RFR: 8373116: Genshen: arraycopy_work should be done unconditionally by arraycopy_marking if the array is in an old region [v6]

[Xiaolong Peng]

> Chasing the root cause of JDK-8372498, I have narrowed down root cause to the commit https://github.com/openjdk/jdk/commit/f8cf9ca69cfef286c80559bfe1d147b6303d10d2
> 
> It is caused by the behavior change from follow code:
> 
> Original:
> 
>   if (ShenandoahSATBBarrier) {
>     T* array = dst;
>     HeapWord* array_addr = reinterpret_cast<HeapWord*>(array);
>     ShenandoahHeapRegion* r = _heap->heap_region_containing(array_addr);
>     if (is_old_marking) {
>       // Generational, old marking
>       assert(_heap->mode()->is_generational(), "Invariant");
>       if (r->is_old() && (array_addr < _heap->marking_context()->top_at_mark_start(r))) {
>         arraycopy_work<T, false, false, true>(array, count);
>       }
>     } else if (_heap->mode()->is_generational()) {
>       // Generational, young marking
>       if (r->is_old() || (array_addr < _heap->marking_context()->top_at_mark_start(r))) {
>         arraycopy_work<T, false, false, true>(array, count);
>       }
>     } else if (array_addr < _heap->marking_context()->top_at_mark_start(r)) {
>       // Non-generational, marking
>       arraycopy_work<T, false, false, true>(array, count);
>     }
>   }
> 
> New:
> 
>   if (ShenandoahSATBBarrier) {
>     if (!_heap->marking_context()->allocated_after_mark_start(reinterpret_cast<HeapWord*>(dst))) {
>       arraycopy_work<T, false, false, true>(dst, count);
>     }
>   }
> 
> 
> 
> With the new STAB barrier code for arraycopy_marking, if is it young GC and the array is in old region, but array is above TAMS, arraycopy_work won't be applied anymore, so we may have missed some pointers in SATB in such case.
> 
> ### Test
> - [x] hotspot_gc_shenandoah
> - [x] repeat gc/TestAllocHumongousFragment.java#generational and sure it won't crash with the fix
> - [x] GHA

Xiaolong Peng has updated the pull request incrementally with one additional commit since the last revision:

  enqueue objects stored in old array at ShenandoahSATBBarrier when concurrent young marking is in progress

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28669/files
  - new: https://git.openjdk.org/jdk/pull/28669/files/49ea3c93..c649cf2b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28669&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28669&range=04-05

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28669.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28669/head:pull/28669

PR: https://git.openjdk.org/jdk/pull/28669