linux-kernel - [PATCH v2 1/2] rust: replace use of system_unbound_wq with system_dfl

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Message-ID: <20250908160224.376634-2-marco.crivellari@suse.com>
Date: Mon,  8 Sep 2025 18:02:23 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: 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>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v2 1/2] rust: replace use of system_unbound_wq with system_dfl_wq

Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.

This lack of consistentcy cannot be addressed without refactoring the API.

system_unbound_wq should be the default workqueue so as not to enforce
locality constraints for random work whenever it's not required.

Adding system_dfl_wq to encourage its use when unbound work should be used.

The old system_unbound_wq will be kept for a few release cycles.

Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 rust/kernel/workqueue.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index f98bd02b838f..01e331a1f11b 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -667,11 +667,18 @@ 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) }
 }
 
+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.
-- 
2.51.0