selftests: mptcp: add test for extra_subflows underflow on userspace PM

Add a test to verify that when userspace PM fails to create a subflow
(e.g. using an unreachable address), the extra_subflows counter is not
decremented below zero.

Fixes: 77e4b94a3de6 ("mptcp: update userspace pm infos")
Cc: stable@vger.kernel.org
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260602-net-mptcp-misc-fixes-7-1-rc7-v2-6-856831229976@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 5acd12021e6e8b18c852d95fc7b5a07124896c63..4b3f71e666092eaf0dcd8dc39cf108e568398824 100755 (executable)
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -4100,6 +4100,10 @@ userspace_tests()
                chk_rm_nr 0 1
                chk_mptcp_info subflows 0 subflows 0
                chk_subflows_total 1 1
+               # check counters are not affected by errors at creation time
+               userspace_pm_add_sf $ns2 10.0.12.2 10 2>/dev/null
+               chk_mptcp_info subflows 0 subflows 0
+               chk_subflows_total 1 1
                kill_events_pids
                mptcp_lib_kill_group_wait $tests_pid
        fi