Re: [PATCH v3 1/2] rust: irq: add support for request_irq()

[Alice Ryhl <aliceryhl@google.com>]

On Wed, May 14, 2025 at 10:04:43PM +0200, Benno Lossin wrote:
> On Wed May 14, 2025 at 9:20 PM CEST, Daniel Almeida wrote:
> > +                )
> > +            });
> > +
> > +            if res.is_err() {
> > +                // SAFETY: We are returning an error, so we can destroy the slot.
> > +                unsafe { core::ptr::drop_in_place(addr_of_mut!((*slot).handler)) };
> > +            }
> > +
> > +            res
> > +        };
> > +
> > +        // SAFETY:
> > +        // - if this returns Ok, then every field of `slot` is fully
> > +        // initialized.
> > +        // - if this returns an error, then the slot does not need to remain
> > +        // valid.
> > +        unsafe { pin_init_from_closure(closure) }
> 
> Please don't use `pin_init_from_closure`, instead do this:
> 
>     pin_init!(Self {
>         irq,
>         handler,
>         _pin: PhantomPinned
>     })
>     .pin_chain(|this| {
>         // SAFETY: TODO: correct FFI safety requirements
>         to_result(unsafe {
>             bindings::request_irq(...)
>         })
>     })
> 
> The `pin_chain` function is exactly for this use-case, doing some
> operation that might fail after initializing & it will drop the value
> when the closure fails.

No, that doesn't work. Using pin_chain will call free_irq if the call to
request_irq fails, which is incorrect.

Alice