Merge branch 'mptcp-pm-misc-cleanups-part-3'

Matthieu Baerts says:

====================
mptcp: pm: misc cleanups, part 3

These cleanups lead the way to the unification of the path-manager
interfaces, and allow future extensions. The following patches are not
all linked to each others, but are all related to the path-managers,
except the last three.

- Patch 1: remove unused returned value in mptcp_nl_set_flags().
- Patch 2: new flag: avoid iterating over all connections if not needed.
- Patch 3: add a build check making sure there is enough space in cb-ctx.
- Patch 4: new mptcp_pm_genl_fill_addr helper to reduce duplicated code.
- Patch 5: simplify userspace_pm_append_new_local_addr helper.
- Patch 6: drop unneeded inet6_sk().
- Patch 7: use ipv6_addr_equal() instead of !ipv6_addr_cmp()
- Patch 8: scheduler: split an interface in two.
- Patch 9: scheduler: save 64 bytes of currently unused data.
- Patch 10: small optimisation to exit early in case of retransmissions.
====================

Link: https://patch.msgid.link/20250221-net-next-mptcp-pm-misc-cleanup-3-v1-0-2b70ab1cee79@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 17 insertions, 13 deletions

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 2dd81e6c26bd..be6c0237e10b 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;
+	/* ... + MP_CAPABLE */
+	if (!subflow->request_mptcp) {
+		/* Mark as blackhole iif the 1st non-MPTCP SYN is accepted */
+		subflow->mpc_drop = 0;
+		return;
+	}
 
-		timeouts = inet_csk(ssk)->icsk_retransmits;
-		to_max = mptcp_get_pernet(net)->syn_retrans_before_tcp_fallback;
+	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);
-		}
-	} else if (ssk->sk_state == TCP_SYN_SENT) {
-		subflow->mpc_drop = 0;
+	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);
 	}
 }