Message-ID: <4F5E5241.7070008@rath.org>
Date: Mon, 12 Mar 2012 15:45:05 -0400
From: Nikolaus Rath <Nikolaus@rath.org>
MIME-Version: 1.0
To: "J. Bruce Fields" <bfields@fieldses.org>
CC: linux-nfs@vger.kernel.org
Subject: Re: NFS4 over VPN hangs when connecting > 2 clients
References: <878vj7x6mj.fsf@vostro.rath.org> <87pqchn64e.fsf@inspiron.ap.columbia.edu> <20120312193115.GA7203@fieldses.org>
In-Reply-To: <20120312193115.GA7203@fieldses.org>
Content-Type: text/plain; charset=ISO-8859-1
Sender: linux-nfs-owner@vger.kernel.org

On 03/12/2012 03:31 PM, J. Bruce Fields wrote:
> On Mon, Mar 12, 2012 at 12:20:17PM -0400, Nikolaus Rath wrote:
>> Nikolaus Rath <Nikolaus-BTH8mxji4b0@public.gmane.org> writes:
>>> The problem is that as soon as more than three clients are accessing the
>>> NFS shares, any operations on the NFS mountpoints by the clients hang.
>>> At the same time, CPU usage of the VPN processes becomes very high. If I
>>> run the VPN in debug mode, all I can see is that it is busy forwarding
>>> lots of packets. I also ran a packet sniffer which showed me that 90% of
>>> the packets were NFS related, but I am not familiar enough with NFS to
>>> be able to tell anything from the packets themselves. I can provide an
>>> example of the dump if that helps.
>>
>> I have put a screenshot of the dump on
>> http://www.rath.org/res/wireshark.png (the full dump is 18 MB, and I'm
>> not sure which parts are important).
> 
> Looks like they're doing SETCLIENTID, SETCLIENTID_CONFIRM, OPEN,
> OPEN_CONFIRM repeatedly.
> 
>> Any suggestions how I could further debug this?
> 
> Could the clients be stepping on each others' state if they all think
> they have the same IP address (because of something to do with the VPN
> networking?)

That sounds like promising path of investigation. What determines the IP
of a client as far as NFS is concerned? ifconfig on the clients reports
different IPs, e.g.

hbt       Link encap:UNSPEC  HWaddr
00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
          inet addr:192.168.1.20  P-t-P:192.168.1.20  Mask:255.255.255.0
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:6285 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6851 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500
          RX bytes:2749422 (2.7 MB)  TX bytes:1860654 (1.8 MB)


hbt       Link encap:UNSPEC  HWaddr
00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
          inet addr:192.168.1.19  P-t-P:192.168.1.19  Mask:255.255.255.0
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:2306277 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1761902 errors:0 dropped:0 overruns:33054 carrier:0
          collisions:0 txqueuelen:500
          RX bytes:2534582154 (2.5 GB)  TX bytes:888058175 (888.0 MB)


> It'd be interesting to know the fields of the setclientid call, and the
> errors that the server is responding with to these calls.  If you look
> at the packet details you'll probably see the same thing happening
> over and over again.
> 
> Filtering to look at traffic between server and one client at a time
> might help to see the pattern.

Hmm. I'm looking at the fields, but I just have no idea what any of
those mean. Would you possibly be willing to take a look? I uploaded a
pcap dump of a few packets to http://www.rath.org/res/sample.pcap.


Best,

   -Nikolaus

-- 
 ?Time flies like an arrow, fruit flies like a Banana.?

  PGP fingerprint: 5B93 61F8 4EA2 E279 ABF6  02CF A9AD B7F8 AE4E 425C