Re: [Question]nfs: never returned delegation

Trond Myklebust
2025-08-11T13:03:16Z

On Mon, 2025-08-11 at 20:48 +0800, zhangjian (CG) wrote:
> Recently, we meet a NFS problem in 5.10. There are so many
> test_state_id request after a non-privilaged request in tcpdump
> result. There are 40w+ delegations in client (I read the delegation
> list from /proc/kcore).
> Firstly, I think state manager cost a lot in
> nfs_server_reap_expired_delegations. But I see they are all in
> NFS_DELEGATION_REVOKED state except 6 in NFS_DELEGATION_REFERENCED (I
> read this from /proc/kcore too).
> I analyze NFS code and find if NFSPROC4_CLNT_DELEGRETURN procedure
> meet ETIMEOUT, delegation will be marked as NFS4ERR_DELEG_REVOKED and
> never return it again. NFS server will keep the revoked delegation in
> clp->cl_revoked forever. This will result in following sequence
> response with RECALLABLE_STATE_REVOKED flag. Client will send
> test_state_id request for all non-revoked delegation.
> This can only be solved by restarting NFS server.
> I think ETIMEOUT in NFSPROC4_CLNT_DELEGRETURN procedure may be not
> the only case that cause lots of non-terminable test_state_id
> requests after any non-privilaged request.
> Wish NFS experts give some advices on this problem.
>

You have the following options:

1. Don't ever use "soft" or "softerr" on the NFS client.
2. Reboot your server every now and again.
3. Change the server code to not bother caching revoked state. Doing
so is rather pointless, since there is nothing a client can do
differently when presented with NFS4ERR_DELEG_REVOKED vs.
NFS4ERR_BAD_STATEID.
4. Change the server code to garbage collect revoked stateids after
a while.

--
Trond Myklebust Linux NFS client maintainer, Hammerspace
trondmy@kernel.org, trond.myklebust@hammerspace.com