Fix signal handler reentrancy deadlock (patroni#3413)

The problem existed only when Patroni is running in Docker container with PID=1

Author: waynerv

patroni/__main__.py

@@ -406,6 +406,12 @@ def passtochild(signo: int, stack_frame: Optional[FrameType]) -> None:
         if pid:
             os.kill(pid, signo)
 
+    import multiprocessing
+    patroni = multiprocessing.Process(target=patroni_main, args=(args.configfile,))
+    patroni.start()
+    pid = patroni.pid
+
+    # Set up signal handlers after fork to prevent child from inheriting them
     if os.name != 'nt':
         signal.signal(signal.SIGCHLD, sigchld_handler)
         signal.signal(signal.SIGHUP, passtochild)
@@ -415,11 +421,6 @@ def passtochild(signo: int, stack_frame: Optional[FrameType]) -> None:
     signal.signal(signal.SIGINT, passtochild)
     signal.signal(signal.SIGABRT, passtochild)
     signal.signal(signal.SIGTERM, passtochild)
-
-    import multiprocessing
-    patroni = multiprocessing.Process(target=patroni_main, args=(args.configfile,))
-    patroni.start()
-    pid = patroni.pid
     patroni.join()
 
 

tests/test_patroni.py

@@ -138,9 +138,13 @@ def test_patroni_main(self, mock_process, mock_getpid):
         def mock_signal(signo, handler):
             handler(signo, None)
 
-        with patch('signal.signal', mock_signal):
-            with patch('os.waitpid', Mock(side_effect=[(1, 0), (0, 0)])):
+        with patch('signal.signal', mock_signal), patch('os.kill') as mock_kill:
+            with patch('os.waitpid', Mock(side_effect=[(1, 0), (0, 0)])), \
+                 patch('patroni.__main__.logger') as mock_logger:
                 _main()
+                mock_kill.assert_called_with(mock_process.return_value.pid, signal.SIGTERM)
+                if os.name != 'nt':
+                    mock_logger.info.assert_called_with('Reaped pid=%s, exit status=%s', 1, 0)
             with patch('os.waitpid', Mock(side_effect=OSError)):
                 _main()