linux-kernel - Re: [RFC PATCH] rust: workqueue: Add an example for try

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Message-Id: <DBQ4VKUDJOF4.1JVIM88YK8V59@kernel.org>
Date: Thu, 31 Jul 2025 11:30:10 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 "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>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "Danilo Krummrich" <dakr@...nel.org>, "Tejun Heo" <tj@...nel.org>, "Tamir
 Duberstein" <tamird@...il.com>, "Hamza Mahfooz"
 <hamzamahfooz@...ux.microsoft.com>, "Alban Kurti" <kurti@...icto.ai>, "Joel
 Fernandes" <joelagnelf@...dia.com>, "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [RFC PATCH] rust: workqueue: Add an example for try_spawn()

On Wed Jul 30, 2025 at 9:38 PM CEST, Boqun Feng wrote:
> On Wed, Jul 30, 2025 at 09:28:05PM +0200, Benno Lossin wrote:
>> On Wed Jul 30, 2025 at 6:34 PM CEST, Boqun Feng wrote:
>> > +    /// workqueue::system().try_spawn(
>> > +    ///     flags::GFP_KERNEL,
>> > +    ///     {
>> > +    ///         let work_done = work_done.clone();
>> > +    ///         let data = data.clone();
>> > +    ///         move || {
>> > +    ///             *data.lock() = 42;
>> > +    ///             work_done.complete_all();
>> > +    ///         }
>> > +    ///     }
>> > +    /// )?;
>> 
>> Not doing your pattern and instead adding a `2` postfix we get:
>> 
>>     let work_done2 = work_done.clone();
>>     let data2 = data.clone();
>> 
>
> Yeah, the thing I want to achieve with my pattern is: make it clear that
> the work and the task that queues the work are sharing the same
> `work_done` and `data` (well, no the same `Arc` exactly, but the `Arc`s
> that are pointing to the same object). This pattern here doesn't show
> that clearly imo.

I think it's fine, that pattern is often used for that. Not heavily
opposed to doing it your way, but I feel like the code looks a bit weird
& my instinct is to move the let bindings out (which would produce code
that doesn't compile).

> That said, I'm not really against using `work_done2` and `data2`, just
> I'm afraid that may be more confusing.

I don't think that's a problem.

>>     workqueue::system().try_spawn(flags::GFP_KERNEL, move || {
>>         *data2.lock() = 42;
>>         work_done2.complete_all();
>>     })?;
>> 
>> There are some discussions of introducing some better syntax for (cheap)
>> cloning, so maybe we can use that in the future.
>
> Do you have links to these discussions.

It's an RFC:

    https://github.com/rust-lang/rfcs/pull/368

There probably are more discussions on zulip, but I haven't read those.
The RFC also has a project goal:

    https://rust-lang.github.io/rust-project-goals/2025h2/ergonomic-rc.html

---
Cheers,
Benno