On 2026-04-27 18:18:38 [+0800], Yuwen Chen wrote:
> 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
This patch.
> in a sleeping state in the main thread.
The pthread_barrier you introduced is not enough?
You also increase the wait-timeout to 3s and parse the wait function.
You could describe what the expectation here is. I would assume that the
barrier on its own should be enough. But the barrier and the state
parsing is a bit much. This makes me curious what is so special on your
side that it does not work as-is. Is this some big-little case where the
big creates the thread and does requeue while the littke is supposed to
do futex_wait but falls behind?
> Fixes: 7cb5dd8e2c8c ("selftests: futex: Add futex compare requeue test")
> Signed-off-by: Yuwen Chen <[email protected]>
> Co-developed-by: Edward Liaw <[email protected]>
> Signed-off-by: Edward Liaw <[email protected]>
> ---
> 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/[email protected]/
> 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));
Why this ASSERT_EQ -> EXPECT_EQ ?
> + 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];
Couldn't that `i# remain where it was and that waiter moved as per Xmas
notation?
>
> 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));
Sebastian
