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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

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: :/#