linux-kernel - Re: [PATCH v4] rust: lock: Export Guard::do

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Message-ID: <aQSOZu7nN56Uqj6V@google.com>
Date: Fri, 31 Oct 2025 10:24:38 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Lyude Paul <lyude@...hat.com>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, Benno Lossin <lossin@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, 
	Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.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>, Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v4] rust: lock: Export Guard::do_unlocked()

On Fri, Oct 31, 2025 at 10:38:32AM +0100, Paolo Bonzini wrote:
> On 10/31/25 10:31, Alice Ryhl wrote:
> > I do agree that this behavior has a lot of potential to surprise
> > users, but I don't think it's incorrect per se. It was done
> > intentionally for Condvar, and it's not unsound. Just surprising.
> 
> Yes, I agree that it is not unsound.`
> 
> For conditional variables, wait() is clearly going to release the mutex to
> wait for someone else so the surprise factor is much less.  Having it return
> a new guard would be closer to std::sync::Condvar::wait, but it'd add churn
> and I'm not sure how much you all care about consistency with std.  std has
> the extra constraint of poisoned locks so it doesn't really have a choice.

I mean, it's not that much different.

	my_method(&mut guard);

might still call Condvar::wait internally, so it can release the lock
today.

Alice