linux-kernel - Re: [PATCH v14 2/9] rust: rename `AlwaysRefCounted` to `RefCounted`.

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Message-Id: <DG72CY2P36F9.2O7OIN36KW8F8@garyguo.net>
Date: Thu, 05 Feb 2026 13:31:01 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Andreas Hindborg" <a.hindborg@...nel.org>, "Miguel Ojeda"
 <ojeda@...nel.org>, "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>, "Greg Kroah-Hartman"
 <gregkh@...uxfoundation.org>, "Dave Ertman" <david.m.ertman@...el.com>,
 "Ira Weiny" <ira.weiny@...el.com>, "Leon Romanovsky" <leon@...nel.org>,
 "Paul Moore" <paul@...l-moore.com>, "Serge Hallyn" <sergeh@...nel.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, "David Airlie"
 <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Alexander Viro"
 <viro@...iv.linux.org.uk>, "Christian Brauner" <brauner@...nel.org>, "Jan
 Kara" <jack@...e.cz>, "Igor Korotin" <igor.korotin.linux@...il.com>,
 "Daniel Almeida" <daniel.almeida@...labora.com>, "Lorenzo Stoakes"
 <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 "Viresh Kumar" <vireshk@...nel.org>, "Nishanth Menon" <nm@...com>, "Stephen
 Boyd" <sboyd@...nel.org>, "Bjorn Helgaas" <bhelgaas@...gle.com>,
 Krzysztof Wilczyński <kwilczynski@...nel.org>
Cc: <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
 <linux-block@...r.kernel.org>, <linux-security-module@...r.kernel.org>,
 <dri-devel@...ts.freedesktop.org>, <linux-fsdevel@...r.kernel.org>,
 <linux-mm@...ck.org>, <linux-pm@...r.kernel.org>,
 <linux-pci@...r.kernel.org>, "Oliver Mangold" <oliver.mangold@...me>
Subject: Re: [PATCH v14 2/9] rust: rename `AlwaysRefCounted` to
 `RefCounted`.

On Wed Feb 4, 2026 at 11:56 AM GMT, Andreas Hindborg wrote:
> From: Oliver Mangold <oliver.mangold@...me>
> 
> There are types where it may both be reference counted in some cases and
> owned in others. In such cases, obtaining `ARef<T>` from `&T` would be
> unsound as it allows creation of `ARef<T>` copy from `&Owned<T>`.
> 
> Therefore, we split `AlwaysRefCounted` into `RefCounted` (which `ARef<T>`
> would require) and a marker trait to indicate that the type is always
> reference counted (and not `Ownable`) so the `&T` -> `ARef<T>` conversion
> is possible.
> 
> - Rename `AlwaysRefCounted` to `RefCounted`.
> - Add a new unsafe trait `AlwaysRefCounted`.
> - Implement the new trait `AlwaysRefCounted` for the newly renamed
>   `RefCounted` implementations. This leaves functionality of existing
>   implementers of `AlwaysRefCounted` intact.
> 
> Original patch by Oliver Mangold <oliver.mangold@...me> [1].
> 
> Link: https://lore.kernel.org/r/20251117-unique-ref-v13-2-b5b243df1250@pm.me [1]
> Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
> Reviewed-by: Daniel Almeida <daniel.almeida@...labora.com>
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>

I think you also need to update the `AlwaysRefCounted` reference mentioned in
the `Owned` patch too? (Or perhaps this patch should be moved before `Owned`
instead?)

With that fixed:

Reviewed-by: Gary Guo <gary@...yguo.net>

> ---
>  rust/kernel/auxiliary.rs        |  7 +++++-
>  rust/kernel/block/mq/request.rs | 15 +++++++------
>  rust/kernel/cred.rs             | 13 ++++++++++--
>  rust/kernel/device.rs           | 10 ++++++---
>  rust/kernel/device/property.rs  |  7 +++++-
>  rust/kernel/drm/device.rs       | 10 ++++++---
>  rust/kernel/drm/gem/mod.rs      |  8 ++++---
>  rust/kernel/fs/file.rs          | 16 ++++++++++----
>  rust/kernel/i2c.rs              | 16 +++++++++-----
>  rust/kernel/mm.rs               | 15 +++++++++----
>  rust/kernel/mm/mmput_async.rs   |  9 ++++++--
>  rust/kernel/opp.rs              | 10 ++++++---
>  rust/kernel/owned.rs            |  2 +-
>  rust/kernel/pci.rs              | 10 ++++++++-
>  rust/kernel/pid_namespace.rs    | 12 +++++++++--
>  rust/kernel/platform.rs         |  7 +++++-
>  rust/kernel/sync/aref.rs        | 47 ++++++++++++++++++++++++++---------------
>  rust/kernel/task.rs             | 10 ++++++---
>  rust/kernel/types.rs            |  3 ++-
>  19 files changed, 164 insertions(+), 63 deletions(-)