[https://nvbugs/5868038][fix] Gracefully terminate disagg serving servers to prevent leftover subprocess warnings (#11395)

Signed-off-by: peihu-nv <259410613+peihu-nv@users.noreply.github.com>

tests/integration/defs/accuracy/test_disaggregated_serving.py

@@ -450,6 +450,30 @@ def launch_disaggregated_llm(
                 _show_kvcache_time(kv_cache_perf_dir)
                 _get_perf_metrics()
 
+            # Gracefully shut down all server processes
+            all_processes = list(
+                itertools.chain(ctx_processes, gen_processes, server_processes))
+
+            # SIGTERM triggers llm.shutdown() inside each trtllm-serve, cleaning up the executor and MPI workers.
+            for process in all_processes:
+                if process.poll() is None:
+                    process.terminate()
+
+            # Wait up to 5s total, then SIGKILL any process that doesn't exit.
+            # This is a safety net for when llm.shutdown() hangs.
+            deadline = time.monotonic() + 5
+            for process in all_processes:
+                remaining = max(0, deadline - time.monotonic())
+                try:
+                    process.wait(timeout=remaining)
+                except subprocess.TimeoutExpired:
+                    try:
+                        process.kill()
+                    except ProcessLookupError:
+                        pass  # already exited between timeout and kill
+                except OSError:
+                    pass  # process already gone
+
 
 def run_parallel_test(model_name: str,
                       model_path: str,