8316436: ContinuationWrapper uses unhandled nullptr oop

Reviewed-by: pchilanomate, eosterlund

src/hotspot/share/runtime/continuationWrapper.cpp

@@ -38,16 +38,12 @@
 #include "runtime/stackChunkFrameStream.inline.hpp"
 
 ContinuationWrapper::ContinuationWrapper(const RegisterMap* map)
-  : _thread(map->thread()),
-    _entry(Continuation::get_continuation_entry_for_continuation(_thread, map->stack_chunk()->cont())),
-    _continuation(map->stack_chunk()->cont())
-  {
-  assert(oopDesc::is_oop(_continuation),"Invalid cont: " INTPTR_FORMAT, p2i((void*)_continuation));
+  : ContinuationWrapper(map->thread(),
+                        Continuation::get_continuation_entry_for_continuation(map->thread(), map->stack_chunk()->cont()),
+                        map->stack_chunk()->cont()) {
   assert(_entry == nullptr || _continuation == _entry->cont_oop(map->thread()),
     "cont: " INTPTR_FORMAT " entry: " INTPTR_FORMAT " entry_sp: " INTPTR_FORMAT,
     p2i( (oopDesc*)_continuation), p2i((oopDesc*)_entry->cont_oop(map->thread())), p2i(entrySP()));
-  disallow_safepoint();
-  read();
 }
 
 const frame ContinuationWrapper::last_frame() {
@@ -96,4 +92,3 @@ bool ContinuationWrapper::chunk_invariant() const {
   return true;
 }
 #endif // ASSERT
-

src/hotspot/share/runtime/continuationWrapper.inline.hpp

@@ -49,6 +49,7 @@ private:
   // These oops are managed by SafepointOp
   oop                _continuation;  // jdk.internal.vm.Continuation instance
   stackChunkOop      _tail;
+  bool               _done;
 
   ContinuationWrapper(const ContinuationWrapper& cont); // no copy constructor
 
@@ -58,6 +59,7 @@ private:
 
   void disallow_safepoint() {
     #ifdef ASSERT
+      assert(!_done, "");
       assert(_continuation != nullptr, "");
       _current_thread = Thread::current();
       if (_current_thread->is_Java_thread()) {
@@ -69,16 +71,19 @@ private:
   void allow_safepoint() {
     #ifdef ASSERT
       // we could have already allowed safepoints in done
-      if (_continuation != nullptr && _current_thread->is_Java_thread()) {
+      if (!_done && _current_thread->is_Java_thread()) {
         JavaThread::cast(_current_thread)->dec_no_safepoint_count();
       }
     #endif
   }
 
+  ContinuationWrapper(JavaThread* thread, ContinuationEntry* entry, oop continuation);
+
 public:
   void done() {
     allow_safepoint(); // must be done first
-    _continuation = nullptr;
+    _done = true;
+    *reinterpret_cast<intptr_t*>(&_continuation) = badHeapOopVal;
     *reinterpret_cast<intptr_t*>(&_tail) = badHeapOopVal;
   }
 
@@ -140,23 +145,19 @@ public:
 #endif
 };
 
-inline ContinuationWrapper::ContinuationWrapper(JavaThread* thread, oop continuation)
-  : _thread(thread), _entry(thread->last_continuation()), _continuation(continuation)
-  {
+inline ContinuationWrapper::ContinuationWrapper(JavaThread* thread, ContinuationEntry* entry, oop continuation)
+  : _thread(thread), _entry(entry), _continuation(continuation), _done(false) {
   assert(oopDesc::is_oop(_continuation),
          "Invalid continuation object: " INTPTR_FORMAT, p2i((void*)_continuation));
   disallow_safepoint();
   read();
 }
 
+inline ContinuationWrapper::ContinuationWrapper(JavaThread* thread, oop continuation)
+  : ContinuationWrapper(thread, thread->last_continuation(), continuation) {}
+
 inline ContinuationWrapper::ContinuationWrapper(oop continuation)
-  : _thread(nullptr), _entry(nullptr), _continuation(continuation)
-  {
-  assert(oopDesc::is_oop(_continuation),
-         "Invalid continuation object: " INTPTR_FORMAT, p2i((void*)_continuation));
-  disallow_safepoint();
-  read();
-}
+  : ContinuationWrapper(nullptr, nullptr, continuation) {}
 
 inline bool ContinuationWrapper::is_preempted() {
   return jdk_internal_vm_Continuation::is_preempted(_continuation);