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>

Index: linux-2.6.21-rc5-mm3/mm/slub.c
===================================================================
--- linux-2.6.21-rc5-mm3.orig/mm/slub.c	2007-03-30 21:51:52.000000000 -0700
+++ linux-2.6.21-rc5-mm3/mm/slub.c	2007-03-30 21:52:37.000000000 -0700
@@ -20,6 +20,7 @@
 #include <linux/mempolicy.h>
 #include <linux/ctype.h>
 #include <linux/kallsyms.h>
+#include <linux/kdebug.h>
 
 /*
  * Lock order:
@@ -128,10 +129,12 @@ LIST_HEAD(slab_caches);
 static int sysfs_slab_add(struct kmem_cache *);
 static int sysfs_slab_alias(struct kmem_cache *, const char *);
 static void sysfs_slab_remove(struct kmem_cache *);
+static void setup_slab_die(void);
 #else
 static int sysfs_slab_add(struct kmem_cache *s) { return 0; }
 static int sysfs_slab_alias(struct kmem_cache *s, const char *p) { return 0; }
 static void sysfs_slab_remove(struct kmem_cache *s) {}
+static void setup_slab_die(void) {};
 #endif
 
 /********************************************************************
@@ -2008,6 +2011,8 @@ void __init kmem_cache_init(void)
 		"Processors=%d, Nodes=%d\n",
 		KMALLOC_SHIFT_HIGH, L1_CACHE_BYTES,
 		nr_cpu_ids, nr_node_ids);
+
+	setup_slab_die();
 }
 
 /*
@@ -2402,6 +2407,67 @@ struct slab_attribute {
 	static struct slab_attribute _name##_attr =  \
 	__ATTR(_name, 0644, _name##_show, _name##_store)
 
+/*
+ * Validation of slabs that are on the lists. The caller must
+ * provide synchronization if necessary.
+ */
+static void 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;
+
+	printk(KERN_ERR "Detail check on slab %p\n", page);
+	/* 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);
+		check_object(s, page, p, 0);
+	}
+
+	for(p = addr; p < addr + s->objects * s->size; p += s->size)
+		if (!test_bit((p - addr) / s->size, map))
+			check_object(s, page, p, 1);
+}
+
+static void validate_slab_cache(struct kmem_cache *s)
+{
+	int node;
+
+	for_each_online_node(node) {
+		struct kmem_cache_node *n = get_node(s, node);
+		struct page *page;
+
+		printk(KERN_ERR "Die: validating partial pages for slab %s\n", s->name);
+		list_for_each_entry(page, &n->partial, lru)
+			validate_slab(s, page);
+	}
+}
+
+static int slab_die_call(struct notifier_block *self,
+		unsigned long val, void *data)
+{
+	struct kmem_cache *s;
+
+	list_for_each_entry(s, &slab_caches, list)
+		validate_slab_cache(s);
+
+	return NOTIFY_OK;
+}
+
+struct notifier_block slab_die_notifier = {
+	.notifier_call = slab_die_call,
+};
+
+static void __init setup_slab_die(void)
+{
+	register_die_notifier(&slab_die_notifier);
+}
 
 static ssize_t slab_size_show(struct kmem_cache *s, char *buf)
 {