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Message-Id: <DAU5TAFKJQOF.2DFO7YAHZA4V2@kernel.org>
Date: Mon, 23 Jun 2025 21:28:53 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>
Cc: "Alice Ryhl" <aliceryhl@...gle.com>, "Danilo Krummrich"
<dakr@...nel.org>, "Daniel Almeida" <daniel.almeida@...labora.com>, "Miguel
Ojeda" <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...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>, "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>, <linux-kernel@...r.kernel.org>,
<rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v4 3/6] rust: irq: add support for non-threaded IRQs and
handlers
On Mon Jun 23, 2025 at 9:18 PM CEST, Boqun Feng wrote:
> On Mon, Jun 23, 2025 at 10:31:16AM -0700, Boqun Feng wrote:
>> On Mon, Jun 23, 2025 at 05:26:14PM +0200, Benno Lossin wrote:
>> > On Mon Jun 23, 2025 at 5:10 PM CEST, Alice Ryhl wrote:
>> > > On Mon, Jun 9, 2025 at 12:47 PM Danilo Krummrich <dakr@...nel.org> wrote:
>> > >> On Sun, Jun 08, 2025 at 07:51:08PM -0300, Daniel Almeida wrote:
>> > >> > + dev: &'a Device<Bound>,
>> > >> > + irq: u32,
>> > >> > + flags: Flags,
>> > >> > + name: &'static CStr,
>> > >> > + handler: T,
>> > >> > + ) -> impl PinInit<Self, Error> + 'a {
>> > >> > + let closure = move |slot: *mut Self| {
>> > >> > + // SAFETY: The slot passed to pin initializer is valid for writing.
>> > >> > + unsafe {
>> > >> > + slot.write(Self {
>> > >> > + inner: Devres::new(
>> > >> > + dev,
>> > >> > + RegistrationInner {
>> > >> > + irq,
>> > >> > + cookie: slot.cast(),
>> > >> > + },
>> > >> > + GFP_KERNEL,
>> > >> > + )?,
>> > >> > + handler,
>> > >> > + _pin: PhantomPinned,
>> > >> > + })
>> > >> > + };
>> > >> > +
>> > >> > + // SAFETY:
>> > >> > + // - The callbacks are valid for use with request_irq.
>> > >> > + // - If this succeeds, the slot is guaranteed to be valid until the
>> > >> > + // destructor of Self runs, which will deregister the callbacks
>> > >> > + // before the memory location becomes invalid.
>> > >> > + let res = to_result(unsafe {
>> > >> > + bindings::request_irq(
>> > >> > + irq,
>> > >> > + Some(handle_irq_callback::<T>),
>> > >> > + flags.into_inner() as usize,
>> > >> > + name.as_char_ptr(),
>> > >> > + slot.cast(),
>> > >> > + )
>> > >> > + });
>> > >> > +
>> > >> > + if res.is_err() {
>> > >> > + // SAFETY: We are returning an error, so we can destroy the slot.
>> > >> > + unsafe { core::ptr::drop_in_place(&raw 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) }
>> > >>
>> > >> Can't we use try_pin_init!() instead, move request_irq() into the initializer of
>> > >> RegistrationInner and initialize inner last?
>> > >
>> > > We need a pointer to the entire struct when calling
>> > > bindings::request_irq. I'm not sure this allows you to easily get one?
>> > > I don't think using container_of! here is worth it.
>> >
>> > There is the `&this in` syntax (`this` is of type `NonNull<Self>`):
>> >
>> > try_pin_init!(&this in Self {
>> > inner: Devres::new(
>> > dev,
>> > RegistrationInner {
>> > irq,
>> > cookie: this.as_ptr().cast(),
>> > },
>> > GFP_KERNEL,
>> > )?,
>> > handler,
>> > _pin: {
>> > to_result(unsafe {
>> > bindings::request_irq(
>> > irq,
>> > Some(handle_irq_callback::<T>),
>> > flags.into_inner() as usize,
>> > name.as_char_ptr(),
>> > slot.as_ptr().cast(),
>>
>> this is "this" instead of "slot", right?
>>
>> > )
>> > })?;
>> > PhantomPinned
>> > },
>> > })
>> >
>> > Last time around, I also asked this question and you replied with that
>> > we need to abort the initializer when `request_irq` returns false and
>> > avoid running `Self::drop` (thus we can't do it using `pin_chain`).
>> >
>> > I asked what we could do instead and you mentioned the `_: {}`
>> > initializers and those would indeed solve it, but we can abuse the
>> > `_pin` field for that :)
>> >
>>
>> Hmm.. but if request_irq() fails, aren't we going to call `drop` on
>> `inner`, which drops the `Devres` which will eventually call
>> `RegistrationInner::drop()`? And that's a `free_irq()` without
>> `request_irq()` succeeded.
>>
>
> This may however work ;-) Because at `request_irq()` time, all it needs
> is ready, and if it fails, `RegistrationInner` won't construct.
>
> try_pin_init!(&this in Self {
> handler,
> inner: Devres::new(
> dev,
> RegistrationInner {
> // Needs to use `handler` address as cookie, same for
> // request_irq().
> cookie: &raw (*(this.as_ptr().cast()).handler),
> irq: {
> to_result(unsafe { bindings::request_irq(...) })?;
> irq
> }
> },
> GFP_KERNEL,
> )?,
> _pin: PhantomPinned
> })
Well yes and no, with the Devres changes, the `cookie` can just be the
address of the `RegistrationInner` & we can do it this way :)
---
Cheers,
Benno
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