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

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Message-ID: <CAH5fLghRi-QAqGdxOhPPdp6bMyGSuDifnxMFBn3a3NWzN4G4vQ@mail.gmail.com>
Date: Mon, 21 Jul 2025 21:33:32 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, 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 Wilczyński <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] rust: irq: add &Device<Bound> argument to irq callbacks

On Mon, Jul 21, 2025 at 9:14 PM Daniel Almeida
<daniel.almeida@...labora.com> wrote:
>
> Alice,
>
> > On 21 Jul 2025, at 11:38, Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > When working with a bus device, many operations are only possible while
> > the device is still bound. The &Device<Bound> type represents a proof in
> > the type system that you are in a scope where the device is guaranteed
> > to still be bound. Since we deregister irq callbacks when unbinding a
> > device, if an irq callback is running, that implies that the device has
> > not yet been unbound.
> >
> > To allow drivers to take advantage of that, add an additional argument
> > to irq callbacks.
> >
> > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> > ---
> > This patch is a follow-up to Daniel's irq series [1] that adds a
> > &Device<Bound> argument to all irq callbacks. This allows you to use
> > operations that are only safe on a bound device inside an irq callback.
> >
> > The patch is otherwise based on top of driver-core-next.
> >
> > [1]: https://lore.kernel.org/r/20250715-topics-tyr-request_irq2-v7-0-d469c0f37c07@collabora.com
>
> I am having a hard time applying this locally.

Your irq series currently doesn't apply cleanly on top of
driver-core-next and requires resolving a minor conflict. You can find
the commits here:
https://github.com/Darksonn/linux/commits/sent/20250721-irq-bound-device-c9fdbfdd8cd9-v1/

> > ///
> > /// 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>) };
> > +    // 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() };
>
> Where was this function introduced? i.e. I am missing the change that brought
> in RegistrationInner::device(), or maybe some Deref impl that would make this
> possible?

In this series:
https://lore.kernel.org/all/20250713182737.64448-2-dakr@kernel.org/

> Also, I wonder if we can't make the scope of this unsafe block smaller?

I guess we could with an extra `let` statement.

Alice