linux-kernel - Re: [PATCH v2] rust: irq: add &Device<Bound> argument to irq callbacks

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Message-ID: <aJn2ogBSmedhpuCa@Mac.home>
Date: Mon, 11 Aug 2025 06:56:50 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Daniel Almeida <daniel.almeida@...labora.com>,
	Miguel Ojeda <ojeda@...nel.org>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Wilczy´nski <kwilczynski@...nel.org>,
	Benno Lossin <lossin@...nel.org>, Dirk Behme <dirk.behme@...il.com>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH v2] rust: irq: add &Device<Bound> argument to irq
 callbacks

On Mon, Aug 11, 2025 at 12:33:51PM +0000, Alice Ryhl wrote:
[...]
> @@ -207,8 +207,8 @@ pub fn new<'a>(
>              inner <- Devres::new(
>                  request.dev,
>                  try_pin_init!(RegistrationInner {
> -                    // SAFETY: `this` is a valid pointer to the `Registration` instance
> -                    cookie: unsafe { &raw mut (*this.as_ptr()).handler }.cast(),
> +                    // INVARIANT: `this` is a valid pointer to the `Registration` instance
> +                    cookie: this.as_ptr().cast::<c_void>(),

At this moment the `Regstration` is not fully initialized...

>                      irq: {
>                          // SAFETY:
>                          // - The callbacks are valid for use with request_irq.
> @@ -221,7 +221,7 @@ pub fn new<'a>(
>                                  Some(handle_irq_callback::<T>),
>                                  flags.into_inner(),
>                                  name.as_char_ptr(),
> -                                (&raw mut (*this.as_ptr()).handler).cast(),
> +                                this.as_ptr().cast::<c_void>(),
>                              )

... and interrupt can happen right after request_irq() ...

>                          })?;
>                          request.irq
> @@ -258,9 +258,13 @@ pub fn synchronize(&self, dev: &Device<Bound>) -> Result {
>  ///
>  /// This function should be only used as the callback in `request_irq`.
>  unsafe extern "C" fn handle_irq_callback<T: Handler>(_irq: i32, ptr: *mut c_void) -> c_uint {
> -    // SAFETY: `ptr` is a pointer to T set in `Registration::new`
> -    let handler = unsafe { &*(ptr as *const T) };
> -    T::handle(handler) as c_uint
> +    // SAFETY: `ptr` is a pointer to `Registration<T>` set in `Registration::new`
> +    let registration = unsafe { &*(ptr as *const Registration<T>) };

... hence it's not correct to construct a reference to `Registration`
here, but yes, both `handler` and the `device` part of `inner` has been
properly initialized. So

	let registration = ptr.cast::<Registration<T>>();

	// SAFETY: The `data` part of `Devres` is `Opaque` and here we
	// only access `.device()`, which has been properly initialized
	// before `request_irq()`.
	let device = unsafe { (*registration).inner.device() };
	
	// SAFETY: The irq callback is removed before the device is
	// unbound, so the fact that the irq callback is running implies
	// that the device has not yet been unbound.
	let device = unsafe { device.as_bound() };

	// SAFETY: `.handler` has been properly initialized before
	// `request_irq()`.
	T::handle(unsafe { &(*registration).handler }, device) as c_uint

Thoughts? Similar for the threaded one.

Regards,
Boqun

> +    // SAFETY: The irq callback is removed before the device is unbound, so the fact that the irq
> +    // callback is running implies that the device has not yet been unbound.
> +    let device = unsafe { registration.inner.device().as_bound() };
> +
> +    T::handle(&registration.handler, device) as c_uint
>  }
>  
[...]