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Subject[PATCH kcsan 3/9] kcsan: test: Fix flaky test case
Date
From: Marco Elver <elver@google.com>

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: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/kcsan/kcsan_test.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
index d93f226327af..e282c1166373 100644
--- a/kernel/kcsan/kcsan_test.c
+++ b/kernel/kcsan/kcsan_test.c
@@ -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);
}
--
2.31.1.189.g2e36527f23
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