In VtableStubs::find_stub we first perform a lookup in the table to check for already created stubs under the VtableStubs_lock, then if not found we create a new stub without the lock held, and then insert it under the VtableStubs_lock without checking for entries inserted between the lookup and insertion.
If the VtableStubs_lock is to protect the table (which is the intention), the lock should not be unlocked before lookup and insert.