The following test failed in the JDK20 CI:

serviceability/attach/ConcAttachTest.java

Here's a snippet from the log file:

----------stdout:(21/1864)----------
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/virtualMemoryTracker.cpp:363
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/opt/mach5/mesos/work_dir/slaves/0c72054a-24ab-4dbb-944f-97f9341a1b96-S8422/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/6e89d8b9-911d-425b-9920-73a9bd0caece/runs/93ec339e-22f4-47ee-8e3a-ddf8e7c3dd20/workspace/open/src/hotspot/share/services/virtualMemoryTracker.cpp:363), pid=1381980, tid=1391565
# guarantee(!CheckJNICalls) failed: Attached JNI thread exited without being detached
#
# JRE version: Java(TM) SE Runtime Environment (20.0+6) (fastdebug build 20-ea+6-268)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 20-ea+6-268, mixed mode, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x1b60ff7] VirtualMemoryTracker::add_reserved_region(unsigned char*, unsigned long, NativeCallStack const&, MEMFLAGS)+0x1037
#
# Core dump will be written. Default location: /opt/mach5/mesos/work_dir/slaves/0c72054a-24ab-4dbb-944f-97f9341a1b96-S19281/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/6eacd903-d30d-438a-ba0a-9ab1aca97499/runs/7ce86dcf-cf49-464a-ac9e-92e9c6ca9f68/testoutput/test-support/jtreg_open_test_hotspot_jtreg_tier1/scratch/3/core
#
# An error report file with more information is saved as:
# /opt/mach5/mesos/work_dir/slaves/0c72054a-24ab-4dbb-944f-97f9341a1b96-S19281/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/6eacd903-d30d-438a-ba0a-9ab1aca97499/runs/7ce86dcf-cf49-464a-ac9e-92e9c6ca9f68/testoutput/test-support/jtreg_open_test_hotspot_jtreg_tier1/scratch/3/hs_err_pid1381980.log
#
# If you would like to submit a bug report, please visit:
# https://bugreport.java.com/bugreport/crash.jsp
#
result: Error. Agent communication error: java.io.EOFException; check console log for any additional details


Here's the crashing thread's stack:

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

Current thread (0x00007f73c003e1b0): JavaThread "process reaper" daemon [_thread_new, id=1391565, stack(0x00007f73fc8e9000,0x00007f73fc90f000)]

Stack: [0x00007f73fc8e9000,0x00007f73fc90f000], sp=0x00007f73fc90dce0, free space=147k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x1b60ff7] VirtualMemoryTracker::add_reserved_region(unsigned char*, unsigned long, NativeCallStack const&, MEMFLAGS)+0x1037
V [libjvm.so+0x1a9f10f] ThreadStackTracker::new_thread_stack(void*, unsigned long, NativeCallStack const&)+0x4f
V [libjvm.so+0x1a876f8] Thread::register_thread_stack_with_NMT()+0x88
V [libjvm.so+0x1a88ded] Thread::call_run()+0x7d
V [libjvm.so+0x174bf14] thread_native_entry(Thread*)+0x104