Slither detects reentrancy vulnerability against the code using a mutex to guard reentrancy.

[c-kado]

Describe the desired feature

Slither detects reentrancy in the code below.
I think the code is safe for reentrancy.
bool locked is a variable for mutex.
Slither detects vulnerabilities by recognizing the variable as a state variable written after an external call.

pragma solidity ^0.7.0;

contract MutexPattern {
    bool locked = false;
    mapping(address => uint256) public balances;

    function withdraw(uint _amount) public payable returns(bool) {
        require(!locked, "Blocked from reentrancy.");
        locked = true;

        require(balances[msg.sender] >= _amount, "No balance to withdraw.");
        
        balances[msg.sender] -= _amount;
        (bool success, ) = msg.sender.call{value: _amount}("");
        require(success);

        locked = false;
        return true;
    }
}

Slither detects the code below using a modifier as safe, although the functionality is the same as the above code.

pragma solidity ^0.7.0;

contract MutexPattern {
    bool locked = false;
    mapping(address => uint256) public balances;
    
    modifier noReentrancy() {
        require(!locked, "Blocked from reentrancy.");
        locked = true;
        _;
        locked = false;
    }

    function withdraw(uint _amount) public payable noReentrancy returns(bool) {
        require(balances[msg.sender] >= _amount, "No balance to withdraw.");
        
        balances[msg.sender] -= _amount;
        (bool success, ) = msg.sender.call{value: _amount}("");
        require(success);

        return true;
    }
}

What differences are in them?