NFS delegations don't expire after unmounting client

[Alan Somers]

On Thu, Feb 11, 2021 at 2:54 PM Rick Macklem <rmacklem at uoguelph.ca> wrote:

> Alan Somers wrote:
> >I have several Linux 5.9.15 clients mounting NFS 4.1 served from a FreeBSD
> >12.2-RELEASE server.  Today, most of those clients' mounts hung, and their
> >dmesg displayed "nfs: server XXX not responding, still trying".
> Usually these messages indicate a networking layer problem.
> Next time (or if it still happening), check basic network connectivity.
> Also, if any net interface does not handle TSO correctly for an RPC
> message near 64Kbytes in size (the nasty one is where the NFS RPC is
> less than 64K by less than 14bytes, so when the MAC layer header is
> prepended, the total exceed 64K), you can get "stuck" TCP connections.
> Most FreeBSD net chip drivers should be fixed for this, but I wouldn't be
> surprised if there are some broken ones out there.
> --> Disabling TSO fixes the problem in this case.


In fact it is still happening.  Basic network connectivity works.  But
tcpdump shows almost no network activity.  Just a few keepalive packets of
length 0-1.  Based on the fact that unmount and even lsof hang on the
client, I'm suspecting a Linux bug somewhere.
-Alan