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

cel
2025-01-14T22:09:27Z

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);
--
2.47.0