selftests/futex: Order calls to futex_lock_pi

[ Upstream commit fbf4dec702774286db409815ffb077711a96b824 ]

Observed occassional failures in the futex_wait_timeout test:

ok 1 futex_wait relative succeeds
ok 2 futex_wait_bitset realtime succeeds
ok 3 futex_wait_bitset monotonic succeeds
ok 4 futex_wait_requeue_pi realtime succeeds
ok 5 futex_wait_requeue_pi monotonic succeeds
not ok 6 futex_lock_pi realtime returned 0
......

The test expects the child thread to complete some steps before
the parent thread gets to run. There is an implicit expectation
of the order of invocation of futex_lock_pi between the child thread
and the parent thread. Make this order explicit. If the order is
not met, the futex_lock_pi call in the parent thread succeeds and
will not timeout.

Fixes: f4addd54b161 ("selftests: futex: Expand timeout test")
Signed-off-by: Nysal Jan K.A <nysal@linux.ibm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/testing/selftests/futex/functional/futex_wait_timeout.c b/tools/testing/selftests/futex/functional/futex_wait_timeout.c
index 3651ce1..d183f87 100644 (file)
--- a/tools/testing/selftests/futex/functional/futex_wait_timeout.c
+++ b/tools/testing/selftests/futex/functional/futex_wait_timeout.c
@@ -24,6 +24,7 @@
 
 static long timeout_ns = 100000;       /* 100us default timeout */
 static futex_t futex_pi;
+static pthread_barrier_t barrier;
 
 void usage(char *prog)
 {
@@ -48,6 +49,8 @@ void *get_pi_lock(void *arg)
        if (ret != 0)
                error("futex_lock_pi failed\n", ret);
 
+       pthread_barrier_wait(&barrier);
+
        /* Blocks forever */
        ret = futex_wait(&lock, 0, NULL, 0);
        error("futex_wait failed\n", ret);
@@ -130,6 +133,7 @@ int main(int argc, char *argv[])
               basename(argv[0]));
        ksft_print_msg("\tArguments: timeout=%ldns\n", timeout_ns);
 
+       pthread_barrier_init(&barrier, NULL, 2);
        pthread_create(&thread, NULL, get_pi_lock, NULL);
 
        /* initialize relative timeout */
@@ -163,6 +167,9 @@ int main(int argc, char *argv[])
        res = futex_wait_requeue_pi(&f1, f1, &futex_pi, &to, 0);
        test_timeout(res, &ret, "futex_wait_requeue_pi monotonic", ETIMEDOUT);
 
+       /* Wait until the other thread calls futex_lock_pi() */
+       pthread_barrier_wait(&barrier);
+       pthread_barrier_destroy(&barrier);
        /*
         * FUTEX_LOCK_PI with CLOCK_REALTIME
         * Due to historical reasons, FUTEX_LOCK_PI supports only realtime