[Bugfix] Keep force-killing the process tree when a child exits mid-walk

tests/utils_/test_system_utils.py

@@ -4,10 +4,15 @@
 import contextlib
 import io
 import os
+import signal
+import subprocess
 import sys
 import tempfile
 from pathlib import Path
 
+import psutil
+
+from vllm.utils import system_utils
 from vllm.utils.system_utils import (
     _maybe_force_spawn,
     suppress_stdout,
@@ -48,3 +53,28 @@ def test_suppress_stdout_keeps_stderr_when_sys_stdout_is_stderr(capfd, monkeypat
     out, err = capfd.readouterr()
     assert "c library output" not in out
     assert "error message" in err
+
+
+def test_kill_process_tree_skips_child_that_exits_mid_walk(monkeypatch):
+    sleep = [sys.executable, "-c", "import time; time.sleep(60)"]
+    target, *children = procs = [subprocess.Popen(sleep) for _ in range(4)]
+    try:
+        # List the children while they are alive, then let one exit and be
+        # reaped before the walk reaches it, so psutil's name() raises.
+        listed = [psutil.Process(p.pid) for p in children]
+        children[1].terminate()
+        children[1].wait(timeout=10)
+        monkeypatch.setattr(
+            psutil.Process, "children", lambda self, recursive=False: listed
+        )
+
+        system_utils.kill_process_tree(target.pid)
+
+        # The exited child died from our SIGTERM; the rest were SIGKILLed.
+        assert children[1].returncode == -signal.SIGTERM
+        for p in (children[0], children[2], target):
+            assert p.wait(timeout=10) == -signal.SIGKILL
+    finally:
+        for p in procs:
+            p.kill()
+            p.wait()

vllm/utils/system_utils.py

@@ -221,7 +221,7 @@ def kill_process_tree(pid: int):
 
     # Send SIGKILL to all children first
     for child in children:
-        with contextlib.suppress(ProcessLookupError):
+        with contextlib.suppress(ProcessLookupError, psutil.NoSuchProcess):
             logger.warning(
                 "[shutdown] force killing sub process %s pid %d",
                 child.name(),