Re: [PATCH v20 5/8] rust: rename `AlwaysRefCounted` to `RefCounted`.

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The `GpuVm` and `GpuVmBo` types in the DRM GPUVM subsystem were not updated to reflect the `AlwaysRefCounted` and `RefCounted` trait split, resulting in a compilation failure.
--

--- Patch [5]: [PATCH v20 5/8] rust: rename `AlwaysRefCounted` to `RefCounted`. ---
commit 7d343e09ba4b06050b444e30c1113ca349f25a78
Author: Oliver Mangold <oliver.mangold@pm.me>

rust: rename AlwaysRefCounted to RefCounted.

This commit splits the AlwaysRefCounted trait into RefCounted and a new 
marker trait AlwaysRefCounted. It updates several subsystems to implement 
the new RefCounted trait while preserving the AlwaysRefCounted marker where 
appropriate.

> diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs
> index 3bd5eb8a1a526..ea5a16b8163a6 100644
> --- a/rust/kernel/sync/aref.rs
> +++ b/rust/kernel/sync/aref.rs
[ ... ]
> @@ -45,9 +43,8 @@
>  /// at least until matching decrements are performed.
>  ///
>  /// Implementers must also ensure that all instances are reference-counted. (Otherwise they
> -/// won't be able to honour the requirement that [`AlwaysRefCounted::inc_ref`] keep the object
> -/// alive.)
> -pub unsafe trait AlwaysRefCounted {
> +/// won't be able to honour the requirement that [`RefCounted::inc_ref`] keep the object alive.)
> +pub unsafe trait RefCounted {
>      /// Increments the reference count on the object.
>      fn inc_ref(&self);

[Severity: Low]
Did this patch miss updating the DRM GPUVM subsystem? 

When CONFIG_RUST_DRM_GPUVM is enabled, the build fails because GpuVm and 
GpuVmBo are still trying to implement inc_ref() and dec_ref() under the 
AlwaysRefCounted trait instead of RefCounted.

For example, in rust/kernel/drm/gpuvm/mod.rs:

unsafe impl<T: DriverGpuVm> AlwaysRefCounted for GpuVm<T> {
    fn inc_ref(&self) {
        // SAFETY: By type invariants, the allocation is managed by the refcount in self.vm.
        unsafe { bindings::drm_gpuvm_get(self.vm.get()) };
    }
    ...
}

And similarly in rust/kernel/drm/gpuvm/vm_bo.rs for GpuVmBo:

unsafe impl<T: DriverGpuVm> AlwaysRefCounted for GpuVmBo<T> {
    fn inc_ref(&self) {
        // SAFETY: By type invariants, the allocation is managed by the refcount in self.inner.
        unsafe { bindings::drm_gpuvm_bo_get(self.inner.get()) };
    }
    ...
}

Should these implementations be updated to use the new RefCounted trait to 
match the changes made to the other subsystems?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260824-unique-ref-v20-0-490735672187@kernel.org?part=5