The following test failed in the JDK21 CI:

serviceability/attach/ConcAttachTest.java

Here's a snippet from the log file:

----------stdout:(19/1638)----------
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/System/Volumes/Data/mesos/work_dir/slaves/91e16c40-06d4-468a-9fc3-7198a5bb7d5a-S84880/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/4352da35-11ea-41df-81aa-3ed43a1cce91/runs/61b4e10e-8005-4b5f-8760-59848362ec2c/workspace/open/src/hotspot/share/opto/parse1.cpp:1051), pid=87609, tid=36867
# assert(false) failed: Can't determine return type.
#
# JRE version: Java(TM) SE Runtime Environment (21.0+16) (fastdebug build 21-ea+16-LTS-1273)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 21-ea+16-LTS-1273, compiled mode, compressed oops, compressed class ptrs, g1 gc, bsd-amd64)
# Core dump will be written. Default location: core.87609
#
# An error report file with more information is saved as:
# /System/Volumes/Data/mesos/work_dir/slaves/741e9afd-8c02-45c3-b2e2-9db1450d0832-S26911/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/c56af949-550d-44e4-a46c-329383f91871/runs/c355f6f2-bfc7-4deb-82b9-73c128844a93/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_serviceability/scratch/1/hs_err_pid87609.log
#
# Compiler replay data is saved as:
# /System/Volumes/Data/mesos/work_dir/slaves/741e9afd-8c02-45c3-b2e2-9db1450d0832-S26911/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/c56af949-550d-44e4-a46c-329383f91871/runs/c355f6f2-bfc7-4deb-82b9-73c128844a93/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_serviceability/scratch/1/replay_pid87609.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 (0x00007fc37b89d610): JavaThread "C2 CompilerThread1" daemon [_thread_in_native, id=36867, stack(0x0000700011920000,0x0000700011a20000)]


Current CompileTask:
C2: 83329 8664 b sun.jvmstat.perfdata.monitor.AbstractPerfDataBufferPrologue::majorVersionBuffer (24 bytes)

Stack: [0x0000700011920000,0x0000700011a20000], sp=0x0000700011a1d8f0, free space=1014k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.dylib+0x129324b] VMError::report_and_die(int, char const*, char const*, __va_list_tag*, Thread*, unsigned char*, void*, void*, char const*, int, unsigned long)+0x5cb (parse1.cpp:1051)
V [libjvm.dylib+0x129393b] VMError::report_and_die(Thread*, void*, char const*, int, char const*, char const*, __va_list_tag*)+0x3b
V [libjvm.dylib+0x6dd145] report_vm_error(char const*, int, char const*, char const*, ...)+0xf5
V [libjvm.dylib+0xf8ec57] Parse::do_exits()+0x667
V [libjvm.dylib+0xf89fb8] Parse::Parse(JVMState*, ciMethod*, float)+0xc18
V [libjvm.dylib+0x52844a] ParseGenerator::generate(JVMState*)+0xaa
V [libjvm.dylib+0x644357] Compile::Compile(ciEnv*, ciMethod*, int, Options, DirectiveSet*)+0x1777
V [libjvm.dylib+0x526157] C2Compiler::compile_method(ciEnv*, ciMethod*, int, bool, DirectiveSet*)+0x167
V [libjvm.dylib+0x663119] CompileBroker::invoke_compiler_on_method(CompileTask*)+0x629
V [libjvm.dylib+0x662858] CompileBroker::compiler_thread_loop()+0x2a8
V [libjvm.dylib+0xa1cc7f] JavaThread::thread_main_inner()+0x1ff
V [libjvm.dylib+0x11db4d7] Thread::call_run()+0x177
V [libjvm.dylib+0xf57cef] thread_native_entry(Thread*)+0x14f
C [libsystem_pthread.dylib+0x6109] _pthread_start+0x94
C [libsystem_pthread.dylib+0x1b8b] thread_start+0xf