On some platforms there's an exclusive lock in socketmodule, used for getaddrinfo, gethostbyname, gethostbyaddr. A thread can hold this lock while another forks, leaving it locked forever in the child process. Calls to these functions in the child process will hang.

(I wrote some more details here: https://emptysqua.re/blog/getaddrinfo-deadlock/ )

I propose that this is a bug, and that it can be fixed in PyOS_AfterFork, where a few similar locks are already reset.