[PATCH] rust: sync: implement Unpin for ARef

[Alice Ryhl]

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.

Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
---
 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 0d24a0432015d09509a255df0a4f114171ae9fb0..c4be6f5d4884ddd6cbfbd7c27d396310a7cde30e 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> Unpin for ARef<T> {}
+
 impl<T: AlwaysRefCounted> ARef<T> {
     /// Creates a new instance of [`ARef`].
     ///

---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251217-unpin-for-aref-3dc0fe3fd5b0

Best regards,
-- 
Alice Ryhl <aliceryhl@xxxxxxxxxx>