thermal: avoid division by zero in power allocator

During boot I get a div by zero Oops regression starting in v4.3-rc3.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Javi Merino <javi.merino@arm.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/thermal/power_allocator.c b/drivers/thermal/power_allocator.c
index 7ff96270c933b1ad577ee3dbb9cedf92d8f07a89..e570ff084add5b0596cbac05d07bca560d350b01 100644 (file)
--- a/drivers/thermal/power_allocator.c
+++ b/drivers/thermal/power_allocator.c
@@ -144,6 +144,16 @@ static void estimate_pid_constants(struct thermal_zone_device *tz,
                switch_on_temp = 0;
 
        temperature_threshold = control_temp - switch_on_temp;
+       /*
+        * estimate_pid_constants() tries to find appropriate default
+        * values for thermal zones that don't provide them. If a
+        * system integrator has configured a thermal zone with two
+        * passive trip points at the same temperature, that person
+        * hasn't put any effort to set up the thermal zone properly
+        * so just give up.
+        */
+       if (!temperature_threshold)
+               return;
 
        if (!tz->tzp->k_po || force)
                tz->tzp->k_po = int_to_frac(sustainable_power) /