Re: [PATCH] i2c: rust: fix I2cAdapter refcounts double increment

[Onur Özkan]

Hi Nicolás

On Sun, 24 May 2026 15:11:50 -0300
Nicolás Antinori <nico.antinori.7@xxxxxxxxx> wrote:

> When `I2cAdapter::get` executes, it first calls
> `bindings::i2c_get_adapter()` which increments the device and module
> reference counts. It then takes a reference to the raw pointer and
> converts it to an `ARef` via `.into()`.
> 
> The implementation of `From<&T> for ARef<T>` where `T: AlwaysRefCounted`
> unconditionally calls `T::inc_ref()`. This leads to a second call to
> `bindings::i2c_get_adapter()` inside `I2cAdapter::inc_ref()`.
> 
> Since the returned `ARef` will only release a single reference when
> dropped via `dec_ref()`, this leaks one device and module reference count
> on every call.
> 
> This fix was suggested by sashiko.dev.

Including the link tag would be great.

> 
> Signed-off-by: Nicolás Antinori <nico.antinori.7@xxxxxxxxx>
> ---
>  rust/kernel/i2c.rs | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/kernel/i2c.rs b/rust/kernel/i2c.rs
> index 7b908f0c5a58..ca6476cf4399 100644
> --- a/rust/kernel/i2c.rs
> +++ b/rust/kernel/i2c.rs
> @@ -405,7 +405,11 @@ pub fn get(index: i32) -> Result<ARef<Self>> {
>  
>          // SAFETY: `adapter` is non-null and points to a live `i2c_adapter`.
>          // `I2cAdapter` is #[repr(transparent)], so this cast is valid.
> -        Ok(unsafe { (&*adapter.as_ptr().cast::<I2cAdapter<device::Normal>>()).into() })
> +        Ok(unsafe {
> +            ARef::from_raw(NonNull::new_unchecked(
> +                adapter.as_ptr().cast::<I2cAdapter<device::Normal>>(),
> +            ))
> +        })
>      }
>  }
>  
> -- 
> 2.53.0
>