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

[Per Liden]

Thanks for reviewing, Robbin!

/Per

On 11/21/18 12:06 PM, Robbin Ehn wrote:
> On 2018-11-21 11:08, Erik Österlund wrote:
>> Hi Per,
>>
>> Looks good.
> 
> Ship it!
> 
> /Robbin
> 
>>
>> 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
>>