linux-kernel - Re: [PATCH v2 1/2] rust: add abstraction for struct device

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Date: Tue, 11 Jun 2024 09:13:20 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Danilo Krummrich <dakr@...hat.com>, rafael@...nel.org,
	mcgrof@...nel.org, russell.h.weight@...el.com, ojeda@...nel.org,
	alex.gaynor@...il.com, wedsonaf@...il.com, gary@...yguo.net,
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	a.hindborg@...sung.com, aliceryhl@...gle.com, airlied@...il.com,
	fujita.tomonori@...il.com, pstanner@...hat.com, ajanulgu@...hat.com,
	lyude@...hat.com, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] rust: add abstraction for struct device

On Tue, Jun 11, 2024 at 03:29:22PM +0200, Greg KH wrote:
> On Tue, Jun 11, 2024 at 03:21:31PM +0200, Danilo Krummrich wrote:
> > ...hence, I agree we should indeed add to the #Invariants and #Safety section
> > that `->release` must be callable  from any thread.
> > 
> > However, this is just theory, do we actually have cases where `device::release`

@Danilo, right, it's only theorical, but it's good to call it out since
it's the requirement for a safe Rust abstraction.

> > is not allowed to be called from any thread? If so, this would be very confusing
> > for a reference counted type from a design point of view...
> 
> What do you mean exactly "by any thread"?  Maybe not from interrupt

The `Send` trait here doesn't really differ between interrupt contexts
and process contexts, so "by any thread", it includes all the contexts.
However, we rely on klint[1] to detect context mismatch in compile time
(it's still a WIP though). For this case, we would need to mark the
`Device::dec_ref` function as might sleep.

Regards,
Boqun

[1]: https://rust-for-linux.com/klint

> context, but any other normal thread (i.e. that you can sleep in), it
> should be fine to call release() in.
> 
> thanks,
> 
> greg k-h