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

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Message-ID: <87wm1sfnra.fsf@t14s.mail-host-address-is-not-set>
Date: Thu, 08 Jan 2026 10:38:01 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Tamir Duberstein <tamird@...il.com>
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`

Tamir Duberstein <tamird@...il.com> writes:

> 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.

I would disagree. Dereferencing any raw pointer requires the same
checks, and knowing this one is valid and satisfies lifetime
requirements is no different than others.

It is also a private method that is only used in this particular impl
block.

At any rate, I'm fine with dropping the change. The reason I did it was
because I had to double take when I read the previous code. I think the
original code is has some unnecessary complexity with the closure.

Best regards,
Andreas Hindborg