Re: [Question]nfs: never returned delegation

[Li Lingfeng <lilingfeng3@huawei.com>]

Hi,

在 2025/8/11 21:03, Trond Myklebust 写道:
> 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.
>
I found that a server-side bug could also cause such behavior, and I've
reproduced the issue based on the master (commit b320789d6883).
nfs4_laundromat                       nfsd4_delegreturn
  list_add // add dp to reaplist
           // by dl_recall_lru
  list_del_init // delete dp from
                // reaplist
                                        destroy_delegation
                                         unhash_delegation_locked
                                          list_del_init
                                          // dp was not added to any list
                                          // via dl_recall_lru
  revoke_delegation
  list_add // add dp to cl_revoked
           // by dl_recall_lru

The delegation will be left in cl_revoked.

I agree with Trond's suggestion to change the server code to fix it.

Thanks,
Lingfeng