RFR(S): 8008301: G1: guarantee(satb_mq_set.completed_buffers_num() == 0) failure

[John Cuthbertson]

Hi Bengt,

Thanks for reviewing these changes.

Cheers,

JohnC

On 3/18/2013 2:10 AM, Bengt Rutisson wrote:
>
>
> Hi John,
>
> Looks good.
>
> Bengt
>
>
> On 3/15/13 1:31 AM, John Cuthbertson wrote:
>> Hi Everyone,
>>
>> Here's another one associated with overflowing the marking stack. The 
>> webrev can be found at:
>>
>> http://cr.openjdk.java.net/~johnc/8008301/webrev.0/
>>
>> Summary:
>> In this case the marking stack overflows during the actual remark 
>> task - when the individual marking tasks are draining the completed 
>> SATB buffers. As a result we exit the remark task (because of the 
>> overflow) with some legitimately unprocessed completed SATB buffers 
>> and trip the guarantee.
>>
>> The main part of the fix is between line 2575 and 2579 where I relax 
>> the guarantee to allow for the overflow. Additionally I've also added 
>> a heap verification for when we restart marking due to overflow. I 
>> added it as part of the debugging and I think it makes sense to leave 
>> it in.
>>
>> The change between lines 2408 and 2416 is to just skip reference 
>> processing. While testing I was running into the hang reported in 
>> 8009536 and added this to work around it. An equivalent change will 
>> be pushed as part of the changes for 8009940.
>>
>> Testing:
>> The failing test case in a loop (with and without instrumentation and 
>> VerifyDuringGC)
>> The GC test suite with a small mark stack size (2K, 4K)
>> The Lucene tests for 8009536 to specifically test the verification 
>> after overflow.
>>
>> Thanks,
>>
>> JohnC
>