Fix racey snapshots.

Fixes bug 949475

Atomically tests and sets the instance task_state before allowing a
snapshot or backup to be initiated.

Change-Id: I40671a80f5e75337e176a715837f62d400cc21b6

2 files changed, 13 insertions, 14 deletions

diff --git a/nova/compute/api.py b/nova/compute/api.py
index e24a3de5b..3279ca546 100644
--- a/nova/compute/api.py
+++ b/nova/compute/api.py
@@ -1083,8 +1083,7 @@ class API(base.Base):
         return self.db.instance_get_all_by_filters(context, filters)
 
     @wrap_check_policy
-    @check_instance_state(vm_state=[vm_states.ACTIVE, vm_states.SHUTOFF],
-                          task_state=[None, task_states.RESIZE_VERIFY])
+    @check_instance_state(vm_state=[vm_states.ACTIVE, vm_states.SHUTOFF])
     def backup(self, context, instance, name, backup_type, rotation,
                extra_properties=None):
         """Backup the given instance
@@ -1102,8 +1101,7 @@ class API(base.Base):
         return recv_meta
 
     @wrap_check_policy
-    @check_instance_state(vm_state=[vm_states.ACTIVE, vm_states.SHUTOFF],
-                          task_state=[None, task_states.RESIZE_VERIFY])
+    @check_instance_state(vm_state=[vm_states.ACTIVE, vm_states.SHUTOFF])
     def snapshot(self, context, instance, name, extra_properties=None):
         """Snapshot the given instance.
 
@@ -1130,9 +1128,18 @@ class API(base.Base):
         :param extra_properties: dict of extra image properties to include
 
         """
-        task_state = instance["task_state"]
         instance_uuid = instance['uuid']
 
+        if image_type == "snapshot":
+            task_state = task_states.IMAGE_SNAPSHOT
+        elif image_type == "backup":
+            task_state = task_states.IMAGE_BACKUP
+        else:
+            raise Exception(_('Image type not recognized %s') % image_type)
+
+        self.db.instance_test_and_set(
+                context, instance_uuid, 'task_state', [None], task_state)
+
         properties = {
             'instance_uuid': instance_uuid,
             'user_id': str(context.user_id),
diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index ef239ba50..1c6de672f 100644
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -912,13 +912,6 @@ class ComputeManager(manager.SchedulerDependentManager):
         :param rotation: int representing how many backups to keep around;
             None if rotation shouldn't be used (as in the case of snapshots)
         """
-        if image_type == "snapshot":
-            task_state = task_states.IMAGE_SNAPSHOT
-        elif image_type == "backup":
-            task_state = task_states.IMAGE_BACKUP
-        else:
-            raise Exception(_('Image type not recognized %s') % image_type)
-
         context = context.elevated()
         instance_ref = self.db.instance_get_by_uuid(context, instance_uuid)
 
@@ -926,8 +919,7 @@ class ComputeManager(manager.SchedulerDependentManager):
         self._instance_update(context,
                               instance_ref['id'],
                               power_state=current_power_state,
-                              vm_state=vm_states.ACTIVE,
-                              task_state=task_state)
+                              vm_state=vm_states.ACTIVE)
 
         LOG.audit(_('instance %s: snapshotting'), instance_uuid,
                   context=context)