workqueue: Skip __WQ_DESTROYING workqueues when updating global unbound cpumask

Skip updating workqueues with __WQ_DESTROYING bit set when updating
global unbound cpumask to avoid unnecessary work and other complications.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -6501,7 +6501,7 @@ static int workqueue_apply_unbound_cpumask(const cpumask_var_t unbound_cpumask)
 	lockdep_assert_held(&wq_pool_mutex);
 
 	list_for_each_entry(wq, &workqueues, list) {
-		if (!(wq->flags & WQ_UNBOUND))
+		if (!(wq->flags & WQ_UNBOUND) || (wq->flags & __WQ_DESTROYING))
 			continue;
 
 		/* creating multiple pwqs breaks ordering guarantee */