> +static int test_fork(int uffd, char *primary_map, size_t len)
> +{
> + int status;
> + int ret = 0;
> + pid_t pid;
> + pthread_t uffd_thd;
> +
> + /*
> + * UFFD_FEATURE_EVENT_FORK will put fork event on the userfaultfd,
> + * which we must read, otherwise we block fork(). Setup a thread to
> + * read that event now.
> + *
> + * Page fault events should result in a SIGBUS, so we expect only a
> + * single event from the uffd (the fork event).
> + */
> + if (read_event_from_uffd(&uffd, &uffd_thd))
> + return -1;
> +
> + pid = fork();
> +
> + if (!pid) {
> + /*
> + * Because we have UFFDIO_REGISTER_MODE_WP and
> + * UFFD_FEATURE_EVENT_FORK, the page tables should be copied
> + * exactly.
> + *
> + * Check that everything except that last 4K has correct
> + * contents, and then check that the last 4K gets a SIGBUS.
> + */
> + printf(PREFIX "child validating...\n");
> + ret = verify_contents(primary_map, len, false) ||
> + test_sigbus(primary_map + len - 1, false);
> + ret = 0;
> + exit(ret ? 1 : 0);
> + } else {
> + /* wait for the child to finish. */
> + waitpid(pid, &status, 0);
> + ret = WEXITSTATUS(status);
> + if (!ret) {
> + printf(PREFIX "parent validating...\n");
> + /* Same check as the child. */
> + ret = verify_contents(primary_map, len, false) ||
> + test_sigbus(primary_map + len - 1, false);
> + ret = 0;
I'm not sure how these 'ret = 0's got here -- they will be removed.
> + }
> + }
This else block also runs when fork() fails; we need to fail the test instead.
> +
> + pthread_join(uffd_thd, NULL);
> + return ret;
> +
> +}
