thermal_sys: check get_temp return value

The return value of the get_temp function is not checked when doing a thermal zone update. This may lead to a critical shutdown if get_temp fails and the content of the temp variable is incorrectly set higher than the critical trip point.
This has been observed on a system with incorrect ACPI implementation where the corresponding methods were not serialized and therefore sometimes triggered ACPI errors (AE_ALREADY_EXISTS). The following critical shutdowns indicated a temperature of 2097 C, which was obviously wrong.

The patch adds a return value check that jumps over all trip point evaluations printing a warning if get_temp fails. The trip points are evaluated again on the next polling interval with successful get_temp execution.

Signed-off-by Michael Brunner <[email protected]>

---

 drivers/thermal/thermal_sys.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

drivers/thermal/thermal_sys.c +8 -1

index 0a69672..4e83c29 100644
@@ -953,7 +953,12 @@ void thermal_zone_device_update(struct thermal_zone_device *tz)
 
 	mutex_lock(&tz->lock);
 
-	tz->ops->get_temp(tz, &temp);
+	if (tz->ops->get_temp(tz, &temp)) {
+		/* get_temp failed - retry it later */
+		printk(KERN_WARNING PREFIX "failed to read out thermal zone "
+		       "%d\n", tz->id);
+		goto leave;
+	}
 
 	for (count = 0; count < tz->trips; count++) {
 		tz->ops->get_trip_type(tz, count, &trip_type);

@@ -1005,6 +1010,8 @@ void thermal_zone_device_update(struct thermal_zone_device *tz)
 					    THERMAL_TRIPS_NONE);
 
 	tz->last_temperature = temp;
+
+      leave:
 	if (tz->passive)
 		thermal_zone_device_set_polling(tz, tz->passive_delay);
 	else if (tz->polling_delay)