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From: Olga Kornievskaia <aglo@umich.edu>
Date: Tue, 14 May 2024 17:49:53 -0400
Message-ID: <CAN-5tyGECFmtzFsYNSZicPcH4SMKF0yovk6V20sWJ1LrZKzzyA@mail.gmail.com>
Subject: Re: sm notify (nlm) question
To: Frank Filz <ffilzlnx@mindspring.com>
Cc: Chuck Lever III <chuck.lever@oracle.com>, 
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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On Tue, May 14, 2024 at 5:36=E2=80=AFPM Frank Filz <ffilzlnx@mindspring.com=
> wrote:
>
> > > On May 14, 2024, at 2:56=E2=80=AFPM, Olga Kornievskaia <aglo@umich.ed=
u> wrote:
> > >
> > > Hi folks,
> > >
> > > Given that not everything for NFSv3 has a specification, I post a
> > > question here (as it concerns linux v3 (client) implementation) but I
> > > ask a generic question with respect to NOTIFY sent by an NFS server.
> >
> > There is a standard:
> >
> > https://pubs.opengroup.org/onlinepubs/9629799/chap11.htm
> >
> >
> > > A NOTIFY message that is sent by an NFS server upon reboot has a
> > > monitor name and a state. This "state" is an integer and is modified
> > > on each server reboot. My question is: what about state value
> > > uniqueness? Is there somewhere some notion that this value has to be
> > > unique (as in say a random value).
> > >
> > > Here's a problem. Say a client has 2 mounts to ip1 and ip2 (both
> > > representing the same DNS name) and acquires a lock per mount. Now sa=
y
> > > each of those servers reboot. Once up they each send a NOTIFY call an=
d
> > > each use a timestamp as basis for their "state" value -- which very
> > > likely is to produce the same value for 2 servers rebooted at the sam=
e
> > > time (or for the linux server that looks like a counter). On the
> > > client side, once the client processes the 1st NOTIFY call, it update=
s
> > > the "state" for the monitor name (ie a client monitors based on a DNS
> > > name which is the same for ip1 and ip2) and then in the current code,
> > > because the 2nd NOTIFY has the same "state" value this NOTIFY call
> > > would be ignored. The linux client would never reclaim the 2nd lock
> > > (but the application obviously would never know it's missing a lock)
> > > --- data corruption.
> > >
> > > Who is to blame: is the server not allowed to send "non-unique" state
> > > value? Or is the client at fault here for some reason?
> >
> > The state value is supposed to be specific to the monitored host. If th=
e client is
> > indeed ignoring the second reboot notification, that's incorrect behavi=
or, IMO.
>
> If you are using multiple server IP addresses with the same DNS name, you=
 may want to set:
>
> sysctl fs.nfs.nsm_use_hostnames=3D0
>
> The NLM will register with statd using the IP address as name instead of =
host name. Then your two IP addresses will each have a separate monitor ent=
ry and state value monitored.

In my setup I already have this set to 0. But I'll look around the
code to see what it is supposed to do.

>
> Frank
>