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

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Message-ID: <aW2Bfykqj7qz79hS@tardis-2.local>
Date: Mon, 19 Jan 2026 08:57:35 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: Benno Lossin <lossin@...nel.org>
Cc: Dirk Behme <dirk.behme@...il.com>, 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 08:59:09PM +0100, Benno Lossin wrote:
> 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",
>     );
> 

Even better! Thanks. I've added a new patch that converts the existing
#[cfg] on impl blocks to this. I've added Suggested-by of both you and
Dirk ;-)

Regards,
Boqun

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