1 files changed, 15 insertions, 20 deletions

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 29db59d6119a..d479f8da8f38 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -35,34 +35,16 @@ pub trait ForeignOwnable: Sized {
     ///
     /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
     /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
-    /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow_mut`]
-    /// for this object must have been dropped.
     unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a>;
 
-    /// Mutably borrows a foreign-owned object.
-    ///
-    /// # Safety
-    ///
-    /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
-    /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
-    /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and
-    /// [`ForeignOwnable::borrow_mut`] for this object must have been dropped.
-    unsafe fn borrow_mut(ptr: *const core::ffi::c_void) -> ScopeGuard<Self, fn(Self)> {
-        // SAFETY: The safety requirements ensure that `ptr` came from a previous call to
-        // `into_foreign`.
-        ScopeGuard::new_with_data(unsafe { Self::from_foreign(ptr) }, |d| {
-            d.into_foreign();
-        })
-    }
-
     /// Converts a foreign-owned object back to a Rust-owned one.
     ///
     /// # Safety
     ///
     /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
     /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
-    /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and
-    /// [`ForeignOwnable::borrow_mut`] for this object must have been dropped.
+    /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] for
+    /// this object must have been dropped.
     unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self;
 }
 
@@ -321,6 +303,19 @@ pub struct ARef<T: AlwaysRefCounted> {
     _p: PhantomData<T>,
 }
 
+// SAFETY: It is safe to send `ARef<T>` to another thread when the underlying `T` is `Sync` because
+// it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
+// `T` to be `Send` because any thread that has an `ARef<T>` may ultimately access `T` using a
+// mutable reference, for example, when the reference count reaches zero and `T` is dropped.
+unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {}
+
+// SAFETY: It is safe to send `&ARef<T>` to another thread when the underlying `T` is `Sync`
+// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
+// it needs `T` to be `Send` because any thread that has a `&ARef<T>` may clone it and get an
+// `ARef<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
+// example, when the reference count reaches zero and `T` is dropped.
+unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {}
+
 impl<T: AlwaysRefCounted> ARef<T> {
     /// Creates a new instance of [`ARef`].
     ///