UMTX_OP_MUTEX_WAIT
_umtx_op_err(mtx, UMTX_OP_MUTEX_WAIT, 0, 0, 0);
ret = _umtx_op_err(mtx, UMTX_OP_MUTEX_WAIT, 0,
_umtx_op_err(mtx, UMTX_OP_MUTEX_WAIT, 0, 0, 0);
[UMTX_OP_MUTEX_WAIT] = __umtx_op_wait_umutex,