openvswitch: Fix ovs_flow_stats_get/clear RCU dereference.

For ovs_flow_stats_get() using ovsl_dereference() was wrong, since
flow dumps call this with RCU read lock.

ovs_flow_stats_clear() is always called with ovs_mutex, so can use
ovsl_dereference().

Also, make the ovs_flow_stats_get() 'flow' argument const to make
later patches cleaner.
Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>

net/openvswitch/flow.c

@@ -122,8 +122,9 @@ void ovs_flow_stats_update(struct sw_flow *flow, struct sk_buff *skb)
 	spin_unlock(&stats->lock);
 }
 
-/* Called with ovs_mutex. */
-void ovs_flow_stats_get(struct sw_flow *flow, struct ovs_flow_stats *ovs_stats,
+/* Must be called with rcu_read_lock or ovs_mutex. */
+void ovs_flow_stats_get(const struct sw_flow *flow,
+			struct ovs_flow_stats *ovs_stats,
 			unsigned long *used, __be16 *tcp_flags)
 {
 	int node;
@@ -133,7 +134,7 @@ void ovs_flow_stats_get(struct sw_flow *flow, struct ovs_flow_stats *ovs_stats,
 	memset(ovs_stats, 0, sizeof(*ovs_stats));
 
 	for_each_node(node) {
-		struct flow_stats *stats = ovsl_dereference(flow->stats[node]);
+		struct flow_stats *stats = rcu_dereference_ovsl(flow->stats[node]);
 
 		if (stats) {
 			/* Local CPU may write on non-local stats, so we must
@@ -150,12 +151,13 @@ void ovs_flow_stats_get(struct sw_flow *flow, struct ovs_flow_stats *ovs_stats,
 	}
 }
 
+/* Called with ovs_mutex. */
 void ovs_flow_stats_clear(struct sw_flow *flow)
 {
 	int node;
 
 	for_each_node(node) {
-		struct flow_stats *stats = rcu_dereference(flow->stats[node]);
+		struct flow_stats *stats = ovsl_dereference(flow->stats[node]);
 
 		if (stats) {
 			spin_lock_bh(&stats->lock);

net/openvswitch/flow.h

@@ -180,10 +180,10 @@ struct arp_eth_header {
 	unsigned char       ar_tip[4];		/* target IP address        */
 } __packed;
 
-void ovs_flow_stats_update(struct sw_flow *flow, struct sk_buff *skb);
-void ovs_flow_stats_get(struct sw_flow *flow, struct ovs_flow_stats *stats,
+void ovs_flow_stats_update(struct sw_flow *, struct sk_buff *);
+void ovs_flow_stats_get(const struct sw_flow *, struct ovs_flow_stats *,
 			unsigned long *used, __be16 *tcp_flags);
-void ovs_flow_stats_clear(struct sw_flow *flow);
+void ovs_flow_stats_clear(struct sw_flow *);
 u64 ovs_flow_used_time(unsigned long flow_jiffies);
 
 int ovs_flow_extract(struct sk_buff *, u16 in_port, struct sw_flow_key *);