linux-kernel - Re: [PATCH v4 1/2] rust: add system_dfl() around the new system_dfl

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Message-Id: <DG5G52FJ0I1F.1OHNFAXKXOZ1R@garyguo.net>
Date: Tue, 03 Feb 2026 15:53:39 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Marco Crivellari" <marco.crivellari@...e.com>,
 <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Cc: "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>, "Alice Ryhl"
 <aliceryhl@...gle.com>
Subject: Re: [PATCH v4 1/2] rust: add system_dfl() around the new
 system_dfl_wq

On Tue Feb 3, 2026 at 3:28 PM GMT, Marco Crivellari wrote:
> The C code defines 2 new workqueues: system_percpu_wq and system_dfl_wq,
> respectively the futures replacement for system_wq and system_unbound_wq.
>
> This change introduce system_dfl(), that use the new system_dfl_wq.
>
> system_unbound_wq will be replaced in a future release cycle and should
> not be used.
>
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
> ---
>  rust/kernel/workqueue.rs | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index 706e833e9702..300cc2bfe012 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -968,11 +968,25 @@ pub fn system_long() -> &'static Queue {
>  /// 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.
> +///
> +/// 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) }
>  }

Hi Marco,

The Rust change looks good to me.

Reviewed-by: Gary Guo <gary@...yguo.net>

Is there any reason that we cannot migrate the user early by just returning
`system_dfl_wq` inside `system_unbound`? (I guess the question also applies on
why system_unbound_wq cannot be the same pointer as system_dfl_wq).

Also, I feel that `dfl` is not a very intuitive name. I searched the list and
the commit history for a while and cannot find the exact explaination on what it
means? Does it mean "default" or something else?

Best,
Gary

>  
> +/// 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.
> +///
> +/// Note: `system_dfl_wq` will replace in a future release cycle [`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) }
> +}
> +
>  /// Returns the system freezable work queue (`system_freezable_wq`).
>  ///
>  /// It is equivalent to the one returned by [`system`] except that it's freezable.