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

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Message-ID: <20250905090130.101724-2-marco.crivellari@suse.com>
Date: Fri,  5 Sep 2025 11:01:30 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-modules@...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>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>
Subject: [PATCH 1/1] module: 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>
---
 kernel/module/dups.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/module/dups.c b/kernel/module/dups.c
index bd2149fbe117..e72fa393a2ec 100644
--- a/kernel/module/dups.c
+++ b/kernel/module/dups.c
@@ -113,7 +113,7 @@ static void kmod_dup_request_complete(struct work_struct *work)
 	 * let this linger forever as this is just a boot optimization for
 	 * possible abuses of vmalloc() incurred by finit_module() thrashing.
 	 */
-	queue_delayed_work(system_wq, &kmod_req->delete_work, 60 * HZ);
+	queue_delayed_work(system_percpu_wq, &kmod_req->delete_work, 60 * HZ);
 }

 bool kmod_dup_request_exists_wait(char *module_name, bool wait, int *dup_ret)
@@ -240,7 +240,7 @@ void kmod_dup_request_announce(char *module_name, int ret)
 	 * There is no rush. But we also don't want to hold the
 	 * caller up forever or introduce any boot delays.
 	 */
-	queue_work(system_wq, &kmod_req->complete_work);
+	queue_work(system_percpu_wq, &kmod_req->complete_work);

 out:
 	mutex_unlock(&kmod_dup_mutex);
-- 
2.51.0