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[Corey Bryant <corey.bryant@xxxxxxxxxxxxx>]

Also marking this as fix-released for Ubuntu since it is available in
nova 13.0.0+.

** Changed in: nova (Ubuntu)
       Status: Confirmed => Fix Released

** Also affects: nova (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Changed in: nova (Ubuntu Xenial)
       Status: New => Fix Released

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https://bugs.launchpad.net/bugs/1515768

Title:
  Instance creation fails with libvirtError: Unable to create tap
  device: Device or resource busy

Status in OpenStack Compute (nova):
  Fix Released
Status in tacker:
  Fix Committed
Status in nova package in Ubuntu:
  Fix Released
Status in nova source package in Xenial:
  Fix Released

Bug description:
  Summary:
  This issue is observed frequently on Jenkins gate and has been reproducible in local setup too.

  Steps:
  Initiate 3 stack create requests at once in a script:

  heat stack-create -f /home/stack/template_file stack1
  heat stack-create -f /home/stack/template_file stack2
  heat stack-create -f /home/stack/template_file stack3

  using the following HOT file:
  http://paste.openstack.org/show/479920/

  
  One of the stack creations fails with CreateFailed: Resource Create Failed: Conflict: Resources. vdu3: Port Is Still In Use.

  From the nova logs, there are duplicate bridges created for one of the
  servers. The qemu xml fails with libvirtError: Unable to create tap
  device tapd3a3d9e9-5d: Device or resource busy. See timestamp
  2015-11-25 23:03:14.940 in n-cpu.log

  Attaching the relevant n-cpu.log, q-svc.log and h-eng.log

  Observation:
  The 1st network interface for the nova instance is a Neutron Port resource provided in HOT template.
  Nova sends a PUT request to update the port information. It also sends 2 POST requests for the 2nd and 3rd network interfaces.
  Neutron receives the PUT request and sends network-event changed event while nova is still waiting for the POST response for the 2 ports.
  If the network-changed event is received before the 3rd port POST response is received, refresh_cache is acquired by nova_service
  Nova sends a query for port information, updates the cache and release the lock.
  By then, POST requests are completed which acquires the cache lock again and sends request for network info. refresh_cache is updated twice and contains duplicate set of ports
  Network vifs are built for all 6 ports and qemu xml is build based on that.
  Duplicate bridges in xml is complained by libvirt as device or resource busy.

  Version and environment:
  Devstack Master

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