linux-kernel - Re: [PATCH v7 6/9] rust: sync: atomic: Add the framework of arithmetic operations

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Message-ID: <aHfJx5_kMcULUd7t@Mac.home>
Date: Wed, 16 Jul 2025 08:48:23 -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 v7 6/9] rust: sync: atomic: Add the framework of
 arithmetic operations

On Wed, Jul 16, 2025 at 05:36:05PM +0200, Benno Lossin wrote:
[..]
> >
> > I have a better solution:
> >
> > in ops.rs
> >
> >     pub struct AtomicRepr<T: AtomicImpl>(UnsafeCell<T>)
> >
> >     impl AtomicArithmeticOps for i32 {
> >         // a *safe* function
> >         fn atomic_add(a: &AtomicRepr, v: i32) {
> > 	    ...
> > 	}
> >     }
> >
> > in generic.rs
> >
> >     pub struct Atomic<T>(AtoimcRepr<T::Repr>);
> >
> >     impl<T: AtomicAdd> Atomic<T> {
> >         fn add(&self, v: .., ...) {
> > 	    T::Repr::atomic_add(&self.0, ...);
> > 	}
> >     }
> >
> > see:
> >
> > 	https://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git/log/?h=rust-atomic-impl
> 
> Hmm what does the additional indirection give you?
> 

What additional indirection you mean? You cannot make atomic_add() safe
with only `UnsafeCell<T::Repr>`.

Regards,
Boqun

> Otherwise this looks like the `T::Repr` approach that I detailed above,
> so I like it :)
> 
> ---
> Cheers,
> Benno