
To prevent that from happening, use thermal zone locking in weight_store()."
>
> Signed-off-by: Lukasz Luba <[email protected]>
> ---
> drivers/thermal/thermal_sysfs.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index eef40d4f3063..df85df7d4a88 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -961,6 +961,7 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
> const char *buf, size_t count)
> {
> struct thermal_instance *instance;
> + struct thermal_zone_device *tz;
IMO the local var doesn't help much. You may as well use
instance->tz->lock directly below.
> int ret, weight;
>
> ret = kstrtoint(buf, 0, &weight);
> @@ -968,7 +969,12 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
> return ret;
>
> instance = container_of(attr, struct thermal_instance, weight_attr);
> + tz = instance->tz;
> +
> + /* Don't race with governors using the 'weight' value */
> + mutex_lock(&tz->lock);
> instance->weight = weight;
> + mutex_unlock(&tz->lock);
>
> return count;
> }
> --
On 12/20/23 14:53, Rafael J. Wysocki wrote:
> On Tue, Dec 12, 2023 at 2:48 PM Lukasz Luba <[email protected]> wrote:
>>
>> The user-space can change thermal instance weight value while the
>> throtte() callback is running for a governor.
>
> This needs to be more precise IMV. Something like
>
> "User space can change the weight of a thermal instance via sysfs
> while the .throttle() callback is running for a governor, because
> weight_store() does not use the zone lock."
Agree, I'll use it.
>
>> The IPA governor uses the
>> 'weight' value for power calculation and also keeps it in 'total_weight'.
>> Therefore, the 'weight' value must not change during the throttle()
>> callback. Use 'tz->lock' mutex which also guards the throttle() to make
>> the update value safe.
>
> "The IPA governor uses instance weight values for power calculations
> and caches the sum of them as total_weight, so it gets confused when
> one of them changes while its .throttle() callback is running.
>
> To prevent that from happening, use thermal zone locking in weight_store()."
Agree, thanks.
>
>>
>> Signed-off-by: Lukasz Luba <[email protected]>
>> ---
>> drivers/thermal/thermal_sysfs.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
>> index eef40d4f3063..df85df7d4a88 100644
>> --- a/drivers/thermal/thermal_sysfs.c
>> +++ b/drivers/thermal/thermal_sysfs.c
>> @@ -961,6 +961,7 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
>> const char *buf, size_t count)
>> {
>> struct thermal_instance *instance;
>> + struct thermal_zone_device *tz;
>
> IMO the local var doesn't help much. You may as well use
> instance->tz->lock directly below.
OK, I'll change that.
>
>> int ret, weight;
>>
>> ret = kstrtoint(buf, 0, &weight);
>> @@ -968,7 +969,12 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
>> return ret;
>>
>> instance = container_of(attr, struct thermal_instance, weight_attr);
>> + tz = instance->tz;
>> +
>> + /* Don't race with governors using the 'weight' value */
>> + mutex_lock(&tz->lock);
>> instance->weight = weight;
>> + mutex_unlock(&tz->lock);
>>
>> return count;
>> }
>> --