linux-kernel - [PATCH v5 2/2] selftests/futex: fix the failed futex

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Message-ID: <tencent_C274DC06E392AEDCE7D1790D5FEC5D164508@qq.com>
Date: Thu,  5 Feb 2026 10:05:41 +0800
From: Yuwen Chen <ywen.chen@...mail.com>
To: tglx@...nel.org
Cc: ywen.chen@...mail.com,
	akpm@...ux-foundation.org,
	andrealmeid@...lia.com,
	bigeasy@...utronix.de,
	colin.i.king@...il.com,
	dave@...olabs.net,
	dvhart@...radead.org,
	edliaw@...gle.com,
	justinstitt@...gle.com,
	kernel-team@...roid.com,
	licayy@...mail.com,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	luto@....edu,
	mingo@...hat.com,
	morbo@...gle.com,
	nathan@...nel.org,
	ndesaulniers@...gle.com,
	peterz@...radead.org,
	shuah@...nel.org,
	usama.anjum@...labora.com,
	wakel@...gle.com
Subject: [PATCH v5 2/2] selftests/futex: fix the failed futex_requeue test issue

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.

This patch avoids 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@...mail.com>
Co-developed-by: Edward Liaw <edliaw@...gle.com>
Signed-off-by: Edward Liaw <edliaw@...gle.com>
---
 .../futex/functional/futex_requeue.c          | 38 +++++++++++--------
 1 file changed, 22 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/futex/functional/futex_requeue.c b/tools/testing/selftests/futex/functional/futex_requeue.c
index dcf0d5f2f3122..ab87bfc4edae0 100644
--- a/tools/testing/selftests/futex/functional/futex_requeue.c
+++ b/tools/testing/selftests/futex/functional/futex_requeue.c
@@ -9,51 +9,53 @@
 #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 3
 
 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];
 
 	f1 = &_f1;
 
 	/*
 	 * Requeue a waiter from f1 to f2, and wake f2.
 	 */
-	ASSERT_EQ(0, pthread_create(&waiter[0], NULL, waiterfn, NULL));
-
-	usleep(WAKE_WAIT_US);
+	ASSERT_EQ(0, futex_thread_create(&waiter, waiterfn, NULL));
+	futex_wait_for_thread(&waiter);
 
 	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;
 
 	f1 = &_f1;
 
@@ -61,13 +63,17 @@ TEST(requeue_multiple)
 	 * Create 10 waiters at f1. At futex_requeue, wake 3 and requeue 7.
 	 * 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));
+	for (int i = 0; i < 10; i++)
+		ASSERT_EQ(0, futex_thread_create(&waiter[i], waiterfn, NULL));
 
-	usleep(WAKE_WAIT_US);
+	for (int i = 0; i < 10; i++)
+		futex_wait_for_thread(&waiter[i]);
 
 	EXPECT_EQ(10, futex_cmp_requeue(f1, 0, &f2, 3, 7, 0));
 	EXPECT_EQ(7, futex_wake(&f2, INT_MAX, 0));
+
+	for (int i = 0; i < 10; i++)
+		EXPECT_EQ(0, futex_thread_destroy(&waiter[i]));
 }
 
 TEST_HARNESS_MAIN
-- 
2.34.1