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

[serguei.spitsyn at oracle.com]

Hi Dean,

It looks good.
Nice catch!

Thanks,
Serguei


On 8/30/16 14:49, Coleen Phillimore wrote:
>
>
> 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 the old methods until they can be freed (they are no longer active 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
>>>>
>>>
>>
>