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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

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?

>              self._qmp.close()
> 
>          self._popen.wait(timeout=timeout)
>