nfsd4: make sure sequence flags are set after destroy_session

If this loses any backchannel, make sure we have a chance to notice that
and set the sequence flags.
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4callback.c

@@ -589,6 +589,12 @@ void nfsd4_probe_callback(struct nfs4_client *clp)
 	do_probe_callback(clp);
 }
 
+void nfsd4_probe_callback_sync(struct nfs4_client *clp)
+{
+	nfsd4_probe_callback(clp);
+	flush_workqueue(callback_wq);
+}
+
 void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
 {
 	clp->cl_cb_state = NFSD4_CB_UNKNOWN;

fs/nfsd/nfs4state.c

@@ -1686,8 +1686,7 @@ nfsd4_destroy_session(struct svc_rqst *r,
 	spin_unlock(&client_lock);
 
 	nfs4_lock_state();
-	/* wait for callbacks */
-	nfsd4_shutdown_callback(ses->se_client);
+	nfsd4_probe_callback_sync(ses->se_client);
 	nfs4_unlock_state();
 
 	nfsd4_del_conns(ses);

fs/nfsd/state.h

@@ -464,6 +464,7 @@ extern __be32 nfs4_check_open_reclaim(clientid_t *clid);
 extern void nfs4_free_stateowner(struct kref *kref);
 extern int set_callback_cred(void);
 extern void nfsd4_probe_callback(struct nfs4_client *clp);
+extern void nfsd4_probe_callback_sync(struct nfs4_client *clp);
 extern void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *);
 extern void nfsd4_do_callback_rpc(struct work_struct *);
 extern void nfsd4_cb_recall(struct nfs4_delegation *dp);