kmemleak: add config to select auto scan

Kmemleak scan can be cpu intensive and can stall user tasks at times.  To
prevent this, add config DEBUG_KMEMLEAK_AUTO_SCAN to enable/disable auto
scan on boot up.  Also protect first_run with DEBUG_KMEMLEAK_AUTO_SCAN as
this is meant for only first automatic scan.

Link: http://lkml.kernel.org/r/1540231723-7087-1-git-send-email-prpatel@nvidia.comSigned-off-by: Sri Krishna chowdary <schowdary@nvidia.com>
Signed-off-by: Sachin Nikam <snikam@nvidia.com>
Signed-off-by: Prateek <prpatel@nvidia.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -593,6 +593,21 @@ config DEBUG_KMEMLEAK_DEFAULT_OFF
 	  Say Y here to disable kmemleak by default. It can then be enabled
 	  on the command line via kmemleak=on.
 
+config DEBUG_KMEMLEAK_AUTO_SCAN
+	bool "Enable kmemleak auto scan thread on boot up"
+	default y
+	depends on DEBUG_KMEMLEAK
+	help
+	  Depending on the cpu, kmemleak scan may be cpu intensive and can
+	  stall user tasks at times. This option enables/disables automatic
+	  kmemleak scan at boot up.
+
+	  Say N here to disable kmemleak auto scan thread to stop automatic
+	  scanning. Disabling this option disables automatic reporting of
+	  memory leaks.
+
+	  If unsure, say Y.
+
 config DEBUG_STACK_USAGE
 	bool "Stack utilization instrumentation"
 	depends on DEBUG_KERNEL && !IA64

mm/kmemleak.c

@@ -1650,7 +1650,7 @@ static void kmemleak_scan(void)
  */
 static int kmemleak_scan_thread(void *arg)
 {
-	static int first_run = 1;
+	static int first_run = IS_ENABLED(CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN);
 
 	pr_info("Automatic memory scanning thread started\n");
 	set_user_nice(current, 10);
@@ -2144,9 +2144,11 @@ static int __init kmemleak_late_init(void)
 		return -ENOMEM;
 	}
 
-	mutex_lock(&scan_mutex);
-	start_scan_thread();
-	mutex_unlock(&scan_mutex);
+	if (IS_ENABLED(CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN)) {
+		mutex_lock(&scan_mutex);
+		start_scan_thread();
+		mutex_unlock(&scan_mutex);
+	}
 
 	pr_info("Kernel memory leak detector initialized\n");