linux-kernel - Re: [PATCH 06/10] rust: xarray: simplify `Guard::load`

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Message-ID: <CAJ-ks9m6Pv85Y-Dfxgf7HxpKdrXsgY4jdpkFX+oYfrLevvd3hg@mail.gmail.com>
Date: Wed, 7 Jan 2026 15:08:00 -0500
From: Tamir Duberstein <tamird@...il.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <lossin@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, Daniel Gomez <da.gomez@...nel.org>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/10] rust: xarray: simplify `Guard::load`

On Wed, Jan 7, 2026 at 2:37 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>
> Tamir Duberstein <tamird@...il.com> writes:
>
> > On Wed, Dec 3, 2025 at 5:27 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
> >>
> >> Simplify the implementation by removing the closure-based API from
> >> `Guard::load` in favor of returning `Option<NonNull<c_void>>` directly.
> >
> > This is not sound. The returned pointer can now outlive the guard and
> > mutation through that pointer is trivial.
>
> I don't think this is unsound. If we returned a reference instead, it
> would be, but we are returning a raw pointer. Dereferencing the pointer
> is unsafe and requires proper safety comments.

You may be right, strictly speaking, but it is most definitely a
footgun. This is a special pointer that requires more careful handling
than other raw pointers.

> Best regards,
> Andreas Hindborg