2 files changed, 20 insertions, 5 deletions

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 9298993ea7d8..289f77abf415 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -19,6 +19,7 @@
 use crate::{
     alloc::{AllocError, Flags, KBox},
     ffi::c_void,
+    fmt,
     init::InPlaceInit,
     sync::Refcount,
     try_init,
@@ -27,7 +28,6 @@ use crate::{
 use core::{
     alloc::Layout,
     borrow::{Borrow, BorrowMut},
-    fmt,
     marker::PhantomData,
     mem::{ManuallyDrop, MaybeUninit},
     ops::{Deref, DerefMut},
@@ -367,10 +367,10 @@ impl<T: ?Sized> Arc<T> {
     }
 }
 
-// SAFETY: The pointer returned by `into_foreign` comes from a well aligned
-// pointer to `ArcInner<T>`.
+// SAFETY: The pointer returned by `into_foreign` was originally allocated as an
+// `KBox<ArcInner<T>>`, so that type is what determines the alignment.
 unsafe impl<T: 'static> ForeignOwnable for Arc<T> {
-    const FOREIGN_ALIGN: usize = core::mem::align_of::<ArcInner<T>>();
+    const FOREIGN_ALIGN: usize = <KBox<ArcInner<T>> as ForeignOwnable>::FOREIGN_ALIGN;
 
     type Borrowed<'a> = ArcBorrow<'a, T>;
     type BorrowedMut<'a> = Self::Borrowed<'a>;
diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs
index dbd77bb68617..0d24a0432015 100644
--- a/rust/kernel/sync/aref.rs
+++ b/rust/kernel/sync/aref.rs
@@ -1,6 +1,21 @@
 // SPDX-License-Identifier: GPL-2.0
 
 //! Internal reference counting support.
+//!
+//! Many C types already have their own reference counting mechanism (e.g. by storing a
+//! `refcount_t`). This module provides support for directly using their internal reference count
+//! from Rust; instead of making users have to use an additional Rust-reference count in the form of
+//! [`Arc`].
+//!
+//! The smart pointer [`ARef<T>`] acts similarly to [`Arc<T>`] in that it holds a refcount on the
+//! underlying object, but this refcount is internal to the object. It essentially is a Rust
+//! implementation of the `get_` and `put_` pattern used in C for reference counting.
+//!
+//! To make use of [`ARef<MyType>`], `MyType` needs to implement [`AlwaysRefCounted`]. It is a trait
+//! for accessing the internal reference count of an object of the `MyType` type.
+//!
+//! [`Arc`]: crate::sync::Arc
+//! [`Arc<T>`]: crate::sync::Arc
 
 use core::{marker::PhantomData, mem::ManuallyDrop, ops::Deref, ptr::NonNull};
 
@@ -97,7 +112,7 @@ impl<T: AlwaysRefCounted> ARef<T> {
     ///
     /// ```
     /// use core::ptr::NonNull;
-    /// use kernel::types::{ARef, AlwaysRefCounted};
+    /// use kernel::sync::aref::{ARef, AlwaysRefCounted};
     ///
     /// struct Empty {}
     ///