Re: [PATCH v3 3/4] rust: devres: get rid of Devres' inner Arc

["Benno Lossin" <lossin@kernel.org>]

On Thu Jun 26, 2025 at 1:07 PM CEST, Danilo Krummrich wrote:
> On Thu, Jun 26, 2025 at 12:27:18PM +0200, Benno Lossin wrote:
>> On Thu Jun 26, 2025 at 12:01 PM CEST, Danilo Krummrich wrote:
>> > On Wed, Jun 25, 2025 at 09:13:24PM -0700, Boqun Feng wrote:
>> >> On Tue, Jun 24, 2025 at 11:54:01PM +0200, Danilo Krummrich wrote:
>> >> [...]
>> >> > +#[pin_data(PinnedDrop)]
>> >> > +pub struct Devres<T> {
>> >> 
>> >> It makes me realize: I think we need to make `T` being `Send`? Because
>> >> the devm callback can happen on a different thread other than
>> >> `Devres::new()` and the callback may drop `T` because of revoke(), so we
>> >> are essientially sending `T`. Alternatively we can make `Devres::new()`
>> >> and its friend require `T` being `Send`.
>> >> 
>> >> If it's true, we need a separate patch that "Fixes" this.
>> >
>> > Indeed, that needs a fix.
>> 
>> Oh and we have no `'static` bound on `T` either... We should require
>> that as well.
>
> I don't think we actually need that, The Devres instance can't out-live a &T
> passed into it. And the &T can't out-live the &Device<Bound>, hence we're
> guaranteed that devres_callback() is never called because Devres::drop() will be
> able successfully unregister the callback given that we're still in the
> &Device<Bound> scope.

Yeah that's correct, I got confused.

> The only thing that could technically out-live the &Device<Bound> would be
> &'static T, but that would obviously be fine.
>
> Do I miss anything?

Nope :)

---
Cheers,
Benno