Yeah, intuitively Mutex is actually one of the tools that you use to negotiate with the borrow checker (it's one implementation of "interior mutability", allowi

Yeah, intuitively Mutex is actually one of the tools that you use to negotiate with the borrow checker (it's one implementation of "interior mutability", allowing conversions from immutable to mutable borrows by taking the lock), so it is kind of by definition not something Rust can prevent, outside of lints and other static analysis. I can't think of a use case for taking a mutex lock multiple times in a code path, but there is a common cache pattern with RwLock, where you have a "fast path" that only takes a read lock to perform a lookup, and then only take a write lock when inserting a new entry. In this case, you should be using an upgradable read lock, so there is technically a "re-lock" of the same RwLock on upgrade in the same codepath. This model does prevent deadlocks because of move semantics.