The following test failed in the JDK16 CI:

runtime/signal/TestSigpoll.java

Here's a snippet from the log file:

 stdout: [SIGPOLL: start testing: signal_num=29, mode=sigaction, scenario=nojvm
SIGPOLL: signal handler using function 'sigaction' has been set
SIGPOLL: signal handler for signal 29 has been processed
SIGPOLL: signal has been sent successfully
SIGPOLL: signal has been received
];
 stderr: []
 exitValue = 0

 stdout: [Addr: 0x0000fffc00490210 Code: 0xa9037bfd
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/barrierSetNMethod_aarch64.cpp:84
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/opt/mach5/mesos/work_dir/slaves/4728e7c1-7e67-490e-be0f-6bbf2a2f33db-S143/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/2c8417b2-f8da-44a2-8655-caa5a0c5a7bc/runs/a605d98f-e3e5-4e37-a7a8-47e41a2748f6/workspace/open/src/hotspot/cpu/aarch64/gc/shared/barrierSetNMethod_aarch64.cpp:84), pid=18576, tid=18600
# fatal error: not an ldr (literal) instruction.
#
# JRE version: Java(TM) SE Runtime Environment (16.0+5) (fastdebug build 16-ea+5-132)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 16-ea+5-132, mixed mode, tiered, z gc, linux-aarch64)
# Problematic frame:
# V [libjvm.so+0x4a2c20] BarrierSetNMethod::disarm(nmethod*)+0x98
#
# Core dump will be written. Default location: Core dumps may be processed with "/opt/core.sh %p" (or dumping to /scratch/opt/mach5/mesos/work_dir/slaves/52628e90-e5e7-4ef3-af97-10d8776d10db-S976/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/c89efe76-e0c8-4dad-8f61-0735fcce16e6/runs/c73941d2-6f04-4eca-ac32-c774dbaab757/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/scratch/1/core.18576)
#
# An error report file with more information is saved as:
# /scratch/opt/mach5/mesos/work_dir/slaves/52628e90-e5e7-4ef3-af97-10d8776d10db-S976/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/c89efe76-e0c8-4dad-8f61-0735fcce16e6/runs/c73941d2-6f04-4eca-ac32-c774dbaab757/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/scratch/1/hs_err_pid18576.log
Compiled method (c1) 206 1 3 java.lang.String::isLatin1 (19 bytes)
 total in heap [0x0000fffc00490010,0x0000fffc00490450] = 1088
 relocation [0x0000fffc00490178,0x0000fffc004901a0] = 40
 main code [0x0000fffc004901c0,0x0000fffc00490340] = 384
 stub code [0x0000fffc00490340,0x0000fffc00490378] = 56
 metadata [0x0000fffc00490378,0x0000fffc00490388] = 16
 scopes data [0x0000fffc00490388,0x0000fffc004903b8] = 48
 scopes pcs [0x0000fffc004903b8,0x0000fffc00490448] = 144
 dependencies [0x0000fffc00490448,0x0000fffc00490450] = 8
Compiled method (c1) 206 1 3 java.lang.String::isLatin1 (19 bytes)
 total in heap [0x0000fffc00490010,0x0000fffc00490450] = 1088
 relocation [0x0000fffc00490178,0x0000fffc004901a0] = 40
 main code [0x0000fffc004901c0,0x0000fffc00490340] = 384
 stub code [0x0000fffc00490340,0x0000fffc00490378] = 56
 metadata [0x0000fffc00490378,0x0000fffc00490388] = 16
 scopes data [0x0000fffc00490388,0x0000fffc004903b8] = 48
 scopes pcs [0x0000fffc004903b8,0x0000fffc00490448] = 144
 dependencies [0x0000fffc00490448,0x0000fffc00490450] = 8
Compiled method (c1) 206 1 3 java.lang.String::isLatin1 (19 bytes)
 total in heap [0x0000fffc00490010,0x0000fffc00490450] = 1088
 relocation [0x0000fffc00490178,0x0000fffc004901a0] = 40
 main code [0x0000fffc004901c0,0x0000fffc00490340] = 384
 stub code [0x0000fffc00490340,0x0000fffc00490378] = 56
 metadata [0x0000fffc00490378,0x0000fffc00490388] = 16
 scopes data [0x0000fffc00490388,0x0000fffc004903b8] = 48
 scopes pcs [0x0000fffc004903b8,0x0000fffc00490448] = 144
 dependencies [0x0000fffc00490448,0x0000fffc00490450] = 8
Compiled method (c1) 209 1 3 java.lang.String::isLatin1 (19 bytes)
 total in heap [0x0000fffc00490010,0x0000fffc00490450] = 1088
 relocation [0x0000fffc00490178,0x0000fffc004901a0] = 40
 main code [0x0000fffc004901c0,0x0000fffc00490340] = 384
 stub code [0x0000fffc00490340,0x0000fffc00490378] = 56
 metadata [0x0000fffc00490378,0x0000fffc00490388] = 16
 scopes data [0x0000fffc00490388,0x0000fffc004903b8] = 48
 scopes pcs [0x0000fffc004903b8,0x0000fffc00490448] = 144
 dependencies [0x0000fffc00490448,0x0000fffc00490450] = 8
#
# Compiler replay data is saved as:
# /scratch/opt/mach5/mesos/work_dir/slaves/52628e90-e5e7-4ef3-af97-10d8776d10db-S976/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/c89efe76-e0c8-4dad-8f61-0735fcce16e6/runs/c73941d2-6f04-4eca-ac32-c774dbaab757/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/scratch/1/replay_pid18576.log
#
# If you would like to submit a bug report, please visit:
# https://bugreport.java.com/bugreport/crash.jsp
#

