RFR(S) 8156137: SIGSEGV in ReceiverTypeData::clean_weak_klass_links

[Coleen Phillimore]

On 8/30/16 5:40 PM, dean.long at oracle.com wrote:
> Thanks for the review.  Do I need another review before pushing?

Maybe Dan or Serguei could look at it too.

Coleen

>
> dl
>
>
> On 8/30/16 1:57 PM, Coleen Phillimore wrote:
>>
>> This change looks good.  Thank you for doing the analysis and 
>> figuring this out.
>> Coleen
>>
>> On 8/30/16 3:24 PM, dean.long at oracle.com wrote:
>>> http://cr.openjdk.java.net/~dlong/8156137/webrev/
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8156137
>>>
>>> The problem: JVMTI RedefineClasses creates scratch classes to hold 
>>> the old methods until they can be freed (they are no longer active 
>>> in a thread stack).  G1ConcurrentMark sees these scratch classes, 
>>> but G1MarkSweep does not.
>>>
>>> The details:
>>>
>>> G1ConcurrentMark uses ClassLoaderDataGraphKlassIteratorAtomic to 
>>> iterate over *all* classes and calls clean_weak_instanceklass_links 
>>> to clean.
>>>
>>> G1MarkSweep (and other GCs) use Klass::clean_weak_klass_links() to 
>>> iterate over *live, non-scratch* classes, and calls 
>>> clean_weak_instanceklass_links to clean.
>>>
>>> Now the problem scenario is:
>>>
>>> 0: scratch class S has MethodData that references a class U that is 
>>> going to be unloaded.
>>>
>>> 1: G1MarkSweep skips class S in Klass::clean_weak_klass_links, 
>>> because scratch classes are not added to the class hierarchy tree. 
>>> The full GC then frees the metadata for class U. Now the MethodData 
>>> for S contains stale metadata.
>>>
>>> 2. When a later G1ConcurrentMark calls 
>>> clean_weak_instanceklass_links on S, it will crash on the stale 
>>> metadata.
>>>
>>> Solution: have Klass::clean_weak_klass_links() process these scratch 
>>> classes that can be found on the "previous versions" list.
>>>
>>> Tested with bigapps/Kitchensink.
>>>
>>> dl
>>>
>>
>