[PATCH] Extend list debugging to cover hlists

[Matthew Wilcox <matthew@wil.cx>]

We've seen a couple of recent reports which point to corrupt hlists.
The DEBUG_LIST config option only checks regular lists, but it's not hard
to cover hlists too.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

diff --git a/include/linux/list.h b/include/linux/list.h
index 08cf4f6..a325d9f 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -714,10 +714,17 @@ static inline int hlist_empty(const struct hlist_head *h)
 	return !h->first;
 }
 
+#ifdef CONFIG_DEBUG_LIST
+extern void hlist_check(struct hlist_node *n);
+#else
+#define hlist_check(n)		do { } while (0)
+#endif
+
 static inline void __hlist_del(struct hlist_node *n)
 {
 	struct hlist_node *next = n->next;
 	struct hlist_node **pprev = n->pprev;
+	hlist_check(n);
 	*pprev = next;
 	if (next)
 		next->pprev = pprev;
@@ -775,6 +782,7 @@ static inline void hlist_replace_rcu(struct hlist_node *old,
 {
 	struct hlist_node *next = old->next;
 
+	hlist_check(old);
 	new->next = next;
 	new->pprev = old->pprev;
 	smp_wmb();
@@ -830,6 +838,7 @@ static inline void hlist_add_head_rcu(struct hlist_node *n,
 static inline void hlist_add_before(struct hlist_node *n,
 					struct hlist_node *next)
 {
+	hlist_check(next);
 	n->pprev = next->pprev;
 	n->next = next;
 	next->pprev = &n->next;
@@ -839,6 +848,7 @@ static inline void hlist_add_before(struct hlist_node *n,
 static inline void hlist_add_after(struct hlist_node *n,
 					struct hlist_node *next)
 {
+	hlist_check(next);
 	next->next = n->next;
 	n->next = next;
 	next->pprev = &n->next;
@@ -868,6 +878,7 @@ static inline void hlist_add_after(struct hlist_node *n,
 static inline void hlist_add_before_rcu(struct hlist_node *n,
 					struct hlist_node *next)
 {
+	hlist_check(next);
 	n->pprev = next->pprev;
 	n->next = next;
 	smp_wmb();
@@ -896,6 +907,7 @@ static inline void hlist_add_before_rcu(struct hlist_node *n,
 static inline void hlist_add_after_rcu(struct hlist_node *prev,
 				       struct hlist_node *n)
 {
+	hlist_check(prev);
 	n->next = prev->next;
 	n->pprev = &prev->next;
 	smp_wmb();
diff --git a/lib/list_debug.c b/lib/list_debug.c
index 4350ba9..00b56bf 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -1,5 +1,8 @@
 /*
  * Copyright 2006, Red Hat, Inc., Dave Jones
+ * Copyright 2008 Intel Corporation
+ * Author: Matthew Wilcox <willy@linux.intel.com>
+ *
  * Released under the General Public License (GPL).
  *
  * This file contains the linked list implementations for
@@ -76,3 +79,18 @@ void list_del(struct list_head *entry)
 	entry->prev = LIST_POISON2;
 }
 EXPORT_SYMBOL(list_del);
+
+void hlist_check(struct hlist_node *n)
+{
+	if (unlikely(*n->pprev != n)) {
+		printk(KERN_ERR "hlist corruption. *pprev should be %p, "
+				"but was %p\n", n, *n->pprev);
+		BUG();
+	}
+	if (unlikely(n->next != NULL && n->next->pprev != &n->next)) {
+		printk(KERN_ERR "hlist corruption. n->next->pprev should be"
+				"%p, but was %p\n", &n->next, n->next->pprev);
+		BUG();
+	}
+}
+EXPORT_SYMBOL(hlist_check);

-- 
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operating system, but compare it to ours.  We can't possibly take such
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