NFS Client looping with STALE_STATE_ID error - 100% load on one CPU core

[Joschi Brauchle <joschi.brauchle@tum.de>]

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Hello everyone,

I am posting to this list as suggested by Neil F Brown in this OpenSUSE 
bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=909634


We are mounting user homes and other shares using 'sec=krb' and NFSv4. 
With kernel 3.16.7+ (includes latest NFS patches, please see BZ link for 
details) we are seeing 100% CPU core usage by a kernel process on some 
machine connected to a 'NetApp FAS 3140 with ONTAP 8.1.4P1 7-mode' 
NFSv3/4 Server. It looks like the problem is triggered when the NFS 
server is unavailable for a short period of time or was rebooted.

Neil F Brown has come to the following conclusion so far:
------------- QUOTE -------------
What I see happening here is that a WRITE or LOCK request gets 
NFS4ERR_STALE_STATEID, and then the client sends a "RENEW" request.

If the stateid is really stale, that should fail, but it doesn't. So the 
client assumes everything is OK and keeps sending requests .... which 
fail with NFS4ERR_STALE_STATEID.

STALE_STATEID means:

       A stateid generated by an earlier server instance was used.

which means that the server must have restarted since that stateid was 
issued.

So there seem to be two possible explanations:

1/ The server is lying.  The stateid isn't really 'stale'.  Maybe it is 
'bad'.
2/ The client has previously handled a STALE_STATEID error and created a 
new "client" handle, but hasn't refreshed all of the stateids that it 
was holding. So it is trying to use old stateid even though it has 
established a new client.

The client code looks OK, though it is sufficiently complex that I 
cannot be certain.  There are no patches in more recent versions.
-------------  END  -------------

We have some RPC/NFS debug logs available here:
https://bugzilla.novell.com/attachment.cgi?id=631962
And a wireshark trace here:
https://bugzilla.novell.com/attachment.cgi?id=632104


What I cannot do:
- Trigger or reproduce the problem reliably. It comes up every once in a 
while. Around 2-3 times a month on a handful of ~50 machines.
- Provide logs from with the latest kernel (because I cannot trigger the 
problem by any means. Updating all ~50 machines is not an option)


What I can do:
- Provide logs from or possibly even access to the machine in the 
'broken' state for the next couple of days. I will have to reboot it at 
some time to take the load of the NFS server.



I would be grateful for any help or comments.

-J Brauchle


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