Re: [PATCH v1 2/3] thermal: Drop redundant and confusing device_is_registered() checks

Daniel Lezcano
2023-12-11T17:39:29Z

On 08/12/2023 20:19, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Multiple places in the thermal subsystem (most importantly, sysfs
> attribute callback functions) check if the given thermal zone device is
> still registered in order to return early in case the device_del() in
> thermal_zone_device_unregister() has run already.
>
> However, after thermal_zone_device_unregister() has been made wait for
> all of the zone-related activity to complete before returning, it is
> not necessary to do that any more, because all of the code holding a
> reference to the thermal zone device object will be waited for even if
> it does not do anything special to enforce this.
>
> Accordingly, drop all of the device_is_registered() checks that are now
> redundant and get rid of the zone locking that is not necessary any more
> after dropping them.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---

[ ... ]

> @@ -132,11 +120,6 @@ trip_point_temp_store(struct device *dev
>
> mutex_lock(&tz->lock);
>
> - if (!device_is_registered(dev)) {
> - ret = -ENODEV;
> - goto unlock;
> - }
> -
> trip = &tz->trips[trip_id];
>
> if (temp != trip->temperature) {
> @@ -162,23 +145,12 @@ trip_point_temp_show(struct device *dev,
> char *buf)
> {
> struct thermal_zone_device *tz = to_thermal_zone(dev);
> - int trip_id, temp;
> + int trip_id;
>
> if (sscanf(attr->attr.name, "trip_point_%d_temp", &trip_id) != 1)
> return -EINVAL;
>
> - mutex_lock(&tz->lock);
> -
> - if (!device_is_registered(dev)) {
> - mutex_unlock(&tz->lock);
> - return -ENODEV;
> - }
> -
> - temp = tz->trips[trip_id].temperature;
> -
> - mutex_unlock(&tz->lock);
> -
> - return sprintf(buf, "%d\n", temp);
> + return sprintf(buf, "%d\n", tz->trips[trip_id].temperature);

Without the lock, could the trip_temp_store() make the value change
while we read it?

[ ... ]

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