FDEFER
atomic_clear_int(&fp->f_flag, FMARK | FDEFER);
if (fp->f_flag & FDEFER)
atomic_clear_int(&fp->f_flag, FDEFER);
if (fp->f_flag & FDEFER) {
atomic_clear_int(&fp->f_flag, FDEFER);
atomic_set_int(&fp->f_flag, FDEFER);
atomic_set_int(&fp->f_flag, FMARK | FDEFER);
} else if (fp->f_flag & FDEFER) {