[PATCH net-next 10/10] mptcp: blackhole: avoid checking the state twice

From: Matthieu Baerts (NGI0)
Date: Fri Feb 21 2025 - 10:52:01 EST


A small cleanup, reordering the conditions to avoid checking things
twice.

The code here is called in case of timeout on a TCP connection, before
triggering a retransmission. But it only acts on SYN + MPC packets.

So the conditions can be re-order to exit early in case of non-MPTCP
SYN + MPC. This also reduce the indentation levels.

Reviewed-by: Mat Martineau <martineau@xxxxxxxxxx>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
---
net/mptcp/ctrl.c | 32 ++++++++++++++++++--------------
1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 2dd81e6c26bdb5220abed68e26d70d2dc3ab14fb..be6c0237e10bfd7520edd3c57ec43ce4377b97d5 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -401,26 +401,30 @@ void mptcp_active_enable(struct sock *sk)
void mptcp_active_detect_blackhole(struct sock *ssk, bool expired)
{
struct mptcp_subflow_context *subflow;
+ u8 timeouts, to_max;
+ struct net *net;

- if (!sk_is_mptcp(ssk))
+ /* Only check MPTCP SYN ... */
+ if (likely(!sk_is_mptcp(ssk) || ssk->sk_state != TCP_SYN_SENT))
return;

subflow = mptcp_subflow_ctx(ssk);

- if (subflow->request_mptcp && ssk->sk_state == TCP_SYN_SENT) {
- struct net *net = sock_net(ssk);
- u8 timeouts, to_max;
-
- timeouts = inet_csk(ssk)->icsk_retransmits;
- to_max = mptcp_get_pernet(net)->syn_retrans_before_tcp_fallback;
-
- if (timeouts == to_max || (timeouts < to_max && expired)) {
- MPTCP_INC_STATS(net, MPTCP_MIB_MPCAPABLEACTIVEDROP);
- subflow->mpc_drop = 1;
- mptcp_subflow_early_fallback(mptcp_sk(subflow->conn), subflow);
- }
- } else if (ssk->sk_state == TCP_SYN_SENT) {
+ /* ... + MP_CAPABLE */
+ if (!subflow->request_mptcp) {
+ /* Mark as blackhole iif the 1st non-MPTCP SYN is accepted */
subflow->mpc_drop = 0;
+ return;
+ }
+
+ net = sock_net(ssk);
+ timeouts = inet_csk(ssk)->icsk_retransmits;
+ to_max = mptcp_get_pernet(net)->syn_retrans_before_tcp_fallback;
+
+ if (timeouts == to_max || (timeouts < to_max && expired)) {
+ MPTCP_INC_STATS(net, MPTCP_MIB_MPCAPABLEACTIVEDROP);
+ subflow->mpc_drop = 1;
+ mptcp_subflow_early_fallback(mptcp_sk(subflow->conn), subflow);
}
}


--
2.47.1