kunit: test: Move fault tests behind KUNIT_FAULT_TEST Kconfig option

The NULL dereference tests in kunit_fault deliberately trigger a kernel
BUG(), and therefore print the associated stack trace, even when the
test passes. This is both annoying (as it bloats the test output), and
can confuse some test harnesses, which assume any BUG() is a failure.

Allow these tests to be specifically disabled (without disabling all
of KUnit's other tests), by placing them behind the
CONFIG_KUNIT_FAULT_TEST Kconfig option. This is enabled by default, but
can be set to 'n' to disable the test. An empty 'kunit_fault' suite is
left behind, which will automatically be marked 'skipped'.

As the fault tests already were disabled under UML (as they weren't
compatible with its fault handling), we can simply adapt those
conditions, and add a dependency on !UML for our new option.
Suggested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/all/928249cc-e027-4f7f-b43f-502f99a1ea63@roeck-us.net/
Fixes: 82b0beff3497 ("kunit: Add tests for fault")
Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Mickaël Salaün <mic@digikod.net>
Reviewed-by: Rae Moar <rmoar@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

lib/kunit/Kconfig

@@ -24,6 +24,17 @@ config KUNIT_DEBUGFS
 	  test suite, which allow users to see results of the last test suite
 	  run that occurred.
 
+config KUNIT_FAULT_TEST
+	bool "Enable KUnit tests which print BUG stacktraces"
+	depends on KUNIT_TEST
+	depends on !UML
+	default y
+	help
+	  Enables fault handling tests for the KUnit framework. These tests may
+	  trigger a kernel BUG(), and the associated stack trace, even when they
+	  pass. If this conflicts with your test infrastrcture (or is confusing
+	  or annoying), they can be disabled by setting this to N.
+
 config KUNIT_TEST
 	tristate "KUnit test for KUnit" if !KUNIT_ALL_TESTS
 	default KUNIT_ALL_TESTS

lib/kunit/kunit-test.c

@@ -109,7 +109,7 @@ static struct kunit_suite kunit_try_catch_test_suite = {
 	.test_cases = kunit_try_catch_test_cases,
 };
 
-#ifndef CONFIG_UML
+#if IS_ENABLED(CONFIG_KUNIT_FAULT_TEST)
 
 static void kunit_test_null_dereference(void *data)
 {
@@ -136,12 +136,12 @@ static void kunit_test_fault_null_dereference(struct kunit *test)
 	KUNIT_EXPECT_TRUE(test, ctx->function_called);
 }
 
-#endif /* !CONFIG_UML */
+#endif /* CONFIG_KUNIT_FAULT_TEST */
 
 static struct kunit_case kunit_fault_test_cases[] = {
-#ifndef CONFIG_UML
+#if IS_ENABLED(CONFIG_KUNIT_FAULT_TEST)
 	KUNIT_CASE(kunit_test_fault_null_dereference),
-#endif /* !CONFIG_UML */
+#endif /* CONFIG_KUNIT_FAULT_TEST */
 	{}
 };