Re: [PATCH] NLM: add network test when host expire but hold lock at nlm_gc_hosts

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Wed, 2009-12-02 at 07:26 -0500, Jeff Layton wrote: 
> On Wed, 02 Dec 2009 17:47:04 +0800
> Mi Jinlong <mijinlong@cn.fujitsu.com> wrote:
> 
> > After a client get lock, it's network partition for some reasons.
> > other client cannot get lock success forever.
> > 
> > This patch can avoid this problem using rpc_ping to test client's
> > network when host expired but hold lock.
> > 
> > If the client's network is partition, server will release client's 
> > lock, other client will get lock success.
> > 
> > Signed-off-by: mijinlong@cn.fujitsu.com
> 
> Yikes! That sounds like it'll make locking subject to the reliability
> of the network. I don't think that's a good idea.
> 
> What might be more reasonable is to consider implementing something
> like the clear_locks command in Solaris. That is, a way for an admin to
> remove server-side locks held by a client that he knows is never going
> to come back. With that, this sort of thing at least becomes a willful
> act...

Agreed on both counts.

We should not be changing the semantics of either NFSv3 or NLM at this
time. That will break existing setups that are treating NFSv3 as being a
stable platform.
As I've said in previous correspondence: NFSv4 already offers lease
based locking. If people are worried about network partitions and/or
locks being held by clients that are dead, then they can switch to that.

On the other hand, a clear_locks command could be useful in order to
tell a server that a given client is dead. It should be fairly easy to
leverage the existing NSM/statd protocol to implement this.

Trond