linux-kernel - [PATCH 1/1] closure: replace use of system_wq with system_percpu

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Message-ID: <20250905085625.97367-2-marco.crivellari@suse.com>
Date: Fri,  5 Sep 2025 10:56:25 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-bcachefs@...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>,
	Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH 1/1] closure: replace use of system_wq with system_percpu_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_wq is a per-CPU worqueue, yet nothing in its name tells about that
CPU affinity constraint, which is very often not required by users. Make
it clear by adding a system_percpu_wq.

queue_work() / queue_delayed_work() mod_delayed_work() will now use the
new per-cpu wq: whether the user still stick on the old name a warn will
be printed along a wq redirect to the new one.

This patch add the new system_percpu_wq except for mm, fs and net
subsystem, whom are handled in separated patches.

The old wq will be kept for a few release cylces.

Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 include/linux/closure.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/closure.h b/include/linux/closure.h
index 880fe85e35e9..959b3c584254 100644
--- a/include/linux/closure.h
+++ b/include/linux/closure.h
@@ -58,7 +58,7 @@
  * bio2->bi_endio = foo_endio;
  * bio_submit(bio2);
  *
- * continue_at(cl, complete_some_read, system_wq);
+ * continue_at(cl, complete_some_read, system_percpu_wq);
  *
  * If closure's refcount started at 0, complete_some_read() could run before the
  * second bio was submitted - which is almost always not what you want! More
-- 
2.51.0