[PATCH v7 2/2] selftests/futex: fix the failed futex_requeue test issue

[Yuwen Chen <ywen.chen@foxmail.com>]

This test item has extremely high requirements for timing and can only
pass the test under specific conditions. The following situations will
lead to test failure:

    MainThread                  Thread1
        |
  pthread_create--------------------
        |                          |
 futex_cmp_requeue                 |
        |                     futex_wait
        |                          |

If the child thread is not waiting in the futex_wait function when the
main thread reaches the futex_cmp_requeue function, the test will fail.

An attempt is made to avoid this problem by checking whether the child
thread is in a sleeping state in the main thread.

Fixes: 7cb5dd8e2c8c ("selftests: futex: Add futex compare requeue test")
Signed-off-by: Yuwen Chen <ywen.chen@foxmail.com>
Co-developed-by: Edward Liaw <edliaw@google.com>
Signed-off-by: Edward Liaw <edliaw@google.com>
---
v6->v7:
    1. Unified error checking to `if (ret < 0)` in both requeue_single
       and requeue_multiple test cases.
    2. Added comment explaining the break logic in requeue_multiple when
       /proc is not available.

 .../futex/functional/futex_requeue.c          | 46 +++++++++++++------
 1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/futex/functional/futex_requeue.c b/tools/testing/selftests/futex/functional/futex_requeue.c
index dcf0d5f2f3122..5c849ccf16e26 100644
--- a/tools/testing/selftests/futex/functional/futex_requeue.c
+++ b/tools/testing/selftests/futex/functional/futex_requeue.c
@@ -9,51 +9,59 @@
 #include <limits.h>
 
 #include "futextest.h"
+#include "futex_thread.h"
 #include "kselftest_harness.h"
 
-#define timeout_ns  30000000
-#define WAKE_WAIT_US 10000
+#define FUTEX_WAIT_TIMEOUT_SECS 1
+#define WAIT_THREAD_CREATE_TIMEOUT_USECS (USEC_PER_SEC / 2) /* 500ms */
 
 volatile futex_t *f1;
 
-void *waiterfn(void *arg)
+static int waiterfn(void *arg)
 {
 	struct timespec to;
 
-	to.tv_sec = 0;
-	to.tv_nsec = timeout_ns;
+	to.tv_sec = FUTEX_WAIT_TIMEOUT_SECS;
+	to.tv_nsec = 0;
 
-	if (futex_wait(f1, *f1, &to, 0))
+	if (futex_wait(f1, *f1, &to, 0)) {
 		printf("waiter failed errno %d\n", errno);
+		return -errno;
+	}
 
-	return NULL;
+	return 0;
 }
 
 TEST(requeue_single)
 {
+	struct futex_thread waiter;
 	volatile futex_t _f1 = 0;
 	volatile futex_t f2 = 0;
-	pthread_t waiter[10];
+	int ret;
 
 	f1 = &_f1;
 
 	/*
 	 * Requeue a waiter from f1 to f2, and wake f2.
 	 */
-	ASSERT_EQ(0, pthread_create(&waiter[0], NULL, waiterfn, NULL));
+	ASSERT_EQ(0, futex_thread_create(&waiter, waiterfn, NULL));
 
-	usleep(WAKE_WAIT_US);
+	ret = futex_wait_for_thread(&waiter, WAIT_THREAD_CREATE_TIMEOUT_USECS);
+	if (ret < 0)
+		usleep(WAIT_THREAD_CREATE_TIMEOUT_USECS);
 
 	EXPECT_EQ(1, futex_cmp_requeue(f1, 0, &f2, 0, 1, 0));
 	EXPECT_EQ(1, futex_wake(&f2, 1, 0));
+
+	EXPECT_EQ(0, futex_thread_destroy(&waiter));
 }
 
 TEST(requeue_multiple)
 {
+	struct futex_thread waiter[10];
 	volatile futex_t _f1 = 0;
 	volatile futex_t f2 = 0;
-	pthread_t waiter[10];
-	int i;
+	int i, ret;
 
 	f1 = &_f1;
 
@@ -62,12 +70,22 @@ TEST(requeue_multiple)
 	 * At futex_wake, wake INT_MAX (should be exactly 7).
 	 */
 	for (i = 0; i < 10; i++)
-		ASSERT_EQ(0, pthread_create(&waiter[i], NULL, waiterfn, NULL));
+		ASSERT_EQ(0, futex_thread_create(&waiter[i], waiterfn, NULL));
 
-	usleep(WAKE_WAIT_US);
+	for (i = 0; i < 10; i++) {
+		ret = futex_wait_for_thread(&waiter[i], WAIT_THREAD_CREATE_TIMEOUT_USECS / 10);
+		if (ret < 0) {
+			/* /proc not available, give all threads time to enter futex wait */
+			usleep(WAIT_THREAD_CREATE_TIMEOUT_USECS);
+			break;
+		}
+	}
 
 	EXPECT_EQ(10, futex_cmp_requeue(f1, 0, &f2, 3, 7, 0));
 	EXPECT_EQ(7, futex_wake(&f2, INT_MAX, 0));
+
+	for (i = 0; i < 10; i++)
+		EXPECT_EQ(0, futex_thread_destroy(&waiter[i]));
 }
 
 TEST_HARNESS_MAIN
-- 
2.34.1