Retry multipath flush when map is in use

When flushing a multipath we are ignoring map in use transient error, so
we log a warning that the flush has not been successful and that we have
received an exit code 1 and we continue to remove the individual paths.

This error is usually transient and a simple retry will succeed in
flushing the multipath.

Failure to retry will leave an empty multipath in our system.

Closes-Bug: #1663936
Change-Id: I710792bd707ad933ef60d11d25f530dddfb6fb2f

os_brick/initiator/linuxscsi.py

@@ -150,12 +150,16 @@ class LinuxSCSI(executor.Executor):
             LOG.warning(_LW("Failed to flush IO buffers prior to removing "
                             "device: %(code)s"), {'code': exc.exit_code})
 
+    @utils.retry(exceptions=putils.ProcessExecutionError)
     def flush_multipath_device(self, device):
         try:
             LOG.debug("Flush multipath device %s", device)
             self._execute('multipath', '-f', device, run_as_root=True,
                           root_helper=self._root_helper)
         except putils.ProcessExecutionError as exc:
+            if exc.exit_code == 1 and 'map in use' in exc.stdout:
+                LOG.debug('Multipath is in use, cannot be flushed yet.')
+                raise
             LOG.warning(_LW("multipath call failed exit %(code)s"),
                         {'code': exc.exit_code})
 

os_brick/tests/initiator/test_linuxscsi.py

@@ -18,6 +18,7 @@ import textwrap
 import time
 
 import mock
+from oslo_concurrency import processutils as putils
 from oslo_log import log as logging
 
 from os_brick import exception
@@ -95,6 +96,24 @@ class LinuxSCSITestCase(base.TestCase):
         expected_commands = [('multipath -f /dev/dm-9')]
         self.assertEqual(expected_commands, self.cmds)
 
+    @mock.patch('retrying.time.sleep', mock.Mock())
+    def test_flush_multipath_device_in_use(self):
+        side_effect = (
+            putils.ProcessExecutionError(
+                stdout='Feb 09 14:38:02 | mpatha: map in use\n'
+                       'Feb 09 14:38:02 | failed to remove multipath map '
+                       'mpatha\n',
+                exit_code=1),
+            ('', '')
+        )
+
+        with mock.patch.object(self.linuxscsi, '_execute') as execute_mock:
+            execute_mock.side_effect = side_effect
+            self.linuxscsi.flush_multipath_device('mpatha')
+            execute_mock.assert_has_calls(
+                [mock.call('multipath', '-f', 'mpatha', run_as_root=True,
+                           root_helper=mock.ANY)] * 2)
+
     def test_flush_multipath_devices(self):
         self.linuxscsi.flush_multipath_devices()
         expected_commands = [('multipath -F')]