linux-kernel - Re: NFSv3 lock recovery

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Date:	Tue, 28 Aug 2007 16:31:08 +1000
From:	Neil Brown <neilb@...e.de>
To:	"Janne Karhunen" <janne.karhunen@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: NFSv3 lock recovery

On Tuesday August 28, janne.karhunen@...il.com wrote:
> Hi,
> 
> Brief question about NFSv3 lock recovery to those who might
> know - does Linux implementation (or NLM/NSM protocol)
> properly support the case in which client and server state
> change simultaneously?

If both crash, there is nothing for a client to reclaim and nothing
for a server to discard, so it is hard to see where a problem could
lie.

> 
> Reason I'm asking is that this very case is occasionally giving
> me stale locks. Given that NFSv3 server crashes it's possible
> that client 'rooting' from it crashes as well. Now, once the
> server comes back up it tries to notify the client that just
> crashed. Hardly surprisingly, this notification doesn't go
> anywhere and server discards the notification/client. And once
> the client starts to boot again it tries to notify the server which
> instantly whines about SM_NOTIFY when no-one is being
> monitored. Thus, whole notification cycle is busted and lock
> states go haywire :/. Is this even supposed to work?
> 

More details.  What, exactly, goes "haywire"...

If your client is diskless and mounting root from the server, then it
should be mounting the root with "-o nolock" and there should be no
locking issues at all.
Possibly it mounts some other filesystems as well, and they are
mounted with locks.  But still, I cannot imagine a problem scenario.

Please explain in detail your configuration (What is mounted where and
with what options etc) and what happens (why does the client crash
just because the server crashed - it shouldn't), and what actually
fails that you expected to work.

NeilBrown
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