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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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4
net/ipv6/tcp_ipv6.c
View file

@ -439,7 +439,7 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
struct flowi *fl,
struct request_sock *req,
struct tcp_fastopen_cookie *foc,
bool attach_req)
enum tcp_synack_type synack_type)
{
struct inet_request_sock *ireq = inet_rsk(req);
struct ipv6_pinfo *np = inet6_sk(sk);
@ -452,7 +452,7 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
IPPROTO_TCP)) == NULL)
goto done;
skb = tcp_make_synack(sk, dst, req, foc, attach_req);
skb = tcp_make_synack(sk, dst, req, foc, synack_type);
if (skb) {
__tcp_v6_send_check(skb, &ireq->ir_v6_loc_addr,