kunit: test: Make filter strings in executor_test writable

KUnit's attribute filtering feature needs the filter strings passed in
to be writable, as it modifies them in-place during parsing. This works
for the filters passed on the kernel command line, but the string
literals used in the executor tests are at least theoretically read-only
(though they work on x86_64 for some reason). s390 wasn't fooled, and
crashed when these tests were run.

Use a 'char[]' instead, (and make an explicit variable for the current
filter in parse_filter_attr_test), which will store the string in a
writable segment.

Fixes: 76066f93f1df ("kunit: add tests for filtering attributes")
Closes: https://lore.kernel.org/linux-kselftest/[e-mail]/
Signed-off-by: David Gow <[e-mail]>
Tested-by: Guenter Roeck <[e-mail]>
Reviewed-by: Rae Moar <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

lib/kunit/executor_test.c

···
 {
 	int j, filter_count;
 	struct kunit_attr_filter *parsed_filters;
-	char *filters = "speed>slow, module!=example";
+	char filters[] = "speed>slow, module!=example", *filter = filters;
 	int err = 0;
 
 	filter_count = kunit_get_filter_count(filters);
···
 	parsed_filters = kunit_kcalloc(test, filter_count, sizeof(*parsed_filters),
 			GFP_KERNEL);
 	for (j = 0; j < filter_count; j++) {
-		parsed_filters[j] = kunit_next_attr_filter(&filters, &err);
+		parsed_filters[j] = kunit_next_attr_filter(&filter, &err);
 		KUNIT_ASSERT_EQ_MSG(test, err, 0, "failed to parse filter '%s'", filters[j]);
 	}
 
···
 		.start = subsuite, .end = &subsuite[2],
 	};
 	struct kunit_suite_set got;
+	char filter[] = "speed>slow";
 	int err = 0;
 
 	subsuite[0] = alloc_fake_suite(test, "normal_suite", dummy_attr_test_cases);
···
 	 * attribute is unset and thus, the filtering is based on the parent attribute
 	 * of slow.
 	 */
-	got = kunit_filter_suites(&suite_set, NULL, "speed>slow", NULL, &err);
+	got = kunit_filter_suites(&suite_set, NULL, filter, NULL, &err);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, got.start);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	kfree_at_end(test, got.start);
···
 		.start = subsuite, .end = &subsuite[2],
 	};
 	struct kunit_suite_set got;
+	char filter[] = "module!=dummy";
 	int err = 0;
 
 	subsuite[0] = alloc_fake_suite(test, "suite1", dummy_attr_test_cases);
 	subsuite[1] = alloc_fake_suite(test, "suite2", dummy_attr_test_cases);
 
-	got = kunit_filter_suites(&suite_set, NULL, "module!=dummy", NULL, &err);
+	got = kunit_filter_suites(&suite_set, NULL, filter, NULL, &err);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	kfree_at_end(test, got.start); /* just in case */
 
···
 		.start = subsuite, .end = &subsuite[1],
 	};
 	struct kunit_suite_set got;
+	char filter[] = "speed>slow";
 	int err = 0;
 
 	subsuite[0] = alloc_fake_suite(test, "suite", dummy_attr_test_cases);
 
 	/* Want: suite(slow, normal), NULL -> suite(slow with SKIP, normal), NULL */
-	got = kunit_filter_suites(&suite_set, NULL, "speed>slow", "skip", &err);
+	got = kunit_filter_suites(&suite_set, NULL, filter, "skip", &err);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, got.start);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	kfree_at_end(test, got.start);