Here's the crashing thread's stack:

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

Current thread (0x0000aaac9a2cf970): JavaThread "C1 CompilerThread0" daemon [_thread_in_vm, id=18600, stack(0x0000fff9c6950000,0x0000fff9c6b50000)]


Current CompileTask:
C1: 201 1 3 java.lang.String::isLatin1 (19 bytes)

Stack: [0x0000fff9c6950000,0x0000fff9c6b50000], sp=0x0000fff9c6b4d900, free space=2038k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x4a2c20] BarrierSetNMethod::disarm(nmethod*)+0x98
V [libjvm.so+0x1553250] ZNMethod::register_nmethod(nmethod*)+0xb8
V [libjvm.so+0x10a2e34] nmethod::nmethod(Method*, CompilerType, int, int, int, CodeOffsets*, int, DebugInformationRecorder*, Dependencies*, CodeBuffer*, int, OopMapSet*, ExceptionHandlerTable*, ImplicitExceptionTable*, AbstractCompiler*, int)+0x3f4
V [libjvm.so+0x10a32fc] nmethod::new_nmethod(methodHandle const&, int, int, CodeOffsets*, int, DebugInformationRecorder*, Dependencies*, CodeBuffer*, int, OopMapSet*, ExceptionHandlerTable*, ImplicitExceptionTable*, AbstractCompiler*, int)+0x224
V [libjvm.so+0x6ce530] ciEnv::register_method(ciMethod*, int, CodeOffsets*, int, CodeBuffer*, int, OopMapSet*, ExceptionHandlerTable*, ImplicitExceptionTable*, AbstractCompiler*, bool, bool, RTMState)+0x4f0
V [libjvm.so+0x532044] Compilation::install_code(int)+0xe4
V [libjvm.so+0x534c98] Compilation::compile_method()+0x620
V [libjvm.so+0x5351d0] Compilation::Compilation(AbstractCompiler*, ciEnv*, ciMethod*, int, BufferBlob*, DirectiveSet*)+0x2c8
V [libjvm.so+0x5364c4] Compiler::compile_method(ciEnv*, ciMethod*, int, DirectiveSet*)+0x10c
V [libjvm.so+0x805cb8] CompileBroker::invoke_compiler_on_method(CompileTask*)+0xcc0
V [libjvm.so+0x807048] CompileBroker::compiler_thread_loop()+0x630
V [libjvm.so+0x13d6ce8] JavaThread::thread_main_inner()+0x1f8
V [libjvm.so+0x13de690] Thread::call_run()+0xf8
V [libjvm.so+0x112baf0] thread_native_entry(Thread*)+0x120
C [libpthread.so.0+0x7d40] start_thread+0xb4

I'm starting this bug in hotspot/compiler for initial triage.