Re: [PATCH] nfsd: remove long-standing revoked delegations by force

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2025-09-02 at 10:22 +0800, Li Lingfeng wrote:
> When file access conflicts occur between clients, the server recalls
> delegations. If the client holding delegation fails to return it after
> a recall, nfs4_laundromat adds the delegation to cl_revoked list.
> This causes subsequent SEQUENCE operations to set the
> SEQ4_STATUS_RECALLABLE_STATE_REVOKED flag, forcing the client to
> validate all delegations and return the revoked one.
> 
> However, if the client fails to return the delegation due to a timeout
> after receiving the recall or a server bug, the delegation remains in the
> server's cl_revoked list. The client marks it revoked and won't find it
> upon detecting SEQ4_STATUS_RECALLABLE_STATE_REVOKED. This leads to a loop:
> the server persistently sets SEQ4_STATUS_RECALLABLE_STATE_REVOKED, and the
> client repeatedly tests all delegations, severely impacting performance
> when numerous delegations exist.
> 

It is a performance impact, but I don't get the "loop" here. Are you
saying that this problem compounds itself? That testing all delegations
causes others to be revoked?

> Since abnormal delegations are removed from flc_lease via nfs4_laundromat
> --> revoke_delegation --> destroy_unhashed_deleg -->
> nfs4_unlock_deleg_lease --> kernel_setlease, and do not block new open
> requests indefinitely, retaining such a delegation on the server is
> unnecessary.
> 
> Reported-by: Zhang Jian <zhangjian496@huawei.com>
> Fixes: 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED")
> Closes: https://lore.kernel.org/all/ff8debe9-6877-4cf7-ba29-fc98eae0ffa0@huawei.com/
> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
> ---
>  fs/nfsd/nfs4state.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 88c347957da5..aa65a685dbb9 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -4326,6 +4326,8 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	int buflen;
>  	struct net *net = SVC_NET(rqstp);
>  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> +	struct list_head *pos, *next;
> +	struct nfs4_delegation *dp;
>  
>  	if (resp->opcnt != 1)
>  		return nfserr_sequence_pos;
> @@ -4470,6 +4472,15 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	default:
>  		seq->status_flags = 0;
>  	}
> +	if (!list_empty(&clp->cl_revoked)) {
> +		list_for_each_safe(pos, next, &clp->cl_revoked) {
> +			dp = list_entry(pos, struct nfs4_delegation, dl_recall_lru);
> +			if (dp->dl_time < (ktime_get_boottime_seconds() - 2 * nn->nfsd4_lease)) {
> +				list_del_init(&dp->dl_recall_lru);
> +				nfs4_put_stid(&dp->dl_stid);
> +			}
> +		}
> +	}
>  	if (!list_empty(&clp->cl_revoked))
>  		seq->status_flags |= SEQ4_STATUS_RECALLABLE_STATE_REVOKED;
>  	if (atomic_read(&clp->cl_admin_revoked))

This seems like a violation of the spec. AIUI, the server is required
to hang onto a record of the delegation until the client does the
TEST_STATEID/FREE_STATEID dance to remove it. Just discarding them like
this seems wrong.

Should we instead just administratively evict the client since it's
clearly not behaving right in this case?
-- 
Jeff Layton <jlayton@kernel.org>