linux-kernel - Re: [PATCH 0/2] rust: replace wq users and add WQ_PERCPU to alloc

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Message-ID: <CAH5fLghpysJv5wt1ANPN+SHE2At8J6MHso7F1HdnNLomqniBrg@mail.gmail.com>
Date: Mon, 8 Sep 2025 12:27:08 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Marco Crivellari <marco.crivellari@...e.com>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Michal Hocko <mhocko@...e.com>, Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>
Subject: Re: [PATCH 0/2] rust: replace wq users and add WQ_PERCPU to
 alloc_workqueue() users

On Mon, Sep 8, 2025 at 12:24 PM Marco Crivellari
<marco.crivellari@...e.com> wrote:
>
> On Sun, Sep 7, 2025 at 12:59 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
> > I mean that instead of:
> >
> > +/// Returns the system unbound work queue (`system_dfl_wq`).
> >  ///
> >  /// Workers are not bound to any specific CPU, not concurrency managed, and all queued work items
> >  /// are executed immediately as long as `max_active` limit is not reached and resources are
> >  /// available.
> >  pub fn system_unbound() -> &'static Queue {
> > -    // SAFETY: `system_unbound_wq` is a C global, always available.
> > -    unsafe { Queue::from_raw(bindings::system_unbound_wq) }
> > +    // SAFETY: `system_dfl_wq` is a C global, always available.
> > +    unsafe { Queue::from_raw(bindings::system_dfl_wq) }
> >  }
> >
> > you add a new function:
> >
> >         pub fn system_dfl() -> &'static Queue {
> >             // SAFETY: `system_dfl_wq` is a C global, always available.
> >             unsafe { Queue::from_raw(bindings::system_dfl_wq) }
> >         }
> >
> > and do *not* modify system_unbound().
> >
> > Alice
>
> Hello Alice,
>
> Ah, perfect. Yes it makes sense this change, you're right.
> I will send the v2 introducing the new functions for both the patches
> in this series.
>
> It would also make sense to also change the above comment, mentioning that
> system_unbound() uses a wq that will be removed in the future, and so
> it is better to
> use system_dfl() instead?
>
> I'm thinking to something like:
>
> +///
> +/// Note: system_unbound_wq will be removed in a future release
> cycle. Use system_dfl_wq instead.
> pub fn system_unbound() -> &'static Queue {
>     // SAFETY: `system_unbound_wq` is a C global, always available.
>     unsafe { Queue::from_raw(bindings::system_unbound_wq) }
> }
>
> +pub fn system_dfl() -> &'static Queue {
> +    // SAFETY: `system_dfl_wq` is a C global, always available.
> +    unsafe { Queue::from_raw(bindings::system_dfl_wq) }
> +}
>
> Sounds good?

That is reasonable, yes. Please make it a link:

/// Note: `system_unbound_wq` will be removed in a future release
cycle. Use [`system_dfl`] instead.

Alice