8331771: ZGC: Remove OopMapCacheAlloc_lock ordering workaround

Reviewed-by: eosterlund, stefank, zgu

Author: shipilev

Diff for: src/hotspot/share/gc/shared/collectedHeap.hpp

@@ -91,7 +91,6 @@ class CollectedHeap : public CHeapObj<mtGC> {
   friend class VMStructs;
   friend class JVMCIVMStructs;
   friend class IsSTWGCActiveMark; // Block structured external access to _is_stw_gc_active
-  friend class DisableIsSTWGCActiveMark; // Disable current IsSTWGCActiveMark
   friend class MemAllocator;
   friend class ParallelObjectIterator;
 

Diff for: src/hotspot/share/gc/shared/isGCActiveMark.cpp

@@ -42,15 +42,3 @@ IsSTWGCActiveMark::~IsSTWGCActiveMark() {
   assert(heap->is_stw_gc_active(), "Sanity");
   heap->_is_stw_gc_active = false;
 }
-
-DisableIsSTWGCActiveMark::DisableIsSTWGCActiveMark() {
-  CollectedHeap* heap = Universe::heap();
-  assert(heap->is_stw_gc_active(), "Not reentrant");
-  heap->_is_stw_gc_active = false;
-}
-
-DisableIsSTWGCActiveMark::~DisableIsSTWGCActiveMark() {
-  CollectedHeap* heap = Universe::heap();
-  assert(!heap->is_stw_gc_active(), "Sanity");
-  heap->_is_stw_gc_active = true;
-}

Diff for: src/hotspot/share/gc/shared/isGCActiveMark.hpp

@@ -36,10 +36,4 @@ class IsSTWGCActiveMark : public StackObj {
   ~IsSTWGCActiveMark();
 };
 
-class DisableIsSTWGCActiveMark : public StackObj {
- public:
-  DisableIsSTWGCActiveMark();
-  ~DisableIsSTWGCActiveMark();
-};
-
 #endif // SHARE_GC_SHARED_ISGCACTIVEMARK_HPP

Diff for: src/hotspot/share/gc/z/zVerify.cpp

@@ -483,9 +483,6 @@ void ZVerify::after_mark() {
     roots_strong(true /* verify_after_old_mark */);
   }
   if (ZVerifyObjects) {
-    // Workaround OopMapCacheAlloc_lock reordering with the StackWatermark_lock
-    DisableIsSTWGCActiveMark mark;
-
     objects(false /* verify_weaks */);
     guarantee(zverify_broken_object == zaddress::null, "Verification failed");
   }