linux-kernel - Re: [PATCH v3 1/2] rust: irq: add support for request

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Message-ID: <aD3BN7-MAyYq2NAX@google.com>
Date: Mon, 2 Jun 2025 15:20:23 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Benno Lossin <lossin@...nel.org>
Cc: Daniel Almeida <daniel.almeida@...labora.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	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>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3 1/2] rust: irq: add support for request_irq()

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