Re: [PATCH v2 3/6] rust: arc: split unsafe block, add missing comment

[Tamir Duberstein]

On Fri, Nov 8, 2024 at 6:38 AM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
> > diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> > index af383bcd003e1122ebe1b62a49fe40279458e379..9adea755a5ad1a7b03f7fc30a7abc76c1f966c6c 100644
> > --- a/rust/kernel/sync/arc.rs
> > +++ b/rust/kernel/sync/arc.rs
> > @@ -377,10 +377,14 @@ fn as_ref(&self) -> &T {
> >
> >  impl<T: ?Sized> Clone for Arc<T> {
> >      fn clone(&self) -> Self {
> > +        // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
> > +        // safe to dereference it.
> > +        let refcount = unsafe { self.ptr.as_ref() }.refcount.get();
>
> I would normally prefer to avoid creating a reference to the entire
> ArcInner, but in this particular case it is okay due to the specifics
> of how Arc works.

Note that this particular line appears also in the Drop impl just
below. That said, can you help me understand the concern with creating
a reference to the entire ArcInner?