--- x/fs/netfs/write_collect.c
+++ y/fs/netfs/write_collect.c
@@ -548,7 +548,9 @@ void netfs_write_collection_worker(struc
 		return;
 	}
 
+	mutex_lock(&ictx->wb_lock);
 	netfs_collect_write_results(wreq);
+	mutex_unlock(&ictx->wb_lock);
 
 	/* We're done when the app thread has finished posting subreqs and all
 	 * the queues in all the streams are empty.