OK, I'm late to the party. But why exactly are we syncing absolutely everything? That seems over-broad.
If we try to be selective, we risk errors of omission, which no one would ever notice until someone's data got eaten in a low-probability crash scenario. It seems more robust (at least to me) to fsync everything we can find. That does require more thought about error cases than went into the original patch ... but I think that we need more thought about error cases even if we do try to be selective.
One thing perhaps we *should* be selective about, though, is which symlinks we try to follow. I think that a good case could be made for ignoring symlinks everywhere except in the pg_tablespace directory. If we did, that would all by itself take care of the Debian scenario, if I understand that case correctly.
People have symlinked the xlog directory. I've done it myself in the past. A better rule might be to ignore symlinks unless either they are in pg_tblspc or they are in the data directory and their name starts with "pg_".
Not just "people". initdb will symlink the xlog directory if you use -x.
