Re: [PATCH 5/5] rust: serdev: Pause receive callback before calling unbind

[Danilo Krummrich]

On Sun Sep 6, 2026 at 5:55 PM CEST, Markus Probst wrote:
> @@ -200,10 +203,14 @@ extern "C" fn receive_buf_callback(
>          // INVARIANT: `sdev` is valid for the duration of `receive_buf_callback()`.
>          let sdev = unsafe { &*sdev.cast::<Device<device::BoundInternal>>() };
>  
> -        // SAFETY: `receive_buf_callback` is only ever called after a successful call to
> -        // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
> -        // and stored a `Pin<KBox<PrivateData<'_, T>>>`.
> -        let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
> +        // SAFETY:
> +        // - `receive_buf_callback` is only ever called after a successful call to `probe_callback`,
> +        //   hence it's guaranteed that `Device::set_drvdata()` has been called and stored a
> +        //   `Pin<KBox<PrivateData<'_, T>>>`.
> +        // - `unbind_callback` calls `serdev_device_pause_rx` before accessing the driver data,
> +        //   which guarantees that this function will not overlap with it. Thus we have exclusive
> +        //   access.
> +        let private_data = unsafe { sdev.as_ref().drvdata_borrow_mut::<PrivateData<'_, T>>() };

This would break the driver core's lifetime design. Any kind of registration
(such as class device, auxiliary, IRQ, etc.) may borrow fields from the bus
device private data. The whole design is based on the guarantee that we never
construct a mutable reference of the bus device private data.