linux-kernel - Re: [PATCH 4/5] rust: sync: atomic: Add Atomic<*mut T> support

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Message-Id: <DFRZCBBXBTM8.2BSEQFA5F28W9@kernel.org>
Date: Sun, 18 Jan 2026 20:59:09 +0100
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>, "Dirk Behme" <dirk.behme@...il.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <rcu@...r.kernel.org>, "Miguel Ojeda" <ojeda@...nel.org>, "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>, "Paul E. McKenney" <paulmck@...nel.org>, "Frederic
 Weisbecker" <frederic@...nel.org>, "Neeraj Upadhyay"
 <neeraj.upadhyay@...nel.org>, "Joel Fernandes" <joelagnelf@...dia.com>,
 "Josh Triplett" <josh@...htriplett.org>, "Uladzislau Rezki"
 <urezki@...il.com>, "Steven Rostedt" <rostedt@...dmis.org>, "Mathieu
 Desnoyers" <mathieu.desnoyers@...icios.com>, "Lai Jiangshan"
 <jiangshanlai@...il.com>, "Zqiang" <qiang.zhang@...ux.dev>, "FUJITA
 Tomonori" <fujita.tomonori@...il.com>
Subject: Re: [PATCH 4/5] rust: sync: atomic: Add Atomic<*mut T> support

On Sun Jan 18, 2026 at 4:05 PM CET, Boqun Feng wrote:
> On Sun, Jan 18, 2026 at 10:57:37PM +0800, Boqun Feng wrote:
>> On Sun, Jan 18, 2026 at 09:38:36AM +0100, Dirk Behme wrote:
>> [...]
>> > >  
>> > > +// The current helpers of load/store uses `{WRITE,READ}_ONCE()` hence the atomicity is only
>> > 
>> > uses -> use ?
>> > 
>> 
>> Will fix, thank you!
>> 
>> > > +// guaranteed against read-modify-write operations if the architecture supports native atomic RmW.
>> > > +#[cfg(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW)]
>> > > +impl AtomicImpl for *const c_void {
>> > > +    type Delta = isize;
>> > > +}
>> > 
>> > Are all users of this guarded with CONFIG_ARCH_SUPPORTS_ATOMIC_RMW as
>> > well? Or do we want (need?) to cover the
>> 
>> No, the users don't need to guard with CONFIG_ARCH_SUPPORTS_ATOMIC_RMW,
>> the purpose of this #[cfg] is to avoid surprise that when
>> CONFIG_ARCH_SUPPORTS_ATOMIC_RMW=n arch supports Rust, when that happens,
>> we need to add the support to the helpers of i8/i16/ptr.
>> 
>
> Hmm... I guess at this moment, I probably should do
>
> #[cfg(not(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW))]
> static_assert!(false,
>                "Support of architectures that don't have native atomic needs to implement helpers in atomic_ext.c");
>
> I can add a patch in the next version if it looks good to everyone.

I think this is a great idea!

By the way, did you know about `cfg!` [1]?:

    static_assert!(
        cfg!(CONFIG_ARCH_SUPPORTS_ATOMIC_RMW),
        "Support of architectures that don't have native atomic needs to implement helpers in atomic_ext.c",
    );

[1]: https://doc.rust-lang.org/core/macro.cfg.html

Cheers,
Benno