rust: sync: implement == operator for ARef

Rust Binder wants to perform a comparison between ARef<Task> and &Task,
so define the == operator for ARef<_> when compared with another ARef<_>
or just a reference. The operator is implemented in terms of the same
operator applied to the inner type.

Note that PartialEq<U> cannot be implemented because it would overlap
with the impl for ARef<U>.

Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260324-close-fd-check-current-v3-1-b94274bedac7@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

rust/kernel/sync/aref.rs

@@ -170,3 +170,25 @@ fn drop(&mut self) {
         unsafe { T::dec_ref(self.ptr) };
     }
 }
+
+impl<T, U> PartialEq<ARef<U>> for ARef<T>
+where
+    T: AlwaysRefCounted + PartialEq<U>,
+    U: AlwaysRefCounted,
+{
+    #[inline]
+    fn eq(&self, other: &ARef<U>) -> bool {
+        T::eq(&**self, &**other)
+    }
+}
+impl<T: AlwaysRefCounted + Eq> Eq for ARef<T> {}
+
+impl<T, U> PartialEq<&'_ U> for ARef<T>
+where
+    T: AlwaysRefCounted + PartialEq<U>,
+{
+    #[inline]
+    fn eq(&self, other: &&U) -> bool {
+        T::eq(&**self, other)
+    }
+}