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Date: Sun, 06 Sep 2026 18:20:23 +0200
Message-Id: <DL8DCNMSENDS.3T14U5W1Y32IX@kernel.org>
Subject: Re: [PATCH 5/5] rust: serdev: Pause receive callback before calling
 unbind
Cc: "Ayush Singh" <ayush@beagleboard.org>, "Johan Hovold"
 <johan@kernel.org>, "Alex Elder" <elder@kernel.org>, "Greg Kroah-Hartman"
 <gregkh@linuxfoundation.org>, "Miguel Ojeda" <ojeda@kernel.org>, "Boqun
 Feng" <boqun@kernel.org>, "Gary Guo" <gary@garyguo.net>,
 =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, "Benno Lossin"
 <lossin@kernel.org>, "Andreas Hindborg" <a.hindborg@kernel.org>, "Alice
 Ryhl" <aliceryhl@google.com>, "Trevor Gross" <tmgross@umich.edu>, "Daniel
 Almeida" <daniel.almeida@collabora.com>, "Tamir Duberstein"
 <tamird@kernel.org>, "Alexandre Courbot" <acourbot@nvidia.com>,
 =?utf-8?q?Onur_=C3=96zkan?= <work@onurozkan.dev>, "Eric Biggers"
 <ebiggers@kernel.org>, "Ard Biesheuvel" <ardb@kernel.org>, "Lorenzo
 Stoakes" <ljs@kernel.org>, "Vlastimil Babka" <vbabka@kernel.org>, "Liam R.
 Howlett" <liam@infradead.org>, "Uladzislau Rezki" <urezki@gmail.com>, "Jiri
 Slaby" <jirislaby@kernel.org>, "Rafael J. Wysocki" <rafael@kernel.org>,
 <greybus-dev@lists.linaro.org>, <linux-serial@vger.kernel.org>,
 <rust-for-linux@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
 <driver-core@lists.linux.dev>
To: "Markus Probst" <markus.probst@posteo.de>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20260906-rust_serdev_probe_refactor-v1-0-69cdae0074ec@posteo.de> <20260906-rust_serdev_probe_refactor-v1-5-69cdae0074ec@posteo.de>
In-Reply-To: <20260906-rust_serdev_probe_refactor-v1-5-69cdae0074ec@posteo.de>

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_c=
allback()`.
>          let sdev =3D unsafe { &*sdev.cast::<Device<device::BoundInternal=
>>() };
> =20
> -        // SAFETY: `receive_buf_callback` is only ever called after a su=
ccessful call to
> -        // `probe_callback`, hence it's guaranteed that `Device::set_drv=
data()` has been called
> -        // and stored a `Pin<KBox<PrivateData<'_, T>>>`.
> -        let private_data =3D unsafe { sdev.as_ref().drvdata_borrow::<Pri=
vateData<'_, T>>() };
> +        // SAFETY:
> +        // - `receive_buf_callback` is only ever called after a successf=
ul 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 acc=
essing the driver data,
> +        //   which guarantees that this function will not overlap with i=
t. Thus we have exclusive
> +        //   access.
> +        let private_data =3D unsafe { sdev.as_ref().drvdata_borrow_mut::=
<PrivateData<'_, T>>() };

This would break the driver core's lifetime design. Any kind of registratio=
n
(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 nev=
er
construct a mutable reference of the bus device private data.