linux-kernel - Re: [PATCH] rust: pin-init: add references to previously initialized fields

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Message-Id: <DCL1DPN708H0.3JTL93J2GD2DR@kernel.org>
Date: Fri, 05 Sep 2025 19:18:25 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Benno Lossin" <lossin@...nel.org>, "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>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "Danilo Krummrich" <dakr@...nel.org>, "Fiona Behrens" <me@...enk.dev>,
 "Alban Kurti" <kurti@...icto.ai>, "Greg Kroah-Hartman"
 <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 "Bjorn Helgaas" <bhelgaas@...gle.com>,
 Krzysztof Wilczyński <kwilczynski@...nel.org>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rust: pin-init: add references to previously
 initialized fields

On Fri Sep 5, 2025 at 4:00 PM CEST, Benno Lossin wrote:
> After initializing a field in an initializer macro, create a variable
> holding a reference that points at that field. The type is either
> `Pin<&mut T>` or `&mut T` depending on the field's structural pinning
> kind.
>
> Link: https://github.com/Rust-for-Linux/pin-init/pull/83/commits/0f658594c39398f58cd5cb99a8141e370e225e74
> Signed-off-by: Benno Lossin <lossin@...nel.org>

I forgot to test with the right configuration and found some errors with
existing code. Here are their fixes. If I don't need to re-send, I will
add them on apply (if you want a v2, let me know).

---
Cheers,
Benno

diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index da18091143a6..91dbf3f4b166 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -134,11 +134,9 @@ pub fn new<'a, E>(
         T: 'a,
         Error: From<E>,
     {
-        let callback = Self::devres_callback;
-
         try_pin_init!(&this in Self {
             dev: dev.into(),
-            callback,
+            callback: Self::devres_callback,
             // INVARIANT: `inner` is properly initialized.
             inner <- {
                 // SAFETY: `this` is a valid pointer to uninitialized memory.
@@ -151,7 +149,7 @@ pub fn new<'a, E>(
                 //    properly initialized, because we require `dev` (i.e. the *bound* device) to
                 //    live at least as long as the returned `impl PinInit<Self, Error>`.
                 to_result(unsafe {
-                    bindings::devm_add_action(dev.as_raw(), Some(callback), inner.cast())
+                    bindings::devm_add_action(dev.as_raw(), Some(*callback), inner.cast())
                 })?;

                 Opaque::pin_init(try_pin_init!(Inner {
diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
index 606946ff4d7f..1ac0b06fa3b3 100644
--- a/samples/rust/rust_driver_pci.rs
+++ b/samples/rust/rust_driver_pci.rs
@@ -78,8 +78,8 @@ fn probe(pdev: &pci::Device<Core>, info: &Self::IdInfo) -> Result<Pin<KBox<Self>

         let drvdata = KBox::pin_init(
             try_pin_init!(Self {
-                pdev: pdev.into(),
                 bar <- pdev.iomap_region_sized::<{ Regs::END }>(0, c_str!("rust_driver_pci")),
+                pdev: pdev.into(),
                 index: *info,
             }),
             GFP_KERNEL,