Lost CLOSE with NFSv4.1 on RHEL7 ( and bejond?)

["Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>]

Dear NFS folks,

we observe orphan open-states on our deployment with nfsv4.1.
Our setup - two client nodes, running RHEL-7.2 with kernel
3.10.0-327.22.2.el7.x86_64. Both nodes running ownCloud (like
a dropbox) which nfsv4.1 mounts to dCache storage. Some clients
connected to node1, others to node2.

Time-to-time we see some 'active' transfers on data our DS
which do nothing. There is a corresponding state on MDS.

I have traced one one such cases:

  - node1 uploads the file.
  - node2 reads the file couple of times, OPEN+LAYOUTGET+CLOSE
  - node2 sends OPEN+LAYOUTGET
  - there is no open file on node2 which points to it.
  - CLOSE never send to the server. 
  - node1 eventually removes the removes the file

We have many other cases where file is not removed, but this one I was
able to trace. The link to capture files:

https://desycloud.desy.de/index.php/s/YldowcRzTGJeLbN

We had ~ 10^6 transfers in last 2 days and 29 files in such state (~0.0029%).

Tigran.