tcp: reflect SYN queue_mapping into SYNACK packets

While testing how linux behaves on SYNFLOOD attack on multiqueue device
(ixgbe), I found that SYNACK messages were dropped at Qdisc level
because we send them all on a single queue.

Obvious choice is to reflect incoming SYN packet @queue_mapping to
SYNACK packet.

Under stress, my machine could only send 25.000 SYNACK per second (for
200.000 incoming SYN per second). NIC : ixgbe with 16 rx/tx queues.

After patch, not a single SYNACK is dropped.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Hans Schillstrom <hans.schillstrom@ericsson.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 3 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index a43b87dfe800..c8d28c433b2b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -824,7 +824,8 @@ static void tcp_v4_reqsk_send_ack(struct sock *sk, struct sk_buff *skb,
  */
 static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
                               struct request_sock *req,
-                              struct request_values *rvp)
+                              struct request_values *rvp,
+                              u16 queue_mapping)
 {
         const struct inet_request_sock *ireq = inet_rsk(req);
         struct flowi4 fl4;
@@ -840,6 +841,7 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
         if (skb) {
                 __tcp_v4_send_check(skb, ireq->loc_addr, ireq->rmt_addr);
 
+                skb_set_queue_mapping(skb, queue_mapping);
                 err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
                                             ireq->rmt_addr,
                                             ireq->opt);
@@ -854,7 +856,7 @@ static int tcp_v4_rtx_synack(struct sock *sk, struct request_sock *req,
                               struct request_values *rvp)
 {
         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
-        return tcp_v4_send_synack(sk, NULL, req, rvp);
+        return tcp_v4_send_synack(sk, NULL, req, rvp, 0);
 }
 
 /*
@@ -1422,7 +1424,8 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
         tcp_rsk(req)->snt_synack = tcp_time_stamp;
 
         if (tcp_v4_send_synack(sk, dst, req,
-                               (struct request_values *)&tmp_ext) ||
+                               (struct request_values *)&tmp_ext,
+                               skb_get_queue_mapping(skb)) ||
             want_cookie)
                 goto drop_and_free;