8275950: Use only _thread_in_vm in ~ThreadBlockInVMPreprocess()

Reviewed-by: dholmes, dcubed

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

@@ -228,15 +228,13 @@ class ThreadBlockInVMPreprocess : public ThreadStateTransition {
   }
   ~ThreadBlockInVMPreprocess() {
     assert(_thread->thread_state() == _thread_blocked, "coming from wrong thread state");
-    // Change to transition state and ensure it is seen by the VM thread.
-    _thread->set_thread_state_fence(_thread_blocked_trans);
+    // Change back to _thread_in_vm and ensure it is seen by the VM thread.
+    _thread->set_thread_state_fence(_thread_in_vm);
 
     if (SafepointMechanism::should_process(_thread, _allow_suspend)) {
       _pr(_thread);
       SafepointMechanism::process_if_requested(_thread, _allow_suspend);
     }
-
-    _thread->set_thread_state(_thread_in_vm);
   }
 
   static void emptyOp(JavaThread* current) {}

src/hotspot/share/runtime/safepoint.cpp

@@ -706,7 +706,6 @@ void SafepointSynchronize::block(JavaThread *thread) {
   }
 
   JavaThreadState state = thread->thread_state();
-  assert(is_a_block_safe_state(state), "Illegal threadstate encountered: %d", state);
   thread->frame_anchor()->make_walkable(thread);
 
   uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();

src/hotspot/share/runtime/safepoint.hpp

@@ -128,14 +128,7 @@ class SafepointSynchronize : AllStatic {
 
   static bool is_a_block_safe_state(JavaThreadState state) {
     // Check that we have a valid thread_state before blocking for safepoints
-    switch(state) {
-      case _thread_in_vm:
-      case _thread_in_Java:        // From compiled code
-      case _thread_blocked_trans:
-        return true;
-      default:
-        return false;
-    }
+    return state == _thread_in_vm || state == _thread_in_Java;
   }
   // Called when a thread voluntarily blocks
   static void block(JavaThread *thread);