v4.19.13 snapshot.
diff --git a/lib/list_debug.c b/lib/list_debug.c
new file mode 100644
index 0000000..5d5424b
--- /dev/null
+++ b/lib/list_debug.c
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2006, Red Hat, Inc., Dave Jones
+ * Released under the General Public License (GPL).
+ *
+ * This file contains the linked list validation for DEBUG_LIST.
+ */
+
+#include <linux/export.h>
+#include <linux/list.h>
+#include <linux/bug.h>
+#include <linux/kernel.h>
+#include <linux/rculist.h>
+
+/*
+ * Check that the data structures for the list manipulations are reasonably
+ * valid. Failures here indicate memory corruption (and possibly an exploit
+ * attempt).
+ */
+
+bool __list_add_valid(struct list_head *new, struct list_head *prev,
+ struct list_head *next)
+{
+ if (CHECK_DATA_CORRUPTION(next->prev != prev,
+ "list_add corruption. next->prev should be prev (%px), but was %px. (next=%px).\n",
+ prev, next->prev, next) ||
+ CHECK_DATA_CORRUPTION(prev->next != next,
+ "list_add corruption. prev->next should be next (%px), but was %px. (prev=%px).\n",
+ next, prev->next, prev) ||
+ CHECK_DATA_CORRUPTION(new == prev || new == next,
+ "list_add double add: new=%px, prev=%px, next=%px.\n",
+ new, prev, next))
+ return false;
+
+ return true;
+}
+EXPORT_SYMBOL(__list_add_valid);
+
+bool __list_del_entry_valid(struct list_head *entry)
+{
+ struct list_head *prev, *next;
+
+ prev = entry->prev;
+ next = entry->next;
+
+ if (CHECK_DATA_CORRUPTION(next == LIST_POISON1,
+ "list_del corruption, %px->next is LIST_POISON1 (%px)\n",
+ entry, LIST_POISON1) ||
+ CHECK_DATA_CORRUPTION(prev == LIST_POISON2,
+ "list_del corruption, %px->prev is LIST_POISON2 (%px)\n",
+ entry, LIST_POISON2) ||
+ CHECK_DATA_CORRUPTION(prev->next != entry,
+ "list_del corruption. prev->next should be %px, but was %px\n",
+ entry, prev->next) ||
+ CHECK_DATA_CORRUPTION(next->prev != entry,
+ "list_del corruption. next->prev should be %px, but was %px\n",
+ entry, next->prev))
+ return false;
+
+ return true;
+
+}
+EXPORT_SYMBOL(__list_del_entry_valid);