cpuidle: menu: Avoid overflows when computing variance

rafaeljw · rafaeljw · commit 814b8797f986 · 2019-03-07T10:54:22.000+01:00
The variance computation in get_typical_interval() may overflow if
the square of the value of diff exceeds the maximum for the int64_t
data type value which basically is the case when it is of the order
of UINT_MAX.

However, data points so far in the future don't matter for idle
state selection anyway, so change the initial threshold value in
get_typical_interval() to INT_MAX which will cause more "outlying"
data points to be discarded without affecting the selection result.

Reported-by: Randy Dunlap &lt;rdunlap@infradead.org&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
@@ -186,7 +186,7 @@ static unsigned int get_typical_interval(struct menu_device *data,
 	unsigned int min, max, thresh, avg;
 	uint64_t sum, variance;
 
-	thresh = UINT_MAX; /* Discard outliers above this value */
+	thresh = INT_MAX; /* Discard outliers above this value */
 
 again:
 
