[PATCH mptcp-next v2 1/2] Squash to "mptcp: explicitly drop over memory limits"

Address comments from Clashiko [1]:

- mib: typo: "constrains" -> "constraints".

- mptcp_over_limit: precise it is not only 0-win, but retrans, dup or
  old acks.

- mptcp_over_limit: bump LINUX_MIB_TCPRCVQDROP, as previously discussed
  in [2].

Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260724-net-next-mptcp-oooq-pruning-v1-0-5dd4dec63a54%40kernel.org?part=3 [1]
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
---
 net/mptcp/mib.h     | 2 +-
 net/mptcp/options.c | 6 +++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
index 18f35f7e0a2d..25f360724c57 100644
--- a/net/mptcp/mib.h
+++ b/net/mptcp/mib.h
@@ -89,7 +89,7 @@ enum linux_mptcp_mib_field {
 	MPTCP_MIB_FALLBACKFAILED,	/* Can't fallback due to msk status */
 	MPTCP_MIB_WINPROBE,		/* MPTCP-level zero window probe */
 	MPTCP_MIB_BACKLOGDROP,		/* Backlog over memory limit */
-	MPTCP_MIB_RCVPRUNED,		/* Dropped due to memory constrains */
+	MPTCP_MIB_RCVPRUNED,		/* Dropped due to memory constraints */
 	MPTCP_MIB_OFO_PRUNED,		/* MPTCP-level OoO queue pruned */
 	__MPTCP_MIB_MAX
 };
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index d6b009319839..7c0bce3780c5 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -1193,7 +1193,7 @@ static bool mptcp_over_limit(struct sock *sk, struct sock *ssk,
 	if (likely(mem <= READ_ONCE(sk->sk_rcvbuf)))
 		return false;
 
-	/* Avoid silently dropping pure acks, fin or zero win probes. */
+	/* Avoid silently dropping pure acks, fin or already-acked segments. */
 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq ||
 	    TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN ||
 	    !after(TCP_SKB_CB(skb)->end_seq, tcp_sk(ssk)->rcv_nxt))
@@ -1202,6 +1202,10 @@ static bool mptcp_over_limit(struct sock *sk, struct sock *ssk,
 	/* Dropped due to memory constraints, schedule an ack. */
 	inet_csk(ssk)->icsk_ack.pending |= ICSK_ACK_NOMEM | ICSK_ACK_NOW;
 	inet_csk_schedule_ack(ssk);
+
+	/* In fallback mode: skb is dropped before the TCP recv queue. */
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
+
 	return true;
 }
 

-- 
2.53.0