Migration with "--p2p --tunnelled" hanging in v6.9.0

[Christian Ehrhardt]

On Wed, Nov 25, 2020 at 1:38 PM Daniel P. Berrangé <berrange at redhat.com> wrote:
>
> On Wed, Nov 25, 2020 at 01:28:09PM +0100, Christian Ehrhardt wrote:
> > On Wed, Nov 25, 2020 at 10:55 AM Christian Ehrhardt
> > <christian.ehrhardt at canonical.com> wrote:
> > >
> > > On Tue, Nov 24, 2020 at 4:30 PM Peter Krempa <pkrempa at redhat.com> wrote:
> > > >
> > > > On Tue, Nov 24, 2020 at 16:05:53 +0100, Christian Ehrhardt wrote:
> > > > > Hi,
> > > >
> > > > [...]
> > >
> > > BTW to reduce the scope what to think about - I have rebuilt 6.8 as
> > > well it works.
> > > Thereby I can confirm that the offending change should be in between
> > > 6.8.0 -> 6.9.0.
> >
> > I was able to get this working in git bisect builds from git between
> > v6.8 / v6.9.
> > I identified the following offending commit:
> >   7d959c30  rpc: Fix virt-ssh-helper detection
> >
> > Ok that makes a bit of sense, first we had in 6.8
> >   f8ec7c84 rpc: use new virt-ssh-helper binary for remote tunnelling
> > That makes it related to tunneling which matches our broken use-case.
> >
> > The identified commit "7d959c30 rpc: Fix virt-ssh-helper detection" might
> > finally really enable the new helper and that is then broken?
> >
> > With that knowledge I was able to confirm that it really is the native mode
> >
> > $ virsh migrate --unsafe --live --p2p --tunnelled h-migr-test
> > qemu+ssh://testkvm-hirsute-to/system?proxy=netcat
> > <works>
> > $ virsh migrate --unsafe --live --p2p --tunnelled h-migr-test
> > qemu+ssh://testkvm-hirsute-to/system?proxy=native
> > <hangs>
> >
> > I recently discussed with Andrea if we'd need apparmor rules for
> > virt-ssh-helper,
> > but there are no denials nor libvirt log entries related to virt-ssh-helper.
> > But we don't need such rules since it is spawned on the ssh login and
> > not under libvirtd itself.
> >
> > PS output of the hanging receiving virt-ssh-helper (looks not too unhappy):
> > Source:
> > 4     0   41305       1  20   0 1627796 23360 poll_s Ssl ?
> > 0:05 /usr/sbin/libvirtd
> > 0     0   41523   41305  20   0   9272  4984 poll_s S    ?
> > 0:02  \_ ssh -T -e none -- testkvm-hirsute-to sh -c 'virt-ssh-helper
> > 'qemu:///system''
> > Target
> > 4     0     213       1  20   0  13276  4132 poll_s Ss   ?
> > 0:00 sshd: /usr/sbin/sshd -D [listener] 0 of 250-500 startups
> > 4     0   35148     213  20   0  19048 11320 poll_s Ss   ?
> > 0:02  \_ sshd: root at notty
> > 4     0   35206   35148  20   0   2584   544 do_wai Ss   ?
> > 0:00      \_ sh -c virt-ssh-helper qemu:///system
> > 0     0   35207   35206  20   0  81348 26684 -      R    ?
> > 0:34          \_ virt-ssh-helper qemu:///system
> >
> > I've looked at it with strace [1] and gdb for backtraces [2] - it is
> > not dead or stuck and keeps working.
> > Could it be just so slow that it appears to hang until it times out?
> > Or is the event mechanism having issues and it wakes up too rarely?
>
> Lets take migration out of the picture. What if you simply do
>
>     virsh -c qemu+ssh://testkvm-hirsute-to/system?proxy=native  list
>
> does that work ?

Yes it does, no hang and proper results

I migrated the system there (with ?proxy=netcat) to ensure there is
something to report and indeed some data is coming back through this.

root at testkvm-hirsute-from:~# virsh migrate --unsafe --live --p2p
--tunnelled h-migr-test
qemu+ssh://testkvm-hirsute-to/system?proxy=netcat
root at testkvm-hirsute-from:~# virsh -c
qemu+ssh://testkvm-hirsute-to/system?proxy=native  list
 Id   Name          State
-----------------------------
 6    h-migr-test   running



> Regards,
> Daniel
> --
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>


-- 
Christian Ehrhardt
Staff Engineer, Ubuntu Server
Canonical Ltd