Commit ade3a58b authored by Marco Elver's avatar Marco Elver Committed by Paul E. McKenney
Browse files

kcsan: test: Fix flaky test case 



If CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY=n, then we may also see data
races between the writers only. If we get unlucky and never capture a
read-write data race, but only the write-write data races, then the
test_no_value_change* test cases may incorrectly fail.

The second problem is that the initial value needs to be reset, as
otherwise we might actually observe a value change at the start.

Fix it by also looking for the write-write data races, and resetting the
value to what will be written.

Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 80804284

kernel/kcsan/kcsan_test.c

+18 −4
Original line number Diff line number Diff line
@@ -493,17 +493,24 @@ static void test_concurrent_races(struct kunit *test) 
__no_kcsan

static void test_novalue_change(struct kunit *test)

{

	const struct expect_report expect = {

	const struct expect_report expect_rw = {

		.access = {

			{ test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },

			{ test_kernel_read, &test_var, sizeof(test_var), 0 },

		},

	};

	const struct expect_report expect_ww = {

		.access = {

			{ test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },

			{ test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },

		},

	};

	bool match_expect = false;



	test_kernel_write_nochange(); /* Reset value. */

	begin_test_checks(test_kernel_write_nochange, test_kernel_read);

	do {

		match_expect = report_matches(&expect);

		match_expect = report_matches(&expect_rw) || report_matches(&expect_ww);

	} while (!end_test_checks(match_expect));

	if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY))

		KUNIT_EXPECT_FALSE(test, match_expect);
@@ -518,17 +525,24 @@ static void test_novalue_change(struct kunit *test) 
__no_kcsan

static void test_novalue_change_exception(struct kunit *test)

{

	const struct expect_report expect = {

	const struct expect_report expect_rw = {

		.access = {

			{ test_kernel_write_nochange_rcu, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },

			{ test_kernel_read, &test_var, sizeof(test_var), 0 },

		},

	};

	const struct expect_report expect_ww = {

		.access = {

			{ test_kernel_write_nochange_rcu, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },

			{ test_kernel_write_nochange_rcu, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },

		},

	};

	bool match_expect = false;



	test_kernel_write_nochange_rcu(); /* Reset value. */

	begin_test_checks(test_kernel_write_nochange_rcu, test_kernel_read);

	do {

		match_expect = report_matches(&expect);

		match_expect = report_matches(&expect_rw) || report_matches(&expect_ww);

	} while (!end_test_checks(match_expect));

	KUNIT_EXPECT_TRUE(test, match_expect);

}