pvpanic: Fix race condition when checking QMP events

[heywji]

When guest triggers panic and QEMU exits quickly (especially on RHEL10), the test may fail with MonitorSocketError due to socket connection being reset while checking QMP events.

ID: 1863
Signed-off-by: Wenkang Ji wji@redhat.com

Summary by CodeRabbit

• Bug Fixes

  • Improved resilience of event monitoring by adding graceful error handling for closed QMP connections with appropriate null responses.

• Refactor

  • Optimized event detection mechanism for better reliability and robustness.

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[coderabbitai]

Walkthrough

This change modifies an event detection function in qemu/tests/pvpanic.py to replace direct polling of a named QMP event with iteration through a list of events returned by get_events(). Error handling has been added to catch MonitorSocketError exceptions, log a warning, and return None instead of propagating the error. This allows the function to gracefully handle closed QMP connections.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Logic refactoring verification: The shift from direct get_event(name) polling to iterating through get_events() requires verification that the new approach produces equivalent behavior and correctly identifies target events.
• Error handling scope: Confirm that MonitorSocketError handling is appropriate and that returning None on socket errors aligns with expected control flow and caller expectations.
• Edge cases: Review whether the iteration logic properly handles empty event lists, malformed events, or other corner cases that may arise from closed connections.

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title directly and clearly summarizes the main change: fixing a race condition in QMP event checking in the pvpanic test.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

qemu/tests/pvpanic.py (1)

54-67: Move MonitorSocketError handling outside _do_check() to avoid timeout waste and log spam

When MonitorSocketError is caught inside _do_check() and returns None (falsy), wait_for() continues polling until the full timeout expires, logging "QMP connection closed" on every iteration. Since wait_for() propagates exceptions from its callback and stops only on a truthy return, this turns a terminal condition into a slow, noisy timeout.

Instead:

• Simplify _do_check() to a clean "event present?" predicate returning only True/False
• Wrap the wait_for() call in try/except MonitorSocketError to log once and return None immediately

This preserves the external behavior (returns True on success, None otherwise) without wasting the full timeout when QMP closes:

     def _do_check(vm, event_names):
-        try:
-            events = vm.monitor.get_events()
-            for event in events:
-                if event.get("event") in event_names:
-                    LOG_JOB.info(
-                        "Receive qmp %s event notification", event.get("event")
-                    )
-                    vm.monitor.clear_event(event.get("event"))
-                    return True
-        except MonitorSocketError:
-            LOG_JOB.warning("QMP connection closed")
-            return None
+        events = vm.monitor.get_events()
+        for event in events:
+            if event.get("event") in event_names:
+                LOG_JOB.info(
+                    "Receive qmp %s event notification", event.get("event")
+                )
+                vm.monitor.clear_event(event.get("event"))
+                return True
         return False
 
-    LOG_JOB.info("Try to get qmp events %s in %s seconds!", event_names, timeout)
-    return wait_for(lambda: _do_check(vm, event_names), timeout, 5, 5)
+    LOG_JOB.info("Try to get qmp events %s in %s seconds!", event_names, timeout)
+    try:
+        return wait_for(lambda: _do_check(vm, event_names), timeout, 5, 5)
+    except MonitorSocketError:
+        LOG_JOB.warning("QMP connection closed while waiting for events %s", event_names)
+        return None

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between f03b470 and 239916d.

📒 Files selected for processing (1)

• qemu/tests/pvpanic.py (2 hunks)

🔇 Additional comments (1)

qemu/tests/pvpanic.py (1)

7-7: Import of MonitorSocketError looks correct

The new import cleanly scopes the QMP error handling to this module and matches its later usage in check_qmp_events(). No issues here.

[heywji]

Test Result: PASS

 (1/2) Host_RHEL.m10.u2.ovmf.qcow2.virtio_scsi.up.virtio_net.Guest.RHEL.10.2.x86_64.io-github-autotest-qemu.pvpanic_basic.nmi.q35:  PASS (61.82 s)
 (2/2) Host_RHEL.m10.u2.ovmf.qcow2.virtio_scsi.up.virtio_net.Guest.RHEL.9.8.0.x86_64.io-github-autotest-qemu.pvpanic_basic.nmi.q35: STARTED
 (2/2) Host_RHEL.m10.u2.ovmf.qcow2.virtio_scsi.up.virtio_net.Guest.RHEL.9.8.0.x86_64.io-github-autotest-qemu.pvpanic_basic.nmi.q35:  PASS (54.19 s)
RESULTS    : PASS 2 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0

[heywji]

@leidwang Hi Leidong, could you please help review this patch?