RFR: 8214068: ZGC crashes with vmTestbase/nsk/jdi/ReferenceType/instances/instances004/TestDescription.java

[Per Liden]

Thanks for reviewing Erik!

/Per

On 11/21/18 11:08 AM, Erik Österlund wrote:
> Hi Per,
> 
> Looks good.
> 
> Thanks,
> /Erik
> 
> On 2018-11-21 10:11, Per Liden wrote:
>> This patch adds a missing load barrier to the JVMTI heap walker. In 
>> VM_HeapWalkOperation::collect_simple_roots() the SimpleRootsClosure 
>> closure should not do raw loads of oops. Instead it should be loading 
>> them using NativeAccess<AS_NO_KEEPALIVE>::oop_load().
>>
>> This problem only affects ZGC, since it's (so far) the only collector 
>> that scans JNIHandles concurrently.
>>
>> The problem was easily reproducible when running 
>> vmTestbase/nsk/jdi/ReferenceType/instances/instances004/TestDescription.java. 
>> However, for some reason this isn't reproducing in our CI pipeline, 
>> likely because of luck with timing. For example, this is harder to 
>> reproduce in a scenario where your using a smaller heap and hence have 
>> GC cycles happen more frequently.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8214068
>> Webrev: http://cr.openjdk.java.net/~pliden/8214068/webrev.0
>>
>> /Per
>