Avoid unhandled exceptions during connecting to iSCSI portals

Currently we don't properly catch some possible exceptions during
connectiing to iSCSI portals, like failures in "iscsiadm -m session".
Because of this _connect_vol threads can abort unexpectedly in some
failure patterns, and this abort causes hung in subsequent steps
waiting for results from _connct_vol threads.

This change ensures that any exceptions during connecting to iSCSI
portals are handled in the _connect_vol method corectly, to avoid
unexpected abort without updating thread results.

Conflicts:
        os_brick/tests/initiator/connectors/test_iscsi.py

Closes-Bug: #1915678
Change-Id: I0278c502806b99f8ec65cb146e3852e43031e9b8
(cherry picked from commit 4478433550)
(cherry picked from commit 57c8f4334c)
(cherry picked from commit c336cb76b3)

os_brick/initiator/connectors/iscsi.py

@@ -630,18 +630,23 @@ class ISCSIConnector(base.BaseLinuxConnector, base_iscsi.BaseISCSIConnector):
         """
         device = hctl = None
         portal = props['target_portal']
-        session, manual_scan = self._connect_to_iscsi_portal(props)
-        do_scans = rescans > 0 or manual_scan
-        # Scan is sent on connect by iscsid, but we must do it manually on
-        # manual scan mode.  This scan cannot count towards total rescans.
-        if manual_scan:
-            num_rescans = -1
-            seconds_next_scan = 0
-        else:
-            num_rescans = 0
-            seconds_next_scan = 4
+        try:
+            session, manual_scan = self._connect_to_iscsi_portal(props)
+        except Exception:
+            LOG.exception('Exception connecting to %s', portal)
+            session = None
 
         if session:
+            do_scans = rescans > 0 or manual_scan
+            # Scan is sent on connect by iscsid, but we must do it manually on
+            # manual scan mode.  This scan cannot count towards total rescans.
+            if manual_scan:
+                num_rescans = -1
+                seconds_next_scan = 0
+            else:
+                num_rescans = 0
+                seconds_next_scan = 4
+
             data['num_logins'] += 1
             LOG.debug('Connected to %s', portal)
             while do_scans:

os_brick/tests/initiator/connectors/test_iscsi.py

@@ -1533,6 +1533,18 @@ Setting up iSCSI targets: unused
         expected.update(failed_logins=1, stopped_threads=1)
         self.assertDictEqual(expected, data)
 
+    @mock.patch.object(iscsi.ISCSIConnector, '_connect_to_iscsi_portal')
+    def test_connect_vol_with_connection_failure(self, connect_mock):
+        data = self._get_connect_vol_data()
+
+        connect_mock.side_effect = Exception()
+
+        self.connector._connect_vol(3, self.CON_PROPS, data)
+
+        expected = self._get_connect_vol_data()
+        expected.update(failed_logins=1, stopped_threads=1)
+        self.assertDictEqual(expected, data)
+
     @mock.patch('time.sleep', mock.Mock())
     @mock.patch.object(linuxscsi.LinuxSCSI, 'scan_iscsi')
     @mock.patch.object(linuxscsi.LinuxSCSI, 'device_name_by_hctl',

releasenotes/notes/bug-1915678-901a6bd24ecede72.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    `Bug #1915678 <https://bugs.launchpad.net/cinder/+bug/1915678>`_: Fix
+    unhandled exception during iscsi volume attachment with multipath enabled
+    that resulted in the cinder-volume service becoming stuck and requiring
+    a restart.