[PATCH v3] module: replace use of system_wq with system_dfl_wq

[PATCH v3] module: replace use of system_wq with system_dfl_wq

[Marco Crivellari]

Currently if a user enqueues 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 consistency cannot be addressed without refactoring the API.

This continues the effort to refactor workqueue APIs, which began with
the introduction of new workqueues and a new alloc_workqueue flag in:

commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")

Switch to using system_dfl_wq, the new unbound workqueue, because the
users do not benefit from a per-cpu workqueue.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
---
Changes in v3:
- rebased on 6.18-rc5
- commit log improved

Changes in v2:
- a per-cpu wq is not needed: replace system_wq with system_dfl_wq
---
 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..0b633f2edda6 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_dfl_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_dfl_wq, &kmod_req->complete_work);
 
 out:
 	mutex_unlock(&kmod_dup_mutex);
-- 
2.51.1

Re: [PATCH v3] module: replace use of system_wq with system_dfl_wq

[Petr Pavlu]

On 11/11/25 10:50 AM, Marco Crivellari wrote:
> Currently if a user enqueues 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 consistency cannot be addressed without refactoring the API.
> 
> This continues the effort to refactor workqueue APIs, which began with
> the introduction of new workqueues and a new alloc_workqueue flag in:
> 
> commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
> 
> Switch to using system_dfl_wq, the new unbound workqueue, because the
> users do not benefit from a per-cpu workqueue.
> 
> Suggested-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

-- 
Thanks,
Petr

Re: [PATCH v3] module: replace use of system_wq with system_dfl_wq

[Sami Tolvanen]

On Tue, 11 Nov 2025 10:50:49 +0100, Marco Crivellari wrote:
> Currently if a user enqueues 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 consistency cannot be addressed without refactoring the API.
> 
> [...]

Applied to modules-next, thanks!

[1/1] module: replace use of system_wq with system_dfl_wq
      commit: 581ac2d4a58b81669cc6abf645a558bce5cf14ab

Best regards,

	Sami

Re: [PATCH v3] module: replace use of system_wq with system_dfl_wq

[Marco Crivellari]

On Mon, Dec 22, 2025 at 9:24 PM Sami Tolvanen <samitolvanen@google.com> wrote:
> Applied to modules-next, thanks!
>
> [1/1] module: replace use of system_wq with system_dfl_wq
>       commit: 581ac2d4a58b81669cc6abf645a558bce5cf14ab
>

Many thanks!

-- 

Marco Crivellari

L3 Support Engineer