NFS Mount Hangs

[tuexen at freebsd.org]

> On 18. Mar 2021, at 21:55, Rick Macklem <rmacklem at uoguelph.ca> wrote:
> 
> Michael Tuexen wrote:
>>> On 18. Mar 2021, at 13:42, Scheffenegger, Richard <Richard.Scheffenegger at netapp.com> wrote:
>>> 
>>>>> Output from the NFS Client when the issue occurs # netstat -an | grep
>>>>> NFS.Server.IP.X
>>>>> tcp        0      0 NFS.Client.IP.X:46896      NFS.Server.IP.X:2049       FIN_WAIT2
>>>> I'm no TCP guy. Hopefully others might know why the client would be stuck in FIN_WAIT2 (I vaguely recall this means it is waiting for a fin/ack, but could be wrong?)
>>> 
>>> When the client is in Fin-Wait2 this is the state you end up when the Client side actively close() the tcp session, and then the server also ACKed the FIN.
> Jason noted:
> 
>> When the issue occurs, this is what I see on the NFS Server.
>> tcp4       0      0 NFS.Server.IP.X.2049      NFS.Client.IP.X.51550     CLOSE_WAIT
>> 
>> which corresponds to the state on the client side. The server received the FIN
>> from the client and acked it.
>> The server is waiting for a close call to happen.
>> So the question is: Is the server also closing the connection?
> Did you mean to say "client closing the connection here?"
Yes.
> 
> The server should call soclose() { it never calls soshutdown() } when
> soreceive(with MSG_WAIT) returns 0 bytes or an error that indicates
> the socket is broken.
> --> The soreceive() call is triggered by an upcall for the rcv side of the socket.
> So, are you saying the FreeBSD NFS server did not call soclose() for this case?
Yes. If the state at the server side is CLOSE_WAIT, no close call has happened yet.
The FIN from the client was received, it was ACKED, but no close() call
(or shutdown(..., SHUT_WR) or shutdown(..., SHUT_RDWR)) was issued. Therefore,
no FIN was sent and the client should be in the FINWAIT-2 state. This was also
reported. So the reported states are consistent.

Best regards
Michael

> 
> rick
> 
> Best regards
> Michael
>> This will last for ~2 min or so, but is asynchronous. However, the same 4-tuple can not be reused during this time.
>> 
>> With other words, from the socket / TCP, a properly executed active close() will end up in this state. (If the other side initiated the close, a passive close, will not end in this state)
>> 
>> 
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> 
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