selftests/timers/posix_timers: Test delivery of signals across threads

Test that POSIX timers using CLOCK_PROCESS_CPUTIME_ID eventually deliver
a signal to all running threads.  This effectively tests that the kernel
doesn't prefer any one thread (or subset of threads) for signal delivery.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230316123028.2890338-2-elver@google.com

diff --git a/tools/testing/selftests/timers/posix_timers.c b/tools/testing/selftests/timers/posix_timers.c
index 0ba5000..8a17c0e 100644 (file)
--- a/tools/testing/selftests/timers/posix_timers.c
+++ b/tools/testing/selftests/timers/posix_timers.c
@@ -188,6 +188,80 @@ static int check_timer_create(int which)
        return 0;
 }
 
+int remain;
+__thread int got_signal;
+
+static void *distribution_thread(void *arg)
+{
+       while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
+       return NULL;
+}
+
+static void distribution_handler(int nr)
+{
+       if (!__atomic_exchange_n(&got_signal, 1, __ATOMIC_RELAXED))
+               __atomic_fetch_sub(&remain, 1, __ATOMIC_RELAXED);
+}
+
+/*
+ * Test that all running threads _eventually_ receive CLOCK_PROCESS_CPUTIME_ID
+ * timer signals. This primarily tests that the kernel does not favour any one.
+ */
+static int check_timer_distribution(void)
+{
+       int err, i;
+       timer_t id;
+       const int nthreads = 10;
+       pthread_t threads[nthreads];
+       struct itimerspec val = {
+               .it_value.tv_sec = 0,
+               .it_value.tv_nsec = 1000 * 1000,
+               .it_interval.tv_sec = 0,
+               .it_interval.tv_nsec = 1000 * 1000,
+       };
+
+       printf("Check timer_create() per process signal distribution... ");
+       fflush(stdout);
+
+       remain = nthreads + 1;  /* worker threads + this thread */
+       signal(SIGALRM, distribution_handler);
+       err = timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id);
+       if (err < 0) {
+               perror("Can't create timer\n");
+               return -1;
+       }
+       err = timer_settime(id, 0, &val, NULL);
+       if (err < 0) {
+               perror("Can't set timer\n");
+               return -1;
+       }
+
+       for (i = 0; i < nthreads; i++) {
+               if (pthread_create(&threads[i], NULL, distribution_thread, NULL)) {
+                       perror("Can't create thread\n");
+                       return -1;
+               }
+       }
+
+       /* Wait for all threads to receive the signal. */
+       while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
+
+       for (i = 0; i < nthreads; i++) {
+               if (pthread_join(threads[i], NULL)) {
+                       perror("Can't join thread\n");
+                       return -1;
+               }
+       }
+
+       if (timer_delete(id)) {
+               perror("Can't delete timer\n");
+               return -1;
+       }
+
+       printf("[OK]\n");
+       return 0;
+}
+
 int main(int argc, char **argv)
 {
        printf("Testing posix timers. False negative may happen on CPU execution \n");
@@ -217,5 +291,8 @@ int main(int argc, char **argv)
        if (check_timer_create(CLOCK_PROCESS_CPUTIME_ID) < 0)
                return ksft_exit_fail();
 
+       if (check_timer_distribution() < 0)
+               return ksft_exit_fail();
+
        return ksft_exit_pass();
 }