net: rps: protect last_qtail with rps_input_queue_tail_save() helper

Removing one unnecessary reader protection and add another writer
protection to finish the locklessly proctection job.

Note: the removed READ_ONCE() is not needed because we only have to protect
the locklessly reader in the different context (rps_may_expire_flow()).

Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index f6c6e494f0a91e23cfa25aa203f53502c9917533..6f027f676243d1236bbf824a043a4ec416414734 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4507,7 +4507,7 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
                struct netdev_rx_queue *rxqueue;
                struct rps_dev_flow_table *flow_table;
                struct rps_dev_flow *old_rflow;
-               u32 flow_id;
+               u32 flow_id, head;
                u16 rxq_index;
                int rc;
 
@@ -4535,8 +4535,8 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
                        old_rflow->filter = RPS_NO_FILTER;
        out:
 #endif
-               rflow->last_qtail =
-                       READ_ONCE(per_cpu(softnet_data, next_cpu).input_queue_head);
+               head = READ_ONCE(per_cpu(softnet_data, next_cpu).input_queue_head);
+               rps_input_queue_tail_save(&rflow->last_qtail, head);
        }
 
        rflow->cpu = next_cpu;
@@ -4619,7 +4619,7 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
                if (unlikely(tcpu != next_cpu) &&
                    (tcpu >= nr_cpu_ids || !cpu_online(tcpu) ||
                     ((int)(READ_ONCE(per_cpu(softnet_data, tcpu).input_queue_head) -
-                     READ_ONCE(rflow->last_qtail))) >= 0)) {
+                     rflow->last_qtail)) >= 0)) {
                        tcpu = next_cpu;
                        rflow = set_rps_cpu(dev, skb, rflow, next_cpu);
                }