linux-kernel - Re: nfsd hang and kernel bug in 2.6.35-rc3

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Date:	Thu, 17 Jun 2010 10:30:43 -0400
From:	Jeff Layton <jlayton@...hat.com>
To:	Chris Vine <chris@...ne.freeserve.co.uk>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: nfsd hang and kernel bug in 2.6.35-rc3

On Thu, 17 Jun 2010 11:38:15 +0100
Chris Vine <chris@...ne.freeserve.co.uk> wrote:

> On Wed, 16 Jun 2010 20:44:15 -0400
> Jeff Layton <jlayton@...hat.com> wrote:
> [snip]
> > I stand corrected then. That's pretty close to the nfsd that I've been
> > testing. I pulled down the nfsd init script and the only thing that
> > looks substantially different is that it sends signals to nfsd to shut
> > it down rather than just running "rpc.nfsd 0". That should work fine,
> > however.
> > 
> > Still I think the problem is basically something like what I've
> > described. You ended up somehow with sockets on the sv_permsocks list
> > that didn't hold lockd references. The way I described is one way that
> > could occur. Another seems to be __write_ports_addxprt (which I think
> > is clearly broken in light of this)...
> > 
> > The root cause of this however is likely to be related to this
> > problem:
> > 
> > > Jun 15 16:07:18 laptop kernel: svc: failed to register lockdv3 RPC
> > > service (errno 110). Jun 15 16:07:18 laptop kernel: lockd_up:
> > > makesock failed, error=-110
> > 
> > ...which means that the kernel couldn't talk to portmap or rpcbind.
> > Maybe it wasn't up at the time? Or a problem with firewalling?
> 
> My initial reaction was "of course it is up" but your mention of
> portmap sent me investigating with interesting results. I was going
> to say "of course its is up" because the standard start-up script for
> nfsd (rc.nfsd) checks whether rpc.portmap and rpc.statd are running, if
> not starts them, and then starts exportfs, rpc.rquotad, rpc.nfsd and
> rpc.mountd.
> 
> However, if I start portmap and statd early on so they do not rely on
> the nfsd start-up script, then nfsd starts fine, so it seems to be a
> timing thing notwithstanding that they are all started (at user level)
> sequentially and in the same thread/process.
> 
> The timing problem does not arise on kernel-2.6.34 and earlier. Nor
> does it arise on my pentium uniprocessor machine with kernel 2.6.35-rc3,
> so it could well be core/thread related.  It looks as if something in
> the kernel has changed on that in 2.6.35 which provokes the kernel bug
> report if timing is wrong.  (If timing is wrong and if this is a user
> tools rather than a kernel deficiency, and I express no view on that,
> then I suppose it probably needs to be handled more gracefully in the
> kernel.)
> 
> Chris
> 
> 

The timing may help tickle the other bugs in nfsd startup/shutdown.
I've just sent another couple of patches to Bruce (and cc'ed you) that
I suspect may help this. With those, it should always be the case that
a nfsd sv_permsocks entry holds a lockd reference.

It would be good if you could test the stack of patches in the
nfsd-error branch of my kernel.org git tree: 

http://git.kernel.org/?p=linux/kernel/git/jlayton/linux.git;a=summary

Thanks,
-- 
Jeff Layton <jlayton@...hat.com>
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