On Tue, Jun 24, 2025 at 07:33:35AM -0700, Boqun Feng wrote:
> On Tue, Jun 24, 2025 at 02:50:23PM +0100, Alice Ryhl wrote:
> > On Tue, Jun 24, 2025 at 1:46 PM Benno Lossin <lossin@xxxxxxxxxx> wrote:
> > >
> > > On Tue Jun 24, 2025 at 2:31 PM CEST, Daniel Almeida wrote:
> > > > On 23 Jun 2025, at 16:28, Benno Lossin <lossin@xxxxxxxxxx> wrote:
> > > >> On Mon Jun 23, 2025 at 9:18 PM CEST, Boqun Feng wrote:
> > > >>> 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
> > > >
> > > >
> > > > No, we need this to be the address of the the whole thing (i.e.
> > > > Registration<T>), otherwise you can’t access the handler in the irq
> > > > callback.
>
> You only need the access of `handler` in the irq callback, right? I.e.
> passing the address of `handler` would suffice (of course you need
> to change the irq callback as well).
>
> > >
> > > Gotcha, so you keep the cookie field, but you should still be able to
> > > use `try_pin_init` & the devres improvements to avoid the use of
> > > `pin_init_from_closure`.
> >
> > It sounds like this is getting too complicated and that
> > `pin_init_from_closure` is the simpler way to go.
>
> Even if we use `pin_init_from_closure`, we still need the other
> `try_pin_init` anyway for `Devres::new()` (or alternatively we can
> implement a `RegistrationInner::new()`).
>
> Below is what would look like with the Devres changes in mind:
>
>
> try_pin_init!(&this in Self {
> handler,
> inner: <- Devres::new(
> dev,
> try_pin_init!( RegistrationInner {
> // Needs to use `handler` address as cookie, same for
> // request_irq().
> cookie: &raw (*(this.as_ptr().cast()).handler),
> // @Benno, would this "this" work here?
> irq: {
> to_result(unsafe { bindings::request_irq(...) })?;
> irq
> }
> }),
> )?,
> _pin: PhantomPinned
> })
>
>
Never mind, `dev` is a `Device<Bound>` so it cannot be unbounded during
the call ;-)
Regards,
Boqun
> Besides, working on this made me realize that we have to request_irq()
> before `Devres::new()`, otherwise we may leak the irq resource,
> considering the follow code from the current `pin_init_from_closure`
> approach:
>
> 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,
> })
> };
>
> `dev` can be unbound at here, right? If so, the devm callback will
> revoke the `RegistrationInner`, `RegistrationInner::drop()` will then
> call `free_irq()` before `request_irq()`, the best case is that we would
> request_irq() with no one going to free it.
>
> // 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(),
> )
> });
> ...
> }
>
> So seems to me the order of initialization has to be:
>
> 1. Initialize the `handler`.
> 2. `request_irq()`, i.e initialize the `RegistrationInner`.
> 3. `Devres::new()`, i.e initialize the `Devres`.
>
> Regards,
> Boqun
