On Fri, May 22, 2026 at 08:23:50AM +0200, Stefano Brivio wrote: > On Fri, 22 May 2026 16:15:08 +1000 > David GIbson wrote: > > > On Fri, May 22, 2026 at 07:44:56AM +0200, Stefano Brivio wrote: > > > On Fri, 22 May 2026 06:22:39 +0200 > > > Stefano Brivio wrote: > > > > > > > On Fri, 22 May 2026 01:13:33 +0200 > > > > Laurent Vivier wrote: > > > > > > > > > On 5/21/26 10:30, Laurent Vivier wrote: > > > > > > On 5/20/26 22:53, Stefano Brivio wrote: > > > > > >> On Wed, 20 May 2026 18:18:52 +0200 > > > > > >> Stefano Brivio wrote: > > > > > >> > > > > > >>> On Wed, 20 May 2026 18:07:08 +0200 > > > > > >>> Stefano Brivio wrote: > > > > > >>> > > > > > >>>> On Wed, 20 May 2026 17:34:45 +0200 > > > > > >>>> Stefano Brivio wrote: > > > > > >>>>> On Wed, 13 May 2026 13:52:08 +0200 > > > > > >>>>> Laurent Vivier wrote: > > > > > >>>>>> Currently, the vhost-user path assumes each virtqueue element contains > > > > > >>>>>> exactly one iovec entry covering the entire frame.  This assumption > > > > > >>>>>> breaks as some virtio-net drivers (notably iPXE) provide descriptors where the > > > > > >>>>>> vnet header and the frame payload are in separate buffers, resulting in > > > > > >>>>>> two iovec entries per virtqueue element. > > > > > >>>>>> > > > > > >>>>>> This series refactors the vhost-user data path so that frame lengths, > > > > > >>>>>> header sizes, and padding are tracked and passed explicitly rather than > > > > > >>>>>> being derived from iovec sizes.  This decoupling is a prerequisite for > > > > > >>>>>> correctly handling padding of multi-buffer frames. > > > > > >>>>> > > > > > >>>>> Sorry to bring (likely) bad news, but this series seems to introduce a > > > > > >>>>> regression: I got the migration/rampstream_in tests fail twice in a > > > > > >>>>> row, which I've never saw happening (I think I saw a single failure a > > > > > >>>>> long time ago when the machine had a high CPU load, but nothing else). > > > > > >>>>> > > > > > >>>>> I'm currently bisecting and the bisect seems to point towards the end > > > > > >>>>> of the series (probably 10/10), but I haven't finished yet. I'll keep > > > > > >>>>> you posted. I haven't spotted anything that might cause issues there. > > > > > >>>> > > > > > >>>> Yeah, that's the one :( > > > > > >>>> > > > > > >>>> $ git bisect bad > > > > > >>>> db798fc60f4c5869cb53168354e068fb4dabd91a is the first bad commit > > > > > >>>> commit db798fc60f4c5869cb53168354e068fb4dabd91a > > > > > >>>> Author: Laurent Vivier > > > > > >>>> Date:   Wed May 13 13:52:18 2026 +0200 > > > > > >>>> > > > > > >>>>      vhost-user: Centralise Ethernet frame padding in vu_collect() and vu_pad() > > > > > > > > > > > > I checked on my system with the commit previous to this series, > > > > > > bcc3d37a6e01 ("util: Fix changes to assert_with_msg()") and rampstream_in fails too (not > > > > > > everytime). > > > > > > > > > > > > > TCP/IPv4: sequence check, ramps, inbound > > > > > > ...failed. > > > > > > > > > > > > and rampstream_out hangs sometime too. > > > > > > > > > > > > I'm going to try with ealier commits. > > > > > > > > > > For me the problem can happen with any commit... > > > > > > > > > > As it depends on the execution path and on the load and speed of the system it looks like > > > > > a race condition. > > > > > > > > Hah, thanks for checking. Maybe... > > > > > > > > > Did you try to test on a host with a kernel patched with > > > > > "[PATCH net v2 0/2] Fix race condition between TCP_REPAIR dump and data receive" ? > > > > > > > > Now I tried, and yes, the test doesn't hang anymore! I seem to have an > > > > issue with teardown functions on recent kernels (current net.git HEAD > > > > more or less): > > > > > > > > --- > > > > + teardown_migrate > > > > + cat /tmp/passt-tests-VVtLn0/migrate/qemu_1.pid > > > > + /home/sbrivio/passt/test/nstool exec /tmp/passt-tests-VVtLn0/migrate/ns1.hold -- kill 16 > > > > qemu-system-x86_64: terminating on signal 15 from pid 34 () > > > > + cat /tmp/passt-tests-VVtLn0/migrate/qemu_2.pid > > > > + /home/sbrivio/passt/test/nstool exec /tmp/passt-tests-VVtLn0/migrate/ns1.hold -- kill 15 > > > > 18.8974: ================ Vhost user message ================ > > > > 18.8974: