net: rps: protect filter locklessly

As we can see, rflow->filter can be written/read concurrently, so
lockless access is needed.
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -4530,9 +4530,9 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 			goto out;
 		old_rflow = rflow;
 		rflow = &flow_table->flows[flow_id];
-		rflow->filter = rc;
-		if (old_rflow->filter == rflow->filter)
-			old_rflow->filter = RPS_NO_FILTER;
+		WRITE_ONCE(rflow->filter, rc);
+		if (old_rflow->filter == rc)
+			WRITE_ONCE(old_rflow->filter, RPS_NO_FILTER);
 	out:
 #endif
 		head = READ_ONCE(per_cpu(softnet_data, next_cpu).input_queue_head);
@@ -4672,7 +4672,7 @@ bool rps_may_expire_flow(struct net_device *dev, u16 rxq_index,
 	if (flow_table && flow_id <= flow_table->mask) {
 		rflow = &flow_table->flows[flow_id];
 		cpu = READ_ONCE(rflow->cpu);
-		if (rflow->filter == filter_id && cpu < nr_cpu_ids &&
+		if (READ_ONCE(rflow->filter) == filter_id && cpu < nr_cpu_ids &&
 		    ((int)(READ_ONCE(per_cpu(softnet_data, cpu).input_queue_head) -
 			   READ_ONCE(rflow->last_qtail)) <
 		     (int)(10 * flow_table->mask)))