PIDFD_STALE
BUILD_BUG_ON(PIDFD_STALE == PIDFD_THREAD);
BUILD_BUG_ON(PIDFD_STALE == PIDFD_NONBLOCK);
flags &= ~PIDFD_STALE;
if (!(flags & PIDFD_STALE)) {
retval = pidfd_prepare(pid, flags | PIDFD_STALE, &pidfile);
pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &pidfd_file);
flags = PIDFD_STALE;