最后一行代码中的无限while循环

任何人都可以在以下方面为我提供帮助：

我有一个代码，该代码读取用户名和密码，然后允许用户访问程序。我有第一个选项来注册一个新用户。我的最后两行代码遇到无限循环问题。我想运行一个字符串，说明如果输入了未注册的用户名，它将返回一个字符串，表明没有这样的注册用户。该字符串仅在循环中运行，有什么我可以做的来更改它。

用户名：admin

密码：adm1n

我的代码如下：

users = {}  
with open ('user.txt', 'rt')as username:
    for line in username:
        username, password = line.split(",")
        users[username.strip()] = password.strip()  # strip removes leading/trailing whitespaces

uinput = input("Please enter your username:\n")
while uinput not in users:
    print("Username incorrect.")
    uinput = input("Please enter a valid username:/n")

if uinput in users:
            print ("Username correct")

with open('user.txt', 'rt') as password:
    for line in password:
        username, password = line.split(",")
        users[password.strip()] = username.strip()  # strip removes leading/trailing whitespaces

uinput2 = input("Please enter your password:\n")
while uinput2 not in users:
    print("Your username is correct but your password is incorrect.")
    uinput2 = input("Please enter a valid password:\n")

if uinput2 in users:
    password2 = ("Password correct")
    print (password2)

if password2 == ("Password correct"):
       menu = (input("\nPlease select one of the following options:\nr - register user\na - add task\nva - view all tasks\nvm - view my tasks\ne - exit\n"))
    if menu == "r" or menu == "R":
                new_user = (input("Please enter a new user name:\n"))
                new_password = (input("Please enter a new password:\n"))
                with open ('user.txt', 'a')as username:
                        username.write("\n" + new_user + ", " + new_password)
    elif menu == "a" or menu == "A":
                task = input("Please enter the username of the person the task is asigned to.\n")
        while task not in username:
                print("User not registered. Please enter a valid username:\n")