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[Robert Kukura <1415526@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

In the non-DVR case, the Ml2Plugin._bind_port() function creates a
models.PortBinding instance with copies of fields from the port's actual
PortBinding instance from the DB, and passes a PortContext referencing
this copy to MechanismManager.bind_port() to attempt to bind the port.
This allows the results from the binding attempt to be discarded if
Ml2Plugin._commit_port_binding determines the port has been concurrently
bound or otherwise modified during the binding attempt, which occurs
outside any transaction.

In the DVR case, Ml2Plugin.update_dvr_port_binding() calls
MechanismManager.bind_port() using a PortContext referencing the actual
models.DVRPortBinding instance associated with the DB. Changes made to
this DVRPortBinding instance during the binding attempt get committed to
the DB in the following transaction, and
Ml2Plugin._commit_dvr_port_binding() is not actually comparing the pre-
binding and post-binding state as intended to determine whether to
commit the changes.

This does not currently cause any obvious issues in normal operation
(unless there are concurrent binding attempts), but the changes in
https://review.openstack.org/#/c/116122/16/neutron/plugins/ml2/plugin.py
expose this issue because db.set_binding_levels() does not get called on
line 366, resulting in DVR tempest failures.

This issue would likely be resolved by the work planned for
https://bugs.launchpad.net/neutron/+bug/1367391, but may need to be
fixed sooner to allow the hierarchical port binding implementation to be
merged.

** Affects: neutron
     Importance: High
     Assignee: Robert Kukura (rkukura)
         Status: New


** Tags: ml2

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https://bugs.launchpad.net/bugs/1415526

Title:
  ML2 DVR port binding does not handle concurrency

Status in OpenStack Neutron (virtual network service):
  New

Bug description:
  In the non-DVR case, the Ml2Plugin._bind_port() function creates a
  models.PortBinding instance with copies of fields from the port's
  actual PortBinding instance from the DB, and passes a PortContext
  referencing this copy to MechanismManager.bind_port() to attempt to
  bind the port. This allows the results from the binding attempt to be
  discarded if Ml2Plugin._commit_port_binding determines the port has
  been concurrently bound or otherwise modified during the binding
  attempt, which occurs outside any transaction.

  In the DVR case, Ml2Plugin.update_dvr_port_binding() calls
  MechanismManager.bind_port() using a PortContext referencing the
  actual models.DVRPortBinding instance associated with the DB. Changes
  made to this DVRPortBinding instance during the binding attempt get
  committed to the DB in the following transaction, and
  Ml2Plugin._commit_dvr_port_binding() is not actually comparing the
  pre-binding and post-binding state as intended to determine whether to
  commit the changes.

  This does not currently cause any obvious issues in normal operation
  (unless there are concurrent binding attempts), but the changes in
  https://review.openstack.org/#/c/116122/16/neutron/plugins/ml2/plugin.py
  expose this issue because db.set_binding_levels() does not get called
  on line 366, resulting in DVR tempest failures.

  This issue would likely be resolved by the work planned for
  https://bugs.launchpad.net/neutron/+bug/1367391, but may need to be
  fixed sooner to allow the hierarchical port binding implementation to
  be merged.

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