// indefinitely...
		timeout = timediv(ns, 1000, nil)
		if timeout == 0 {
			timeout = 1
		}
	}

	// sys_umtx_sleep will return EWOULDBLOCK (EAGAIN) when the timeout
	// expires or EBUSY if the mutex value does not match.
	ret := sys_umtx_sleep(addr, int32(val), timeout)
	if ret >= 0 || ret == -_EINTR || ret == -_EAGAIN || ret == -_EBUSY {
		return
	}

	SYS_MOUNTCTL               = 468 // { int mountctl(const char *path, int op, int fd, const void *ctl, int ctllen, void *buf, int buflen); }
	SYS_UMTX_SLEEP             = 469 // { int umtx_sleep(volatile const int *ptr, int value, int timeout); }
	SYS_UMTX_WAKEUP            = 470 // { int umtx_wakeup(volatile const int *ptr, int count); }

	SYS_MOUNTCTL               = 468 // { int mountctl(const char *path, int op, int fd, const void *ctl, int ctllen, void *buf, int buflen); }
	SYS_UMTX_SLEEP             = 469 // { int umtx_sleep(volatile const int *ptr, int value, int timeout); }
	SYS_UMTX_WAKEUP            = 470 // { int umtx_wakeup(volatile const int *ptr, int count); }