linux-kernel - Re: [PATCH v8 5/6] rust: ww_mutex: add Mutex, AcquireCtx and MutexGuard

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Message-ID: <aTFPRv2ahM_KA3AB@google.com>
Date: Thu, 4 Dec 2025 09:07:18 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: "Onur Özkan" <work@...rozkan.dev>, rust-for-linux@...r.kernel.org, lossin@...nel.org, 
	lyude@...hat.com, ojeda@...nel.org, alex.gaynor@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, a.hindborg@...nel.org, 
	tmgross@...ch.edu, dakr@...nel.org, peterz@...radead.org, mingo@...hat.com, 
	will@...nel.org, longman@...hat.com, felipe_life@...e.com, daniel@...lak.dev, 
	thomas.hellstrom@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 5/6] rust: ww_mutex: add Mutex, AcquireCtx and MutexGuard

On Wed, Dec 03, 2025 at 02:23:14PM -0300, Daniel Almeida wrote:
> 
> 
> > On 3 Dec 2025, at 10:26, Alice Ryhl <aliceryhl@...gle.com> wrote:
> > 
> > On Mon, Dec 01, 2025 at 01:28:54PM +0300, Onur Özkan wrote:
> >> Yeah :(. We could get rid of them easily by keeping the class that was
> >> passed to the constructor functions but that becomes a problem for the
> >> from_raw implementations.
> >> 
> >> I think the best solution would be to expose ww_class type from
> >> ww_acquire_ctx and ww_mutex unconditionally (right now it depends on
> >> DEBUG_WW_MUTEXES). That way we can just access the class and verify
> >> that the mutex and acquire_ctx classes match.
> >> 
> >> What do you think? I can submit a patch for the C-side implementation.
> >> It should be straightforward and shouldn't have any runtime impact.
> > 
> > I think there is a better solution. We can create a different type for
> > every single class, like how rust/kernel/sync/lock/global.rs creates a
> > different type for every single mutex. Then, you know that the classes
> > are the same since the class is part of the type.
> 
> I don’t think this would work with the from_raw() functions. What class
> would you assign then? I think this is precisely what sparked the current
> solution.

There can be a way to create a type for a C-defined class, and
from_raw() can require that you don't use the same Rust type for
different C classes.

Alice