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tcp: do not mess with listener sk_wmem_alloc

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When removing sk_refcnt manipulation on synflood, I missed that
using skb_set_owner_w() was racy, if sk->sk_wmem_alloc had already
transitioned to 0.

We should hold sk_refcnt instead, but this is a big deal under attack.
(Doing so increase performance from 3.2 Mpps to 3.8 Mpps only)

In this patch, I chose to not attach a socket to syncookies skb.

Performance is now 5 Mpps instead of 3.2 Mpps.

Following patch will remove last known false sharing in
tcp_rcv_state_process()

Fixes: 3b24d854cb ("tcp/dccp: do not touch listener sk_refcnt under synflood")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2016-04-13 22:05:39 -07:00
committed by David S. Miller
parent ac18dd9e84
commit b3d051477c
5 changed files with 27 additions and 13 deletions
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7
net/ipv4/tcp_input.c
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@@ -6327,7 +6327,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
}
if (fastopen_sk) {
af_ops->send_synack(fastopen_sk, dst, &fl, req,
&foc, false);
&foc, TCP_SYNACK_FASTOPEN);
/* Add the child socket directly into the accept queue */
inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
sk->sk_data_ready(sk);
@@ -6337,8 +6337,9 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
tcp_rsk(req)->tfo_listener = false;
if (!want_cookie)
inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
af_ops->send_synack(sk, dst, &fl, req,
&foc, !want_cookie);
af_ops->send_synack(sk, dst, &fl, req, &foc,
!want_cookie ? TCP_SYNACK_NORMAL :
TCP_SYNACK_COOKIE);
if (want_cookie) {
reqsk_free(req);
return 0;