datapath: Make flow mask removal symmetric.

Masks are inserted when flows are inserted to the table, so it is
logical to correspondingly remove masks when flows are removed from
the table, in ovs_flow_table_remove().

This allows ovs_flow_free() to be called without locking, which will
be used by later patches.

Signed-off-by: Jarno Rajahalme <[email protected]>
Signed-off-by: Pravin B Shelar <[email protected]>Summary:

datapath/flow_table.c

@@ -168,25 +168,6 @@ void ovs_flow_free(struct sw_flow *flow, bool deferred)
 	if (!flow)
 		return;
 
-	if (flow->mask) {
-		struct sw_flow_mask *mask = flow->mask;
-
-		/* ovs-lock is required to protect mask-refcount and
-		 * mask list.
-		 */
-		ASSERT_OVSL();
-		BUG_ON(!mask->ref_count);
-		mask->ref_count--;
-
-		if (!mask->ref_count) {
-			list_del_rcu(&mask->list);
-			if (deferred)
-				call_rcu(&mask->rcu, rcu_free_sw_flow_mask_cb);
-			else
-				kfree(mask);
-		}
-	}
-
 	if (deferred)
 		call_rcu(&flow->rcu, rcu_free_flow_callback);
 	else
@@ -500,13 +481,36 @@ static struct table_instance *table_instance_expand(struct table_instance *ti)
 	return table_instance_rehash(ti, ti->n_buckets * 2);
 }
 
+/* Remove 'mask' from the mask list, if it is not needed any more. */
+static void flow_mask_remove(struct flow_table *tbl, struct sw_flow_mask *mask)
+{
+	if (mask) {
+		/* ovs-lock is required to protect mask-refcount and
+		 * mask list.
+		 */
+		ASSERT_OVSL();
+		BUG_ON(!mask->ref_count);
+		mask->ref_count--;
+
+		if (!mask->ref_count) {
+			list_del_rcu(&mask->list);
+			call_rcu(&mask->rcu, rcu_free_sw_flow_mask_cb);
+		}
+	}
+}
+
+/* Must be called with OVS mutex held. */
 void ovs_flow_tbl_remove(struct flow_table *table, struct sw_flow *flow)
 {
 	struct table_instance *ti = ovsl_dereference(table->ti);
 
 	BUG_ON(table->count == 0);
 	hlist_del_rcu(&flow->hash_node[ti->node_ver]);
 	table->count--;
+
+	/* RCU delete the mask. 'flow->mask' is not NULLed, as it should be
+	 * accessible as long as the RCU read lock is held. */
+	flow_mask_remove(table, flow->mask);
 }
 
 static struct sw_flow_mask *mask_alloc(void)
@@ -569,6 +573,7 @@ static int flow_mask_insert(struct flow_table *tbl, struct sw_flow *flow,
 	return 0;
 }
 
+/* Must be called with OVS mutex held. */
 int ovs_flow_tbl_insert(struct flow_table *table, struct sw_flow *flow,
 			struct sw_flow_mask *mask)
 {