Fix controller hang when submission exits early

Author: simonlindholm

cms/grading/tasktypes/interactive_keeper.py

@@ -87,10 +87,8 @@ def main():
     for i in range(process_limit):
         c_to_u_r, c_to_u_w = os.pipe()
         u_to_c_r, u_to_c_w = os.pipe()
-        os.set_inheritable(c_to_u_r, True)
         os.set_inheritable(c_to_u_w, True)
         os.set_inheritable(u_to_c_r, True)
-        os.set_inheritable(u_to_c_w, True)
         pipes.append({"c_to_u": (c_to_u_r, c_to_u_w), "u_to_c": (u_to_c_r, u_to_c_w)})
 
     controller_sandbox = Sandbox(0, shard, name="controller", temp_dir=temp_dir)
@@ -165,7 +163,8 @@ def main():
                 wait=False,
             )
 
-            os.close(p["c_to_u"][0])
+            # We do not close p["c_to_u"][0] -- it only risks crashing the
+            # controller with SIGPIPE if the submission exits early.
             os.close(p["u_to_c"][1])
 
             try: