Race condition in LifetimeManager could result in access to freed memory

[Nischal Sheth]

Access to freed memory can happen in the following scenario:

- LifetimeActor::Delete is called from main thread i.e. not from any Task
- LifetimeActor::Delete sets the deleted_ flag on the actor but it hasn't
yet enqueued the actor to the LifetimeManager
- LifetimeActor::RemoveDependency gets called on the actor in question
- If the dependent being removed is the last one, refcount_ is incremented
to 1 and the actor is added to LifetimeManager queue
- LifetimeManager::DeleteExecutor calls ReferenceDecrementAndTest on the
actor in question, which returns true because the deleted_ flag is set and
the refcount_ just became 0
- LifetimeManager::DeleteExecutor calls destroy on the actor
- LifetimeActor::Delete now calls LifetimeManager::Enqueue which accesses
the destroyed actor

Note that this problem will not happen if LifetimeActor::Delete is called
from any Task, since all Tasks are mutually exclusive with bgp::Config and
LifetimeManager::DeleteExecutor runs in context of bgp::Config Task.

Since LifetimeActor::Delete is called from main thread only during control
node shutdown and in unit tests, this problem shouldn't impact normal
operation of control node.

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/10015
Submitter: Nischal Sheth (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/10017
Submitter: Nischal Sheth (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/10015
Committed: http://github.org/Juniper/contrail-controller/commit/46f43c82cc11c801191e10b546fdac1d704d0be4
Submitter: Zuul
Branch: master

commit 46f43c82cc11c801191e10b546fdac1d704d0be4
Author: Nischal Sheth <email address hidden>
Date: Wed May 6 09:52:48 2015 -0700

Fix race condition in LifetimeManager

Use the mutex to prevent LifetimeActor::ReferenceDecrementAndTest
from running in parallel with LifetimeActor::Delete.

Change-Id: If539c9a2f5f84780e19128477fe62dc177006571
Closes-Bug: 1452122

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/10017
Committed: http://github.org/Juniper/contrail-controller/commit/78d842d7b1108988bba85631fe25e005eadac9eb
Submitter: Zuul
Branch: R2.20

commit 78d842d7b1108988bba85631fe25e005eadac9eb
Author: Nischal Sheth <email address hidden>
Date: Wed May 6 09:52:48 2015 -0700

Fix race condition in LifetimeManager

Use the mutex to prevent LifetimeActor::ReferenceDecrementAndTest
from running in parallel with LifetimeActor::Delete.

Change-Id: If539c9a2f5f84780e19128477fe62dc177006571
Closes-Bug: 1452122