EXCEPTION_ACCESS_VIOLATION in BFSClosure::closure_impl

The following tests intermittently failed with EXCEPTION_ACCESS_VIOLATION using jdk18 win32 client jvm:
jdk/jfr/event/oldobject/TestG1.java
jdk/jfr/event/oldobject/TestHeapDeep.java
jdk/jfr/event/oldobject/TestReferenceChainLimit.java
jdk/jfr/jcmd/TestJcmdDumpPathToGCRoots.java

Full hs_err logs are attached for jdk18 release build (hs_err_pid768.log) and jdk15u-dev slowdebug build (hs_err_pid2068.log), that has the same crash, but more representative stacktrace.

#
# A fatal error has been detected by the Java Runtime Environment:
#
# EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x7421d704, pid=768, tid=396
#
# JRE version: OpenJDK Runtime Environment (18.0) (build 18-internal+0-adhoc.tester.jdk)
# Java VM: OpenJDK Client VM (18-internal+0-adhoc.tester.jdk, mixed mode, emulated-client, serial gc, windows-x86)
# Problematic frame:
# V [jvm.dll+0x2d704] BFSClosure::closure_impl+0x54
#
# Core dump will be written. Default location: C:\Users\tester\tmp\JTwork\scratch\hs_err_pid768.mdmp
#
# JFR recording file will be written. Location: C:\Users\tester\tmp\JTwork\scratch\hs_err_pid768.jfr
#
# If you would like to submit a bug report, please visit:
# https://bugreport.java.com/bugreport/crash.jsp
#

--------------- S U M M A R Y ------------

Command Line: -Dtest.vm.opts= -Dtest.tool.vm.opts= -Dtest.compiler.opts= -Dtest.java.opts= -Dtest.jdk=C:\Users\tester\tmp\jdk -Dcompile.jdk=C:\Users\tester\tmp\jdk -Dtest.timeout.factor=1.0 -Dtest.root=C:\Users\tester\tmp\openjdk\test\jdk -Dtest.name=jdk/jfr/jcmd/TestJcmdDumpPathToGCRoots.java -Dtest.file=C:\Users\tester\tmp\openjdk\test\jdk\jdk\jfr\jcmd\TestJcmdDumpPathToGCRoots.java -Dtest.src=C:\Users\tester\tmp\openjdk\test\jdk\jdk\jfr\jcmd -Dtest.src.path=C:\Users\tester\tmp\openjdk\test\jdk\jdk\jfr\jcmd;C:\Users\tester\tmp\openjdk\test\lib;C:\Users\tester\tmp\openjdk\test\jdk -Dtest.classes=C:\Users\tester\tmp\JTwork\classes\jdk\jfr\jcmd\TestJcmdDumpPathToGCRoots.d -Dtest.class.path=C:\Users\tester\tmp\JTwork\classes\jdk\jfr\jcmd\TestJcmdDumpPathToGCRoots.d;C:\Users\tester\tmp\JTwork\classes\test\lib;C:\Users\tester\tmp\JTwork\classes\test\jdk -Dtest.modules=jdk.jfr/jdk.jfr.internal.test --add-modules=jdk.jfr --add-exports=jdk.jfr/jdk.jfr.internal.test=ALL-UNNAMED -XX:TLABSize=2k com.sun.javatest.regtest.agent.MainWrapper C:\Users\tester\tmp\JTwork\jdk\jfr\jcmd\TestJcmdDumpPathToGCRoots.d\main.1.jta

Host: AMD EPYC 7R32, 8 cores, 15G, Windows Server 2012 R2 , 64 bit Build 9600 (6.3.9600.19994)
Time: Mon Sep 27 20:33:26 2021 /GM elapsed time: 0.497426 seconds (0d 0h 0m 0s)

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

Current thread (0x13c247e0): VMThread "VM Thread" [stack: 0x03300000,0x03350000] [id=396]

Stack: [0x03300000,0x03350000], sp=0x0334f270, free space=316k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [jvm.dll+0x2d704] BFSClosure::closure_impl+0x54 (bfsclosure.cpp:131)

siginfo: EXCEPTION_ACCESS_VIOLATION (0xc0000005), reading address 0x00000000