Catch some "easy to spot" double frees in TCMalloc

third_party/tcmalloc/chromium/src/free_list.h

 // Copyright (c) 2011, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 22 matching lines @@
 // This file contains declarations of functions that implement doubly
 // linked lists and definitions of functions that implement singly
 // linked lists.  It also contains macros to tell the SizeMap class
 // how much space a node in the freelist needs so that SizeMap can
 // create large enough size classes.
 
 #ifndef TCMALLOC_FREE_LIST_H_
 #define TCMALLOC_FREE_LIST_H_
 
 #include <stddef.h>
+#include "internal_logging.h"  // For CRASH() macro.
 #include "linked_list.h"
 
 namespace tcmalloc {
 
 #ifdef TCMALLOC_USE_DOUBLYLINKED_FREELIST
 
 // size class information for common.h.
 static const bool kSupportsDoublyLinkedList = true;
 
 void *FL_Next(void *t);
 void FL_Init(void *t);
 void FL_Push(void **list, void *element);
 void *FL_Pop(void **list);
 void FL_PopRange(void **head, int n, void **start, void **end);
 void FL_PushRange(void **head, void *start, void *end);
 size_t FL_Size(void *head);
 
 #else // TCMALLOC_USE_DOUBLYLINKED_FREELIST not defined
 static const bool kSupportsDoublyLinkedList = false;
 
 inline void *FL_Next(void *t) {
   return SLL_Next(t);
 }
 
 inline void FL_Init(void *t) {
   SLL_SetNext(t, NULL);
 }
 
 inline void FL_Push(void **list, void *element) {
-  SLL_Push(list,element);
+  if(*list != element) {
+    SLL_Push(list,element);
+    return;
+  }
+  CRASH("Double Free of %p detected", element);
 }
 
 inline void *FL_Pop(void **list) {
   return SLL_Pop(list);
 }
 
 // Removes |N| elements from a linked list to which |head| points.
 // |head| will be modified to point to the new |head|.  |start| and
 // |end| will point to the first and last nodes of the range.  Note
 // that |end| will point to NULL after this function is called.
 inline void FL_PopRange(void **head, int n, void **start, void **end) {
   SLL_PopRange(head, n, start, end);
 }
 
 inline void FL_PushRange(void **head, void *start, void *end) {
   SLL_PushRange(head,start,end);
 }
 
 inline size_t FL_Size(void *head) {
   return SLL_Size(head);
 }
 
 #endif // TCMALLOC_USE_DOUBLYLINKED_FREELIST
 
 } // namespace tcmalloc
 
 #endif // TCMALLOC_FREE_LIST_H_