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>

fs/gfs2/glock.c

@@ -1781,7 +1781,13 @@ int __init gfs2_glock_init(void)
 		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;
 }

fs/gfs2/main.c

@@ -145,7 +145,9 @@ static int __init init_gfs2_fs(void)
 	if (!gfs2_qadata_cachep)
 		goto fail;
 
-	register_shrinker(&gfs2_qd_shrinker);
+	error = register_shrinker(&gfs2_qd_shrinker);
+	if (error)
+		goto fail;
 
 	error = register_filesystem(&gfs2_fs_type);
 	if (error)