[15] RFR 8239926: Shenandoah: Shenandoah needs to mark nmethod's metadata

[Zhengyu Gu]

Revised based on offline discussions.

Piggyback on stack code root rescanning to SATB draining task.

Webrev: http://cr.openjdk.java.net/~zgu/JDK-8239926/webrev.02/

Reran tests:
   hotspot_gc_shenandoah
   tools/javac

Thanks,

-Zhengyu

On 3/4/20 6:06 PM, Zhengyu Gu wrote:
> Traversal GC has the same issue, also need to remark on stack code roots 
> in final traversal.
> 
> @@ -263,11 +263,12 @@
>       if (!_heap->is_degenerated_gc_in_progress()) {
>         ShenandoahTraversalRootsClosure roots_cl(q, rp);
>         ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
>         if (unload_classes) {
>           ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
> -        _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, 
> NULL, &tc);
> +        MarkingCodeBlobClosure code_cl(&roots_cl, 
> CodeBlobToOopClosure::FixRelocations);
> +        _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, 
> &code_cl, &tc);
>         } else {
>           CLDToOopClosure cld_cl(&roots_cl, 
> ClassLoaderData::_claim_strong);
>           _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
>         }
>       } else {
> 
> 
> Updated webrev: http://cr.openjdk.java.net/~zgu/JDK-8239926/webrev.01/
> 
> Thank,
> 
> -Zhengyu
> 
> On 2/25/20 12:13 PM, Zhengyu Gu wrote:
>> Shenandoah encounters a few test failures with tools/javac. Verifier 
>> catches unmarked oops in nmethod's metadata during root evacuation in 
>> final mark phase.
>>
>> The problem is that, Shenandoah marks on stack nmethods in init mark 
>> pause, but it does not mark nmethod's metadata during concurrent mark 
>> phase, when new nmethod is about to be executed.
>>
>> The solution:
>> 1) Use nmethod_entry_barrier to keep nmethod's metadata alive when the 
>> nmethod is about to be executed, when nmethod entry barrier is supported.
>>
>> 2) Remark on stack nmethod's metadata at final mark pause.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8239926
>> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8239926/webrev.00/
>>
>> Test:
>>    hotspot_gc_shenandoah (fastdebug and release)
>>    tools/javac with ShenandoahCodeRootsStyle = 1 and 2 (fastdebug and 
>> release)
>>
>> Thanks,
>>
>> -Zhengyu