Re: [PATCH v3 0/3] python/machine.py: refactor shutdown

[John Snow]

On 6/15/20 6:21 PM, Eduardo Habkost wrote:
> On Mon, Jun 15, 2020 at 05:21:18PM +0200, Philippe Mathieu-Daudé wrote:
>> On 6/9/20 11:55 PM, John Snow wrote:
>>>
>>>
>>> On 6/9/20 9:08 AM, Philippe Mathieu-Daudé wrote:
>>>> Hi John,
>>>>
>>>> On 6/4/20 9:52 PM, John Snow wrote:
>>>>> v3:
>>>>>  - Split _post_shutdown refactor into own patch (now 1/3)
>>>>>  - Re-add sigkill warning squelch (now 3/3)
>>>>>
>>>>> NOTE: I re-added the squelch in its own patch for review purposes, but
>>>>> for the purposes of avoiding temporary breakage, a maintainer may wish
>>>>> to squash patches 2 and 3 if they are accepted.
>>>>>
>>>>> v2: Philippe took patches 1, 3 and 4.
>>>>>
>>>>> This is a re-write of what was:
>>>>> [PATCH RFC 03/32] python//machine.py: remove bare except
>>>>> [PATCH 2/4] python/machine.py: remove bare except
>>>>>
>>>>> It's a bit heavier handed, but it should address some of kwolf's
>>>>> feedback from the RFC version.
>>>>>
>>>>> Applies straight to origin/master, ought to pass pylint and flake8:
>>>>>
>>>>>> cd ~/src/qemu/python/qemu
>>>>>> pylint *.py
>>>>>> flake8 *.py
>>>>>
>>>>> John Snow (3):
>>>>>   python/machine.py: consolidate _post_shutdown()
>>>>>   python/machine.py: refactor shutdown
>>>>>   python/machine.py: re-add sigkill warning suppression
>>>>>
>>>>>  python/qemu/machine.py | 100 +++++++++++++++++++++++++++++------------
>>>>>  1 file changed, 71 insertions(+), 29 deletions(-)
>>>>>
>>>>
>>>> I'm now seeing this error:
>>>>
>>>> 21:31:58 DEBUG| / # reboot
>>>> 21:32:01 DEBUG| / # reboot: Restarting system
>>>> 21:32:01 DEBUG| >>> {'execute': 'quit'}
>>>> 21:32:01 WARNI| qemu received signal 9; command:
>>>> "mips-softmmu/qemu-system-mips -display none -vga none -chardev
>>>> socket,id=mon,path=/tmp/tmp679upvrk/qemu-10292-monitor.sock -mon
>>>> chardev=mon,mode=control -machine malta -chardev
>>>> socket,id=console,path=/tmp/tmp679upvrk/qemu-10292-console.sock,server,nowait
>>>> -serial chardev:console -kernel
>>>> /tmp/avocado_b3aaagr9/avocado_job_5bj0xe1h/12-tests_acceptance_boot_linux_console.py_BootLinuxConsole.test_mips_malta_cpio/boot/vmlinux-4.5.0-2-4kc-malta
>>>> -initrd
>>>> /tmp/avocado_b3aaagr9/avocado_job_5bj0xe1h/12-tests_acceptance_boot_linux_console.py_BootLinuxConsole.test_mips_malta_cpiorootfs.cpio
>>>> -append printk.time=0 console=ttyS0 console=tty rdinit=/sbin/init
>>>> noreboot -no-reboot"
>>>> 21:32:01 ERROR|
>>>> 21:32:01 ERROR| Reproduced traceback from:
>>>> /home/travis/build/philmd/qemu/build/tests/venv/lib/python3.6/site-packages/avocado/core/test.py:886
>>>> 21:32:01 ERROR| Traceback (most recent call last):
>>>> 21:32:01 ERROR|   File
>>>> "/home/travis/build/philmd/qemu/build/tests/acceptance/avocado_qemu/__init__.py",
>>>> line 195, in tearDown
>>>> 21:32:01 ERROR|     vm.shutdown()
>>>> 21:32:01 ERROR|   File
>>>> "/home/travis/build/philmd/qemu/python/qemu/machine.py", line 449, in
>>>> shutdown
>>>> 21:32:01 ERROR|     self._do_shutdown(has_quit)
>>>> 21:32:01 ERROR|   File
>>>> "/home/travis/build/philmd/qemu/python/qemu/machine.py", line 426, in
>>>> _do_shutdown
>>>> 21:32:01 ERROR|     self._soft_shutdown(has_quit, timeout)
>>>> 21:32:01 ERROR|   File
>>>> "/home/travis/build/philmd/qemu/python/qemu/machine.py", line 413, in
>>>> _soft_shutdown
>>>> 21:32:01 ERROR|     self._qmp.cmd('quit')
>>>> 21:32:01 ERROR|   File
>>>> "/home/travis/build/philmd/qemu/python/qemu/qmp.py", line 271, in cmd
>>>> 21:32:01 ERROR|     return self.cmd_obj(qmp_cmd)
>>>> 21:32:01 ERROR|   File
>>>> "/home/travis/build/philmd/qemu/python/qemu/qmp.py", line 249, in cmd_obj
>>>> 21:32:01 ERROR|     
>>>> self.__sock.sendall(json.dumps(qmp_cmd).encode('utf-8'))
