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

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Message-ID: <20250905090819.107694-2-marco.crivellari@suse.com>
Date: Fri,  5 Sep 2025 11:08:18 +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>
Subject: [PATCH 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.

queue_work() / queue_delayed_work() / mod_delayed_work() will now use the
new unbound wq: whether the user still use the old wq a warn will be
printed along with a wq redirect to the new one.

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 | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index f98bd02b838f..8ca813d68a1a 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -662,14 +662,14 @@ pub fn system_long() -> &'static Queue {
     unsafe { Queue::from_raw(bindings::system_long_wq) }
 }

-/// Returns the system unbound work queue (`system_unbound_wq`).
+/// 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) }
 }

 /// Returns the system freezable work queue (`system_freezable_wq`).
-- 
2.51.0