thermal/sysfs: Update instance->weight under tz lock

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 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 <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/thermal/thermal_sysfs.c

@@ -936,7 +936,11 @@ ssize_t weight_store(struct device *dev, struct device_attribute *attr,
 		return ret;
 
 	instance = container_of(attr, struct thermal_instance, weight_attr);
+
+	/* Don't race with governors using the 'weight' value */
+	mutex_lock(&instance->tz->lock);
 	instance->weight = weight;
+	mutex_unlock(&instance->tz->lock);
 
 	return count;
 }