connection: Protect conn state tick() updates with a lock

If the mainloop is backed up, tick_send_signals might not run before
another conn.tick call is scheduled by the tick thread. conn.tick would
then be operating on incorrect self._vms since it was never updated.

Don't run another tick() until tick_send_signals has released a lock.

https://www.redhat.com/archives/virt-tools-list/2015-April/msg00009.html

Reported-by: Charles Arnold <carnold@suse.com>

virtManager/connection.py

@@ -23,13 +23,14 @@ from gi.repository import GObject
 import logging
 import os
 import socket
+import threading
 import time
 import traceback
-from virtinst import support
 
 import libvirt
 import virtinst
 from virtinst import pollhelpers
+from virtinst import support
 from virtinst import util
 
 from . import connectauth
@@ -119,6 +120,8 @@ class vmmConnection(vmmGObject):
         self.record = []
         self.hostinfo = None
 
+        self._tick_lock = threading.Lock()
+
         self.mediadev_initialized = False
         self.mediadev_error = ""
         self.mediadev_use_libvirt = False
@@ -1144,6 +1147,13 @@ class vmmConnection(vmmGObject):
 
         self.hostinfo = self._backend.getInfo()
 
+        try:
+            # We take the ticklock before using the conn object lists
+            # like self._vms. This ensures that those lists were updated
+            # by tick_send_signals since the last time we ran tick()
+            # https://www.redhat.com/archives/virt-tools-list/2015-April/msg00009.html
+            self._tick_lock.acquire()
+
             (goneNets, newNets, nets) = self._update_nets(pollnet)
             self._refresh_new_objects(newNets.values())
             (gonePools, newPools, pools) = self._update_pools(pollpool)
@@ -1159,6 +1169,9 @@ class vmmConnection(vmmGObject):
             # These are refreshing in their __init__ method, because the
             # data is wanted immediately
             (goneVMs, newVMs, vms) = self._update_vms(pollvm)
+        except:
+            self._tick_lock.release()
+            raise
 
         def tick_send_signals():
             """
@@ -1166,6 +1179,7 @@ class vmmConnection(vmmGObject):
             updates need to go here to enable threading that doesn't block the
             app with long tick operations.
             """
+            try:
                 # Connection closed out from under us
                 if not self._backend.is_open():
                     return
@@ -1180,6 +1194,8 @@ class vmmConnection(vmmGObject):
                     self._pools = pools
                 if pollnodedev:
                     self._nodedevs = nodedevs
+            finally:
+                self._tick_lock.release()
 
             if not self.mediadev_initialized:
                 self._init_mediadev()
@@ -1239,6 +1255,8 @@ class vmmConnection(vmmGObject):
             if finish_connecting:
                 self._change_state(self._STATE_ACTIVE)
 
+        # Anything that could possibly fail before this call needs to go
+        # in the try/except that handles the tick lock
         self.idle_add(tick_send_signals)
 
         ticklist = []