G1: FreeRegionList_test() fails with G1 after the JDK-8058534 fix to HeapRegion::orig_end()

The internal VM tests fail when they are run with G1:

$ java -XX:+UseG1GC -XX:+ExecuteInternalVMTests -version

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/localhome/repos/jdk9-hs-gc-push/hotspot/src/share/vm/gc_implementation/g1/heapRegion.cpp:202), pid=29853, tid=139726758901504
# assert(_end == orig_end()) failed: we should have already filtered out humongous regions
#
# JRE version: Java(TM) SE Runtime Environment (9.0-b30) (build 1.9.0-ea-b30)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (1.9.0-internal mixed mode linux-amd64 compressed oops)
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
#

--------------- T H R E A D ---------------

Current thread (0x00007f14a400b800): JavaThread "main" [_thread_in_vm, id=29858, stack(0x00007f14abc47000,0x00007f14abd48000)]

Stack: [0x00007f14abc47000,0x00007f14abd48000], sp=0x00007f14abd45b00, free space=1018k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x10a5690] VMError::report_and_die()+0x160
V [libjvm.so+0x74096b] report_vm_error(char const*, int, char const*, char const*)+0x7b
V [libjvm.so+0x90b41f] HeapRegion::initialize(MemRegion, bool, bool)+0x10f
V [libjvm.so+0x90b9fd] HeapRegion::HeapRegion(unsigned int, G1BlockOffsetSharedArray*, MemRegion)+0x29d
V [libjvm.so+0x91b7fc] FreeRegionList_test()+0x26c
V [libjvm.so+0xa6a9f6] execute_internal_vm_tests()+0x2d6
V [libjvm.so+0xab0197] JNI_CreateJavaVM+0x287
C [libjli.so+0x747c] JavaMain+0x8c
C [libpthread.so.0+0x8182] start_thread+0xc2


The test fails on this assert in HeapRegion::hr_clear():

assert(_end == orig_end(),

The reason for the failure is that the internal test, FreeRegionList_test() in heapRegionSet.cpp, creates heap regions with invalid memory regions. There is this comment in the test:


  // Create a fake heap. It does not need to be valid, as the HeapRegion constructor
  // does not access it.
  MemRegion heap(NULL, num_regions_in_test * HeapRegion::GrainWords);

The problem is that this is no longer true. The assert in HeapRegion::hr_clear() actually looks at the memory region.

So, my guess is that the fix is to create more consistent memory regions in the test.