Similar to tcp, provide a new tracepoint to better understand
mptcp_rcv_space_adjust() behavior, which presents many artifacts.

Note that the used format string is so long that I preferred
wrap it, contrary to guidance for quoted strings.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v2 -> v3:
  - use __entry->family; note that its value is show as raw number
    instead of string, as show_family_name is available only to
    net/core/ trace and I preferred not moving the mptcp traces
    there as we need mptcp-specific helpers, too.
---
 include/trace/events/mptcp.h | 77 ++++++++++++++++++++++++++++++++++++
 net/mptcp/protocol.c         |  3 ++
 2 files changed, 80 insertions(+)

diff --git a/include/trace/events/mptcp.h b/include/trace/events/mptcp.h
index 085b749cdd97..0f24ec65cea6 100644
--- a/include/trace/events/mptcp.h
+++ b/include/trace/events/mptcp.h
@@ -5,7 +5,13 @@
 #if !defined(_TRACE_MPTCP_H) || defined(TRACE_HEADER_MULTI_READ)
 #define _TRACE_MPTCP_H
 
+#include <linux/ipv6.h>
+#include <linux/tcp.h>
 #include <linux/tracepoint.h>
+#include <net/ipv6.h>
+#include <net/tcp.h>
+#include <linux/sock_diag.h>
+#include <net/rstreason.h>
 
 #define show_mapping_status(status)					\
 	__print_symbolic(status,					\
@@ -178,6 +184,77 @@ TRACE_EVENT(subflow_check_data_avail,
 		  __entry->skb)
 );
 
+#include <trace/events/net_probe_common.h>
+
+TRACE_EVENT(mptcp_rcvbuf_grow,
+
+	TP_PROTO(struct sock *sk, int time),
+
+	TP_ARGS(sk, time),
+
+	TP_STRUCT__entry(
+		__field(int, time)
+		__field(__u32, rtt_us)
+		__field(__u32, copied)
+		__field(__u32, inq)
+		__field(__u32, space)
+		__field(__u32, ooo_space)
+		__field(__u32, rcvbuf)
+		__field(__u32, rcv_wnd)
+		__field(__u8, scaling_ratio)
+		__field(__u16, sport)
+		__field(__u16, dport)
+		__field(__u16, family)
+		__array(__u8, saddr, 4)
+		__array(__u8, daddr, 4)
+		__array(__u8, saddr_v6, 16)
+		__array(__u8, daddr_v6, 16)
+		__field(const void *, skaddr)
+	),
+
+	TP_fast_assign(
+		struct mptcp_sock *msk = mptcp_sk(sk);
+		struct inet_sock *inet = inet_sk(sk);
+		__be32 *p32;
+
+		__entry->time = time;
+		__entry->rtt_us = msk->rcvq_space.rtt_us >> 3;
+		__entry->copied = msk->rcvq_space.copied;
+		__entry->inq = mptcp_inq_hint(sk);
+		__entry->space = msk->rcvq_space.space;
+		__entry->ooo_space = RB_EMPTY_ROOT(&msk->out_of_order_queue) ? 0 :
+				     MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq -
+				     msk->ack_seq;
+
+		__entry->rcvbuf = sk->sk_rcvbuf;
+		__entry->rcv_wnd = atomic64_read(&msk->rcv_wnd_sent) -  msk->ack_seq;
+		__entry->scaling_ratio = msk->scaling_ratio;
+		__entry->sport = ntohs(inet->inet_sport);
+		__entry->dport = ntohs(inet->inet_dport);
+		__entry->family = sk->sk_family;
+
+		p32 = (__be32 *) __entry->saddr;
+		*p32 = inet->inet_saddr;
+
+		p32 = (__be32 *) __entry->daddr;
+		*p32 = inet->inet_daddr;
+
+		TP_STORE_ADDRS(__entry, inet->inet_saddr, inet->inet_daddr,
+			       sk->sk_v6_rcv_saddr, sk->sk_v6_daddr);
+
+		__entry->skaddr = sk;
+	),
+
+	TP_printk("time=%u rtt_us=%u copied=%u inq=%u space=%u ooo=%u scaling_ratio=%u "
+		  "rcvbuf=%u rcv_wnd=%u family=%d sport=%hu dport=%hu saddr=%pI4 "
+		  "daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c skaddr=%p",
+		  __entry->time, __entry->rtt_us, __entry->copied,
+		  __entry->inq, __entry->space, __entry->ooo_space,
+		  __entry->scaling_ratio, __entry->rcvbuf, __entry->rcv_wnd,
+		  __entry->family, __entry->sport,
+		  __entry->dport, __entry->saddr, __entry->daddr,
+		  __entry->saddr_v6, __entry->daddr_v6, __entry->skaddr)
+);
 #endif /* _TRACE_MPTCP_H */
 
 /* This part must be outside protection */
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index dce9f7a1b0eb..7510bc634585 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -28,6 +28,8 @@
 #include "protocol.h"
 #include "mib.h"
 
+static unsigned int mptcp_inq_hint(const struct sock *sk);
+
 #define CREATE_TRACE_POINTS
 #include <trace/events/mptcp.h>
 
@@ -2103,6 +2105,7 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
 	if (msk->rcvq_space.copied <= msk->rcvq_space.space)
 		goto new_measure;
 
+	trace_mptcp_rcvbuf_grow(sk, time);
 	if (mptcp_rcvbuf_grow(sk, msk->rcvq_space.copied)) {
 		/* Make subflows follow along.  If we do not do this, we
 		 * get drops at subflow level if skbs can't be moved to
-- 
2.51.1

On Wed, 12 Nov 2025, Paolo Abeni wrote:

> Similar to tcp, provide a new tracepoint to better understand
> mptcp_rcv_space_adjust() behavior, which presents many artifacts.
>
> Note that the used format string is so long that I preferred
> wrap it, contrary to guidance for quoted strings.
>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> v2 -> v3:
>  - use __entry->family; note that its value is show as raw number
>    instead of string, as show_family_name is available only to
>    net/core/ trace and I preferred not moving the mptcp traces
>    there as we need mptcp-specific helpers, too.
> ---
> include/trace/events/mptcp.h | 77 ++++++++++++++++++++++++++++++++++++
> net/mptcp/protocol.c         |  3 ++
> 2 files changed, 80 insertions(+)

Reviewed-by: Mat Martineau <martineau@kernel.org>