Shenandoah Generational: JBB 2015 crash on PPC64 product build

# Internal Error (shenandoahHeapRegion.cpp:93), pid=32884, tid=32890
# fatal error: Illegal region state transition from "Empty Committed", at cset
  | 2021|EC |F|BTE 7f7000000, 7f7000000, 7f7800000|TAMS 7f7000000|UWM 7f7000000|U 0B|T 0B|G
   0B|G 0B|S 0B|L 0B|CP 0
 
#3 0x00007fff937bf710 in VMError::report_and_die (id=<optimized out>, message=<optimized out>,
    detail_fmt=<optimized out>, detail_args=0x7fff7144d370 "0\207\032\214\377\177", thread=<optimized out>,
    pc=<optimized out>, siginfo=<optimized out>, context=<optimized out>,
    filename=0x7fff938edf98 "src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp", lineno=93, size=0)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/utilities/vmError.cpp:1750
#4 0x00007fff92ce2684 in report_fatal (error_type=<optimized out>,
    file=0x7fff938edf98 "src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp", line=<optimized out>,
    detail_fmt=0x7fff938f8908 "%s")
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/runtime/thread.hpp:654
#5 0x00007fff935055f4 in ShenandoahHeapRegion::report_illegal_transition (this=0x7fff900df280,
    method=0x7fff938d17e0 "cset")
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp:93
#6 0x00007fff935068ec in ShenandoahHeapRegion::make_cset (this=<optimized out>)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp:260
#7 0x00007fff934b7fb0 in ShenandoahCollectionSet::add_region (this=<optimized out>, r=<optimized out>)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/gc/shenandoah/shenandoahCollectionSet.cpp:104
#8 0x00007fff935fa3d0 in ShenandoahOldHeuristics::prime_collection_set (this=0x7fff8c0e9ce0,
    collection_set=0x7fff8c0fc490)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.cpp:139
#9 0x00007fff9350cc64 in ShenandoahHeuristics::choose_collection_set (this=0x7fff8c0d8b00,
    collection_set=0x7fff8c0fc490, old_heuristics=0x7fff8c0e9ce0)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.cpp:187
#10 0x00007fff934dca10 in ShenandoahGeneration::prepare_regions_and_collection_set (this=<optimized out>,
    concurrent=<optimized out>)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/gc/shenandoah/shenandoahHeap.hpp:783
#11 0x00007fff934bdfb8 in ShenandoahConcurrentGC::op_final_mark (this=0x7fff7195e258)
   henandoah/src/hotspot/share/gc/shenandoah/shenandoahConcurrentGC.cpp:686
#12 0x00007fff934ba330 in ShenandoahConcurrentGC::entry_final_mark (this=0x7fff7195e258)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/gc/shenandoah/shenandoahConcurrentGC.cpp:333
#13 0x00007fff936273d0 in VM_ShenandoahFinalMarkStartEvac::doit (this=0x7fff7195e0b8)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/gc/shenandoah/shenandoahVMOperations.cpp:57
#14 0x00007fff937c7974 in VM_Operation::evaluate (this=0x7fff7195e0b8)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/runtime/vmOperations.cpp:70
#15 0x00007fff937ca174 in VMThread::evaluate_operation (this=0x7fff8c1ad520, op=0x7fff7195e0b8)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/runtime/vmThread.cpp:282
#16 0x00007fff937caacc in VMThread::inner_execute (this=0x7fff8c1ad520, op=<optimized out>)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/runtime/vmThread.cpp:429
#17 0x00007fff937caedc in VMThread::loop (this=0x7fff8c1ad520)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/runtime/vmThread.hpp:99
#18 VMThread::run (this=0x7fff8c1ad520)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/runtime/vmThread.cpp:175
#19 0x00007fff93716218 in Thread::call_run (this=0x7fff8c1ad520)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/share/runtime/thread.cpp:356
#20 0x00007fff9338b9b4 in thread_native_entry (thread=0x7fff8c1ad520)
    at /usr/work/d056149/openjdk/shenandoah/src/hotspot/os/linux/os_linux.cpp:705
#21 0x00007fff93ea9b48 in start_thread () from /lib64/libpthread.so.0
 
The affected HeapRegion is:
(gdb) p r
$1 = (ShenandoahHeapRegion *) 0x7fff900df280
(gdb) p *r
$2 = {static RegionCount = 2039, static RegionSizeBytes = 8388608, static RegionSizeWords = 1048576,
  static RegionSizeBytesShift = 23, static RegionSizeWordsShift = 20, static RegionSizeBytesMask = 8388607,
  static RegionSizeWordsMask = 1048575, static HumongousThresholdBytes = 8388608,
  static HumongousThresholdWords = 1048576, static MaxTLABSizeBytes = 8388608, static MaxTLABSizeWords = 1048576,
  _index = 2021, _bottom = 0x7f7000000, _end = 0x7f7800000, _new_top = 0x7f7000000,
  _empty_time = 3827.6774025059999, _state = ShenandoahHeapRegion::_empty_committed,
  _coalesce_and_fill_boundary = 0x7f7000000, _top = 0x7f7000000, _tlab_allocs = 0, _gclab_allocs = 0,
  _plab_allocs = 0, _has_young_lab = false, _live_data = 0, _critical_pins = 0, _update_watermark = 0x7f7000000,
  _affiliation = FREE, _age = 0, static MIN_NUM_REGIONS = 10}