linux-kernel - Re: [PATCH v8 4/9] rust: sync: atomic: Add generic atomics

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Message-ID: <aKCtxVSm9kYD8NcK@tardis-2.local>
Date: Sat, 16 Aug 2025 09:11:49 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Benno Lossin <lossin@...nel.org>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	lkmm@...ts.linux.dev, linux-arch@...r.kernel.org,
	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 v8 4/9] rust: sync: atomic: Add generic atomics

On Tue, Aug 12, 2025 at 09:59:39AM +0200, Benno Lossin wrote:
> On Sat Jul 19, 2025 at 5:08 AM CEST, Boqun Feng wrote:
> > To provide using LKMM atomics for Rust code, a generic `Atomic<T>` is
> > added, currently `T` needs to be Send + Copy because these are the
> > straightforward usages and all basic types support this.
> >
> > Implement `AtomicType` for `i32` and `i64`, and so far only basic
> > operations load() and store() are introduced.
> >
> > Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> > Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> 
> Reviewed-by: Benno Lossin <lossin@...nel.org>
> 

Thanks!

> > ---
> >  rust/kernel/sync/atomic.rs           | 274 +++++++++++++++++++++++++++
> >  rust/kernel/sync/atomic/predefine.rs |  15 ++
> >  2 files changed, 289 insertions(+)
> >  create mode 100644 rust/kernel/sync/atomic/predefine.rs
> 
> > +/// # Limitations
> > +///
> > +/// Because C primitives are used to implement the atomic operations, and a C function requires a
> > +/// valid object of a type to operate on (i.e. no `MaybeUninit<_>`), hence at the Rust <-> C
> > +/// surface, only types with all the bits initialized can be passed. As a result, types like `(u8,
> > +/// u16)` (padding bytes are uninitialized) are currently not supported. Note that technically
> > +/// these types can be supported if some APIs are removed for them and the inner implementation is
> > +/// tweaked, but the justification of support such a type is not strong enough at the moment. This
> > +/// should be resolved if there is an implementation for `MaybeUninit<i32>` as `AtomicImpl`.
> 
> I'd remove the last sentence, as it makes it sound like one only would
> have to add that impl and be finished.
> 

Yeah, sounds good to me, will remove the last sentence starting with
"Note that technically .."

Regards,
Boqun

> ---
> Cheers,
> Benno
>