Raise more exceptions from None in MP engine

This PR is a follow-up to #17800
We should `raise e from None`, otherwise, re-raised error is considered new while processing the original one.

Signed-off-by: Vadim Markovtsev <[email protected]>

Author: vmarkovtsev

vllm/engine/multiprocessing/engine.py

@@ -229,8 +229,8 @@ def engine_step(self) -> List[RequestOutput]:
         """Engine step wrapper with error handling."""
         try:
             return self.engine.step()
-        except SystemExit:
-            raise
+        except SystemExit as e:
+            raise e from None
         except InputProcessingError as e:
             # Special case where we handle an error preparing the inputs for
             # a single request in the batch
@@ -245,7 +245,7 @@ def engine_step(self) -> List[RequestOutput]:
                                is_engine_errored=True,
                                exception=e)
             self._send_outputs(rpc_err)
-            raise e
+            raise e from None
 
     def handle_new_input(self):
         """Handle new input from the socket"""