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From: "Frank Filz" <ffilzlnx@mindspring.com>
To: "'Chuck Lever III'" <chuck.lever@oracle.com>,
	"'Olga Kornievskaia'" <aglo@umich.edu>
Cc: "'Linux NFS Mailing List'" <linux-nfs@vger.kernel.org>
References:  <CAN-5tyFBn3C_CTrsftuYeWJHe7KWxd82YFCyrN9t=az8J4RU0w@mail.gmail.com> <2C80B5BC-AAEC-41F8-BEB6-C920F88C89BB@oracle.com>
In-Reply-To: <2C80B5BC-AAEC-41F8-BEB6-C920F88C89BB@oracle.com>
Subject: RE: sm notify (nlm) question
Date: Tue, 14 May 2024 14:36:46 -0700
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> > On May 14, 2024, at 2:56=E2=80=AFPM, Olga Kornievskaia =
<aglo@umich.edu> 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.
>=20
> There is a standard:
>=20
> https://pubs.opengroup.org/onlinepubs/9629799/chap11.htm
>=20
>=20
> > 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 =
say
> > each of those servers reboot. Once up they each send a NOTIFY call =
and
> > 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 =
same
> > time (or for the linux server that looks like a counter). On the
> > client side, once the client processes the 1st NOTIFY call, it =
updates
> > 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?
>=20
> The state value is supposed to be specific to the monitored host. If =
the client is
> indeed ignoring the second reboot notification, that's incorrect =
behavior, 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 =
entry and state value monitored.

Frank