There are some potential feefilter cleanups mentioned and motivated in comment https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-805808485 . If you address the locking one, please be careful and make sure that `round()` is only called under a lock. See https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-807992199

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if (!stop_index || !BlockRequestAllowed(stop_index)) {
            LogPrint(BCLog::NET, "peer %d requested invalid block hash: %s\n",
                     peer.GetId(), stop_hash.ToString());
            peer.fDisconnect = true;
            return false;
        }
    }
    uint32_t stop_height = stop_index->nHeight;
    if (start_height > stop_height) {
        LogPrint(BCLog::NET, "peer %d sent invalid getcfilters/getcfheaders with " 
                 "start height %d and stop height %d\n",
                 peer.GetId(), start_height, stop_height);
        peer.fDisconnect = true;
        return false;
    }
    if (stop_height - start_height >= max_height_diff) {
        LogPrint(BCLog::NET, "peer %d requested too many cfilters/cfheaders: %d / %d\n",
                 peer.GetId(), stop_height - start_height + 1, max_height_diff);
        peer.fDisconnect = true;
        return false;
    }
    filter_index = GetBlockFilterIndex(filter_type);
    if (!filter_index) {
        LogPrint(BCLog::NET, "Filter index for supported type %s not found\n", BlockFilterTypeName(filter_type));
        return false;
    }
    return true;
}
void PeerManagerImpl::ProcessGetCFilters(CNode& peer, CDataStream& vRecv)