linux-kernel - [for-next][PATCH 07/11] tracing: replace use of system_wq with system_percpu

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Message-ID: <20250930170302.375260552@kernel.org>
Date: Tue, 30 Sep 2025 13:01:42 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lai Jiangshan <jiangshanlai@...il.com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Michal Hocko <mhocko@...e.com>,
 Tejun Heo <tj@...nel.org>,
 Marco Crivellari <marco.crivellari@...e.com>
Subject: [for-next][PATCH 07/11] tracing: replace use of system_wq with system_percpu_wq

From: Marco Crivellari <marco.crivellari@...e.com>

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.

Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Link: https://lore.kernel.org/20250905091040.109772-2-marco.crivellari@suse.com
Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_events_user.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index af42aaa3d172..3169182229ad 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -835,7 +835,7 @@ void user_event_mm_remove(struct task_struct *t)
 	 * so we use a work queue after call_rcu() to run within.
 	 */
 	INIT_RCU_WORK(&mm->put_rwork, delayed_user_event_mm_put);
-	queue_rcu_work(system_wq, &mm->put_rwork);
+	queue_rcu_work(system_percpu_wq, &mm->put_rwork);
 }

 void user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm)
-- 
2.50.1