Here's a patch just for Modules/selectmodule.c (and related files), based on Georg's patch, updated to apply against current default, including fixes thanks to Serhiy's review.

It took a while since I had to get a Linux VM up to run the epoll tests. And it was good that I did, since Georg's patch had several errors in that area.

It is important to note that epoll.poll now raises a different exception when called with invalid arguments after it has been closed. It used to raise ValueError since it first checked whether it was closed before checking the parameters. With this patch, the parameters are checked first so a TypeError is raised. This behavior wasn't documented and wasn't tested, so it seems relatively safe to change. At Serhiy's suggestion, I added a test for the new behavior. Perhaps this should be mentioned in the release notes and/or "what's new"?