[PATCH] Debug variants of linked list macros

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

4 files changed, 102 insertions, 0 deletions

diff --git a/include/linux/list.h b/include/linux/list.h
index 65a5b5ceda49..a9c90287c0ff 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -39,6 +39,7 @@ static inline void INIT_LIST_HEAD(struct list_head *list)
  * This is only for internal list manipulation where we know
  * the prev/next entries already!
  */
+#ifndef CONFIG_DEBUG_LIST
 static inline void __list_add(struct list_head *new,
                               struct list_head *prev,
                               struct list_head *next)
@@ -48,6 +49,11 @@ static inline void __list_add(struct list_head *new,
         new->prev = prev;
         prev->next = new;
 }
+#else
+extern void __list_add(struct list_head *new,
+                              struct list_head *prev,
+                              struct list_head *next);
+#endif
 
 /**
  * list_add - add a new entry
@@ -57,10 +63,15 @@ static inline void __list_add(struct list_head *new,
  * Insert a new entry after the specified head.
  * This is good for implementing stacks.
  */
+#ifndef CONFIG_DEBUG_LIST
 static inline void list_add(struct list_head *new, struct list_head *head)
 {
         __list_add(new, head, head->next);
 }
+#else
+extern void list_add(struct list_head *new, struct list_head *head);
+#endif
+
 
 /**
  * list_add_tail - add a new entry
@@ -153,12 +164,16 @@ static inline void __list_del(struct list_head * prev, struct list_head * next)
  * Note: list_empty on entry does not return true after this, the entry is
  * in an undefined state.
  */
+#ifndef CONFIG_DEBUG_LIST
 static inline void list_del(struct list_head *entry)
 {
         __list_del(entry->prev, entry->next);
         entry->next = LIST_POISON1;
         entry->prev = LIST_POISON2;
 }
+#else
+extern void list_del(struct list_head *entry);
+#endif
 
 /**
  * list_del_rcu - deletes entry from list without re-initialization
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b0f5ca72599f..f9ae75cc0145 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -320,6 +320,15 @@ config DEBUG_VM
 
           If unsure, say N.
 
+config DEBUG_LIST
+        bool "Debug linked list manipulation"
+        depends on DEBUG_KERNEL
+        help
+          Enable this to turn on extended checks in the linked-list
+          walking routines.
+
+          If unsure, say N.
+
 config FRAME_POINTER
         bool "Compile the kernel with frame pointers"
         depends on DEBUG_KERNEL && (X86 || CRIS || M68K || M68KNOMMU || FRV || UML || S390 || AVR32 || SUPERH)
diff --git a/lib/Makefile b/lib/Makefile
index ef1d37afbbb6..402762fead70 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -28,6 +28,7 @@ lib-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
 obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
 obj-$(CONFIG_PLIST) += plist.o
 obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o
+obj-$(CONFIG_DEBUG_LIST) += list_debug.o
 
 ifneq ($(CONFIG_HAVE_DEC_LOCK),y)
   lib-y += dec_and_lock.o
diff --git a/lib/list_debug.c b/lib/list_debug.c
new file mode 100644
index 000000000000..1aae85cef92c
--- /dev/null
+++ b/lib/list_debug.c
@@ -0,0 +1,77 @@
+/*
+ * Copyright 2006, Red Hat, Inc., Dave Jones
+ * Released under the General Public License (GPL).
+ *
+ * This file contains the linked list implementations for
+ * DEBUG_LIST.
+ */
+
+#include <linux/module.h>
+#include <linux/list.h>
+
+/*
+ * Insert a new entry between two known consecutive entries.
+ *
+ * This is only for internal list manipulation where we know
+ * the prev/next entries already!
+ */
+
+void __list_add(struct list_head *new,
+                              struct list_head *prev,
+                              struct list_head *next)
+{
+        if (unlikely(next->prev != prev)) {
+                printk(KERN_ERR "list_add corruption. next->prev should be %p, but was %p\n",
+                        prev, next->prev);
+                BUG();
+        }
+        if (unlikely(prev->next != next)) {
+                printk(KERN_ERR "list_add corruption. prev->next should be %p, but was %p\n",
+                        next, prev->next);
+                BUG();
+        }
+        next->prev = new;
+        new->next = next;
+        new->prev = prev;
+        prev->next = new;
+}
+EXPORT_SYMBOL(__list_add);
+
+/**
+ * list_add - add a new entry
+ * @new: new entry to be added
+ * @head: list head to add it after
+ *
+ * Insert a new entry after the specified head.
+ * This is good for implementing stacks.
+ */
+void list_add(struct list_head *new, struct list_head *head)
+{
+        __list_add(new, head, head->next);
+}
+EXPORT_SYMBOL(list_add);
+
+/**
+ * list_del - deletes entry from list.
+ * @entry: the element to delete from the list.
+ * Note: list_empty on entry does not return true after this, the entry is
+ * in an undefined state.
+ */
+void list_del(struct list_head *entry)
+{
+        if (unlikely(entry->prev->next != entry)) {
+                printk(KERN_ERR "list_del corruption. prev->next should be %p, but was %p\n",
+                        entry, entry->prev->next);
+                BUG();
+        }
+        if (unlikely(entry->next->prev != entry)) {
+                printk(KERN_ERR "list_del corruption. next->prev should be %p, but was %p\n",
+                        entry, entry->next->prev);
+                BUG();
+        }
+        __list_del(entry->prev, entry->next);
+        entry->next = LIST_POISON1;
+        entry->prev = LIST_POISON2;
+}
+EXPORT_SYMBOL(list_del);
+