Re: [PATCH v5 03/10] rust: sync: atomic: Add ordering annotation types

Peter Zijlstra
2025-06-19T10:32:02Z

On Wed, Jun 18, 2025 at 09:49:27AM -0700, Boqun Feng wrote:

> +//! Memory orderings.
> +//!
> +//! The semantics of these orderings follows the [`LKMM`] definitions and rules.
> +//!
> +//! - [`Acquire`] and [`Release`] are similar to their counterpart in Rust memory model.

So I've no clue what the Rust memory model states, and I'm assuming
it is very similar to the C11 model. I have also forgotten what LKMM
states :/

Do they all agree on what RELEASE+ACQUIRE makes?

> +//! - [`Full`] means "fully-ordered", that is:
> +//! - It provides ordering between all the preceding memory accesses and the annotated operation.
> +//! - It provides ordering between the annotated operation and all the following memory accesses.
> +//! - It provides ordering between all the preceding memory accesses and all the fllowing memory
> +//! accesses.
> +//! - All the orderings are the same strong as a full memory barrier (i.e. `smp_mb()`).

s/strong/strength/ ?

> +//! - [`Relaxed`] is similar to the counterpart in Rust memory model, except that dependency
> +//! orderings are also honored in [`LKMM`]. Dependency orderings are described in "DEPENDENCY
> +//! RELATIONS" in [`LKMM`]'s [`explanation`].
> +//!
> +//! [`LKMM`]: srctree/tools/memory-model/
> +//! [`explanation`]: srctree/tools/memory-model/Documentation/explanation.txt