thermal: add sanity check for the passive attribute

Values below 1000 milli-celsius don't make sense and can cause the
system to go into a thermal heart attack: the actual temperature
will always be lower and thus the system will be throttled down to
its lowest setting.

An additional problem is that values below 1000 will show as 0 in
/proc/acpi/thermal/TZx/trip_points:passive.

cat passive
0
echo -n 90 >passive
bash: echo: write error: Invalid argument
echo -n 90000 >passive
cat passive
90000

Signed-off-by: Frans Pop <elendil@planet.nl>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>

2 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/thermal/sysfs-api.txt b/Documentation/thermal/sysfs-api.txt
index a87dc277a5ca..cb3d15bc1aeb 100644
--- a/Documentation/thermal/sysfs-api.txt
+++ b/Documentation/thermal/sysfs-api.txt
@@ -206,6 +206,7 @@ passive
         passive trip point for the zone. Activation is done by polling with
         an interval of 1 second.
         Unit: millidegrees Celsius
+        Valid values: 0 (disabled) or greater than 1000
         RW, Optional
 
 *****************************
diff --git a/drivers/thermal/thermal_sys.c b/drivers/thermal/thermal_sys.c
index 6f8d8f971212..310e40ab00b6 100644
--- a/drivers/thermal/thermal_sys.c
+++ b/drivers/thermal/thermal_sys.c
@@ -225,6 +225,12 @@ passive_store(struct device *dev, struct device_attribute *attr,
         if (!sscanf(buf, "%d\n", &state))
                 return -EINVAL;
 
+        /* sanity check: values below 1000 millicelcius don't make sense
+         * and can cause the system to go into a thermal heart attack
+         */
+        if (state && state < 1000)
+                return -EINVAL;
+
         if (state && !tz->forced_passive) {
                 mutex_lock(&thermal_list_lock);
                 list_for_each_entry(cdev, &thermal_cdev_list, node) {