Avoid incrementing bg process utime/stime counters by negative durations (#14323)

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/metrics/test_background_process_metrics.py b/tests/metrics/test_background_process_metrics.py
new file mode 100644

index 0000000000..f0f6cb2912
--- /dev/null
+++ b/tests/metrics/test_background_process_metrics.py
@@ -0,0 +1,19 @@
+from unittest import TestCase as StdlibTestCase
+from unittest.mock import Mock
+
+from synapse.logging.context import ContextResourceUsage, LoggingContext
+from synapse.metrics.background_process_metrics import _BackgroundProcess
+
+
+class TestBackgroundProcessMetrics(StdlibTestCase):
+    def test_update_metrics_with_negative_time_diff(self) -> None:
+        """We should ignore negative reported utime and stime differences"""
+        usage = ContextResourceUsage()
+        usage.ru_stime = usage.ru_utime = -1.0
+
+        mock_logging_context = Mock(spec=LoggingContext)
+        mock_logging_context.get_resource_usage.return_value = usage
+
+        process = _BackgroundProcess("test process", mock_logging_context)
+        # Should not raise
+        process.update_metrics()