Validate slabs on oops

I am not sure if this is a good thing to have but if there is slab corruption
leading to a failure then this patch will detect a corrupted objects
after the oops occured.

[This should not go into mm. Just for discussion]

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 mm/slub.c |   87 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 86 insertions(+), 1 deletion(-)

Index: linux-2.6.21-rc5-mm4/mm/slub.c
===================================================================
--- linux-2.6.21-rc5-mm4.orig/mm/slub.c	2007-04-08 18:12:23.000000000 -0700
+++ linux-2.6.21-rc5-mm4/mm/slub.c	2007-04-08 18:44:39.000000000 -0700
@@ -2310,6 +2310,75 @@ void *__kmalloc_node_track_caller(size_t
 
 #ifdef CONFIG_SYSFS
 
+static int validate_slab(struct kmem_cache *s, struct page *page)
+{
+	void *p;
+	void *addr = page_address(page);
+	unsigned long map[BITS_TO_LONGS(s->objects)];
+
+	if (!check_slab(s, page) ||
+			!on_freelist(s, page, NULL))
+		return 0;
+
+	/* Now we know that a valid freelist exists */
+	bitmap_zero(map, s->objects);
+
+	for(p = page->freelist; p; p = get_freepointer(s, p)) {
+		set_bit((p - addr) / s->size, map);
+		if (!check_object(s, page, p, 0))
+			return 0;
+	}
+
+	for(p = addr; p < addr + s->objects * s->size; p += s->size)
+		if (!test_bit((p - addr) / s->size, map))
+			if (!check_object(s, page, p, 1))
+				return 0;
+	return 1;
+}
+
+static void validate_slab_slab(struct kmem_cache *s, struct page *page)
+{
+	if (slab_trylock(page)) {
+		validate_slab(s, page);
+		slab_unlock(page);
+	} else
+		printk(KERN_INFO "Skipped busy slab %p\n", page);
+}
+
+static int validate_slab_node(struct kmem_cache *s, struct kmem_cache_node *n)
+{
+	int count = 0;
+	struct page *page;
+	unsigned long flags;
+
+	spin_lock_irqsave(&n->list_lock, flags);
+	list_for_each_entry(page, &n->partial, lru) {
+		validate_slab_slab(s, page);
+		count++;
+	}
+	list_for_each_entry(page, &n->full, lru) {
+		validate_slab_slab(s, page);
+		count++;
+	}
+	spin_unlock_irqrestore(&n->list_lock, flags);
+	return count;
+}
+
+static void validate_slab_cache(struct kmem_cache *s)
+{
+	int node;
+	int count = 0;
+
+	flush_all(s);
+	for_each_online_node(node) {
+		struct kmem_cache_node *n = get_node(s, node);
+
+		count += validate_slab_node(s, n);
+	}
+	printk(KERN_INFO "SLUB: Validated %d slabs in '%s'\n",
+		count, s->name);
+}
+
 static unsigned long count_partial(struct kmem_cache_node *n)
 {
 	unsigned long flags;
@@ -2432,7 +2501,6 @@ struct slab_attribute {
 	static struct slab_attribute _name##_attr =  \
 	__ATTR(_name, 0644, _name##_show, _name##_store)
 
-
 static ssize_t slab_size_show(struct kmem_cache *s, char *buf)
 {
 	return sprintf(buf, "%d\n", s->size);
@@ -2639,6 +2707,22 @@ static ssize_t store_user_store(struct k
 }
 SLAB_ATTR(store_user);
 
+static ssize_t validate_show(struct kmem_cache *s, char *buf)
+{
+	return 0;
+}
+
+static ssize_t validate_store(struct kmem_cache *s,
+			const char *buf, size_t length)
+{
+	if (buf[0] == '1')
+		validate_slab_cache(s);
+	else
+		return -EINVAL;
+	return length;
+}
+SLAB_ATTR(validate);
+
 #ifdef CONFIG_NUMA
 static ssize_t defrag_ratio_show(struct kmem_cache *s, char *buf)
 {
@@ -2678,6 +2762,7 @@ static struct attribute * slab_attrs[] =
 	&red_zone_attr.attr,
 	&poison_attr.attr,
 	&store_user_attr.attr,
+	&validate_attr.attr,
 #ifdef CONFIG_ZONE_DMA
 	&cache_dma_attr.attr,
 #endif