workqueue: Make rescuer initialization as the last step of the creation of a new wq

For early wq allocation, rescuer initialization is the last step of the
creation of a new wq.  Make the behavior the same for all allocations.

Prepare for initializing rescuer's affinities with the default pwq's
affinities.

Prepare for moving the whole workqueue initializing procedure into
wq_pool_mutex and cpu hotplug locks.

Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -5681,9 +5681,6 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 	if (alloc_and_link_pwqs(wq) < 0)
 		goto err_free_node_nr_active;
 
-	if (wq_online && init_rescuer(wq) < 0)
-		goto err_destroy;
-
 	/*
 	 * wq_pool_mutex protects global freeze state and workqueues list.
 	 * Grab it, adjust max_active and add the new @wq to workqueues
@@ -5699,6 +5696,9 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 
 	mutex_unlock(&wq_pool_mutex);
 
+	if (wq_online && init_rescuer(wq) < 0)
+		goto err_destroy;
+
 	if ((wq->flags & WQ_SYSFS) && workqueue_sysfs_register(wq))
 		goto err_destroy;