In updateServerList there is this comment:

However, when the method is called here:

I don't see that it is called with any mutex held. I only see clusterConfigMU ever held with a read-lock.

However, I believe there isn't actually a thread safety concern here. The prevClusterConfig appears to only be read/updated from readConfigAndUpdateServerList which is never called concurrently in the current code. The SetServers call on the ServerList is protected by a mutex so that is already protected. From what I can tell, the clusterConfigMU lock and thread safety comments could likely be removed to avoid confusion.