The following test fails in the Valhalla CI with a SIGSEGV in JvmtiTagMapKey::heapwalk_object:

vmTestbase/nsk/jvmti/scenarios/allocation/AP04/ap04t001/TestDescription.java

Here's a snippet from the log file:

#section:main
----------messages:(7/410)----------
command: main -agentlib:ap04t001=-waittime=5,-verbose nsk.jvmti.scenarios.allocation.AP04.ap04t001
reason: User specified action: run main/othervm/native -agentlib:ap04t001=-waittime=5,-verbose nsk.jvmti.scenarios.allocation.AP04.ap04t001
started: Sun Jan 11 01:50:31.112 UTC 2026
Mode: othervm [/othervm specified]
Process id: 2654616
finished: Sun Jan 11 01:50:37.055 UTC 2026
elapsed time (seconds): 5.943
----------configuration:(0/0)----------
----------System.out:(77/4021)----------
- ap04t001.cpp, 480: setting event callbacks ...
- ap04t001.cpp, 489: setting event callbacks done.
- ap04t001.cpp, 491: enabling JVMTI events ...
- ap04t001.cpp, 495: enabling the events done.
- ap04t001.cpp, 499: agentProc has been set

- ap04t001.cpp, 389: Wait for debugee start

<snip>

[1:50:32.485] CASE #3:
[1:50:32.485] Allocating objects...
#
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x00007fe6def24ca0, pid=2654616, tid=2654689
#
# JRE version: Java(TM) SE Runtime Environment (27.0+1) (fastdebug build 27-valhalla+1-29)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 27-valhalla+1-29, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x1596ca0] JvmtiTagMapKey::heapwalk_object() const+0x2a0
#
# Core dump will be written. Default location: Determined by the following: "/opt/core.sh %p" (alternatively, falling back to /opt/mach5/mesos/work_dir/slaves/da1065b5-7b94-4f0d-85e9-a3a252b9a32e-S35600/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/09348f18-4ebe-4aa8-98ad-729c32e5a2b8/runs/ef8ab001-76a9-4a1f-aa22-83b49b4a4837/testoutput/test-support/jtreg_open_test_hotspot_jtreg_vmTestbase_nsk_jvmti/scratch/2/core.2654616)
#
# An error report file with more information is saved as:
# /opt/mach5/mesos/work_dir/slaves/da1065b5-7b94-4f0d-85e9-a3a252b9a32e-S35600/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/09348f18-4ebe-4aa8-98ad-729c32e5a2b8/runs/ef8ab001-76a9-4a1f-aa22-83b49b4a4837/testoutput/test-support/jtreg_open_test_hotspot_jtreg_vmTestbase_nsk_jvmti/scratch/2/hs_err_pid2654616.log
[3.744s][warning][os] Loading hsdis library failed
     Locks owned:
    Mutex: [0x00007fe67003e818] JvmtiTagMap_lock - owner: 0x00007fe6d81ebbc0 allow_vm_block nosafepoint
#
# If you would like to submit a bug report, please visit:
# https://bugreport.java.com/bugreport/crash.jsp
#
----------System.err:(0/0)----------
----------rerun:(40/9721)*----------

There are currently six sightings of this failure mode in the Valhalla
CI on linux-aarch64 and linux-x64 configs.