Re: [PATCH] tests/functional: fix race in virtio balloon test

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Mar 06, 2025 at 08:23:15PM +0100, Thomas Huth wrote:
> On 06/03/2025 18.42, Thomas Huth wrote:
> > On 05/03/2025 13.25, Philippe Mathieu-Daudé wrote:
> > > Hi Daniel,
> > > 
> > > On 4/3/25 19:33, Daniel P. Berrangé wrote:
> > > > There are two race conditions in the recently added virtio balloon
> > > > test
> > > > 
> > > >   * The /dev/vda device node is not ready
> > > >   * The virtio-balloon driver has not issued the first stats refresh
> > > > 
> > > > To fix the former, monitor dmesg for a line about 'vda'.
> > > > 
> > > > To fix the latter, retry the stats query until seeing fresh data.
> > > > 
> > > > Adding 'quiet' to the kernel command line reduces serial output
> > > > which otherwise slows boot, making it less likely to hit the former
> > > > race too.
> > > > 
> > > > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > > > ---
> > > >   tests/functional/test_virtio_balloon.py | 24 +++++++++++++++++++-----
> > > >   1 file changed, 19 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/tests/functional/test_virtio_balloon.py
> > > > b/tests/functional/ test_virtio_balloon.py
> > > > index 67b48e1b4e..308d197eb3 100755
> > > > --- a/tests/functional/test_virtio_balloon.py
> > > > +++ b/tests/functional/test_virtio_balloon.py
> > > > @@ -32,7 +32,7 @@ class VirtioBalloonx86(QemuSystemTest):
> > > > 'e3c1b309d9203604922d6e255c2c5d098a309c2d46215d8fc026954f3c5c27a0')
> > > >       DEFAULT_KERNEL_PARAMS = ('root=/dev/vda1 console=ttyS0 net.ifnames=0 '
> > > > -                             'rd.rescue')
> > > > +                             'rd.rescue quiet')
> > > >       def wait_for_console_pattern(self, success_message, vm=None):
> > > >           wait_for_console_pattern(
> > > > @@ -47,6 +47,9 @@ def mount_root(self):
> > > >           prompt = '# '
> > > >           self.wait_for_console_pattern(prompt)
> > > > +        # Synchronize on virtio-block driver creating the root device
> > > > +        exec_command_and_wait_for_pattern(self, "while ! (dmesg
> > > > -c | grep vda:) ; do sleep 1 ; done", "vda1")
> > > > +
> > > >           exec_command_and_wait_for_pattern(self, 'mount
> > > > /dev/vda1 / sysroot',
> > > >                                             prompt)
> > > >           exec_command_and_wait_for_pattern(self, 'chroot /sysroot',
> > > > @@ -65,10 +68,21 @@ def assert_initial_stats(self):
> > > >               assert val == UNSET_STATS_VALUE
> > > >       def assert_running_stats(self, then):
> > > > -        ret = self.vm.qmp('qom-get',
> > > > -                          {'path': '/machine/peripheral/balloon',
> > > > -                           'property': 'guest-stats'})['return']
> > > > -        when = ret.get('last-update')
> > > > +        # We told the QEMU to refresh stats every 100ms, but
> > > > +        # there can be a delay between virtio-ballon driver
> > > > +        # being modprobed and seeing the first stats refresh
> > > > +        # Retry a few times for robustness under heavy load
> > > > +        retries = 10
> > > > +        when = 0
> > > > +        while when == 0 and retries:
> > > > +            ret = self.vm.qmp('qom-get',
> > > > +                              {'path': '/machine/peripheral/balloon',
> > > > +                               'property': 'guest-stats'})['return']
> > > > +            when = ret.get('last-update')
> > > > +            if when == 0:
> > > > +                retries = retries - 1
> > > > +                time.sleep(0.5)
> > > > +
> > > >           now = time.time()
> > > >           assert when > then and when < now
> > > 
> > > Unfortunately I'm still getting a timeout:
> > > https://gitlab.com/philmd/qemu/-/jobs/9318095233
> > > 
> > > 2025-03-05 12:09:55,360 - DEBUG: Console interaction:
> > > success_msg='Entering emergency mode.' failure_msg='Kernel panic -
> > > not syncing' send_string='None'
> > > 2025-03-05 12:09:55,360 - DEBUG: Opening console socket
> > > 2025-03-05 12:10:32,722 - DEBUG: Console interaction: success_msg='#
> > > ' failure_msg='Kernel panic - not syncing' send_string='None'
> > > 2025-03-05 12:10:32,823 - DEBUG: Console interaction:
> > > success_msg='vda1' failure_msg='None' send_string='while ! (dmesg -c
> > > | grep vda:) ; do sleep 1 ; done
> > > 
> > > 2025-03-05 12:10:30,534: Warning: /dev/vda1 does not exist
> > > 2025-03-05 12:10:30,535:
> > > 2025-03-05 12:10:30,598: Generating "/run/initramfs/rdsosreport.txt"
> > > 2025-03-05 12:10:32,720:
> > > 2025-03-05 12:10:32,721:
> > > 2025-03-05 12:10:32,722: Entering emergency mode.
> > > 2025-03-05 12:10:32,724: Exit the shell to continue.
> > > 2025-03-05 12:10:32,726: Type "journalctl" to view system logs.
> > > 2025-03-05 12:10:32,727: You might want to save "/run/initramfs/
> > > rdsosreport.txt" to a USB stick or /boot
> > > 2025-03-05 12:10:32,728: after mounting them and attach it to a bug report.
> > > 2025-03-05 12:10:32,729:
> > > 2025-03-05 12:10:32,731:
> > > 2025-03-05 12:10:32,823: :/#
> > 
> > Same for me, it always seems to hang when being run with the gitlab
> > shared runners:
> > 
> >   https://gitlab.com/thuth/qemu/-/jobs/9333926038#L612
> >   https://gitlab.com/thuth/qemu/-/jobs/9333926046#L625
> > 
> > ... no clue what's still going wrong, though ...
> 
> ... but I just noticed that all other functional tests that use the same
> assets are using:
> 
>         self.require_accelerator('kvm')
>         self.vm.add_args('-accel', 'kvm')

Hmm, yes, and my testing locally will be with kvm too.

> so they are skipped on the gitlab shared runners (but still executed in the
> custom runners of the qemu-project), while your test also is enabled for TCG
> and thus runs in the shared runners, too.
> So unless you've got a clue what's going wrong here (I fail to see the
> reason for the problem unfortunately), I'd suggest that we mark the
> virtio_balloon test with require_accelerator('kvm'), too, to get the CI
> working with the shared runners again. WDYT?

Lets do that for now

With regards,
Daniel
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