From e5ddf19dbc3e24cce508de0dab0e8df5b7417de8 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov <0x7f454c46@gmail.com> Date: Wed, 2 Apr 2025 01:59:31 +0100 Subject: [PATCH] net/selftests: Add loopback link local route for self-connect self-connect-ipv6 got slightly flaky on netdev: > # timeout set to 120 > # selftests: net/tcp_ao: self-connect_ipv6 > # 1..5 > # # 708[lib/setup.c:250] rand seed 1742872572 > # TAP version 13 > # # 708[lib/proc.c:213] Snmp6 Ip6OutNoRoutes: 0 => 1 > # not ok 1 # error 708[self-connect.c:70] failed to connect() > # ok 2 No unexpected trace events during the test run > # # Planned tests != run tests (5 != 2) > # # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:1 > ok 1 selftests: net/tcp_ao: self-connect_ipv6 I can not reproduce it on my machines, but judging by "Ip6OutNoRoutes" there is no route to the local_addr (::1). Looking at the kernel code, I see that kernel does add link-local address automatically in init_loopback(), but that is called from ipv6 notifier block. So, in turn the userspace that brought up the loopback interface may see rtnetlink ACK earlier than addrconf_notify() does it's job (at least, on a slow VM such as netdev). Probably, for ipv4 it's the same, judging by inetdev_event(). The fix is quite simple: set the link-local route straight after bringing the loopback interface. That will make it synchronous. Signed-off-by: Dmitry Safonov <0x7f454c46@gmail.com> Link: https://patch.msgid.link/20250402-tcp-ao-selfconnect-flake-v1-1-8388d629ef3d@gmail.com Signed-off-by: Jakub Kicinski --- tools/testing/selftests/net/tcp_ao/self-connect.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/tools/testing/selftests/net/tcp_ao/self-connect.c b/tools/testing/selftests/net/tcp_ao/self-connect.c index 73b2f2276f3f..2c73bea698a6 100644 --- a/tools/testing/selftests/net/tcp_ao/self-connect.c +++ b/tools/testing/selftests/net/tcp_ao/self-connect.c @@ -16,6 +16,9 @@ static void __setup_lo_intf(const char *lo_intf, if (link_set_up(lo_intf)) test_error("Failed to bring %s up", lo_intf); + + if (ip_route_add(lo_intf, TEST_FAMILY, local_addr, local_addr)) + test_error("Failed to add a local route %s", lo_intf); } static void setup_lo_intf(const char *lo_intf)