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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Neil Brown <neilb@suse.de>
CC:     Jeff Layton <jlayton@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Olga Kornievskaia <kolga@netapp.com>,
        Dai Ngo <dai.ngo@oracle.com>, Tom Talpey <tom@talpey.com>
Subject: Re: [PATCH 6/6] nfsd: allow delegation state ids to be revoked and
 then freed
Thread-Topic: [PATCH 6/6] nfsd: allow delegation state ids to be revoked and
 then freed
Thread-Index: AQHaDF75bEKrShy72kWA52GSBv2SfLBkuEKAgAAOcICAACzEgA==
Date:   Wed, 1 Nov 2023 05:41:58 +0000
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> On Oct 31, 2023, at 8:01 PM, NeilBrown <neilb@suse.de> wrote:
>=20
> On Wed, 01 Nov 2023, Chuck Lever III wrote:
>> Howdy Neil-
>>=20
>>> On Oct 31, 2023, at 5:57 PM, NeilBrown <neilb@suse.de> wrote:
>>>=20
>>> Revoking state through 'unlock_filesystem' now revokes any delegation
>>> states found.  When the stateids are then freed by the client, the
>>> revoked stateids will be cleaned up correctly.
>>=20
>> Here's my derpy question of the day.
>>=20
>> "When the stateids are then freed by the client" seems to be
>> a repeating trope, and it concerns me a bit (probably because
>> I haven't yet learned how this mechanism /currently/ works)...
>>=20
>> In the case when the client has actually vanished (eg, was
>> destroyed by an orchestrator), it's not going to be around
>> to actively free revoked state. Doesn't that situation result
>> in pinned state on the server? I would expect that's a primary
>> use case for "unlock_filesystem."
>=20
> If a client is de-orchestrated then it will stop renewing its lease, and
> regular cleanup of expired state will kick in after one lease period.

Thanks for educating me.

Such state actually stays around for much longer now as
expired but renewable state. Does unlock_filesystem need
to purge courtesy state too, to make the target filesystem
unexportable and unmountable?


> So for NFSv4 we don't need to worry about disappearing clients.
> For NFSv3 (or more specifically for NLM) we did and locks could hang
> around indefinitely if the client died.
> For that reason we have /proc/fs/nfsd/unlock_ip which discards all NFSv3
> lock state for a given client.  Extending that to NFSv4 is not needed
> because of leases, and not meaningful because of trunking - a client
> might have several IP's.
>=20
> unlock_filesystem is for when the client is still active and we want to
> let it (them) continue accessing some filesystems, but not all.
>=20
> NeilBrown
>=20
>=20
>>=20
>> Maybe I've misunderstood something fundamental.
>>=20
>>=20
>> --
>> Chuck Lever


--
Chuck Lever