8259574: SIGSEGV in BFSClosure::closure_impl

Reviewed-by: stefank, egahlin

Author: Markus Grönlund

src/hotspot/share/jfr/leakprofiler/chains/bfsClosure.cpp

@@ -229,7 +229,7 @@ void BFSClosure::do_oop(narrowOop* ref) {
 }
 
 void BFSClosure::do_root(UnifiedOopRef ref) {
-  assert(!ref.is_null(), "invariant");
+  assert(ref.dereference() != NULL, "pointee must not be null");
   if (!_edge_queue->is_full()) {
     _edge_queue->add(NULL, ref);
   }

src/hotspot/share/jfr/leakprofiler/chains/rootSetClosure.cpp

@@ -57,7 +57,7 @@ template <typename Delegate>
 void RootSetClosure<Delegate>::do_oop(narrowOop* ref) {
   assert(ref != NULL, "invariant");
   assert(is_aligned(ref, sizeof(narrowOop)), "invariant");
-  if (CompressedOops::is_null(*ref)) {
+  if (!CompressedOops::is_null(*ref)) {
     _delegate->do_root(UnifiedOopRef::encode_in_native(ref));
   }
 }

src/hotspot/share/jfr/recorder/repository/jfrEmergencyDump.cpp

@@ -524,7 +524,6 @@ class JavaThreadInVMAndNative : public StackObj {
 };
 
 static void post_events(bool exception_handler, Thread* thread) {
-  DEBUG_ONLY(JfrJavaSupport::check_java_thread_in_vm(thread));
   if (exception_handler) {
     EventShutdown e;
     e.set_reason("VM Error");