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

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Message-ID: <CAAofZF77saPdGYXt-oYkfV=2pRCRtso5eJuw+FqmS8b8WERgOA@mail.gmail.com>
Date: Mon, 8 Sep 2025 12:24:17 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: Alice Ryhl <aliceryhl@...gle.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 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?

Thanks!

-- 

Marco Crivellari

L3 Support Engineer, Technology & Product

marco.crivellari@...e.com