If you
- mount and NFSv3 filesystem
- do some file locking which requires the server
to make a GRANT call back
- unmount
- mount again and do the same locking
then the second attempt at locking suffers a 30 second delay.
Unmounting and remounting causes lockd to stop and restart,
which causes it to bind to a new port.
The server still thinks the old port is valid and gets ECONNREFUSED
when trying to contact it.
ECONNREFUSED should be seen as a hard error that is not worth
retrying. Rebinding is the only reasonable response.