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[PATCH 5/7] python/machine: handle "fast" QEMU terminations
From: |
John Snow |
Subject: |
[PATCH 5/7] python/machine: handle "fast" QEMU terminations |
Date: |
Thu, 18 Nov 2021 15:46:18 -0500 |
In the case that the QEMU process actually launches -- but then dies so
quickly that we can't establish a QMP connection to it -- QEMUMachine
currently calls _post_shutdown() assuming that it never launched the VM
process.
This isn't true, though: it "merely" may have failed to establish a QMP
connection and the process is in the middle of its own exit path.
If we don't wait for the subprocess, the caller may get a bogus `None`
return for .exitcode(). This behavior was observed from
device-crash-test; after the switch to Async QMP, the timings were
changed such that it was now seemingly possible to witness the failure
of "vm.launch()" *prior* to the exitcode becoming available.
The semantic of the `_launched` property is changed in this
patch. Instead of representing the condition "launch() executed
successfully", it will now represent "has forked a child process
successfully". This way, wait() when called in the exit path won't
become a no-op.
Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
---
python/qemu/machine/machine.py | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index f92e73de40..67ab06ca2b 100644
--- a/python/qemu/machine/machine.py
+++ b/python/qemu/machine/machine.py
@@ -349,9 +349,6 @@ def _post_shutdown(self) -> None:
Called to cleanup the VM instance after the process has exited.
May also be called after a failed launch.
"""
- # Comprehensive reset for the failed launch case:
- self._early_cleanup()
-
try:
self._close_qmp_connection()
except Exception as err: # pylint: disable=broad-except
@@ -400,9 +397,16 @@ def launch(self) -> None:
try:
self._launch()
- self._launched = True
except:
- self._post_shutdown()
+ # We may have launched the process but it may
+ # have exited before we could connect via QMP.
+ # Assume the VM didn't launch or is exiting.
+ # If we don't wait for the process, exitcode() may still be
+ # 'None' by the time control is ceded back to the caller.
+ if self._launched:
+ self.wait()
+ else:
+ self._post_shutdown()
LOG.debug('Error launching VM')
if self._qemu_full_args:
@@ -426,6 +430,7 @@ def _launch(self) -> None:
stderr=subprocess.STDOUT,
shell=False,
close_fds=False)
+ self._launched = True
self._post_launch()
def _close_qmp_connection(self) -> None:
@@ -457,8 +462,8 @@ def _early_cleanup(self) -> None:
"""
Perform any cleanup that needs to happen before the VM exits.
- May be invoked by both soft and hard shutdown in failover scenarios.
- Called additionally by _post_shutdown for comprehensive cleanup.
+ This method may be called twice upon shutdown, once each by soft
+ and hard shutdown in failover scenarios.
"""
# If we keep the console socket open, we may deadlock waiting
# for QEMU to exit, while QEMU is waiting for the socket to
--
2.31.1
- [PATCH 0/7] python: More fixes for 6.2, John Snow, 2021/11/18
- [PATCH 1/7] python/machine: add @sock_dir property, John Snow, 2021/11/18
- [PATCH 5/7] python/machine: handle "fast" QEMU terminations,
John Snow <=
- [PATCH 2/7] python/machine: remove _remove_monitor_sockfile property, John Snow, 2021/11/18
- [PATCH 4/7] python/machine: move more variable initializations to _pre_launch, John Snow, 2021/11/18
- [PATCH 6/7] scripts/device-crash-test: Use a QMP timeout, John Snow, 2021/11/18
- [PATCH 3/7] python/machine: add instance disambiguator to default nickname, John Snow, 2021/11/18
- [PATCH 7/7] python/aqmp: fix send_fd_scm for python 3.6.x, John Snow, 2021/11/18