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

[Per Liden]

On 2018-11-21 15:58, Daniel D. Daugherty wrote:
> On 11/21/18 4:11 AM, 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
> 
> src/hotspot/share/prims/jvmtiTagMap.cpp
>      No comments.
> 
> Nice catch! Thumbs up.

Thanks for reviewing, Dan!

> 
> Since this is in the JVM/TI heap walker, I wonder if there are other
> sightings in JBS that might be tracked back to this. Looks like
> Zhengyu put a nice stack trace in the bug report so dup matching
> should be easy (if there are any).

I did a quick search, but didn't stumble onto anything relevant. This 
bug has "only" been in there since Oct 16 (which is when ZGC started to 
process JNIHandles concurrently).

cheers,
Per