workqueue: Link pwq's into wq->pwqs from oldest to newest

Add a new pwq into the tail of wq->pwqs so that pwq iteration will
start from the oldest pwq to the newest. This ordering will facilitate
the inclusion of ordered workqueues in a wq_unbound_cpumask update.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -4804,7 +4804,7 @@ static void link_pwq(struct pool_workqueue *pwq)
 	pwq->work_color = wq->work_color;
 
 	/* link in @pwq */
-	list_add_rcu(&pwq->pwqs_node, &wq->pwqs);
+	list_add_tail_rcu(&pwq->pwqs_node, &wq->pwqs);
 }
 
 /* obtain a pool matching @attr and create a pwq associating the pool and @wq */