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

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Message-ID: <aJoEyvq66sD_RtAU@Mac.home>
Date: Mon, 11 Aug 2025 07:57:14 -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 04:37:44PM +0200, Alice Ryhl wrote:
> On Mon, Aug 11, 2025 at 4:31 PM Boqun Feng <boqun.feng@...il.com> wrote:
> >
> > On Mon, Aug 11, 2025 at 04:25:50PM +0200, Alice Ryhl wrote:
> > > On Mon, Aug 11, 2025 at 4:24 PM Boqun Feng <boqun.feng@...il.com> wrote:
> > > >
> > > > On Mon, Aug 11, 2025 at 04:05:31PM +0200, Alice Ryhl wrote:
> > > > > On Mon, Aug 11, 2025 at 3:56 PM Boqun Feng <boqun.feng@...il.com> wrote:
> > > > > >
> > > > > > 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.
[...]
> >
> > Ah, right. I was missing that. Then back to the "we have to mention that
> > we are not accessing the data of Devres" suggestion, which I think is
> > more appropriate for this case.
> 
> I will add:
> 
> // - When `request_irq` is called, everything that `handle_irq_callback`
> //   will touch has already been initialized, so it's safe for the callback
> //   to be called immediately.
> 

This looks good to me.

> Will you offer your Reviewed-by ?
> 

I want to wait and see Daniel's new version with your patch included.
But overall LGTM. Thanks!

Regards,
Boqun

> Alice