>>>> 21:32:01 ERROR| BrokenPipeError: [Errno 32] Broken pipe
>>>> 21:32:01 ERROR|
>>>> 21:32:01 DEBUG| DATA (filename=output.expected) => NOT FOUND (data
>>>> sources: variant, test, file)
>>>> 21:32:01 DEBUG| DATA (filename=stdout.expected) => NOT FOUND (data
>>>> sources: variant, test, file)
>>>> 21:32:01 DEBUG| DATA (filename=stderr.expected) => NOT FOUND (data
>>>> sources: variant, test, file)
>>>> 21:32:01 DEBUG| Not logging /var/log/syslog (lack of permissions)
>>>> 21:32:01 ERROR| ERROR
>>>> 12-tests/acceptance/boot_linux_console.py:BootLinuxConsole.test_mips_malta_cpio
>>>> -> TestSetupFail: [Errno 32] Broken pipe
>>>> 21:32:01 INFO |
>>>>
>>>> https://travis-ci.org/github/philmd/qemu/jobs/696142277#L5329
>>>>
>>>
>>> Gotcha.
>>>
>>> The problem here is that `test_mips_malta_cpio` in boot_linux_console.py
>>> does this:
>>>
>>>         self.vm.add_args('-kernel', kernel_path,
>>>                          '-initrd', initrd_path,
>>>                          '-append', kernel_command_line,
>>>                          '-no-reboot')
>>>
>>> and then:
>>>
>>> exec_command_and_wait_for_pattern(self, 'reboot',
>>>                          'reboot: Restarting system')
>>>
>>> and (in avocado_qemu/) __init__.py does this:
>>>
>>>     def tearDown(self):
>>>         for vm in self._vms.values():
>>>             vm.shutdown()
>>>
>>>
>>>
>>> What's happening here is that we are instructing QEMU to *close* when
>>> the guest reboots instead of allowing it to reboot. Then, we are issuing
>>> a reboot command to the guest, which will effectively terminate QEMU as
>>> well. Finally, we are trying to send a shutdown command to QEMU, but
>>> QEMU has already gone.
>>>
>>> Now, in the shutdown code, we do make an attempt to catch this:
>>>
>>> def is_running(self):
>>>     """Returns true if the VM is running."""
>>>     return self._popen is not None and self._popen.poll() is None
>>>
>>> But, well, race conditions.
>>>
>>> When we make it here:
>>>
>>>         if self._qmp is not None:
>>>             if not has_quit:
>>>                 self._qmp.cmd('quit')
>>>             self._qmp.close()
>>>
>>> We believe we are running and we believe we have an open QMP socket.
>>> Attempting to engage the socket by sending 'quit' causes the error.
>>>
>>> It's a tight window: if quit happens earlier, we send the command
>>> successfully and everything's OK. If quit happens later, we realize QEMU
>>> isn't running and proceed to cleanup.
>>
>> Nice debugging :)
>>
>>>
>>> Ultimately:
>>>
>>> - Avocado should not try to shut down QEMU twice, but
>>> - machine.py shouldn't enable the race condition either.
>>>
>>>
>>>
>>> for my part, how about this:
>>>
>>> diff --git a/python/qemu/machine.py b/python/qemu/machine.py
>>> index 99bcb499878..813f8e477db 100644
>>> --- a/python/qemu/machine.py
>>> +++ b/python/qemu/machine.py
>>> @@ -385,7 +385,14 @@ def _soft_shutdown(self, has_quit: bool = False,
>>> timeout: int = 3) -> None:
>>>
>>>          if self._qmp is not None:
>>>              if not has_quit:
>>> -                self._qmp.cmd('quit')
>>> +                try:
>>> +                    self._qmp.cmd('quit')
>>> +                except (BrokenPipeError, ConnectionResetError):
>>> +                    # QMP went away just before or just after sending
>>> 'quit'
>>> +                    if not self.is_running():
>>> +                        # "Mission Accomplished"
>>> +                        pass
>>> +                    raise
>>
>> Looks OK to me, Cleber/Eduardo can you Ack?
> 
> Looks good to me.
> 
> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
> 
> 
>>
>>>              self._qmp.close()
>>>
>>>          self._popen.wait(timeout=timeout)
>>>
>>
> 

I'll respin with the fix squashed.

Thanks!

--js