On Mon, Aug 11, 2025 at 3:56 PM Boqun Feng <boqun.feng@xxxxxxxxx> 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.
This code is no different. It creates a reference to `inner` before
the `irq` field is written. Of course, it's also no different in that
since data of a `Devres` is in `Opaque`, this is not actually UB.
What I can offer you is to use the closure form of pin-init to call
request_irq after initialization has fully completed.
Alice
