Re: [RFC PATCH] NFSD: Skip sending CB_RECALL_ANY when the backchannel isn't up

Jeff Layton
2025-01-14T22:47:00Z

On Tue, 2025-01-14 at 17:09 -0500, cel@kernel.org wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
>
> NFSD sends CB_RECALL_ANY to clients when the server is low on
> memory or that client has a large number of delegations outstanding.
>
> We've seen cases where NFSD attempts to send CB_RECALL_ANY requests
> to disconnected clients, and gets confused. These calls never go
> anywhere if a backchannel transport to the target client isn't
> available. Before the server can send any backchannel operation, the
> client has to connect first and then do a BIND_CONN_TO_SESSION.
>
> This patch doesn't address the root cause of the confusion, but
> there's no need to queue up these optional operations if they can't
> go anywhere.
>
> Fixes: 44df6f439a17 ("NFSD: add delegation reaper to react to low memory condition")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
> fs/nfsd/nfs4state.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index b7a0cfd05401..9ef32b19198c 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -6867,7 +6867,8 @@ deleg_reaper(struct nfsd_net *nn)
> clp->cl_ra_time < 5)) {
> continue;
> }
> - list_add(&clp->cl_ra_cblist, &cblist);
> + if (clp->cl_cb_state == NFSD4_CB_UP)
> + list_add(&clp->cl_ra_cblist, &cblist);
>
> /* release in nfsd4_cb_recall_any_release */
> kref_get(&clp->cl_nfsdfs.cl_ref);

Sounds like a reasonable thing to do.

Reviewed-by: Jeff Layton <jlayton@kernel.org>