Avoid accidental fork bombs due to try/except (#51633) (#51636)

WorkerProcess exceptions could previously cause StrategyBase loop to
resume in every child. See ticket description.

lib/ansible/executor/process/worker.py

@@ -87,7 +87,40 @@ class WorkerProcess(multiprocessing.Process):
             # set to /dev/null
             self._new_stdin = os.devnull
 
+    def _hard_exit(self, e):
+        '''
+        There is no safe exception to return to higher level code that does not
+        risk an innocent try/except finding itself executing in the wrong
+        process. All code executing above WorkerProcess.run() on the stack
+        conceptually belongs to another program.
+        '''
+
+        try:
+            display.debug(u"WORKER HARD EXIT: %s" % to_text(e))
+        except BaseException:
+            # If the cause of the fault is IOError being generated by stdio,
+            # attempting to log a debug message may trigger another IOError.
+            # Try printing once then give up.
+            pass
+
+        os._exit(1)
+
     def run(self):
+        '''
+        Wrap _run() to ensure no possibility an errant exception can cause
+        control to return to the StrategyBase task loop, or any other code
+        higher in the stack.
+
+        As multiprocessing in Python 2.x provides no protection, it is possible
+        a try/except added in far-away code can cause a crashed child process
+        to suddenly assume the role and prior state of its parent.
+        '''
+        try:
+            return self._run()
+        except BaseException as e:
+            self._hard_exit(e)
+
+    def _run(self):
         '''
         Called when the process is started.  Pushes the result onto the
         results queue. We also remove the host from the blocked hosts list, to