linux-kernel - [PATCH 3/4] rust: lock: Pin the inner data

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Message-ID: <20250919091241.32138-4-boqun.feng@gmail.com>
Date: Fri, 19 Sep 2025 11:12:40 +0200
From: Boqun Feng <boqun.feng@...il.com>
To: "Peter Zijlstra" <peterz@...adead.org>,
	"Ingo Molnar" <mingo@...nel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>
Cc: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lkmm@...ts.linux.dev,
	"Will Deacon" <will@...nel.org>,
	"Peter Zijlstra" <peterz@...radead.org>,
	Waiman Long <longman@...hat.com>,
	"Miguel Ojeda" <ojeda@...nel.org>,
	alex.gaynor@...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>,
	"Andreas Hindborg" <a.hindborg@...nel.org>,
	Daniel Almeida <daniel.almeida@...labora.com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [PATCH 3/4] rust: lock: Pin the inner data

From: Daniel Almeida <daniel.almeida@...labora.com>

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>
Reviewed-by: Benno Lossin <lossin@...nel.org>
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
Signed-off-by: Daniel Almeida <daniel.almeida@...labora.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---

Notes:
    SubmissionLink: https://lore.kernel.org/all/20250828-lock-t-when-t-is-pinned-v2-2-b067c4b93fd6@collabora.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 b482f34bf0ce..9242790d15db 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.
-- 
2.51.0