[ovirt-devel] Issues on master with releasing a lock

[Ravi Shankar Nori]

Hi All,

We have some issues with a few flows on master where the lock acquired is
being
released more than once. This could be a real problem in cases where the
lock is
prematurely released for a second command that had acquired the lock which
the first
command has released.

For instance

1. Command A has acquired the VM lock and executes a child command.
2. The child command releases the lock
3. Command B now acquires the VM lock
4. Command A continues execution and finally releases the lock the second
time
5. The Command B's lock has now been released prematurely by Command A.

The tell tale sign indicating that a flow is one of the offending flows is
the warning
message in the logs indicating that a previously released lock is being
released again.

[org.ovirt.engine.core.bll.lock.InMemoryLockManager]
(EE-ManagedThreadFactory-engine-Thread-6) [1435f925] Trying to release
exclusive lock which does not exist, lock key:
'53cfa6c3-ecd6-4796-84cb-5c53d7c2a77fVDS_FENCE'


I have seen issues with Live Merge [1], Moving storage domain to
maintenance[2] ,
VdsNotRespondingTreatmentCommand [3] and Creating a snapshot [4].

I have submitted some patches to fix the issue with Live Merge [5], Moving
storage domain to maintenance [6]  and VdsNotRespondingTreatmentCommand [7].

The multiple lock release issue needs to fixed and if you are the owner of
a flow please
make sure the flow does not log a warning message to the logs. There is no
single
solution to fix the issue, this has be done flow by flow. But below are a
few pointers

1. If a command has a callback and the command is executing a child
command, which
in turn is executing a few child commands. The child command should also
have a
command callback so that the locks are released by the framework. Example
patch [6]

2. If a parent has acquired the lock and is executing a child command with
cloned
context, to make sure that the child does not release the locks acquired by
the parent
pass the cloned parent context with out locks to the child. Example patch
[7]


Thanks

Ravi


[1] https://bugzilla.redhat.com/1568556
[2] https://bugzilla.redhat.com/1568447
[3] https://bugzilla.redhat.com/1571300
[4] https://bugzilla.redhat.com/1569625

<https://bugzilla.redhat.com/1569625>
[5] https://gerrit.ovirt.org/#/c/90482/
[6] https://gerrit.ovirt.org/#/c/90411/
[7] https://gerrit.ovirt.org/#/c/90568/
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