[PATCH] thermal: of-thermal: avoid NULL ops dereference when writing trip temperature

[Akinobu Mita <akinobu.mita@gmail.com>]

While no sensor is registered to a DT thermal zone, __thermal_zone->ops
(struct thermal_zone_of_device_ops) is set to NULL.
This causes a NULL pointer dereference when writing trip point temperature
(i.e. trip_point_[0-*]_temp).

Fix it by checking if ops is NULL under thermal_zone_device's lock that
protects against concurrent access by thermal_zone_of_sensor_register() and
thermal_zone_of_sensor_unregister().

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 drivers/thermal/of-thermal.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/thermal/of-thermal.c b/drivers/thermal/of-thermal.c
index dc5093b..c207075 100644
--- a/drivers/thermal/of-thermal.c
+++ b/drivers/thermal/of-thermal.c
@@ -332,17 +332,20 @@ static int of_thermal_set_trip_temp(struct thermal_zone_device *tz, int trip,
 				    int temp)
 {
 	struct __thermal_zone *data = tz->devdata;
+	int ret = 0;
 
 	if (trip >= data->ntrips || trip < 0)
 		return -EDOM;
 
-	if (data->ops->set_trip_temp) {
-		int ret;
+	mutex_lock(&tz->lock);
 
+	if (data->ops && data->ops->set_trip_temp)
 		ret = data->ops->set_trip_temp(data->sensor_data, trip, temp);
-		if (ret)
-			return ret;
-	}
+
+	mutex_unlock(&tz->lock);
+
+	if (ret)
+		return ret;
 
 	/* thermal framework should take care of data->mask & (1 << trip) */
 	data->trips[trip].temperature = temp;
-- 
2.7.4