The readdir interface allows processes to be in the middle of reading a directory and unless a kernel was happy to either materialize the entire directory list when the readdir starts, or lock the entire directory against modification for the entire time the a process has a readdir fd open it's always going to be possible for the a process to have previously read the old directory entry and later see the new directory entry. Kernels don't do any MVCC or cmin type of games so they're not going to be able to prevent it.
What's worse of course is that it may only happen in very large directories. Most directories fit on a single block and readdir may buffer up all the entries a block at a time for efficiency. So it may only be visible on very large directories that span multiple blocks.
