net: openvswitch: introduce common code for flushing flows

To avoid some issues, for example RCU usage warning and double free,
we should flush the flows under ovs_lock. This patch refactors
table_instance_destroy and introduces table_instance_flow_flush
which can be invoked by __dp_destroy or ovs_flow_tbl_flush.

Fixes: 50b0e61 ("net: openvswitch: fix possible memleak on destroy flow-table")
Reported-by: Johan Knöös <jknoos@google.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2020-August/050489.html
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/openvswitch/datapath.c

@@ -1756,6 +1756,7 @@ static int ovs_dp_cmd_new(struct sk_buff *skb, struct genl_info *info)
 /* Called with ovs_mutex. */
 static void __dp_destroy(struct datapath *dp)
 {
+	struct flow_table *table = &dp->table;
 	int i;
 
 	for (i = 0; i < DP_VPORT_HASH_BUCKETS; i++) {
@@ -1774,7 +1775,14 @@ static void __dp_destroy(struct datapath *dp)
 	 */
 	ovs_dp_detach_port(ovs_vport_ovsl(dp, OVSP_LOCAL));
 
-	/* RCU destroy the flow table */
+	/* Flush sw_flow in the tables. RCU cb only releases resource
+	 * such as dp, ports and tables. That may avoid some issues
+	 * such as RCU usage warning.
+	 */
+	table_instance_flow_flush(table, ovsl_dereference(table->ti),
+				  ovsl_dereference(table->ufid_ti));
+
+	/* RCU destroy the ports, meters and flow tables. */
 	call_rcu(&dp->rcu, destroy_dp_rcu);
 }
 

net/openvswitch/flow_table.c

@@ -473,19 +473,15 @@ static void table_instance_flow_free(struct flow_table *table,
 	flow_mask_remove(table, flow->mask);
 }
 
-static void table_instance_destroy(struct flow_table *table,
-				   struct table_instance *ti,
-				   struct table_instance *ufid_ti,
-				   bool deferred)
+/* Must be called with OVS mutex held. */
+void table_instance_flow_flush(struct flow_table *table,
+			       struct table_instance *ti,
+			       struct table_instance *ufid_ti)
 {
 	int i;
 
-	if (!ti)
-		return;
-
-	BUG_ON(!ufid_ti);
 	if (ti->keep_flows)
-		goto skip_flows;
+		return;
 
 	for (i = 0; i < ti->n_buckets; i++) {
 		struct sw_flow *flow;
@@ -497,18 +493,16 @@ static void table_instance_destroy(struct flow_table *table,
 
 			table_instance_flow_free(table, ti, ufid_ti,
 						 flow, false);
-			ovs_flow_free(flow, deferred);
+			ovs_flow_free(flow, true);
 		}
 	}
+}
 
-skip_flows:
-	if (deferred) {
-		call_rcu(&ti->rcu, flow_tbl_destroy_rcu_cb);
-		call_rcu(&ufid_ti->rcu, flow_tbl_destroy_rcu_cb);
-	} else {
-		__table_instance_destroy(ti);
-		__table_instance_destroy(ufid_ti);
-	}
+static void table_instance_destroy(struct table_instance *ti,
+				   struct table_instance *ufid_ti)
+{
+	call_rcu(&ti->rcu, flow_tbl_destroy_rcu_cb);
+	call_rcu(&ufid_ti->rcu, flow_tbl_destroy_rcu_cb);
 }
 
 /* No need for locking this function is called from RCU callback or
@@ -523,7 +517,7 @@ void ovs_flow_tbl_destroy(struct flow_table *table)
 
 	call_rcu(&mc->rcu, mask_cache_rcu_cb);
 	call_rcu(&ma->rcu, mask_array_rcu_cb);
-	table_instance_destroy(table, ti, ufid_ti, false);
+	table_instance_destroy(ti, ufid_ti);
 }
 
 struct sw_flow *ovs_flow_tbl_dump_next(struct table_instance *ti,
@@ -641,7 +635,8 @@ int ovs_flow_tbl_flush(struct flow_table *flow_table)
 	flow_table->count = 0;
 	flow_table->ufid_count = 0;
 
-	table_instance_destroy(flow_table, old_ti, old_ufid_ti, true);
+	table_instance_flow_flush(flow_table, old_ti, old_ufid_ti);
+	table_instance_destroy(old_ti, old_ufid_ti);
 	return 0;
 
 err_free_ti:

net/openvswitch/flow_table.h

@@ -105,5 +105,8 @@ void ovs_flow_mask_key(struct sw_flow_key *dst, const struct sw_flow_key *src,
 		       bool full, const struct sw_flow_mask *mask);
 
 void ovs_flow_masks_rebalance(struct flow_table *table);
+void table_instance_flow_flush(struct flow_table *table,
+			       struct table_instance *ti,
+			       struct table_instance *ufid_ti);
 
 #endif /* flow_table.h */