linux-kernel - Re: [PATCH v5 0/3] rust: add `ww

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Message-ID: <20250814185622.468aad30@nimda.home>
Date: Thu, 14 Aug 2025 18:56:22 +0300
From: Onur <work@...rozkan.dev>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Benno Lossin <lossin@...nel.org>, Lyude Paul <lyude@...hat.com>,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com,
 gary@...yguo.net, a.hindborg@...nel.org, aliceryhl@...gle.com,
 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, bjorn3_gh@...tonmail.com
Subject: Re: [PATCH v5 0/3] rust: add `ww_mutex` support

On Thu, 14 Aug 2025 09:38:38 -0300
Daniel Almeida <daniel.almeida@...labora.com> wrote:

> Hi Onur,
> 
> > On 14 Aug 2025, at 08:13, Onur Özkan <work@...rozkan.dev> wrote:
> > 
> > Hi all,
> > 
> > I have been brainstorming on the auto-unlocking (on dynamic number
> > of mutexes) idea we have been discussing for some time.
> > 
> > There is a challange with how we handle lock guards and my current
> > thought is to remove direct data dereferencing from guards. Instead,
> > data access would only be possible through a fallible method (e.g.,
> > `try_get`). If the guard is no longer valid, this method would fail
> > to not allow data-accessing after auto-unlock.
> > 
> > In practice, it would work like this:
> > 
> > let a_guard = ctx.lock(mutex_a)?;
> > let b_guard = ctx.lock(mutex_b)?;
> > 
> > // Suppose user tries to lock `mutex_c` without aborting the
> > // entire function (for some reason). This means that even on
> > // failure, `a_guard` and `b_guard` will still be accessible.
> > if let Ok(c_guard) = ctx.lock(mutex_c) {
> >     // ...some logic
> > }
> > 
> > let a_data = a_guard.try_get()?;
> > let b_data = b_guard.try_get()?;
> 
> Can you add more code here? How is this going to look like with the
> two closures we’ve been discussing?

Didn't we said that tuple-based closures are not sufficient when
dealing with a dynamic number of locks (ref [1]) and ww_mutex is mostly
used with dynamic locks? I thought implementing that approach is not
worth it (at least for now) because of that.

[1]: https://lore.kernel.org/all/DBS8REY5E82S.3937FAHS25ANA@kernel.org

Regards,
Onur