Subject: Re: 2.6.38.6 - state manager constantly respawns
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: "Dr. J. Bruce Fields" <bfields@fieldses.org>
Cc: Harry Edmon <harry@uw.edu>, Chuck Lever <chuck.lever@oracle.com>,
        linux-nfs@vger.kernel.org
Date: Fri, 20 May 2011 13:52:43 -0400
In-Reply-To: <20110520172639.GA11670@fieldses.org>
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On Fri, 2011-05-20 at 13:26 -0400, Dr. J. Bruce Fields wrote: 
> On Fri, May 20, 2011 at 09:20:47AM -0700, Harry Edmon wrote:
> > On 05/16/11 13:53, Dr. J. Bruce Fields wrote:
> > >Hm, so the renews all have clid 465ccc4d09000000, and the reads all have
> > >a stateid (0, 465ccc4dc24c0a0000000000).
> > >
> > >So the first 4 bytes matching just tells me both were handed out by the
> > >same server instance (so there was no server reboot in between); there's
> > >no way for me to tell whether they really belong to the same client.
> > >
> > >The server does assume that any stateid from the current server instance
> > >that no longer exists in its table is expired.  I believe that's
> > >correct, given a correctly functioning client, but perhaps I'm missing a
> > >case.
> > >
> > >--b.
> > I am very appreciative of the quick initial comments I receive from
> > all of you on my NFS problem.   I notice that there has been silence
> > on the problem since the 16th, so I assume that either this is a
> > hard bug to track down or you have been busy with higher priority
> > tasks.  Is there anything I can do to help develop a solution to
> > this problem?
> 
> Well, the only candidate explanation for the problem is that my
> assumption--that any time the server gets a stateid from the current
> boot instance that it doesn't recognize as an active stateid, it is safe
> for the server to return EXPIRED--is wrong.
> 
> I don't immediately see why it's wrong, and based on the silence nobody
> else does either, but I'm not 100% convinced I'm right either.
> 
> So one approach might be to add server code that makes a better effort
> to return EXPIRED only when we're sure it's a stateid from an expired
> client, and see if that solves your problem.
> 
> Remind me, did you have an easy way to reproduce your problem?

My silence is simply because I'm mystified as to how this can happen.
Patching for it is trivial (see below).

When the server tells us that our lease is expired, the normal behaviour
for the client is to re-establish the lease, and then proceed to recover
all known stateids. I don't see how we can 'miss' a stateid that then
needs to be recovered afterwards...

Cheers
  Trond

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