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authorEric Dumazet <edumazet@google.com>2016-04-14 08:05:39 +0300
committerDavid S. Miller <davem@davemloft.net>2016-04-15 23:45:44 +0300
commitb3d051477cf94e9d71d6acadb8a90de15237b9c1 (patch)
tree59009bc698f472b31b15059972e6904cd9272d32 /net/ipv4/tcp_output.c
parentac18dd9e842294377dbaf1e8d169493567a81fa1 (diff)
downloadlinux-b3d051477cf94e9d71d6acadb8a90de15237b9c1.tar.xz
tcp: do not mess with listener sk_wmem_alloc
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: 3b24d854cb35 ("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>
Diffstat (limited to 'net/ipv4/tcp_output.c')
-rw-r--r--net/ipv4/tcp_output.c16
1 files changed, 12 insertions, 4 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7d2dc015cd19..6451b83d81e9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2944,7 +2944,7 @@ int tcp_send_synack(struct sock *sk)
struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
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);
const struct tcp_sock *tp = tcp_sk(sk);
@@ -2964,14 +2964,22 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
/* Reserve space for headers. */
skb_reserve(skb, MAX_TCP_HEADER);
- if (attach_req) {
+ switch (synack_type) {
+ case TCP_SYNACK_NORMAL:
skb_set_owner_w(skb, req_to_sk(req));
- } else {
+ break;
+ case TCP_SYNACK_COOKIE:
+ /* Under synflood, we do not attach skb to a socket,
+ * to avoid false sharing.
+ */
+ break;
+ case TCP_SYNACK_FASTOPEN:
/* sk is a const pointer, because we want to express multiple
* cpu might call us concurrently.
* sk->sk_wmem_alloc in an atomic, we can promote to rw.
*/
skb_set_owner_w(skb, (struct sock *)sk);
+ break;
}
skb_dst_set(skb, dst);
@@ -3516,7 +3524,7 @@ int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
int res;
tcp_rsk(req)->txhash = net_tx_rndhash();
- res = af_ops->send_synack(sk, NULL, &fl, req, NULL, true);
+ res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
if (!res) {
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);