From: Geliang Tang <geliangtang@xiaomi.com>

./mptcp_join.sh -Cf

Signed-off-by: Geliang Tang <geliangtang@xiaomi.com>
---
 net/mptcp/protocol.c                           |  9 +++++++++
 .../testing/selftests/net/mptcp/mptcp_join.sh  | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index b14023301975..b7f344fbe322 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1289,6 +1289,8 @@ static void mptcp_update_infinite_mapping(struct mptcp_sock *msk, struct mptcp_e
 	WRITE_ONCE(msk->snd_infinite_mapping_enable, false);
 }
 
+static int j;
+
 static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
 			      struct mptcp_data_frag *dfrag,
 			      struct mptcp_sendmsg_info *info)
@@ -1423,6 +1425,13 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
 		mptcp_update_data_checksum(skb, copy);
 	if (READ_ONCE(msk->snd_infinite_mapping_enable))
 		mptcp_update_infinite_mapping(msk, mpext);
+
+	pr_debug("%s j=%d", __func__, j++);
+	if (j == 20)
+		skb->data_len = 1;
+	if (j > 40)
+		j = 0;
+
 	mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
 	return copy;
 }
diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index fe0c8f3164a7..38663f6373b8 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -977,6 +977,24 @@ chk_link_usage()
 
 subflows_tests()
 {
+	# 1 subflow
+	reset
+	ip netns exec $ns1 ./pm_nl_ctl limits 0 2
+	ip netns exec $ns2 ./pm_nl_ctl limits 0 2
+	run_tests $ns1 $ns2 10.0.1.1 0 0 0 slow
+	chk_join_nr "1 subflow" 0 0 0
+
+	exit
+
+	# multiple subflows
+	reset
+	ip netns exec $ns1 ./pm_nl_ctl limits 0 2
+	ip netns exec $ns2 ./pm_nl_ctl limits 0 2
+	ip netns exec $ns2 ./pm_nl_ctl add 10.0.3.2 flags subflow
+	ip netns exec $ns2 ./pm_nl_ctl add 10.0.2.2 flags subflow
+	run_tests $ns1 $ns2 10.0.1.1 0 0 0 slow
+	chk_join_nr "multiple subflows" 2 2 2
+
 	reset
 	run_tests $ns1 $ns2 10.0.1.1
 	chk_join_nr "no JOIN" "0" "0" "0"
-- 
2.31.1