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/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 554d5999abc4..3a9aec29581a 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -476,7 +476,8 @@ out:
 
 
 static int tcp_v6_send_synack(struct sock *sk, struct request_sock *req,
-                              struct request_values *rvp)
+                              struct request_values *rvp,
+                              u16 queue_mapping)
 {
         struct inet6_request_sock *treq = inet6_rsk(req);
         struct ipv6_pinfo *np = inet6_sk(sk);
@@ -513,6 +514,7 @@ static int tcp_v6_send_synack(struct sock *sk, struct request_sock *req,
                 __tcp_v6_send_check(skb, &treq->loc_addr, &treq->rmt_addr);
 
                 fl6.daddr = treq->rmt_addr;
+                skb_set_queue_mapping(skb, queue_mapping);
                 err = ip6_xmit(sk, skb, &fl6, opt, np->tclass);
                 err = net_xmit_eval(err);
         }
@@ -528,7 +530,7 @@ static int tcp_v6_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_v6_send_synack(sk, req, rvp);
+        return tcp_v6_send_synack(sk, req, rvp, 0);
 }
 
 static void tcp_v6_reqsk_destructor(struct request_sock *req)
@@ -1213,7 +1215,8 @@ have_isn:
         security_inet_conn_request(sk, skb, req);
 
         if (tcp_v6_send_synack(sk, req,
-                               (struct request_values *)&tmp_ext) ||
+                               (struct request_values *)&tmp_ext,
+                               skb_get_queue_mapping(skb)) ||
             want_cookie)
                 goto drop_and_free;