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Message-ID: <tencent_FC5FB35D2545AFDCA6E377AE4DE75C79AF08@qq.com>
Date: Wed, 28 Jan 2026 15:16:12 +0800
From: Yuwen Chen <ywen.chen@...mail.com>
To: tglx@...nel.org
Cc: 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,
Yuwen Chen <ywen.chen@...mail.com>
Subject: [PATCH v3] 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>
---
v1->v2:
1. Fix the issue of abnormal use of fscanf in the get_thread_state function
2. Add timeout logic
v2->v3: https://lore.kernel.org/all/tencent_B9DBF2ECBE56BAB68BDAB949C6935D01CE09@qq.com/
1. Use /proc/[pid]/wchan instead of /proc/[pid]/stat to check if a process has entered the sleep state
2. Refactor part of the logic to facilitate code reuse.
.../futex/functional/futex_requeue.c | 91 ++++++++++++++++---
1 file changed, 77 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..7163e827691e4 100644
--- a/tools/testing/selftests/futex/functional/futex_requeue.c
+++ b/tools/testing/selftests/futex/functional/futex_requeue.c
@@ -11,8 +11,9 @@
#include "futextest.h"
#include "kselftest_harness.h"
-#define timeout_ns 30000000
-#define WAKE_WAIT_US 10000
+#define FUTEX_WAIT_TIMEOUT_S 3 /* 3s */
+#define WAIT_THREAD_RETRIES 100
+#define WAIT_THREAD_DELAY_US (10000 * 100) /* 1s */
volatile futex_t *f1;
@@ -20,8 +21,8 @@ void *waiterfn(void *arg)
{
struct timespec to;
- to.tv_sec = 0;
- to.tv_nsec = timeout_ns;
+ to.tv_sec = FUTEX_WAIT_TIMEOUT_S;
+ to.tv_nsec = 0;
if (futex_wait(f1, *f1, &to, 0))
printf("waiter failed errno %d\n", errno);
@@ -29,20 +30,83 @@ void *waiterfn(void *arg)
return NULL;
}
+struct futex_thread {
+ pthread_t thread;
+ pthread_barrier_t barrier;
+ pid_t tid;
+ void *(*threadfn)(void *);
+ void *arg;
+};
+
+static int wait_for_thread(FILE *fp, int timeout_us)
+{
+ char buf[80] = "";
+
+ for (int i = 0; i < WAIT_THREAD_RETRIES; i++) {
+ if (!fgets(buf, sizeof(buf), fp))
+ return -EIO;
+ if (!strncmp(buf, "futex", 5))
+ return 0;
+ usleep(timeout_us / WAIT_THREAD_RETRIES);
+ rewind(fp);
+ }
+ return -ETIMEDOUT;
+}
+
+int futex_wait_for_thread(struct futex_thread *t, int timeout_us)
+{
+ char fname[80];
+ FILE *fp;
+ int res;
+
+ snprintf(fname, sizeof(fname), "/proc/%d/wchan", t->tid);
+ fp = fopen(fname, "r");
+ if (!fp)
+ return -EIO;
+ res = wait_for_thread(fp, timeout_us);
+ fclose(fp);
+ return res;
+}
+
+static void *futex_thread_fn(void *arg)
+{
+ struct futex_thread *t = arg;
+
+ t->tid = gettid();
+ pthread_barrier_wait(&t->barrier);
+ return t->threadfn(t->arg);
+}
+
+int futex_thread_create(struct futex_thread *t, void *(*threadfn)(void *), void *arg)
+{
+ int ret;
+
+ pthread_barrier_init(&t->barrier, NULL, 2);
+ t->tid = 0;
+ t->threadfn = threadfn;
+ t->arg = arg;
+
+ ret = pthread_create(&t->thread, NULL, futex_thread_fn, t);
+ if (ret)
+ return ret;
+
+ pthread_barrier_wait(&t->barrier);
+ return 0;
+}
+
TEST(requeue_single)
{
volatile futex_t _f1 = 0;
volatile futex_t f2 = 0;
- pthread_t waiter[10];
+ struct futex_thread waiter;
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);
+ EXPECT_EQ(0, futex_thread_create(&waiter, waiterfn, NULL));
+ futex_wait_for_thread(&waiter, WAIT_THREAD_DELAY_US);
EXPECT_EQ(1, futex_cmp_requeue(f1, 0, &f2, 0, 1, 0));
EXPECT_EQ(1, futex_wake(&f2, 1, 0));
@@ -52,8 +116,7 @@ TEST(requeue_multiple)
{
volatile futex_t _f1 = 0;
volatile futex_t f2 = 0;
- pthread_t waiter[10];
- int i;
+ struct futex_thread waiter[10];
f1 = &_f1;
@@ -61,10 +124,10 @@ 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));
-
- usleep(WAKE_WAIT_US);
+ for (int i = 0; i < 10; i++) {
+ EXPECT_EQ(0, futex_thread_create(&waiter[i], waiterfn, NULL));
+ futex_wait_for_thread(&waiter[i], WAIT_THREAD_DELAY_US / 10);
+ }
EXPECT_EQ(10, futex_cmp_requeue(f1, 0, &f2, 3, 7, 0));
EXPECT_EQ(7, futex_wake(&f2, INT_MAX, 0));
--
2.34.1
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