kmemleak: Slightly change the policy on newly allocated objects

Newly allocated objects are more likely to be reported as false
positives. Kmemleak ignores the reporting of objects younger than 5
seconds. However, this age was calculated after the memory scanning
completed which usually takes longer than 5 seconds. This patch
make the minimum object age calculation in relation to the start of the
memory scanning.
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

mm/kmemleak.c

@@ -190,7 +190,9 @@ static unsigned long max_addr;
 static unsigned long next_scan_yield;
 static struct task_struct *scan_thread;
 static unsigned long jiffies_scan_yield;
+/* used to avoid reporting of recently allocated objects */
 static unsigned long jiffies_min_age;
+static unsigned long jiffies_last_scan;
 /* delay between automatic memory scannings */
 static signed long jiffies_scan_wait;
 /* enables or disables the task stacks scanning */
@@ -284,7 +286,8 @@ static int color_gray(const struct kmemleak_object *object)
 static int unreferenced_object(struct kmemleak_object *object)
 {
 	return (object->flags & OBJECT_ALLOCATED) && color_white(object) &&
-		time_is_before_eq_jiffies(object->jiffies + jiffies_min_age);
+		time_before_eq(object->jiffies + jiffies_min_age,
+			       jiffies_last_scan);
 }
 
 /*
@@ -927,6 +930,8 @@ static void kmemleak_scan(void)
 	int i;
 	int new_leaks = 0;
 
+	jiffies_last_scan = jiffies;
+
 	/* prepare the kmemleak_object's */
 	rcu_read_lock();
 	list_for_each_entry_rcu(object, &object_list, object_list) {