CreateEntry is a FindEntry-then-write with no lock, so concurrent creates to
the same path race: OExcl can admit two creators, and a conditional write has
no atomic check-then-act. Add a per-path exclusive lock (util.LockTable, which
evicts idle keys so it stays bounded) in the CreateEntry handler so the read
and the write are atomic on this filer. Once callers route a key's writes to
its owner filer, this local lock is the authoritative serialization point.
AppendToEntry moves from the distributed lock to the same per-path lock.
Chris Lu
56c51e7f50