TSAN: unexpected deadlock detection.

[JackyWoo]

Env

clang -v
Ubuntu clang version 15.0.7
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Candidate multilib: .;@m64
Selected multilib: .;@m64

Description

1. no deadlock, but report potential deadlock

/ not deadlock, but report potential deadlock
void notDeadlockButReport()
{
    std::mutex m1;
    std::mutex m2;

    // m1 => m2
    std::cout << "t try to acquire m1\n";
    m1.lock();
    std::cout << "t got m1\n";

    //std::this_thread::sleep_for(std::chrono::microseconds (2)); // wait main got m2

    // code never executed
    std::cout << "t try to acquire m2\n";
    m2.lock();
    std::cout << "t got m2\n";

    m2.unlock();
    m1.unlock();

    // m2 => m1
    std::cout << "main try to acquire m2\n";
    m2.lock();
    std::cout << "main got m2\n";

    // code never executed
    std::cout << "main try to acquire m1\n";
    m1.lock();
    std::cout << "main got m1\n";

    m1.unlock();
    m2.unlock();
}

2. deadlock but not report

void deadlockButNotReport()
{
    std::mutex m1;
    std::mutex m2;

    std::thread t([&] {

        std::cout << "t try to acquire m1\n";
        m1.lock();
        std::cout << "t got m1\n";

        std::this_thread::sleep_for(std::chrono::milliseconds (20)); // wait main got m2

        std::cout << "t try to acquire m2\n";
        m2.lock();
        std::cout << "t got m2\n"; // code never executed

        m2.unlock();
        m1.unlock();
    });

    std::this_thread::sleep_for(std::chrono::milliseconds(10)); // wait t got m1

    std::cout << "main try to acquire m2\n";
    m2.lock();
    std::cout << "main got m2\n";

    std::cout << "main try to acquire m1\n";
    m1.lock();
    std::cout << "main got m1\n"; // code never executed

    m1.unlock();
    m2.unlock();

    t.join();
}