Received-SPF: pass (google.com: domain of linux-kernel+bounces-210219-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Feedback-ID: iad51458e:Fastmail
Date: Tue, 11 Jun 2024 09:13:20 -0700
From: Boqun Feng <boqun.feng@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Danilo Krummrich <dakr@redhat.com>, rafael@kernel.org,
	mcgrof@kernel.org, russell.h.weight@intel.com, ojeda@kernel.org,
	alex.gaynor@gmail.com, wedsonaf@gmail.com, gary@garyguo.net,
	bjorn3_gh@protonmail.com, benno.lossin@proton.me,
	a.hindborg@samsung.com, aliceryhl@google.com, airlied@gmail.com,
	fujita.tomonori@gmail.com, pstanner@redhat.com, ajanulgu@redhat.com,
	lyude@redhat.com, rust-for-linux@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] rust: add abstraction for struct device
Message-ID: <Zmh3oN9sWamaYHOD@Boquns-Mac-mini.home>
References: <20240610180318.72152-1-dakr@redhat.com>
 <20240610180318.72152-2-dakr@redhat.com>
 <ZmdID8AlXtoxUfC1@boqun-archlinux>
 <ZmhPW9yq7y6jbmIg@pollux>
 <2024061136-unbridle-confirm-c653@gregkh>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <2024061136-unbridle-confirm-c653@gregkh>

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