Fix concurrent access to VMState::current_state_.

src/vm-state-inl.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 56 matching lines @@
 
   disabled_ = false;
 #if !defined(ENABLE_HEAP_PROTECTION)
   // When not protecting the heap, there is no difference between
   // EXTERNAL and OTHER.  As an optimization in that case, we will not
   // perform EXTERNAL->OTHER transitions through the API.  We thus
   // compress the two states into one.
   if (state == EXTERNAL) state = OTHER;
 #endif
   state_ = state;
-  previous_ = current_state_;  // Save the previous state.
-  current_state_ = this;       // Install the new state.
+  // Save the previous state.
+  previous_ = reinterpret_cast<VMState*>(current_state_);
+  // Install the new state.
+  OS::ReleaseStore(&current_state_, reinterpret_cast<AtomicWord>(this));
 
 #ifdef ENABLE_LOGGING_AND_PROFILING
   if (FLAG_log_state_changes) {
     LOG(UncheckedStringEvent("Entering", StateToString(state_)));
     if (previous_ != NULL) {
       LOG(UncheckedStringEvent("From", StateToString(previous_->state_)));
     }
   }
 #endif
 
 #ifdef ENABLE_HEAP_PROTECTION
   if (FLAG_protect_heap) {
     if (state_ == EXTERNAL) {
       // We are leaving V8.
       ASSERT((previous_ != NULL) && (previous_->state_ != EXTERNAL));
       Heap::Protect();
     } else if ((previous_ == NULL) || (previous_->state_ == EXTERNAL)) {
       // We are entering V8.
       Heap::Unprotect();
     }
   }
 #endif
 }
 
 
 VMState::~VMState() {
   if (disabled_) return;
-  current_state_ = previous_;  // Return to the previous state.
+  // Return to the previous state.
+  OS::ReleaseStore(&current_state_, reinterpret_cast<AtomicWord>(previous_));
 
 #ifdef ENABLE_LOGGING_AND_PROFILING
   if (FLAG_log_state_changes) {
     LOG(UncheckedStringEvent("Leaving", StateToString(state_)));
     if (previous_ != NULL) {
       LOG(UncheckedStringEvent("To", StateToString(previous_->state_)));
     }
   }
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 #ifdef ENABLE_HEAP_PROTECTION
   if (FLAG_protect_heap) {
     if (state_ == EXTERNAL) {
       // We are reentering V8.
       ASSERT((previous_ != NULL) && (previous_->state_ != EXTERNAL));
       Heap::Unprotect();
     } else if ((previous_ == NULL) || (previous_->state_ == EXTERNAL)) {
       // We are leaving V8.
       Heap::Protect();
     }
   }
 #endif  // ENABLE_HEAP_PROTECTION
 }
 #endif  // ENABLE_VMSTATE_TRACKING
 
 } }  // namespace v8::internal
 
 #endif  // V8_VM_STATE_INL_H_