[heap] Make object field write atomic if concurrent marking is enabled.

src/heap/concurrent-marking.cc

 // Copyright 2017 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/concurrent-marking.h"
 
 #include <stack>
 #include <unordered_map>
 
 #include "src/heap/concurrent-marking-deque.h"
@@ skipping 19 matching lines @@
   explicit ConcurrentMarkingVisitor(ConcurrentMarkingDeque* deque)
       : deque_(deque) {}
 
   bool ShouldVisit(HeapObject* object) override {
     return ObjectMarking::GreyToBlack<MarkBit::AccessMode::ATOMIC>(
         object, marking_state(object));
   }
 
   void VisitPointers(HeapObject* host, Object** start, Object** end) override {
     for (Object** p = start; p < end; p++) {
-      if (!(*p)->IsHeapObject()) continue;
-      MarkObject(HeapObject::cast(*p));
+      Object* object = reinterpret_cast<Object*>(
+          base::NoBarrier_Load(reinterpret_cast<const base::AtomicWord*>(p)));
+      if (!object->IsHeapObject()) continue;
+      MarkObject(HeapObject::cast(object));
     }
   }
 
   // ===========================================================================
   // JS object =================================================================
   // ===========================================================================
 
   int VisitJSObject(Map* map, JSObject* object) override {
     // TODO(ulan): impement snapshot iteration.
     return BaseClass::VisitJSObject(map, object);
@@ skipping 160 matching lines @@
 }
 
 void ConcurrentMarking::EnsureTaskCompleted() {
   if (IsTaskPending()) {
     WaitForTaskToComplete();
   }
 }
 
 }  // namespace internal
 }  // namespace v8