Re: [PATCH 2/2] rust: sync: atomic: clarify AtomicAdd safety comment

Gary Guo
2026-04-27T23:04:17Z

On Mon Apr 27, 2026 at 9:32 PM BST, Sagar Taunk wrote:
> The previous safety comment for AtomicAdd was marked with a TODO
> and contained a grammatically broken sentence that was difficult to
> parse. Rewrite the safety requirement to clearly state the actual
> contract: calling wrapping_add with a delta from rhs_into_delta()
> on a repr obtained via into_repr() from a valid Self must produce
> a bit pattern valid for Self.

Where's patch 1/2?

>
> Signed-off-by: Sagar Taunk <sagartaunk2@gmail.com>
> ---
> rust/kernel/sync/atomic.rs | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
> index 9cd009d57e35..b38d9a17f9e8 100644
> --- a/rust/kernel/sync/atomic.rs
> +++ b/rust/kernel/sync/atomic.rs
> @@ -127,10 +127,9 @@ pub unsafe trait AtomicType: Sized + Copy {
> ///
> /// # Safety
> ///
> -// TODO: Properly defines `wrapping_add` in the following comment.
> -/// `wrapping_add` any value of type `Self::Repr::Delta` obtained by [`Self::rhs_into_delta()`] to
> -/// any value of type `Self::Repr` obtained through transmuting a value of type `Self` to must
> -/// yield a value with a bit pattern also valid for `Self`.
> +/// Calling `wrapping_add` with any value of type `Self::Repr::Delta` produced by

It does not read to me there's any clarification being done here.

Best,
Gary

> +/// `Self::rhs_into_delta()`, on any `Self::Repr` value obtained via `into_repr()` from a valid
> +/// `Self`, must produce a bit pattern also valid for `Self`.
> pub unsafe trait AtomicAdd<Rhs = Self>: AtomicType {
> /// Converts `Rhs` into the `Delta` type of the atomic implementation.
> fn rhs_into_delta(rhs: Rhs) -> <Self::Repr as AtomicImpl>::Delta;