linux-kernel - Re: [PATCH v3 10/16] rust: add devres abstraction

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Message-ID: <CAH5fLgg9xkMeGZi_4aN60UMtpvOx2CY5JQc26swMtXTaJsE=-w@mail.gmail.com>
Date: Wed, 27 Nov 2024 14:20:38 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, bhelgaas@...gle.com, 
	ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com, 
	gary@...yguo.net, bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, 
	tmgross@...ch.edu, a.hindborg@...sung.com, airlied@...il.com, 
	fujita.tomonori@...il.com, lina@...hilina.net, pstanner@...hat.com, 
	ajanulgu@...hat.com, lyude@...hat.com, robh@...nel.org, 
	daniel.almeida@...labora.com, saravanak@...gle.com, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v3 10/16] rust: add devres abstraction

On Wed, Nov 27, 2024 at 2:19 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> On 11/27/24 1:21 PM, Alice Ryhl wrote:
> > On Tue, Oct 22, 2024 at 11:33 PM Danilo Krummrich <dakr@...nel.org> wrote:
> >> +impl<T> Drop for Devres<T> {
> >> +    fn drop(&mut self) {
> >> +        // Revoke the data, such that it gets dropped already and the actual resource is freed.
> >> +        // `DevresInner` has to stay alive until the devres callback has been called. This is
> >> +        // necessary since we don't know when `Devres` is dropped and calling
> >> +        // `devm_remove_action()` instead could race with `devres_release_all()`.
> >> +        self.revoke();
> >
> > When the destructor runs, it's guaranteed that nobody is accessing the
> > inner resource since the only way to do that is through the Devres
> > handle, but its destructor is running. Therefore, you can skip the
> > synchronize_rcu() call in this case.
>
> Yeah, I think this optimization should be possible.
>
> We'd require `Revocable` to have a `revoke_nosync` method for that I guess...

Agreed, you could have an unsafe method for revoking where you assert
that nobody else is accessing the value.

Alice