mm/kmemleak: add support for re-enable kmemleak at runtime

index 31f01c5..02f292c 100644
@@ -260,6 +260,7 @@ static struct early_log
 static int crt_early_log __initdata;
 
 static void kmemleak_disable(void);
+static void kmemleak_enable(void);
 
 /*
  * Print a warning and dump the stack trace.

@@ -1616,9 +1617,6 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
 	int buf_size;
 	int ret;
 
-	if (!atomic_read(&kmemleak_enabled))
-		return -EBUSY;
-
 	buf_size = min(size, (sizeof(buf) - 1));
 	if (strncpy_from_user(buf, user_buf, buf_size) < 0)
 		return -EFAULT;

@@ -1628,6 +1626,19 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
 	if (ret < 0)
 		return ret;
 
+	if (strncmp(buf, "on", 2) == 0) {
+		if (atomic_read(&kmemleak_enabled))
+			ret = -EBUSY;
+		else
+			kmemleak_enable();
+		goto out;
+	}
+
+	if (!atomic_read(&kmemleak_enabled)) {
+		ret = -EBUSY;
+		goto out;
+	}
+
 	if (strncmp(buf, "off", 3) == 0)
 		kmemleak_disable();
 	else if (strncmp(buf, "stack=on", 8) == 0)

@@ -1703,7 +1714,7 @@ static DECLARE_WORK(cleanup_work, kmemleak_do_cleanup);
 
 /*
  * Disable kmemleak. No memory allocation/freeing will be traced once this
- * function is called. Disabling kmemleak is an irreversible operation.
+ * function is called.
  */
 static void kmemleak_disable(void)
 {

@@ -1721,6 +1732,24 @@ static void kmemleak_disable(void)
 	pr_info("Kernel memory leak detector disabled\n");
 }
 
+static void kmemleak_enable(void)
+{
+	struct kmemleak_object *object;
+
+	/* free the kmemleak internal objects the previous thread scanned */
+	rcu_read_lock();
+	list_for_each_entry_rcu(object, &object_list, object_list)
+		delete_object_full(object->pointer);
+	rcu_read_unlock();
+
+	atomic_set(&kmemleak_enabled, 1);
+	atomic_set(&kmemleak_error, 0);
+
+	start_scan_thread();
+
+	pr_info("Kernel memory leak detector enabled\n");
+}
+
 /*
  * Allow boot-time kmemleak disabling (enabled by default).
  */