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);