Re: memory corruptor in .18rc1-git

Dave Jones
2006-07-15T20:04:24Z

On Sat, Jul 15, 2006 at 03:54:35PM -0400, Chuck Ebbert wrote:

> Shouldn't those four 'if' statements use unlikely()? There's no sense
> causing more slowdown than necessary, even in debug code.

good point.

> And I'd change the messages slightly, e.g.:
>
> "list_add: corruption: next->prev should be %p, was %p\n"
>
> Some people build (accidentally?) without verbose debug info and
> don't get line numbers.

Ok, you're the second person to ask for this, so I'll make the change.

Andrew,Linus, here's the latest incarnation.
(Not build-tested yet, willdo after packing for OLS, but the changes
should be trivial enough not to blow up).

Dave

Debug variants of linked-list manipulation macros.

Signed-off-by: Dave Jones <davej@redhat.com>

diff --git a/include/linux/list.h b/include/linux/list.h
index 6b74adf..5617c77 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -39,6 +39,7 @@ static inline void INIT_LIST_HEAD(struct
* 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 lis
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 lis
* 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 lis
* 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 e5889b1..bb17ce3 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -311,6 +311,15 @@ 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)
diff --git a/lib/Makefile b/lib/Makefile
index be9719a..7d7da98 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -28,6 +28,7 @@ lib-$(CONFIG_GENERIC_HWEIGHT) += hweight
obj-$(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 0000000..0b48b95
--- /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("list_add corruption. next->prev should be %p, but was %p\n",
+ prev, next->prev);
+ BUG();
+ }
+ if (unlikely(prev->next != next)) {
+ printk("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("list_del corruption. prev->next should be %p, but was %p\n",
+ entry, entry->prev->next);
+ BUG();
+ }
+ if (unlikely(entry->next->prev != entry)) {
+ printk("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);
+