linux-kernel - Re: [PATCH 2/2] rust: sync: atomic: Add atomic operation helpers over raw pointers

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Message-ID: <aXDL5NUOH_qr390Q@tardis-2.local>
Date: Wed, 21 Jan 2026 20:51:48 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: Marco Elver <elver@...gle.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Gary Guo <gary@...yguo.net>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, kasan-dev@...glegroups.com,
	Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Elle Rhumsaa <elle@...thered-steel.dev>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	FUJITA Tomonori <fujita.tomonori@...il.com>
Subject: Re: [PATCH 2/2] rust: sync: atomic: Add atomic operation helpers
 over raw pointers

On Wed, Jan 21, 2026 at 01:36:04PM +0100, Marco Elver wrote:
[..]
> >
> > > However this will mean that Rust code will have one more ordering than the C
> > > API, so I am keen on knowing how Boqun, Paul, Peter and others think about this.
> >
> > On that point, my suggestion would be to use the standard LKMM naming
> > such as rcu_dereference() or READ_ONCE().

I don't think we should confuse Rust users that `READ_ONCE()` has
dependency orderings but `atomc_load()` doesn't. They are the same on
the aspect. One of the reasons that I don't want to introduce
rcu_dereference() and READ_ONCE() on Rust side is exactly this, they are
the same at LKMM level, so should not be treated differently.

> >
> > I'm told that READ_ONCE() apparently has stronger guarantees than an
> > atomic consume load, but I'm not clear on what they are.
> 
> It's also meant to enforce ordering through control-dependencies, such as:
> 
>    if (READ_ONCE(x)) WRITE_ONCE(y, 1);

Note that it also applies to atomic_read() and atomic_set() as well.

Regards,
Boqun