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Thu, 17 Sep 2026 22:52:52 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 18 Sep 2026 05:52:50 +0000 Message-Id: Subject: Re: [PATCH net-next v2 2/2] selftests: net: test untracked NA recovery of FAILED neighbors From: "Lawrence Lee" To: Cc: , , , , , , , , , , , , , , , , , , , , X-Mailer: aerc 0.17.0 References: <3f33052571409614b953a3dc7778114c51c43669.1789448374.git.lfqlee314@gmail.com> <178966456270.22033.8952247046783062389@kernel.org> In-Reply-To: <178966456270.22033.8952247046783062389@kernel.org> > [Severity: Low] > Should verify_ndisc() also check the link-layer address that the > advertisement carried? > > The seed in test_unsolicited_na_common() deliberately creates the entry > without one: > > ${IP_ROUTER} neigh replace "${HOST_ADDR}" dev "${ROUTER_INTF}" \ > nud failed extern_learn > > while the recovery path in net/ipv6/ndisc.c:ndisc_recv_na() pulls the tar= get > link-layer address out of the options and passes it down: > > lladdr =3D ndisc_opt_addr_data(ndopts.nd_opts_tgt_lladdr, dev); > ... > __ndisc_update(dev, neigh, lladdr, > new_state, update_flags, neigh_failed, > NDISC_NEIGHBOUR_ADVERTISEMENT, &ndopts); > > Since the only assertions here are the state substring and extern_learn, > would a change that moves FAILED -> STALE but installs no lladdr, or an > incorrect one, still report OK? Comparing the resulting lladdr against t= he > host veth MAC would close that gap. > I will update the tests to verify the lladdr > [Severity: Low] > Can this switch actually isolate the mode 2 in-prefix gate? > > Moving HOST_ADDR from 2000:20::2 to 2000:21::2 changes the source address= of > the advertisement, its target address, and the key of the seeded neighbou= r > entry all at once, while the router keeps 2000:20::1/64. > > The advertisement under test comes from addrconf_dad_completed(), and > ndisc_send_na() uses the same address for both fields when it is local: > > net/ipv6/ndisc.c:ndisc_send_na() { > ifp =3D ipv6_get_ifaddr(dev_net(dev), solicited_addr, dev, 1); > if (ifp) { > src_addr =3D solicited_addr; > ... > .target =3D *solicited_addr, > } > > so saddr =3D=3D target for every packet this test generates. The kernel = gate is > source based: > > net/ipv6/ndisc.c:accept_untracked_na() { > case 2: > return !!ipv6_chk_prefix(saddr, idev->dev); > } > > and Documentation/networking/ip-sysctl.rst describes mode 2 in terms of "= the > source IP address". Would a change that tested msg->target instead of sa= ddr > leave both new mode 2 rows green? Keeping HOST_ADDR fixed and instead > varying the prefix configured on the router side would exercise the gate > without also moving the target and the entry key. > Will update the tests to cover one source address outside the prefix and=20 one inside. > [Severity: Medium] > The comment says "add a delay to ensure neighbour processing is done", bu= t > link_up, start_tcpdump and verify_ndisc run back to back with no sleep an= d no > retry. Where is the delay? > > start_tcpdump() blocks on: > > ${IP_ROUTER_EXEC} timeout 15s \ > tcpdump --immediate-mode -tpni ${ROUTER_INTF} -c 1 \ > "icmp6 && icmp6[0] =3D=3D 136 && src ${HOST_ADDR}" > > but the AF_PACKET tap that satisfies -c 1 is fed from ptype_all delivery = in > __netif_receive_skb_core(), which runs ahead of the state change the test > looks at: > > ipv6_rcv() -> icmpv6_rcv() -> ndisc_recv_na() -> __ndisc_update() -> > neigh_update() > > Does tcpdump exiting really order against that update, given verify_ndisc= () > takes a single un-retried snapshot of ip neigh show? > > There is a second effect for the new rows. In the four expect-FAILED=20 > cases: > > test_unsolicited_na_combination 0 0 1 failed > test_unsolicited_na_combination 0 1 0 failed > test_unsolicited_na_combination 1 1 1 failed > test_unsolicited_na_combination 0 2 1 failed 0 > > the expected value FAILED is exactly the state the entry was seeded with,= so > "still FAILED" and "the advertisement was never processed" look identical= . > Would a bounded poll for the expected state, or an explicit settle, make > these rows able to distinguish the two? > > Related question on ordering of the capture: tcpdump is started after > link_up, so can the single unsolicited advertisement emitted at DAD > completion be missed if the fork and exec are slow? In that case timeout > exits 124 while set -e is in effect inside start_tcpdump, which aborts th= e > whole script rather than failing one row. Would arming the capture befor= e > link_up avoid that? > Will change the tests to start the capture prior to bringing up the host=20 side