linux-kernel - [PATCH 2/3] rust: lock: guard: add T: Unpin bound to DerefMut

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Message-Id: <20250730-lock-t-when-t-is-pinned-v1-2-1b97d5f28aa2@collabora.com>
Date: Wed, 30 Jul 2025 14:14:45 -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 2/3] rust: lock: guard: add T: Unpin bound to DerefMut

A core property of pinned types is not handing a mutable reference to the
inner data in safe code, as this trivially allows that data to be moved.

Enforce this condition by adding a bound on lock::Guard's DerefMut
implementation, so that it's only implemented for pinning-agnostic types.

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        | 5 ++++-
 rust/kernel/sync/lock/global.rs | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 9715463cbab867a2cf59e75f03001d75e91bd7b6..087bc0391f92a73b9af18ca31461b513bb5a9bcd 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -254,7 +254,10 @@ fn deref(&self) -> &Self::Target {
     }
 }
 
-impl<T: ?Sized, B: Backend> core::ops::DerefMut for Guard<'_, T, B> {
+impl<T: ?Sized, B: Backend> core::ops::DerefMut for Guard<'_, T, B>
+where
+    T: Unpin,
+{
     fn deref_mut(&mut self) -> &mut Self::Target {
         // SAFETY: The caller owns the lock, so it is safe to deref the protected data.
         unsafe { &mut *self.lock.data.get() }
diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
index d65f94b5caf2668586088417323496629492932f..38b44803279986275616eef499fd40b8d4e97fdf 100644
--- a/rust/kernel/sync/lock/global.rs
+++ b/rust/kernel/sync/lock/global.rs
@@ -106,7 +106,10 @@ fn deref(&self) -> &Self::Target {
     }
 }
 
-impl<B: GlobalLockBackend> core::ops::DerefMut for GlobalGuard<B> {
+impl<B: GlobalLockBackend> core::ops::DerefMut for GlobalGuard<B>
+where
+    B::Item: Unpin,
+{
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.inner
     }

-- 
2.50.1