linux-kernel - Re: [PATCH v3 1/2] rust: irq: add support for request

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Message-ID: <aD7DvBfAxKi7Fpg_@cassiopeiae>
Date: Tue, 3 Jun 2025 11:43:24 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Daniel Almeida <daniel.almeida@...labora.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	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>, linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3 1/2] rust: irq: add support for request_irq()

On Tue, Jun 03, 2025 at 11:18:40AM +0200, Alice Ryhl wrote:
> I don't think that helps. If Devres::drop gets to swap is_available
> before the devm callback performs the swap, then the devm callback is
> just a no-op and the device still doesn't wait for free_irq() to
> finish running.

True, this will indeed always be racy. The rule from the C API has always been
that devm_{remove,release}_action() must not be called if a concurrent unbind
can't be ruled out. Consequently, the same is true for Revocable::revoke() in
this case.

I think Devres::drop() shouldn't do anything then and instead we should provide
Devres::release() and Devres::remove(), which require the &Device<Bound>
reference the Devres object was created with, in order to prove that there
can't be a concurrent unbind, just like Devres::access().