You can play with atomics as much as you want in safe Rust but you can't cause a data race without aliased mutability, which means using UnsafeCell, raw pointer

You can play with atomics as much as you want in safe Rust but you can't cause a data race without aliased mutability, which means using UnsafeCell, raw pointer operations or a & to &mut transmute (unsound and UB as long as noalias is enabled in LLVM), and all require unsafe.