RCU publishes a new pointer after Copying and Updating the copied state. It's not mutating in-place. You don't use it for frequent updates.

https://en.wikipedia.org/wiki/Read-copy-update#Name_and_over...

You may not use it for frequent updates; we do.

There is state.

It is shared state.

It is mutable state.

There are readers, who can see the shared state.

There are writers, who copy it, update it and push it back so that the new state is visible to everyone else.

I have no idea what your definition of mutable shared state might be if that doesn't fit it.