rust/kernel/sync/aref.rs | 3 +++ 1 file changed, 3 insertions(+)
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>
---
Changes in v2:
- Add T: AlwaysRefCounted bound.
- Link to v1: https://lore.kernel.org/r/20251217-unpin-for-aref-v1-1-84711b747d02@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 0d24a0432015d09509a255df0a4f114171ae9fb0..a297477f23a3960928302709f6aeb322fd4d1bd0 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`].
///
---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251217-unpin-for-aref-3dc0fe3fd5b0
Best regards,
--
Alice Ryhl <aliceryhl@google.com>On Thu Dec 18, 2025 at 5:25 PM JST, Alice Ryhl wrote:
> 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>
On Thu, Dec 18, 2025 at 9:25 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> +// Even if T is pinned, pointers to T can still move.
Boqun, if you pick this up, then please tweak this to:
// Even if `T` is pinned, pointers to `T` can still move.
Otherwise, if you want me to pick it up, please let me know -- thanks!
Cheers,
Miguel
On Thu, Dec 18, 2025 at 11:26:19AM +0100, Miguel Ojeda wrote: > On Thu, Dec 18, 2025 at 9:25 AM Alice Ryhl <aliceryhl@google.com> wrote: > > > > +// Even if T is pinned, pointers to T can still move. > > Boqun, if you pick this up, then please tweak this to: > > // Even if `T` is pinned, pointers to `T` can still move. > Done: https://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git/ rust-sync Thanks! Regards, Boqun > Otherwise, if you want me to pick it up, please let me know -- thanks! > > Cheers, > Miguel
On Thu Dec 18, 2025 at 9:25 AM CET, Alice Ryhl wrote:
> 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: Benno Lossin <lossin@kernel.org>
Cheers,
Benno
> ---
> Changes in v2:
> - Add T: AlwaysRefCounted bound.
> - Link to v1: https://lore.kernel.org/r/20251217-unpin-for-aref-v1-1-84711b747d02@google.com
> ---
> rust/kernel/sync/aref.rs | 3 +++
> 1 file changed, 3 insertions(+)
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`].
///© 2016 - 2026 Red Hat, Inc.