I finally watched the talk today and that wasn’t what I thought he meant. What I thought he was getting at was that the rust parts of the kernel interact with lots of other modules written by people who don’t know rust. When those C modules change their semantics in ways that break the rust code, they can’t go fix it because they don’t know rust. In fact, whenever they make a change, they don’t even know if they broke some rust module, because they don’t understand the rust code well enough. And this is something that everyone is going to have to live with for the foreseeable future, because you can’t force all those other kernel hackers to learn rust.