SIGSEGV at ModuleEntryTable::purge_all_module_reads() called from G1ConcurrentMark

## Summary
Running AdoptOpenJDK 11.0.10+9 application crashes randomly with SIGSEGV (0xb) error:

```
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x00007fb83ec2bfe3, pid=12547, tid=12555
#
# JRE version: OpenJDK Runtime Environment AdoptOpenJDK (11.0.10+9) (build 11.0.10+9)
# Java VM: OpenJDK 64-Bit Server VM AdoptOpenJDK (11.0.10+9, mixed mode, tiered, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0xbf5fe3] ModuleEntryTable::purge_all_module_reads()+0x163
#
# No core dump will be written. 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:
# https://github.com/AdoptOpenJDK/openjdk-support/issues
#

```
Host: Intel(R) Xeon(R) Platinum 8259CL CPU @ 2.50GHz, 16 cores, 124G, CentOS Linux release 7.9.2009 (Core)
Time: Mon Jun 7 01:33:07 2021 CDT elapsed time: 290185.968425 seconds (3d 8h 36m 25s)

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

Current thread (0x000055fff9b22000): VMThread "VM Thread" [stack: 0x00007fa0c3f19000,0x00007fa0c4019000] [id=12555]

Stack: [0x00007fa0c3f19000,0x00007fa0c4019000], sp=0x00007fa0c40170a0, free space=1016k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0xbf5fe3] ModuleEntryTable::purge_all_module_reads()+0x163
V [libjvm.so+0x60bcb4] ClassLoaderDataGraph::do_unloading(bool)+0x134
V [libjvm.so+0xe80e58] SystemDictionary::do_unloading(GCTimer*, bool)+0x1a8
V [libjvm.so+0x7ac2f0] G1ConcurrentMark::weak_refs_work(bool)+0x410
V [libjvm.so+0x7af4d8] G1ConcurrentMark::remark()+0xd8
V [libjvm.so+0xf3a891] VM_CGC_Operation::doit()+0x221
V [libjvm.so+0xf323f7] VM_Operation::evaluate()+0xe7
V [libjvm.so+0xf3877f] VMThread::evaluate_operation(VM_Operation*) [clone .constprop.66]+0xff
V [libjvm.so+0xf38cf8] VMThread::loop()+0x428
V [libjvm.so+0xf39193] VMThread::run()+0x73
V [libjvm.so+0xebd9bf] Thread::call_run()+0x14f
V [libjvm.so+0xc5dbde] thread_native_entry(Thread*)+0xee

siginfo: si_signo: 11 (SIGSEGV), si_code: 128 (SI_KERNEL), si_addr: 0x0000000000000000

## Steps to reproduce

The problem is random and occurred twice in last three days in AWS hosted environment.
The problem is similar to https://bugs.openjdk.java.net/browse/JDK-8251945, which was included in oracle 11.0.10 release and is available on http://hg.openjdk.java.net/jdk/jdk branch. We think merging it to AdoptOpentJDK should solve the issue. Can you confirm the theory and merge the changes?

## Triaging info

Java version:
openjdk version "11.0.10" 2021-01-19
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.10+9)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.10+9, mixed mode)

What is your operating system and platform?
CentOS Linux release 7.9.2009 (Core)

How did you install Java?
Used a binary archive (tar.gz)

Did it work before?
It crashed in prod env, worked in lower envs. The load was low.
It was running fine with Oracle JDK 1.8.0_92

Did you test with other Java versions?
No, it's random with no reproduction pattern till now.

Start with the supplied stack at ModuleEntryTable::purge_all_module_reads() during G1ConcurrentMark, then compare the referenced JDK-8251945 change with the AdoptOpenJDK 11.0.10+9 sources. Reproduce or validate on CentOS 7.9 using the reported Java version; done requires confirming the diagnosis and determining whether the change belongs in a supported build, but no deterministic test case is provided.

Written by the indexing model from the issue text.