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rust: sync: Implement Unpin for ARef

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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 66f1ea83d9 ("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
This commit is contained in:
Alice Ryhl 2025-12-18 08:25:13 +00:00 • committed by Boqun Feng
parent 8a581130b1
commit 09248ed8cd
1 changed files with 3 additions and 0 deletions
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3
rust/kernel/sync/aref.rs
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@ -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`].
///