8353263: Parallel: Remove locking in PSOldGen::resize

Reviewed-by: tschatzl, zgu

Author: albertnetymk

src/hotspot/share/gc/parallel/psOldGen.cpp

@@ -262,8 +262,9 @@ bool PSOldGen::expand_to_reserved() {
 }
 
 void PSOldGen::shrink(size_t bytes) {
-  assert_lock_strong(PSOldGenExpand_lock);
-  assert_locked_or_safepoint(Heap_lock);
+  assert(Thread::current()->is_VM_thread(), "precondition");
+  assert(SafepointSynchronize::is_at_safepoint(), "precondition");
+  assert(bytes > 0, "precondition");
 
   size_t size = align_down(bytes, virtual_space()->alignment());
   if (size > 0) {
@@ -314,11 +315,9 @@ void PSOldGen::resize(size_t desired_free_space) {
   }
   if (new_size > current_size) {
     size_t change_bytes = new_size - current_size;
-    MutexLocker x(PSOldGenExpand_lock);
     expand(change_bytes);
   } else {
     size_t change_bytes = current_size - new_size;
-    MutexLocker x(PSOldGenExpand_lock);
     shrink(change_bytes);
   }