linux-kernel - Re: [PATCH v6 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

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Message-Id: <DB9GL8R8BBDJ.2ZDO26DR404JL@kernel.org>
Date: Fri, 11 Jul 2025 21:05:34 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Miguel Ojeda" <miguel.ojeda.sandonis@...il.com>
Cc: "Boqun Feng" <boqun.feng@...il.com>, <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>, "Matthew Wilcox"
 <willy@...radead.org>
Subject: Re: [PATCH v6 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

On Fri Jul 11, 2025 at 3:45 PM CEST, Miguel Ojeda wrote:
> On Fri, Jul 11, 2025 at 11:00 AM Benno Lossin <lossin@...nel.org> wrote:
>>
>> Do we have a static assert with these cfgs that `isize` has the same
>> size as these?
>>
>> If not, then it would probably make sense to add them now.
>
> Yeah, according to e.g. Matthew et al., we may end up with 128-bit
> pointers in the kernel fairly soon (e.g. a decade):
>
>     https://lwn.net/Articles/908026/
>
> I rescued part of what I wrote in the old `mod assumptions` which I
> never got to send back then -- most of the `static_asserts` are
> redundant now that we define directly the types in the `ffi` crate (I
> mean, we could still assert that `size_of::<c_char>() == 1` and so on,
> but they are essentially a tautology now), so I adapted the comments.
> Please see below (draft).

Ahhh yes the `mod assumptions` was the thing I remembered! I think it's
still useful as a file where we can put other global assumptions as
well.

---
Cheers,
Benno