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

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Message-ID: <aD62ZGBwqXxTroeX@cassiopeiae>
Date: Tue, 3 Jun 2025 10:46:28 +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 08:28:42AM +0000, Alice Ryhl wrote:
> That optimization sounds like something we definitely want, but I have
> one question: is free_irq() safe to use in atomic context / inside
> rcu_read_lock()? What about the threaded-irq variant?

No, free_irq() must not be called from atomic context. Hence, it's not valid to
call it from within an RCU read-side critical section.

I assume you're confusing something, free_irq() is called from the destructor of
the irq::Registration object, hence it is either called when the object itself
is dropped or from the devres callback, which is called after the
synchronize_rcu(), but not from an RCU read-side critical section.