Revert 196997 "Oilpan: Defer reusing freed memory for one GC cycle"

trunk/Source/platform/heap/Heap.cpp

Index: trunk/Source/platform/heap/Heap.cpp
===================================================================
--- trunk/Source/platform/heap/Heap.cpp	(revision 197018)
+++ trunk/Source/platform/heap/Heap.cpp	(working copy)
@@ -206,10 +206,28 @@
 void HeapObjectHeader::finalize(Address object, size_t objectSize)
 {
     const GCInfo* gcInfo = Heap::gcInfo(gcInfoIndex());
-    if (gcInfo->hasFinalizer())
+    if (gcInfo->hasFinalizer()) {
         gcInfo->m_finalize(object);
+    }
 
     ASAN_RETIRE_CONTAINER_ANNOTATION(object, objectSize);
+
+#if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER)
+    // In Debug builds, memory is zapped when it's freed, and the zapped memory
+    // is zeroed out when the memory is reused.  Memory is also zapped when
+    // using Leak Sanitizer because the heap is used as a root region for LSan
+    // and therefore pointers in unreachable memory could hide leaks.
+    for (size_t i = 0; i < objectSize; ++i)
+        object[i] = finalizedZapValue;
+
+    // Zap the primary vTable entry (secondary vTable entries are not zapped).
+    if (gcInfo->hasVTable()) {
+        *(reinterpret_cast<uintptr_t*>(object)) = zappedVTable;
+    }
+#endif
+    // In Release builds, the entire object is zeroed out when it is added to
+    // the free list.  This happens right after sweeping the page and before the
+    // thread commences execution.
 }
 
 BaseHeap::BaseHeap(ThreadState* state, int index)
@@ -599,13 +617,6 @@
     page->link(&m_firstPage);
 
     Heap::increaseAllocatedSpace(page->size());
-#if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER)
-    // Allow the following addToFreeList() to add the newly allocated memory
-    // to the free list.
-    Address address = page->payload();
-    for (size_t i = 0; i < page->payloadSize(); i++)
-        address[i] = reuseAllowedZapValue;
-#endif
     addToFreeList(page->payload(), page->payloadSize());
 }
 
@@ -1062,49 +1073,16 @@
         return;
     }
     entry = new (NotNull, address) FreeListEntry(size);
-
-#if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER)
-    // The following logic delays reusing free lists for (at least) one GC
-    // cycle or coalescing. This is helpful to detect use-after-free errors
-    // that could be caused by lazy sweeping etc.
-    size_t allowedCount = 0;
-    size_t forbiddenCount = 0;
-    for (size_t i = sizeof(FreeListEntry); i < size; i++) {
-        if (address[i] == reuseAllowedZapValue) {
-            allowedCount++;
-        } else if (address[i] == reuseForbiddenZapValue) {
-            forbiddenCount++;
-        } else {
-            ASSERT_NOT_REACHED();
-        }
-    }
-    size_t entryCount = size - sizeof(FreeListEntry);
-    if (forbiddenCount == entryCount) {
-        // If all values in the memory region are reuseForbiddenZapValue,
-        // we flip them to reuseAllowedZapValue. This allows the next
-        // addToFreeList() to add the memory region to the free list
-        // (unless someone concatenates the memory region with another memory
-        // region that contains reuseForbiddenZapValue.)
-        for (size_t i = sizeof(FreeListEntry); i < size; i++)
-            address[i] = reuseAllowedZapValue;
-        // Don't add the memory region to the free list in this addToFreeList().
+#if defined(ADDRESS_SANITIZER)
+    BasePage* page = pageFromObject(address);
+    ASSERT(!page->isLargeObjectPage());
+    // For ASan we don't add the entry to the free lists until the
+    // asanDeferMemoryReuseCount reaches zero.  However we always add entire
+    // pages to ensure that adding a new page will increase the allocation
+    // space.
+    if (static_cast<NormalPage*>(page)->payloadSize() != size && !entry->shouldAddToFreeList())
         return;
-    }
-    if (allowedCount != entryCount) {
-        // If the memory region mixes reuseForbiddenZapValue and
-        // reuseAllowedZapValue, we (conservatively) flip all the values
-        // to reuseForbiddenZapValue. These values will be changed to
-        // reuseAllowedZapValue in the next addToFreeList().
-        for (size_t i = sizeof(FreeListEntry); i < size; i++)
-            address[i] = reuseForbiddenZapValue;
-        // Don't add the memory region to the free list in this addToFreeList().
-        return;
-    }
-    // We reach here only when all the values in the memory region are
-    // reuseAllowedZapValue. In this case, we are allowed to add the memory
-    // region to the free list and reuse it for another object.
 #endif
-
     int index = bucketIndexForSize(size);
     entry->link(&m_freeLists[index]);
     if (index > m_biggestFreeListIndex)
@@ -1111,17 +1089,6 @@
         m_biggestFreeListIndex = index;
 }
 
-#if ENABLE(ASSERT) || defined(LEAK_SANITIZER) || defined(ADDRESS_SANITIZER)
-void FreeList::zapFreedMemory(Address address, size_t size)
-{
-    for (size_t i = 0; i < size; i++) {
-        // See the comment in addToFreeList().
-        if (address[i] != reuseAllowedZapValue)
-            address[i] = reuseForbiddenZapValue;
-    }
-}
-#endif
-
 void FreeList::clear()
 {
     m_biggestFreeListIndex = 0;