Re: NFS4 over VPN hangs when connecting > 2 clients

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Mar 12, 2012 at 04:30:42PM -0400, Nikolaus Rath wrote:
> On 03/12/2012 04:15 PM, J. Bruce Fields wrote:
> > On Mon, Mar 12, 2012 at 03:45:05PM -0400, Nikolaus Rath wrote:
> >> 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?
> > 
> > I don't remember where it gets the ip it uses to construct clientid's
> > from....  But there is a mount option (clientaddr=) that will let you
> > change what it uses.  So it *might* be worth checking whether using a
> > clientaddr= option on each client (giving it a different ipaddr on each
> > client) would change the behavior.
> 
> I'll try that.
> 
> Since there seems to be some problem with client identity: all the
> clients are generated using the same disk image. This image also
> includes some stuff in /var/lib/nfs. I already tried emptying this on
> every client and did not help, but maybe there is another directory with
> state data that could cause problems?

The state in there is used by the v2/v3 client, and by the server with
v4 as well, but not by the v4 client, so I wouldn't expect that to be an
issue.

> >>> 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.
> > 
> > Looking at the packet details, under the client id field, the clients
> > are all using:
> > 
> > 	"0.0.0.0/192.168.1.2 tcp UNIX 0"
> 
> Hmm. 192.168.1.2 is the server's address on the VPN. Is that supposed to
> be there?

Yes,and the first ip is usually the ip of the client, which does suggest
the client is guessing it's ip wrong; so the "clientaddr=" option will
likely help.

Hm, perhaps the server should be rejecting these SETCLIENTID's with
INUSE.  It used to do that, and the client would likely recover from
that more easily.

--b.