8212205 (XS) VM asserts after CDS archive has been unmapped

[Ioi Lam]

Hi Harold,


On 10/25/18 11:34 AM, Harold David Seigel wrote:
> HI Ioi,
>
> This looks good.
>
> What regression tests were run?
>
I did manual testing to trigger the condition, and could reproduce it 
100% before, and could not reproduce after the fix.

This is an intermittent failure but has happened a lot in tier 1, I'll 
do a round of tier1/2 testing before pushing. But I guess we needs a few 
weeks of runs to confirm that the intermittent failures don't happen 
anymore.

Thanks
- Ioi

> Thanks, Harold
>
> On 10/25/2018 2:22 PM, Ioi Lam wrote:
>> https://bugs.openjdk.java.net/browse/JDK-8212205
>> http://cr.openjdk.java.net/~iklam/jdk12/8212205-crash-after-cds-unmap.v01/ 
>>
>>
>> This is a silly bug but it happens only rarely, when address space 
>> randomization
>> causes insufficient memory to be reservable at addresses required by 
>> CDS. In this
>> case, the CDS archive is unmapped, but we forget to clean up
>> _shared_metaspace_{base,top}. As a result, the JVM will misidentify 
>> metaspace
>> objects allocated in certain address ranges to be "shared", in the 
>> following function:
>>
>> class MetaspaceObj {
>>   bool is_shared() const {
>>     return (((void*)this) < _shared_metaspace_top && ((void*)this) >= 
>> _shared_metaspace_base);
>>   }
>> }
>>
>> The fix is to reset those pointers after CDS has been unmapped.
>>
>> Thanks
>> - Ioi
>>
>