yahoo-eng-team team mailing list archive

[Kailun Qin <1795126@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

Current DHCP port management in Neutron makes the server to clear the
device_id while the agent is responsible for setting it.

This may cause a potential race condition, for example during network
rescheduling. The server aims to clear the device_id on a DHCP port and
assign the network to another agent while the old agent might just be
taking possession of the port. If the DHCP agent takes possession of the
port (i.e., update port...set the device_id) before the server clears
it, then there is no issue. However, if this happens after the clear
operation by server then the DHCP port would be updated/marked to be
owned by the old agent.

When the new agent takes over the network scheduled to it, it won't be able to find a port to reuse so that an extra port might need to be created. This leads to two issues:
1) an extra port is created and never deleted;
2) the extra port creation may fail if there are no available IP addresses.

** Affects: neutron
     Importance: Undecided
     Assignee: Kailun Qin (kailun.qin)
         Status: New

** Changed in: neutron
     Assignee: (unassigned) => Kailun Qin (kailun.qin)

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https://bugs.launchpad.net/bugs/1795126

Title:
  Race condition of DHCP agent updating port after ownership removed and
  given to another agent will cause extra port creation

Status in neutron:
  New

Bug description:
  Current DHCP port management in Neutron makes the server to clear the
  device_id while the agent is responsible for setting it.

  This may cause a potential race condition, for example during network
  rescheduling. The server aims to clear the device_id on a DHCP port
  and assign the network to another agent while the old agent might just
  be taking possession of the port. If the DHCP agent takes possession
  of the port (i.e., update port...set the device_id) before the server
  clears it, then there is no issue. However, if this happens after the
  clear operation by server then the DHCP port would be updated/marked
  to be owned by the old agent.

  When the new agent takes over the network scheduled to it, it won't be able to find a port to reuse so that an extra port might need to be created. This leads to two issues:
  1) an extra port is created and never deleted;
  2) the extra port creation may fail if there are no available IP addresses.

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