Creating a QPointer on the same object in multiple threads can trigger ASSERT: "!weakref.load()" in qsharedpointer_impl.h

I've been getting random crashes caused by a failing assertion in QWeakPointer, used internally by QPointer:

ASSERT: "!weakref.load()" in file c:\users\qt\work\qt\qtbase\include\qtcore\../../src/corelib/tools/qsharedpointer_impl.h line 155

I was able to isolate the crash into a simple test case, attached to this bug. The crash is very easy to trigger, usually after a couple iterations.

The crash is caused by a bug in QtSharedPointer::ExternalRefCountData::getAndRef() that only occurs with specific timing of multiple threads trying to create the QPointer to the same object at the same time, thus the use of a thread pool in my test program.

I have a simple fix ready to submit on gerrit already. I'm just baffled because git blame shows that this code hasn't changed in the last 8 years, so I guess this is an 8-year-old bug that somehow nobody managed to hit until I did?

Also interestingly, the test program doesn't hit the assert on Linux. However it happens pretty easily on Windows. Maybe a difference in how quickly QThreadPool spins the worker threads on each platform?

I've also verified that QPointer is meant to be thread-safe so my usage is correct, which is the case and in fact the bug is part of the code meant to handle the thread safety.