NFSD: Skip sending CB_RECALL_ANY when the backchannel isn't up

commit 8a388c1 upstream.

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: 44df6f4 ("NFSD: add delegation reaper to react to low memory condition")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: chucklever

fs/nfsd/nfs4state.c

@@ -6882,14 +6882,19 @@ deleg_reaper(struct nfsd_net *nn)
 	spin_lock(&nn->client_lock);
 	list_for_each_safe(pos, next, &nn->client_lru) {
 		clp = list_entry(pos, struct nfs4_client, cl_lru);
-		if (clp->cl_state != NFSD4_ACTIVE ||
-			list_empty(&clp->cl_delegations) ||
-			atomic_read(&clp->cl_delegs_in_recall) ||
-			test_bit(NFSD4_CLIENT_CB_RECALL_ANY, &clp->cl_flags) ||
-			(ktime_get_boottime_seconds() -
-				clp->cl_ra_time < 5)) {
+
+		if (clp->cl_state != NFSD4_ACTIVE)
+			continue;
+		if (list_empty(&clp->cl_delegations))
+			continue;
+		if (atomic_read(&clp->cl_delegs_in_recall))
+			continue;
+		if (test_bit(NFSD4_CLIENT_CB_RECALL_ANY, &clp->cl_flags))
+			continue;
+		if (ktime_get_boottime_seconds() - clp->cl_ra_time < 5)
+			continue;
+		if (clp->cl_cb_state != NFSD4_CB_UP)
 			continue;
-		}
 		list_add(&clp->cl_ra_cblist, &cblist);
 
 		/* release in nfsd4_cb_recall_any_release */