Problem with mutex.lock()

[Banta Plan]

I compiled this program and it crashes if executed.

Compiled with: FreeBSD clang version 6.0.1 (tags/RELEASE_601/final 335540) (based on LLVM 6.0.1)

## CMakeLists.txt
cmake_minimum_required(VERSION 3.13)
project(mainP)

set(CMAKE_CXX_STANDARD 17)

add_executable(mainP main.cpp)

find_package(Threads)
target_link_libraries(mainP ${CMAKE_THREAD_LIBS_INIT})

## main.cpp

#include <iostream>
#include <thread>
#include <mutex>
#include <chrono>
#include <functional>

int main() {
    using namespace std::chrono_literals;
    std::mutex m;
    m.lock();
    std::thread([&] {
        std::cout << "Before sleepFor" << std::endl;
        std::this_thread::sleep_for(2s);

        std::cout << "Before unlock" << std::endl;
        m.unlock();
        std::cout << "After unlock" << std::endl;

    }).detach();
    std::cout << "Before lock2" << std::endl;
    m.lock();
    std::cout << "After lock2" << std::endl;

    return 0;
}
##

This program compiles and runs under MacOS (Clang Version: Apple LLVM version 10.0.0 (clang-1000.11.45.5)) and
manjaro arm64 with gcc (GCC) 8.2.1 20180831