Re: [PATCH v3 07/27] rust: auxiliary: implement Sync for Device<Bound>

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The commit implements `Sync` for `Device<device::Bound>` but omits the corresponding `Send` implementation.
--

commit 2db1931adb556a37661b5663fe290ef2d37425ff
Author: Danilo Krummrich <dakr@kernel.org>
rust: auxiliary: implement Sync for Device<Bound>

This commit implements the Sync trait for Device<Bound> in the auxiliary
bus abstraction. This allows drivers to safely store shared references to
the bound device in their private data.

> diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
> --- a/rust/kernel/auxiliary.rs
> +++ b/rust/kernel/auxiliary.rs

[ ... ]

> @@ -369,6 +369,10 @@ unsafe impl Send for Device {}
>  // (i.e. `Device<Normal>) are thread safe.
>  unsafe impl Sync for Device {}
>  
> +// SAFETY: Same as `Device<Normal>` -- the underlying `struct auxiliary_device` is the same;
> +// `Bound` is a zero-sized type-state marker that does not affect thread safety.
> +unsafe impl Sync for Device<device::Bound> {}

Should we also implement Send for Device<device::Bound>?

The commit message correctly notes that the Bound type-state marker is
zero-sized and does not alter the thread safety properties of the underlying
auxiliary_device struct. However, omitting the Send implementation creates
an API asymmetry compared to Device<Normal>.

Because ARef<T> requires T: Send + Sync for the reference-counted pointer
itself to be Send, the missing Send implementation prevents drivers from
safely sending an ARef<Device<Bound>> across threads.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260517000149.3226762-1-dakr@kernel.org?part=7