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Date:   Thu, 26 Sep 2019 12:05:56 -0400
From:   Bruce Fields <bfields@fieldses.org>
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Kevin Vasko <kvasko@gmail.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: NFSv4 client locks up on larger writes with Kerberos enabled
Message-ID: <20190926160556.GC29192@fieldses.org>
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On Thu, Sep 26, 2019 at 08:55:17AM -0700, Chuck Lever wrote:
> > On Sep 25, 2019, at 1:07 PM, Bruce Fields <bfields@fieldses.org> wrote:
> > 
> > On Wed, Sep 25, 2019 at 11:49:14AM -0700, Chuck Lever wrote:
> >> Sounds like the NFS server is dropping the connection. With
> >> GSS enabled, that's usually a sign that the GSS window has
> >> overflowed.
> > 
> > Would that show up in the rpc statistics on the client somehow?
> 
> More likely on the server. The client just sees a disconnect
> without any explanation attached.

So watching a count of disconnects might at least tell us something?

> gss_verify_header is where the checking is done on the server.
> Disappointingly, I see some dprintk's in there, but no static
> trace events.

Kevin, was this a Linux server?

--b.

> > In that case--I seem to remember there's a way to configure the size of
> > the client's slot table, maybe lowering that (decreasing the number of
> > rpc's allowed to be outstanding at a time) would work around the
> > problem.
> 
> > Should the client be doing something different to avoid or recover from
> > overflows of the gss window?
> 
> The client attempts to meter the request stream so that it stays
> within the bounds of the GSS sequence number window. The stream
> of requests is typically unordered coming out of the transmit
> queue.
> 
> There is some new code (since maybe v5.0?) that handles the
> metering: gss_xmit_need_reencode().