Description of problem:

If one forks a process, the original process dies and then the second one forks again the last forked process can have the same pid as the original and so getpid will not detect a change.  This was a widely noted weakness in LibreSSL (see https://www.agwa.name/blog/post/libressls_prng_is_unsafe_on_linux.)

How reproducible:

This is very probably systematically reproducible in possibly affected libraries but in practise should never really happen.