From: Dmitry Safonov 0x7f454c46@gmail.com

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 --- Sorry to send this during the merge window, it's a test stability fix. It seems that netdev build bot has hit the issue a couple of times, but seems not hitting it constantly at this moment:

https://netdev.bots.linux.dev/flakes.html?br-cnt=150&tn-needle=tcp-ao

I'm marking it net-next, so that build bot carries it until the merge closes. If it's not fine, I can re-send it after the merge window. --- 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 73b2f2276f3f5410aaa74bede7f366f81761bd6e..2c73bea698a677f9aedd7bec28f6e7fee7845d2e 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)

--- base-commit: 1a9239bb4253f9076b5b4b2a1a4e8d7defd77a95 change-id: 20250402-tcp-ao-selfconnect-flake-e0aabc03c076

Best regards,