linux-kernel - Re: [PATCH v7 4/9] rust: sync: atomic: Add generic atomics

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Message-Id: <DBBVLUSF4TVV.2GCXLLC9JS2II@kernel.org>
Date: Mon, 14 Jul 2025 17:16:59 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>, "Miguel Ojeda"
 <miguel.ojeda.sandonis@...il.com>
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 4/9] rust: sync: atomic: Add generic atomics

On Mon Jul 14, 2025 at 4:53 PM CEST, Boqun Feng wrote:
> On Mon, Jul 14, 2025 at 04:34:39PM +0200, Miguel Ojeda wrote:
>> On Mon, Jul 14, 2025 at 4:22 PM Boqun Feng <boqun.feng@...il.com> wrote:
>> >
>> > Hmm.. why? This is the further information about what the above
>> > "Examples" section just mentioned?
>> 
>> I think Benno may be trying to point out is may be confusing what
>> "this" may be referring to, i.e. is it referring to something concrete
>> about the example, or about `from_ptr` as a whole / in all cases?
>> 
>
> Ok, how about I do this:
>
> diff --git a/rust/kernel/sync/atomic/generic.rs b/rust/kernel/sync/atomic/generic.rs
> index 26d9ff3f7c35..e40010394536 100644
> --- a/rust/kernel/sync/atomic/generic.rs
> +++ b/rust/kernel/sync/atomic/generic.rs
> @@ -135,6 +135,9 @@ pub const fn new(v: T) -> Self {
>
>      /// Creates a reference to an atomic `T` from a pointer of `T`.
>      ///
> +    /// This usually is used when when communicating with C side or manipulating a C struct, see
> +    /// examples below.

I don't think it's necessary to mention the examples below, but this is
what I had in mind.

---
Cheers,
Benno

> +    ///
>      /// # Safety
>      ///
>      /// - `ptr` is aligned to `align_of::<T>()`.
> @@ -185,9 +188,6 @@ pub const fn new(v: T) -> Self {
>      /// // no data race.
>      /// unsafe { Atomic::from_ptr(foo_a_ptr) }.store(2, Release);
>      /// ```
> -    ///
> -    /// However, this should be only used when communicating with C side or manipulating a C
> -    /// struct.
>      pub unsafe fn from_ptr<'a>(ptr: *mut T) -> &'a Self
>      where
>          T: Sync,
>
> ?
>
> Regards,
> Boqun
>
>> Cheers,
>> Miguel