workqueue: fix bugs in wq_update_unbound_numa() failure path

wq_update_unbound_numa() failure path has the following two bugs.
- alloc_unbound_pwq() is called without holding wq->mutex; however, if the allocation fails, it jumps to out_unlock which tries to unlock wq->mutex.

- The function should switch to dfl_pwq on failure but didn't do so after alloc_unbound_pwq() failure.

Fix it by regrabbing wq->mutex and jumping to use_dfl_pwq on alloc_unbound_pwq() failure.

---
 kernel/workqueue.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

index 0ee63af..3150b21 100644
@@ -4100,7 +4100,8 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
 	if (!pwq) {
 		pr_warning("workqueue: allocation failed while updating NUMA affinity of \"%s\"\n",
 			   wq->name);
-		goto out_unlock;
+		mutex_lock(&wq->mutex);
+		goto use_dfl_pwq;
 	}
 
 	/*

1.7.4.4