linux-kernel - [PATCH 1/3] rust: lock: pin the inner data

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Message-Id: <20250730-lock-t-when-t-is-pinned-v1-1-1b97d5f28aa2@collabora.com>
Date: Wed, 30 Jul 2025 14:14:44 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
 Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>, 
 Waiman Long <longman@...hat.com>, Miguel Ojeda <ojeda@...nel.org>, 
 Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
 Danilo Krummrich <dakr@...nel.org>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
 Daniel Almeida <daniel.almeida@...labora.com>
Subject: [PATCH 1/3] rust: lock: pin the inner data

In preparation to support Lock<T> where T is pinned, the first thing that
needs to be done is to structurally pin the 'data' member. This switches
the 't' parameter in Lock<T>::new() to take in an impl PinInit<T> instead
of a plain T. This in turn uses the blanket implementation "impl PinInit<T>
for T".

Subsequent patches will touch on Guard<T>.

Link: https://github.com/Rust-for-Linux/linux/issues/1181
Suggested-by: Benno Lossin <lossin@...nel.org>
Suggested-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Daniel Almeida <daniel.almeida@...labora.com>
---
 rust/kernel/sync/lock.rs | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index e82fa5be289c169b0c9cfe277e15988958563430..9715463cbab867a2cf59e75f03001d75e91bd7b6 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -11,7 +11,7 @@
     types::{NotThreadSafe, Opaque, ScopeGuard},
 };
 use core::{cell::UnsafeCell, marker::PhantomPinned, pin::Pin};
-use pin_init::{pin_data, pin_init, PinInit};
+use pin_init::{pin_data, pin_init, PinInit, Wrapper};
 
 pub mod mutex;
 pub mod spinlock;
@@ -115,6 +115,7 @@ pub struct Lock<T: ?Sized, B: Backend> {
     _pin: PhantomPinned,
 
     /// The data protected by the lock.
+    #[pin]
     pub(crate) data: UnsafeCell<T>,
 }
 
@@ -127,9 +128,13 @@ unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {}
 
 impl<T, B: Backend> Lock<T, B> {
     /// Constructs a new lock initialiser.
-    pub fn new(t: T, name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {
+    pub fn new(
+        t: impl PinInit<T>,
+        name: &'static CStr,
+        key: Pin<&'static LockClassKey>,
+    ) -> impl PinInit<Self> {
         pin_init!(Self {
-            data: UnsafeCell::new(t),
+            data <- UnsafeCell::pin_init(t),
             _pin: PhantomPinned,
             // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have
             // static lifetimes so they live indefinitely.

-- 
2.50.1