[PATCH net v2] rps: Correct wrong skb_flow_limit check when enable RPS

[gfree.wind@vip.163.com]

From: Gao Feng <gfree.wind@vip.163.com>

The skb flow limit is implemented for each CPU independently. In the
current codes, the function skb_flow_limit gets the softnet_data by
this_cpu_ptr. But the target cpu of enqueue_to_backlog would be not
the current cpu when enable RPS. As the result, the skb_flow_limit checks
the stats of current CPU, while the skb is going to append the queue of
another CPU. It isn't the expected behavior.

Now pass the softnet_data as a param to make consistent.

Fixes: 99bbc7074190 ("rps: selective flow shedding during softnet overflow")
Signed-off-by: Gao Feng <gfree.wind@vip.163.com>
---
 v2: Add Fixes tag per Eric, and enhance the commit log
 v1: intial version

 net/core/dev.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index af0558b..0f98eff 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3883,18 +3883,15 @@ static int rps_ipi_queued(struct softnet_data *sd)
 int netdev_flow_limit_table_len __read_mostly = (1 << 12);
 #endif
 
-static bool skb_flow_limit(struct sk_buff *skb, unsigned int qlen)
+static bool skb_flow_limit(struct softnet_data *sd, struct sk_buff *skb, unsigned int qlen)
 {
 #ifdef CONFIG_NET_FLOW_LIMIT
 	struct sd_flow_limit *fl;
-	struct softnet_data *sd;
 	unsigned int old_flow, new_flow;
 
 	if (qlen < (netdev_max_backlog >> 1))
 		return false;
 
-	sd = this_cpu_ptr(&softnet_data);
-
 	rcu_read_lock();
 	fl = rcu_dereference(sd->flow_limit);
 	if (fl) {
@@ -3938,7 +3935,7 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
 	if (!netif_running(skb->dev))
 		goto drop;
 	qlen = skb_queue_len(&sd->input_pkt_queue);
-	if (qlen <= netdev_max_backlog && !skb_flow_limit(skb, qlen)) {
+	if (qlen <= netdev_max_backlog && !skb_flow_limit(sd, skb, qlen)) {
 		if (qlen) {
 enqueue:
 			__skb_queue_tail(&sd->input_pkt_queue, skb);
-- 
1.9.1