The following test failed in the JDK16 CI:

tools/javac/tree/SourceTreeScannerTest.java

Here's a snippet from the log file:

----------stdout:(21/1323)----------
#
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x000000010cf4a8a4, pid=50244, tid=40963
#
# JRE version: Java(TM) SE Runtime Environment (16.0+14) (build 16-ea+14-540)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (16-ea+14-540, mixed mode, tiered, compressed oops, g1 gc, bsd-amd64)
# Problematic frame:
# V [libjvm.dylib+0x94a8a4] _ZN6Symbol18decrement_refcountEv+0x4
#
# Core dump will be written. Default location: core.50244
#
# An error report file with more information is saved as:
# /System/Volumes/Data/mesos/work_dir/slaves/4076d11c-c6ed-4d07-84c1-4ab8d55cd975-S47664/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/fe3a6e6b-082d-420a-9a99-4fa941e56219/runs/c3b078c5-6fad-4974-9c5f-ec3acab618ff/testoutput/test-support/jtreg_open_test_langtools_tier1/scratch/3/hs_err_pid50244.log
#
# Compiler replay data is saved as:
# /System/Volumes/Data/mesos/work_dir/slaves/4076d11c-c6ed-4d07-84c1-4ab8d55cd975-S47664/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/fe3a6e6b-082d-420a-9a99-4fa941e56219/runs/c3b078c5-6fad-4974-9c5f-ec3acab618ff/testoutput/test-support/jtreg_open_test_langtools_tier1/scratch/3/replay_pid50244.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 (0x00007fc23780a400): JavaThread "C2 CompilerThread0" daemon [_thread_in_vm, id=40963, stack(0x000070000f12e000,0x000070000f22e000)]


Current CompileTask:
C2: 82667 10224 4 com.sun.tools.javac.parser.JavacParser::term3 (2676 bytes)

Stack: [0x000070000f12e000,0x000070000f22e000], sp=0x000070000f22dad0, free space=1022k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.dylib+0x94a8a4] _ZN6Symbol18decrement_refcountEv+0x4
V [libjvm.dylib+0x26e201] _ZN15ciObjectFactory14remove_symbolsEv+0x31
V [libjvm.dylib+0x2558e9] _ZN5ciEnvD2Ev+0xa9
V [libjvm.dylib+0x2d59d0] _ZN13CompileBroker25invoke_compiler_on_methodEP11CompileTask+0x7a0
V [libjvm.dylib+0x2d503b] _ZN13CompileBroker20compiler_thread_loopEv+0x31b
V [libjvm.dylib+0x99da4d] _ZN10JavaThread17thread_main_innerEv+0xcd
V [libjvm.dylib+0x99ab91] _ZN6Thread8call_runEv+0x71
V [libjvm.dylib+0x82d1b7] _ZL19thread_native_entryP6Thread+0x187
C [libsystem_pthread.dylib+0x6109] _pthread_start+0x94
C [libsystem_pthread.dylib+0x1b8b] thread_start+0xf


siginfo: si_signo: 11 (SIGSEGV), si_code: 1 (SEGV_MAPERR), si_addr: 0x00003fc266e2b3c0


Starting this bug as a P2 since this is a Tier1 failure.
Starting it in hotspot/runtime since the crash is in Symbol::decrement_refcount