We get occasional build timeouts on b.a.o after pytest becomes unresponsive for over 20 minutes. This will result in a thread dump like this one:
If you look for "Log-watching thread starting" messages and the dump, it becomes quite obvious whats the issue here.
I had a quick look at the python3 / pytest related changes in
CASSANDRA-14134 and it seems that some of the handling around dtest_setup's log_watch_thread var has been changed in a way that would prevent eventually yielding the allocated thread.