gfs2: fix to detect failure of register_shrinker

register_shrinker can fail after commit 1d3d4437eae1 ("vmscan: per-node
deferred work"), we should detect the failure of it, otherwise we may
fail to register shrinker after gfs2 module was been inited successfully.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index c8e2e7f..14cbf60 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1781,7 +1781,13 @@
 		return -ENOMEM;
 	}
 
-	register_shrinker(&glock_shrinker);
+	ret = register_shrinker(&glock_shrinker);
+	if (ret) {
+		destroy_workqueue(gfs2_delete_workqueue);
+		destroy_workqueue(glock_workqueue);
+		rhashtable_destroy(&gl_hash_table);
+		return ret;
+	}
 
 	return 0;
 }