tty: 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.

This patch continues the effort to refactor worqueue APIs, which has begun
with the change introducing new workqueues and a new alloc_workqueue flag:

commit 128ea9f ("workqueue: Add system_percpu_wq and system_dfl_wq")
commit 930c2ea ("workqueue: Add new WQ_PERCPU flag")

system_dfl_wq should be the default workqueue so as not to enforce
locality constraints for random work whenever it's not required.

The old system_unbound_wq will be kept for a few release cycles.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Link: https://patch.msgid.link/20251104105446.110884-1-marco.crivellari@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: DispatchCode

drivers/tty/serial/8250/8250_dw.c

@@ -361,7 +361,7 @@ static int dw8250_clk_notifier_cb(struct notifier_block *nb,
 	 * deferred event handling complication.
 	 */
 	if (event == POST_RATE_CHANGE) {
-		queue_work(system_unbound_wq, &d->clk_work);
+		queue_work(system_dfl_wq, &d->clk_work);
 		return NOTIFY_OK;
 	}
 
@@ -680,7 +680,7 @@ static int dw8250_probe(struct platform_device *pdev)
 		err = clk_notifier_register(data->clk, &data->clk_notifier);
 		if (err)
 			return dev_err_probe(dev, err, "Failed to set the clock notifier\n");
-		queue_work(system_unbound_wq, &data->clk_work);
+		queue_work(system_dfl_wq, &data->clk_work);
 	}
 
 	platform_set_drvdata(pdev, data);

drivers/tty/tty_buffer.c

@@ -76,7 +76,7 @@ void tty_buffer_unlock_exclusive(struct tty_port *port)
 	mutex_unlock(&buf->lock);
 
 	if (restart)
-		queue_work(system_unbound_wq, &buf->work);
+		queue_work(system_dfl_wq, &buf->work);
 }
 EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
 
@@ -530,7 +530,7 @@ void tty_flip_buffer_push(struct tty_port *port)
 	struct tty_bufhead *buf = &port->buf;
 
 	tty_flip_buffer_commit(buf->tail);
-	queue_work(system_unbound_wq, &buf->work);
+	queue_work(system_dfl_wq, &buf->work);
 }
 EXPORT_SYMBOL(tty_flip_buffer_push);
 
@@ -560,7 +560,7 @@ int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
 		tty_flip_buffer_commit(buf->tail);
 	spin_unlock_irqrestore(&port->lock, flags);
 
-	queue_work(system_unbound_wq, &buf->work);
+	queue_work(system_dfl_wq, &buf->work);
 
 	return size;
 }
@@ -613,7 +613,7 @@ void tty_buffer_set_lock_subclass(struct tty_port *port)
 
 bool tty_buffer_restart_work(struct tty_port *port)
 {
-	return queue_work(system_unbound_wq, &port->buf.work);
+	return queue_work(system_dfl_wq, &port->buf.work);
 }
 
 bool tty_buffer_cancel_work(struct tty_port *port)