linux-kernel - Re: [PATCH 1/2] rust: pci: impl Send + Sync for pci::Device

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Message-ID: <Z9rP8BO1rAYI7UBK@cassiopeiae>
Date: Wed, 19 Mar 2025 15:08:48 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: bhelgaas@...gle.com, gregkh@...uxfoundation.org, rafael@...nel.org,
	ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com,
	gary@...yguo.net, bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	a.hindborg@...nel.org, tmgross@...ch.edu, linux-pci@...r.kernel.org,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] rust: pci: impl Send + Sync for pci::Device

On Wed, Mar 19, 2025 at 02:50:49PM +0100, Danilo Krummrich wrote:
> On Wed, Mar 19, 2025 at 02:30:31PM +0100, Danilo Krummrich wrote:
> > On Wed, Mar 19, 2025 at 01:16:52PM +0000, Alice Ryhl wrote:
> > > On Wed, Mar 19, 2025 at 01:47:01PM +0100, Danilo Krummrich wrote:
> > > > On Wed, Mar 19, 2025 at 12:05:13PM +0000, Alice Ryhl wrote:
> > > > > On Tue, Mar 18, 2025 at 10:29:21PM +0100, Danilo Krummrich wrote:
> > > > > > Commit 7b948a2af6b5 ("rust: pci: fix unrestricted &mut pci::Device")
> > > > > > changed the definition of pci::Device and discarded the implicitly
> > > > > > derived Send and Sync traits.
> > > > > > 
> > > > > > This isn't required by upstream code yet, and hence did not cause any
> > > > > > issues. However, it is relied on by upcoming drivers, hence add it back
> > > > > > in.
> > > > > > 
> > > > > > Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> > > > > 
> > > > > I have a question related to this ... does the Driver trait need to
> > > > > require T: Send?
> > > > 
> > > > The driver trait does not have a generic, it doesn't need one. But I think I
> > > > still get what you're asking.
> > 
> > Turns out I did not. :)
> > 
> > > Right I mean, should it be:
> > > 
> > > trait Driver: Send + Sync {
> > >     ...
> > > }
> > 
> > Yes, you're absolutely right with this, thanks for pointing this out.
> 
> Just to clarify, the reason we need Sync is that we want to be able to access
> the driver's private data from an IRQ handler. Otherwise, we can only ever
> safely access the driver's private data from bus callbacks, which should be
> synchronized by the device' mutex.

On the other hand, that's up to the IRQ handler abstraction. So, we really
should be good with only requiring Send.

> 
> > 
> > > 
> > > > The driver trait never owns a shared reference of the device, it only ever gives
> > > > out a reference that the driver core guarantees to be valid.
> > > > 
> > > > > The change itself LGTM, so:
> > > > > 
> > > > > Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> > > > > 
> > > > > Alice