chunk zap when returning chunk to chunk manager

Author: tstuefe

src/hotspot/share/memory/metaspace/chunkManager.cpp

@@ -243,6 +243,7 @@ Metachunk* ChunkManager::get_chunk_locked(chunklevel_t preferred_level, chunklev
 // !! Note: this may invalidate the chunk. Do not access the chunk after
 //    this function returns !!
 void ChunkManager::return_chunk(Metachunk* c) {
+  DEBUG_ONLY(c->zap();)
   // It is valid to poison the chunk payload area at this point since its physically separated from
   // the chunk meta info.
   ASAN_POISON_MEMORY_REGION(c->base(), c->word_size() * BytesPerWord);

src/hotspot/share/memory/metaspace/metachunk.cpp

@@ -27,6 +27,7 @@
 #include "memory/metaspace/metachunk.hpp"
 #include "memory/metaspace/metaspaceCommon.hpp"
 #include "memory/metaspace/metaspaceSettings.hpp"
+#include "memory/metaspace/metaspaceZapper.hpp"
 #include "memory/metaspace/virtualSpaceNode.hpp"
 #include "runtime/mutexLocker.hpp"
 #include "runtime/os.hpp"
@@ -183,6 +184,12 @@ void Metachunk::zap_header(uint8_t c) {
   memset(this, c, sizeof(Metachunk));
 }
 
+// Zaps the chunk itself
+void Metachunk::zap() {
+  // Only committed portion, obviously
+  Zapper::zap_memory(base(), committed_words());
+}
+
 // Verifies linking with neighbors in virtual space.
 // Can only be done under expand lock protection.
 void Metachunk::verify_neighborhood() const {

src/hotspot/share/memory/metaspace/metachunk.hpp

@@ -340,7 +340,10 @@ class Metachunk {
   void verify() const;
   // Verifies linking with neighbors in virtual space. Needs expand lock protection.
   void verify_neighborhood() const;
+  // Zaps the header (this structure); Note: physically disjunct from the actual chunk!
   void zap_header(uint8_t c = 0x17);
+  // Zaps the chunk itself
+  void zap();
 
   // Returns true if given pointer points into the payload area of this chunk.
   bool is_valid_pointer(const MetaWord* p) const {