linux-kernel - Re: [PATCH v6 3/9] rust: sync: atomic: Add ordering annotation types

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Message-Id: <DB8BTA477Z2V.1J7XFLDXHMN2S@kernel.org>
Date: Thu, 10 Jul 2025 13:08:19 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <lkmm@...ts.linux.dev>,
 <linux-arch@...r.kernel.org>
Cc: "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>,
 "Trevor Gross" <tmgross@...ch.edu>, "Danilo Krummrich" <dakr@...nel.org>,
 "Will Deacon" <will@...nel.org>, "Peter Zijlstra" <peterz@...radead.org>,
 "Mark Rutland" <mark.rutland@....com>, "Wedson Almeida Filho"
 <wedsonaf@...il.com>, "Viresh Kumar" <viresh.kumar@...aro.org>, "Lyude
 Paul" <lyude@...hat.com>, "Ingo Molnar" <mingo@...nel.org>, "Mitchell Levy"
 <levymitchell0@...il.com>, "Paul E. McKenney" <paulmck@...nel.org>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Linus Torvalds"
 <torvalds@...ux-foundation.org>, "Thomas Gleixner" <tglx@...utronix.de>,
 "Alan Stern" <stern@...land.harvard.edu>
Subject: Re: [PATCH v6 3/9] rust: sync: atomic: Add ordering annotation
 types

On Thu Jul 10, 2025 at 8:00 AM CEST, Boqun Feng wrote:
> Preparation for atomic primitives. Instead of a suffix like _acquire, a
> method parameter along with the corresponding generic parameter will be
> used to specify the ordering of an atomic operations. For example,
> atomic load() can be defined as:
>
> 	impl<T: ...> Atomic<T> {
> 	    pub fn load<O: AcquireOrRelaxed>(&self, _o: O) -> T { ... }
> 	}
>
> and acquire users would do:
>
> 	let r = x.load(Acquire);
>
> relaxed users:
>
> 	let r = x.load(Relaxed);
>
> doing the following:
>
> 	let r = x.load(Release);
>
> will cause a compiler error.
>
> Compared to suffixes, it's easier to tell what ordering variants an
> operation has, and it also make it easier to unify the implementation of
> all ordering variants in one method via generic. The `TYPE` associate
> const is for generic function to pick up the particular implementation
> specified by an ordering annotation.
>
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>

One naming comment below, with that fixed:

Reviewed-by: Benno Lossin <lossin@...nel.org>

> ---
>  rust/kernel/sync/atomic.rs          |  3 +
>  rust/kernel/sync/atomic/ordering.rs | 97 +++++++++++++++++++++++++++++
>  2 files changed, 100 insertions(+)
>  create mode 100644 rust/kernel/sync/atomic/ordering.rs

> +/// The trait bound for annotating operations that support any ordering.
> +pub trait Any: internal::Sealed {

I don't like the name `Any`, how about `AnyOrdering`? Otherwise we
should require people to write `ordering::Any` because otherwise it's
pretty confusing.

---
Cheers,
Benno

> +    /// Describes the exact memory ordering.
> +    const TYPE: OrderingType;
> +}