linux-kernel - Re: [PATCH v7 3/6] rust: irq: add support for non-threaded IRQs and handlers

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Message-ID: <aIEDbB_FcgHgzfKd@google.com>
Date: Wed, 23 Jul 2025 15:44:44 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Daniel Almeida <daniel.almeida@...labora.com>, Boqun Feng <boqun.feng@...il.com>, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, 
	"Krzysztof Wilczy´nski" <kwilczynski@...nel.org>, Benno Lossin <lossin@...nel.org>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v7 3/6] rust: irq: add support for non-threaded IRQs and handlers

On Wed, Jul 23, 2025 at 05:03:12PM +0200, Danilo Krummrich wrote:
> On Wed Jul 23, 2025 at 4:56 PM CEST, Daniel Almeida wrote:
> >> On 23 Jul 2025, at 11:35, Danilo Krummrich <dakr@...nel.org> wrote:
> >> On 7/23/25 4:26 PM, Boqun Feng wrote:
> >>> On Wed, Jul 23, 2025 at 10:55:20AM -0300, Daniel Almeida wrote:
> >>> But sure, this and the handler pinned initializer thing is not a blocker
> >>> issue. However, I would like to see them resolved as soon as possible
> >>> once merged.
> >> 
> >> I think it would be trivial to make the T an impl PinInit<T, E> and use a
> >> completion as example instead of an atomic. So, we should do it right away.
> >> 
> >> - Danilo
> >
> >
> > I agree that this is a trivial change to make. My point here is not to postpone
> > the work; I am actually somewhat against switching to completions, as per the
> > reasoning I provided in my latest reply to Boqun. My plan is to switch directly
> > to whatever will substitute AtomicU32.
> 
> I mean, Boqun has a point. AFAIK, the Rust atomics are UB in the kernel.
> 
> So, this is a bit as if we would use spin_lock() instead of spin_lock_irq(),
> it's just not correct. Hence, we may not want to showcase it until it's actually
> resolved.
> 
> The plain truth is, currently there's no synchronization primitive for getting
> interior mutability in interrupts.

Is the actual argument here "we are getting rid of Rust atomics in the
next cycle, so please don't introduce any more users during the next
cycle because if you do it will take one cycle longer to get rid of
all Rust atomics"?

I can accept that argument. But I don't accept the argument that we
shouldn't use them here because of the UB technicality. That is an
isolated demand for rigor and I think it is unreasonable. Using Rust
atomics is an accepted workaround until the LKMM atomics land.

Alice