NFSv4/pnfs: Ensure we don't miss a file extension

NFSv4/pnfs: Ensure we don't miss a file extension

commit 2b83d3de4c18af49800e0b26ae013db4fcf43a4a upstream.

pNFS writes don't return attributes, however that doesn't mean that we
should ignore the fact that they may be extending the file. This patch
ensures that if a write is seen to extend the file, then we always set
an attribute barrier, and update the cached file size.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>