Lots of JDI tests crash in the debugee process when run with -XX:+UseConcMarkSweepGC.  The crash is:

#
# An unexpected error has been detected by Java Runtime Environment:
#
#  Internal Error (/BUILD_AREA/jdk7/hotspot/src/share/vm/runtime/mutexLocker.cpp:125), pid=21193, tid=2
#  Error: must own lock UNKNOWN

Stack looks like:
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [libjvm.so+0x130fa44];;  void VMError::report(outputStream*)+0x784
V  [libjvm.so+0x1310a13];;  void VMError::report_and_die()+0x4c3
V  [libjvm.so+0x73cc3b];;  void report_fatal_vararg(const char*,int,const char*,...)+0x10b
V  [libjvm.so+0xf23bad];;  void assert_locked_or_safepoint(const Monitor*)+0xad
V  [libjvm.so+0x671aba];;  HeapWord*CompactibleFreeListSpace::block_start(const
void*)const+0x2a
V  [libjvm.so+0x839e48];;  void GenerationBlockStartClosure::do_space(Space*)+0x38
V  [libjvm.so+0x6c6b0a];;  void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure*,bool)+0x1a
V  [libjvm.so+0x837a18];;  HeapWord*Generation::block_start(const void*)const+0x38
V  [libjvm.so+0x81e031];;  HeapWord*GenCollectedHeap::block_start(const void*)const+0x131
V  [libjvm.so+0xef8c72];;  methodOop methodOopDesc::method_from_bcp(unsigned char*)+0x52
V  [libjvm.so+0x512bff];;  Bytecodes::Code Bytecodes::non_breakpoint_code_at(unsigned char*,methodOop)+0x2f
V  [libjvm.so+0x901f8a];;  void InterpreterRuntime::resolve_get_put(JavaThread*,Bytecodes::Code)+0x97a
j  nsk.jdi.MethodEntryRequest.addInstanceFilter.instancefilter001a.methodForCommunication()V+0
j  nsk.jdi.MethodEntryRequest.addInstanceFilter.instancefilter001a.main([Ljava/lang/String;)V+56
v  ~StubRoutines::call_stub

hs.err.cms stack attached.

There are about 71 affected tests.  Run this command for one such test (all one line)

runnsk -XX:+UseConcMarkSweepGC nsk/jdi/MethodEntryRequest/addInstanceFilter/instancefilter001 -jdk $JAVA_HOME -tongajdk $JAVA_HOME

This crash occurs with the b24 fastdebug jdk.  I searched for duplicates but didn't find any.