slub: Add method to verify memory is not freed

This is for tracking down suspect memory usage.

Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

include/linux/slub_def.h

@@ -218,6 +218,19 @@ kmalloc_order(size_t size, gfp_t flags, unsigned int order)
 	return ret;
 }
 
+/**
+ * Calling this on allocated memory will check that the memory
+ * is expected to be in use, and print warnings if not.
+ */
+#ifdef CONFIG_SLUB_DEBUG
+extern bool verify_mem_not_deleted(const void *x);
+#else
+static inline bool verify_mem_not_deleted(const void *x)
+{
+	return true;
+}
+#endif
+
 #ifdef CONFIG_TRACING
 extern void *
 kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size);

mm/slub.c

@@ -2964,6 +2964,42 @@ size_t ksize(const void *object)
 }
 EXPORT_SYMBOL(ksize);
 
+#ifdef CONFIG_SLUB_DEBUG
+bool verify_mem_not_deleted(const void *x)
+{
+	struct page *page;
+	void *object = (void *)x;
+	unsigned long flags;
+	bool rv;
+
+	if (unlikely(ZERO_OR_NULL_PTR(x)))
+		return false;
+
+	local_irq_save(flags);
+
+	page = virt_to_head_page(x);
+	if (unlikely(!PageSlab(page))) {
+		/* maybe it was from stack? */
+		rv = true;
+		goto out_unlock;
+	}
+
+	slab_lock(page);
+	if (on_freelist(page->slab, page, object)) {
+		object_err(page->slab, page, object, "Object is on free-list");
+		rv = false;
+	} else {
+		rv = true;
+	}
+	slab_unlock(page);
+
+out_unlock:
+	local_irq_restore(flags);
+	return rv;
+}
+EXPORT_SYMBOL(verify_mem_not_deleted);
+#endif
+
 void kfree(const void *x)
 {
 	struct page *page;