ZGC: Kitchensink SIGSEGV in FinalizerThread.run

The following test failed in the JDK14 CI:

applications/kitchensink/Kitchensink24HStress.java

Here's a snippet from the hs_err_pid file:

# SIGSEGV (0xb) at pc=0x00007f3b247907b4, pid=10391, tid=10431
#
# JRE version: Java(TM) SE Runtime Environment (14.0+24) (build 14-ea+24-1081)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (14-ea+24-1081, mixed mode, tiered, z gc, linux-amd64)
# Problematic frame:
# J 115924% c2 java.lang.ref.Finalizer$FinalizerThread.run()V java.base@14-ea (56 bytes) @ 0x00007f3b247907b4 [0x00007f3b247904c0+0x00000000000002f4]

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

Current thread (0x00007f3b34134fb0): JavaThread "Finalizer" daemon [_thread_in_Java, id=10431, stack(0x00007f3b1c111000,0x00007f3b1c212000)]

Stack: [0x00007f3b1c111000,0x00007f3b1c212000], sp=0x00007f3b1c2109f0, free space=1022k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
J 115924% c2 java.lang.ref.Finalizer$FinalizerThread.run()V java.base@14-ea (56 bytes) @ 0x00007f3b247907b4 [0x00007f3b247904c0+0x00000000000002f4]
v ~StubRoutines::call_stub
V [libjvm.so+0x80824b] JavaCalls::call_helper(JavaValue*, methodHandle const&, JavaCallArguments*, Thread*)+0x2fb
V [libjvm.so+0x808529] JavaCalls::call_virtual(JavaValue*, Klass*, Symbol*, Symbol*, JavaCallArguments*, Thread*)+0x179
V [libjvm.so+0x8085f1] JavaCalls::call_virtual(JavaValue*, Handle, Klass*, Symbol*, Symbol*, Thread*)+0x81
V [libjvm.so+0x8b10cc] thread_entry(JavaThread*, Thread*)+0x6c
V [libjvm.so+0xd45112] JavaThread::thread_main_inner()+0xe2
V [libjvm.so+0xd49b5d] Thread::call_run()+0x10d
V [libjvm.so+0xba6037] thread_native_entry(Thread*)+0xe7