Aleksey reported:

Lots of CTW failures in jdk/jdk with Shenandoah enabled. Seems to be problematic with Traversal:

$ CONF=linux-x86_64-server-fastdebug make run-test TEST=applications/ctw/modules/
TEST_VM_OPTS="-XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+UseShenandoahGC
-XX:-TieredCompilation -XX:+ShenandoahVerifyOptoBarriers -XX:ShenandoahGCHeuristics=traversal"

Sample hs_errs:
 http://cr.openjdk.java.net/~shade/shenandoah/crashes/ctw-traversal/

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/home/shade/trunks/jdk-jdk/src/hotspot/cpu/x86/relocInfo_x86.cpp:56), pid=25735,
tid=25748
# guarantee(*(uint32_t*) disp == CompressedOops::encode((oop)x)) failed: instructions must match

...
V [libjvm.so+0x1559b99] Relocation::pd_set_data_value(unsigned char*, long, bool)+0x369
V [libjvm.so+0x9dcfb3] CompiledMethod::verify_oop_relocations()+0x133
V [libjvm.so+0x138f962] nmethod::oops_do_marking_epilogue()+0x72
V [libjvm.so+0x1694541] ShenandoahTraversalGC::init_traversal_collection()+0x381
V [libjvm.so+0x163e8c1] ShenandoahHeap::entry_init_traversal()+0x101
V [libjvm.so+0x16c618a] VM_ShenandoahInitTraversalGC::doit()+0x2a
V [libjvm.so+0x18d7b21] VM_Operation::evaluate()+0x1f1
V [libjvm.so+0x19080f0] VMThread::evaluate_operation(VM_Operation*) [clone .constprop.64]+0x180
V [libjvm.so+0x1908b4c] VMThread::loop()+0x71c
V [libjvm.so+0x190919a] VMThread::run()+0xca
V [libjvm.so+0x1813b66] Thread::call_run()+0xf6
V [libjvm.so+0x141c40e] thread_native_entry(Thread*)+0x10e