better testing and threadsafety

cloudinit/signal_handler.py

@@ -7,6 +7,7 @@
 # This file is part of cloud-init. See LICENSE file for license information.
 import contextlib
 import inspect
+import threading
 import logging
 import signal
 import sys
@@ -36,6 +37,7 @@ class ExitBehavior(NamedTuple):
 SIGNAL_EXIT_BEHAVIOR_CRASH: Final = ExitBehavior(1, logging.ERROR)
 SIGNAL_EXIT_BEHAVIOR_QUIET: Final = ExitBehavior(0, logging.INFO)
 _SIGNAL_EXIT_BEHAVIOR = SIGNAL_EXIT_BEHAVIOR_CRASH
+_SUSPEND_WRITE_LOCK = threading.RLock()
 
 
 def inspect_handler(sig: Union[int, Callable, None]) -> None:
@@ -99,8 +101,14 @@ def suspend_crash():
     This allow signal handling without a crash where it is expected. The
     call stack is still printed if signal is received during this context, but
     the return code is 0 and no traceback is printed.
+
+    Threadsafe.
     """
     global _SIGNAL_EXIT_BEHAVIOR
-    _SIGNAL_EXIT_BEHAVIOR = SIGNAL_EXIT_BEHAVIOR_QUIET
-    yield
-    _SIGNAL_EXIT_BEHAVIOR = SIGNAL_EXIT_BEHAVIOR_CRASH
+
+    # If multiple threads simultaneously were to modify this
+    # global state, this function would not behave as expected.
+    with _SUSPEND_WRITE_LOCK:
+        _SIGNAL_EXIT_BEHAVIOR = SIGNAL_EXIT_BEHAVIOR_QUIET
+        yield
+        _SIGNAL_EXIT_BEHAVIOR = SIGNAL_EXIT_BEHAVIOR_CRASH

tests/unittests/test_signal_handler.py

@@ -8,8 +8,8 @@
 
 from cloudinit import signal_handler
 
+REENTRANT = "reentrant"
 
-@patch.object(signal_handler.sys, "exit", Mock())
 class TestSignalHandler:
 
     @pytest.mark.parametrize(
@@ -21,7 +21,30 @@ class TestSignalHandler:
             (1, inspect.currentframe()),
         ],
     )
-    def test_suspend_signal(self, m_args):
+    @pytest.mark.parametrize(
+        "m_suspended",
+        [
+            (REENTRANT, 0),
+            (True, 0),
+            (False, 1),
+        ],
+    )
+    def test_suspend_signal(self, m_args, m_suspended):
+        """suspend_crash should prevent crashing (exit 1) on signal
+
+        otherwise cloud-init should exit 1
+        """
         sig, frame = m_args
-        with signal_handler.suspend_crash():
-            signal_handler._handle_exit(sig, frame)
+        suspended, rc = m_suspended
+
+        with patch.object(signal_handler.sys, "exit", Mock()) as m_exit:
+            if suspended is True:
+                with signal_handler.suspend_crash():
+                    signal_handler._handle_exit(sig, frame)
+            elif suspended == REENTRANT:
+                with signal_handler.suspend_crash(
+                    ), signal_handler.suspend_crash():
+                    signal_handler._handle_exit(sig, frame)
+            else:
+                signal_handler._handle_exit(sig, frame)
+        m_exit.assert_called_with(rc)