anchor.diff:  handle_info({'EXIT', Pid, normal}, #state{phase = rr_blobs_wait, rr_pid = RR} = S)
     when Pid == RR  ->
       % The RR process has finished normally, and we can proceed to the
  -    % second phase of RR: start updating the tags.
  +    % second phase of RR: start updating the tags.  Also, we
  +    % initialize the safe blacklist here.
       error_logger:info_report({"GC: done with blob replication, entering rr_tags"}),
       gen_server:cast(self(), {rr_tags, S#state.tags}),
  -    {noreply, S#state{rr_pid = undefined, phase = rr_tags}};
  +    {noreply, S#state{rr_pid = undefined,
  +                      safe_blacklist = gb_sets:from_list(S#state.blacklist),
  +                      phase = rr_tags}};
   handle_info({'EXIT', Pid, Reason}, #state{phase = Phase, rr_pid = RR} = S)
     when Pid == RR  ->
       % Unexpected exit of RR process; exit.
  
positive.code: % the blacklisted node (3).  The actual removal is performed by the
  % corresponding ddfs_tag.
  %
  % The blacklisted node can be removed by the admin from the config
  % after ensuring that no tag contains references to data hosted on it.
  % After a node is put on the blacklist, there might need to be several
  % runs of GC/RR before the node removal is safe.
  %
  % The blob reference removal requires an invariant: that any operations
  % on a tag do not modify the replica set for a blob in the tag, other
  % than perhaps removing the replica set completely.  This is because
  
negative.code:                           andalso (length(SafePresent) >= S#state.blobk)) of
                          true ->
                              Update = {BlobName, filter},
                              collect(S, Rest, {[Update | Updates], NewSBL});
                          false ->
                              % Blacklist filtering is not needed, or
                              % it's not yet safe.
                              collect(S, Rest, {Updates, NewSBL})
                      end;
                  [{_, _P, R, {update, NewUrls}}] ->
                      AccUpdates = add_blob_update(S, BlobName, R, NewUrls, Updates),
                      collect(S, Rest, {AccUpdates, NewSBL})
              end
      end.
  
  