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

[John Snow]

On 6/20/20 6:14 AM, Philippe Mathieu-Daudé wrote:
> On 6/17/20 7:13 PM, Philippe Mathieu-Daudé wrote:
>> On 6/16/20 11:49 PM, Cleber Rosa 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?
>>>>
>>>
>>> John's description seems spot on, and so does the solution.  I was
>>> unable, though, to reproduce it given that the window is indeed tiny.
> 
> Still doesn't work...
> https://travis-ci.org/github/philmd/qemu/jobs/700309163#L5445
> 
I have overlooked a very fundamental mistake!

'pass' does not terminate execution of an exception handler...

It needs to be:

except (BrokenPipeError, ConnectionResetError):
    if self.is_running():
        raise

Will re-spin, sorry about that.

--js