[tip: locking/core] rust: sync: Implement Unpin for ARef

["tip-bot2 for Alice Ryhl" <tip-bot2@linutronix.de>]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     09248ed8cdb6345afc883c02aecd79dfbd9c2a9c
Gitweb:        https://git.kernel.org/tip/09248ed8cdb6345afc883c02aecd79dfbd9c2a9c
Author:        Alice Ryhl <aliceryhl@google.com>
AuthorDate:    Thu, 18 Dec 2025 08:25:13 
Committer:     Boqun Feng <boqun.feng@gmail.com>
CommitterDate: Fri, 09 Jan 2026 19:01:40 +08:00

rust: sync: Implement Unpin for ARef

The default implementation of Unpin for ARef<T> is conditional on T
being Unpin due to its PhantomData<T> field. However, this is overly
strict as pointers to T are legal to move even if T itself cannot move.

Since commit 66f1ea83d9f8 ("rust: lock: Add a Pin<&mut T> accessor")
this causes build failures when combined with a Mutex that contains an
field ARef<T>, because almost any type that ARef is used with is !Unpin.

Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://patch.msgid.link/20251218-unpin-for-aref-v2-1-30d77129cbc6@google.com
---
 rust/kernel/sync/aref.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs
index 0d24a04..0616c03 100644
--- a/rust/kernel/sync/aref.rs
+++ b/rust/kernel/sync/aref.rs
@@ -83,6 +83,9 @@ unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {}
 // example, when the reference count reaches zero and `T` is dropped.
 unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {}
 
+// Even if `T` is pinned, pointers to `T` can still move.
+impl<T: AlwaysRefCounted> Unpin for ARef<T> {}
+
 impl<T: AlwaysRefCounted> ARef<T> {
     /// Creates a new instance of [`ARef`].
     ///