task_state may be overwritten in race condition

[Yun Mao]

task_state acts like a guard to avoid concurrent tasks to be scheduled. There might be two race conditions:

1) two tasks are concurrently accepted by api, check task_state to be None and allow the tasks to be executed concurrently.

2) one ordinary task is running, so that task_state is set. The delete task is accepted at API, and will "take over" and change task_state to DELETING. However the first task may continue to update task_state or set it to None as it finishes.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/11895

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/11895
Committed: http://github.com/openstack/nova/commit/85b9ee6b5b74d15a6455cb6632578bea07d8eb11
Submitter: Jenkins
Branch: master

commit 85b9ee6b5b74d15a6455cb6632578bea07d8eb11
Author: Yun Mao <email address hidden>
Date: Thu Aug 23 11:13:58 2012 -0400

    Make instance_update_and_get_original() atomic

    Use the same session object within a transaction to retrieve
    and update the instance object, including metadata and system
    metadata.

    In preparation to fix bug 1037372

    Change-Id: I886da12bb85f60c2b23609a35b6d9a43040216ce

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/12222

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/12222
Committed: http://github.com/openstack/nova/commit/4082c8375a6ae7e7e67c7ad2e263be2d5fc3dd1f
Submitter: Jenkins
Branch: master

commit 4082c8375a6ae7e7e67c7ad2e263be2d5fc3dd1f
Author: Yun Mao <email address hidden>
Date: Thu Aug 30 14:55:13 2012 -0400

    Address race condition from concurrent task state update

    task_state acts like a guard to avoid concurrent tasks to be
    scheduled. There might be two race conditions:

     1) two tasks are concurrently accepted by api, check task_state to be
     None and allow the tasks to be executed concurrently.

     2) one ordinary task is running, so that task_state is set. The delete
     task is accepted at API, and will "take over" and change task_state to
     DELETING. However the first task may continue to update task_state or
     set it to None as it finishes.

    This patch specifies current expected task_state when updating task_state.
    If unexpected state is met, abort the task without updating. Various
    compute tests are fixed accordingly to set the pre condition of the
    task state.

    Part of bug 1037372
    Change-Id: I5fdf0946c728a47febb56ad468043a828b2736c8