nfsd4: set sequence flag when backchannel is down

Implement the SEQ4_STATUS_CB_PATH_DOWN flag.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 919ad25..15bd1cc 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1800,8 +1800,12 @@
 out:
 	/* Hold a session reference until done processing the compound. */
 	if (cstate->session) {
+		struct nfs4_client *clp = session->se_client;
+
 		nfsd4_get_session(cstate->session);
-		atomic_inc(&session->se_client->cl_refcount);
+		atomic_inc(&clp->cl_refcount);
+		if (clp->cl_cb_state == NFSD4_CB_DOWN)
+			seq->status_flags |= SEQ4_STATUS_CB_PATH_DOWN;
 	}
 	kfree(conn);
 	spin_unlock(&client_lock);