kmemleak: Enable task stacks scanning by default

This is to reduce the number of false positives reported.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Documentation/kmemleak.txt

@@ -31,12 +31,12 @@ Memory scanning parameters can be modified at run-time by writing to the
 /sys/kernel/debug/kmemleak file. The following parameters are supported:
 
   off		- disable kmemleak (irreversible)
-  stack=on	- enable the task stacks scanning
+  stack=on	- enable the task stacks scanning (default)
   stack=off	- disable the tasks stacks scanning
-  scan=on	- start the automatic memory scanning thread
+  scan=on	- start the automatic memory scanning thread (default)
   scan=off	- stop the automatic memory scanning thread
-  scan=<secs>	- set the automatic memory scanning period in seconds (0
-		  to disable it)
+  scan=<secs>	- set the automatic memory scanning period in seconds
+		  (default 600, 0 to stop the automatic scanning)
 
 Kmemleak can also be disabled at boot-time by passing "kmemleak=off" on
 the kernel command line.

mm/kmemleak.c

@@ -194,7 +194,7 @@ static unsigned long jiffies_min_age;
 /* delay between automatic memory scannings */
 static signed long jiffies_scan_wait;
 /* enables or disables the task stacks scanning */
-static int kmemleak_stack_scan;
+static int kmemleak_stack_scan = 1;
 /* mutex protecting the memory scanning */
 static DEFINE_MUTEX(scan_mutex);
 /* mutex protecting the access to the /sys/kernel/debug/kmemleak file */