Merge "Fix race condition when getting cmdline"

neutron/agent/linux/utils.py

@@ -323,8 +323,13 @@ def process_is_running(pid):
 def get_cmdline_from_pid(pid):
     if not process_is_running(pid):
         return []
+    # NOTE(jh): Even after the above check, the process may terminate
+    # before the open below happens
+    try:
         with open('/proc/%s/cmdline' % pid, 'r') as f:
             cmdline = f.readline().split('\0')[:-1]
+    except IOError:
+        return []
 
     # NOTE(slaweq): sometimes it may happen that values in
     # /proc/{pid}/cmdline are separated by space instead of NUL char,

neutron/tests/unit/agent/linux/test_utils.py

@@ -336,6 +336,16 @@ class TestGetCmdlineFromPid(base.BaseTestCase):
         mock_open.assert_not_called()
         self.assertEqual([], cmdline)
 
+    def test_cmdline_process_disappearing(self):
+        self.process_is_running_mock.return_value = True
+        mock_open = self.useFixture(
+            lib_fixtures.OpenFixture('/proc/%s/cmdline' % self.pid, 'process')
+        ).mock_open
+        mock_open.side_effect = IOError()
+        cmdline = utils.get_cmdline_from_pid(self.pid)
+        mock_open.assert_called_once_with('/proc/%s/cmdline' % self.pid, 'r')
+        self.assertEqual([], cmdline)
+
 
 class TestFindChildPids(base.BaseTestCase):