SAFETY comment in rustdoc example was just 'TODO'. Fixed.

Signed-off-by: Oliver Mangold <oliver.mangold@pm.me>
---
 rust/kernel/sync/aref.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs
index e029b4c046449a6b0bb61bb6369ac26f9495b2ad..97cfddd9ec2ad788a4a659f404a9b6790da08e29 100644
--- a/rust/kernel/sync/aref.rs
+++ b/rust/kernel/sync/aref.rs
@@ -119,7 +119,9 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
     ///
     /// struct Empty {}
     ///
-    /// # // SAFETY: TODO.
+    /// // SAFETY: The `RefCounted` implementation for `Empty` does not count references and
+    /// // never frees the underlying object. Thus we can act as having a refcount on the object
+    /// // that we pass to the newly created `ARef`.
     /// unsafe impl RefCounted for Empty {
     ///     fn inc_ref(&self) {}
     ///     unsafe fn dec_ref(_obj: NonNull<Self>) {}
@@ -127,7 +129,7 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
     ///
     /// let mut data = Empty {};
     /// let ptr = NonNull::<Empty>::new(&mut data).unwrap();
-    /// # // SAFETY: TODO.
+    /// // SAFETY: We keep `data` around longer than the `ARef`.
     /// let data_ref: ARef<Empty> = unsafe { ARef::from_raw(ptr) };
     /// let raw_ptr: NonNull<Empty> = ARef::into_raw(data_ref);
     ///

-- 
2.51.0