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

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Nov 4, 2024 at 10:20 PM Tamir Duberstein <tamird@gmail.com> wrote:
>
> The new SAFETY comment style is taken from existing comments in `deref`
> and `drop.
>
> Signed-off-by: Tamir Duberstein <tamird@gmail.com>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

> 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.

Alice