Fixes a race between parent and child threads in futex_requeue.
Similar to commit fbf4dec70277 ("selftests/futex: Order calls to
futex_lock_pi"), which fixed a flake in futex_lock_pi due to racing
between the parent and child threads.
The same issue can occur in the futex_requeue test, because it expects
waiterfn to make progress to futex_wait before the parent starts to
requeue. This is mitigated by the parent sleeping for WAKE_WAIT_US, but
it still fails occasionally. This can be reproduced by adding a sleep in
the waiterfn before futex_wait:
TAP version 13
1..2
not ok 1 futex_requeue simple returned: 0
not ok 2 futex_requeue simple returned: 0
not ok 3 futex_requeue many returned: 0
not ok 4 futex_requeue many returned: 0
This issue can be resolved by checking whether the child thread is in a
sleeping state. This is because when the child thread goes to sleep, it
indicates that it is waiting for the futex lock.
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]>
---
.../futex/functional/futex_requeue.c | 58 ++++++++++++++++---
1 file changed, 51 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/futex/functional/futex_requeue.c
b/tools/testing/selftests/futex/functional/futex_requeue.c
index 7a22458c7fc96..994295fac6972 100644
--- a/tools/testing/selftests/futex/functional/futex_requeue.c
+++ b/tools/testing/selftests/futex/functional/futex_requeue.c
@@ -7,6 +7,7 @@
#include <pthread.h>
#include <limits.h>
+#include <linux/compiler.h>
#include "futextest.h"
#include "../../kselftest_harness.h"
@@ -15,6 +16,7 @@
#define WAKE_WAIT_US 10000
volatile futex_t *f1;
+static pthread_barrier_t barrier;
void *waiterfn(void *arg)
{
@@ -23,28 +25,59 @@ void *waiterfn(void *arg)
to.tv_sec = 0;
to.tv_nsec = timeout_ns;
+ WRITE_ONCE(*((pid_t *)arg), gettid());
+ pthread_barrier_wait(&barrier);
+
if (futex_wait(f1, *f1, &to, 0))
printf("waiter failed errno %d\n", errno);
return NULL;
}
+static int get_thread_state(pid_t pid)
+{
+ FILE *fp;
+ char buf[80], tag[80];
+ char val = 0;
+
+ snprintf(buf, sizeof(buf), "/proc/%d/status", pid);
+ fp = fopen(buf, "r");
+ if (!fp)
+ return -1;
+
+ while (fgets(buf, sizeof(buf), fp))
+ if (fscanf(fp, "%s %c\n", tag, &val) == 2 && !strcmp(tag,
"State:"))
+ break;
+
+ fclose(fp);
+ return val;
+}
+
TEST(requeue_single)
{
volatile futex_t _f1 = 0;
volatile futex_t f2 = 0;
pthread_t waiter;
- int res;
+ pid_t tids;
+ int res, state;
f1 = &_f1;
+ pthread_barrier_init(&barrier, NULL, 2);
/*
* Requeue a waiter from f1 to f2, and wake f2.
*/
- if (pthread_create(&waiter, NULL, waiterfn, NULL))
+ if (pthread_create(&waiter, NULL, waiterfn, &tids))
ksft_exit_fail_msg("pthread_create failed\n");
- usleep(WAKE_WAIT_US);
+ pthread_barrier_wait(&barrier);
+ pthread_barrier_destroy(&barrier);
+ while ((state = get_thread_state(READ_ONCE(tids))) != 'S') {
+ usleep(WAKE_WAIT_US);
+
+ if (state < 0)
+ break;
+ }
ksft_print_dbg_msg("Requeuing 1 futex from f1 to f2\n");
res = futex_cmp_requeue(f1, 0, &f2, 0, 1, 0);
@@ -71,7 +104,8 @@ TEST(requeue_multiple)
volatile futex_t _f1 = 0;
volatile futex_t f2 = 0;
pthread_t waiter[10];
- int res, i;
+ pid_t tids[10];
+ int res, i, state;
f1 = &_f1;
@@ -80,11 +114,21 @@ TEST(requeue_multiple)
* At futex_wake, wake INT_MAX (should be exactly 7).
*/
for (i = 0; i < 10; i++) {
- if (pthread_create(&waiter[i], NULL, waiterfn, NULL))
+ pthread_barrier_init(&barrier, NULL, 2);
+
+ if (pthread_create(&waiter[i], NULL, waiterfn, &tids[i]))
ksft_exit_fail_msg("pthread_create failed\n");
- }
- usleep(WAKE_WAIT_US);
+ pthread_barrier_wait(&barrier);
+ pthread_barrier_destroy(&barrier);
+
+ while ((state = get_thread_state(READ_ONCE(tids[i]))) != 'S') {
+ usleep(WAKE_WAIT_US);
+
+ if (state < 0)
+ break;
+ }
+ }
ksft_print_dbg_msg("Waking 3 futexes at f1 and requeuing 7 futexes from
f1 to f2\n");
res = futex_cmp_requeue(f1, 0, &f2, 3, 7, 0);
--
2.34.1