Request: VHOST_USER_GET_VRING_BASE (11) > > > > 18.8974: Flags: 0x1 > > > > 18.8974: Size: 8 > > > > 18.8974: State.index: 0 > > > > 18.8975: ================ Vhost user message ================ > > > > 18.8975: Request: VHOST_USER_GET_VRING_BASE (11) > > > > 18.8975: Flags: 0x1 > > > > 18.8975: Size: 8 > > > > 18.8975: State.index: 1 > > > > qemu-system-x86_64: terminating on signal 15 from pid 35 () > > > > 18.7961: Client connection closed > > > > 18.7962: Closing TCP_REPAIR helper socket > > > > + context_wait qemu_1 > > > > + __name=qemu_1 > > > > + __pidfile=/tmp/passt-tests-VVtLn0/migrate/context_qemu_1.pid > > > > + cat /tmp/passt-tests-VVtLn0/migrate/context_qemu_1.pid > > > > + rc=0 > > > > + rm /tmp/passt-tests-VVtLn0/migrate/context_passt_repair_2.stdout.9pwpVbQr /tmp/passt-tests-VVtLn0/migrate/context_passt_repair_2.stderr.dSY5hBu1 > > > > + __pid=67766 > > > > + rm /tmp/passt-tests-VVtLn0/migrate/context_qemu_1.pid > > > > + [ 1 -eq 1 ] > > > > + echo [Exit code: 0] > > > > + echo -n passt_repair_2$ > > > > + return 0 > > > > 18.9016: Client connection closed > > > > 18.9018: Closing TCP_REPAIR helper socket > > > > + wait 67766 > > > > + rc=0 > > > > + rm /tmp/passt-tests-VVtLn0/migrate/context_passt_repair_1.stdout.JEyDGxXe /tmp/passt-tests-VVtLn0/migrate/context_passt_repair_1.stderr.WU550iEI > > > > + [ 1 -eq 1 ] > > > > + echo [Exit code: 0] > > > > + echo -n passt_repair_1$ > > > > + return 0 > > > > + rc=0 > > > > + rm /tmp/passt-tests-VVtLn0/migrate/context_qemu_2.stdout.Dm8EAhfl /tmp/passt-tests-VVtLn0/migrate/context_qemu_2.stderr.207qJYPA > > > > + [ 1 -eq 1 ] > > > > + echo [Exit code: 0] > > > > + echo -n qemu_2$ > > > > + return 0 > > > > 2026/05/22 04:08:23 socat[73089] E connect(5, AF=40 cid:94558 port:22, 16): Connection timed out > > > > Connection closed by UNKNOWN port 65535 > > > > ... > > > > --- > > > > > > > > it looks like we stop QEMU a bit too early. But it should be unrelated. > > > > > > > > I'm now trying to find some kind of workaround for existing (not fixed) > > > > kernel versions. Maybe stopping rampstream_in for a moment or something > > > > like that. > > > > > > For some weird reason even very blatant throttling (100 ms - 1 s delays > > > every 10000 ramps, or an explicit 500 ms pause via signal before > > > migration) doesn't help. > > > > > > So it doesn't seem to be *that* kind of race. I should probably check > > > the same exact kernel version with fix and without... > > > > If it's due to the kernel not stopping the queues on REPAIR, then the > > only real way to fix the test is to cut off the source machine's > > network before we trigger migration. > > Well, that's a rather complicated way to do it. One could simply stop > the traffic instead. I don't know that "simply" is quite so simple. You can suspend the source of the data, but you need to wait a difficult to ascertain amount of time for that to make it to the guest, and all the acks to come back. For rampstream_out it's worse: the source is in the guest which isn't supposed to know about the migration in advance, so you can't really stop it without stopping the guest's whole network. > But it doesn't help, so there's probably another > issue. > > > That could be done with > > netfilter (in a user+netns). But probably more natural would be to > > not do the migration between local passt instances, but actually > > between two host namespaces, with separate netifs for external > > connectivity and for the migration. Remove the external netif on the > > source, then trigger migration, then add the external netif on the > > destination. > > > > It's quite a bit of hassle :(. But it does model something much > > closer to a real migration scenario. As a bonus it would mean we'd no > > longer rely on the hack of guessing when to exit the source passt in > > order to allow the destination passt to bind. > > I struggle to see how that would be worth the investment, especially if > we're working around a kernel issue that should eventually be fixed. > > Or, at least, right now, I'm just trying to get tests to pass while > keeping Laurent changes in the tree.. > > -- > Stefano > -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson