Intermittent crashes with

# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/safepoint.cpp:760
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/scratch/opt/mach5/mesos/work_dir/slaves/83bb4d84-382c-4ead-b585-d8ef0018fefe-S325/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/75ec2191-60db-49ac-b29e-d46c19941909/runs/96d9467d-d155-46c4-8655-70508fc50116/workspace/open/src/hotspot/share/runtime/safepoint.cpp:760), pid=12987, tid=13002
# assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable()) failed: blocked and not walkable
#
# JRE version: Java(TM) SE Runtime Environment (12.0+14) (fastdebug build 12-ea+14)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 12-ea+14, mixed mode, tiered, compressed oops, g1 gc, linux-amd64)
# Core dump will be written. Default location: /scratch/opt/mach5/mesos/work_dir/slaves/c4ee7e63-1ded-4e8c-9581-ce26f27e3af4-S404/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/08404ba8-b487-4fb0-8607-b0b248d80b56/runs/ab378eeb-3b93-4456-8582-4e1bca9892fb/testoutput/jtreg/JTwork/scratch/2/core.12987
#
# An error report file with more information is saved as:
# /scratch/opt/mach5/mesos/work_dir/slaves/c4ee7e63-1ded-4e8c-9581-ce26f27e3af4-S404/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/08404ba8-b487-4fb0-8607-b0b248d80b56/runs/ab378eeb-3b93-4456-8582-4e1bca9892fb/testoutput/jtreg/JTwork/scratch/2/hs_err_pid12987.log
#
# If you would like to submit a bug report, please visit:
# http://bugreport.java.com/bugreport/crash.jsp
#
Current thread is 13002