Index: kern/kern_malloc.c
===================================================================
--- kern/kern_malloc.c	(revision 238532)
+++ kern/kern_malloc.c	(working copy)
@@ -549,9 +549,13 @@
 	if (!(slab->us_flags & UMA_SLAB_MALLOC)) {
 #ifdef INVARIANTS
 		struct malloc_type **mtpp = addr;
+                static int malloc_trash_free = 1;
 #endif
 		size = slab->us_keg->uk_size;
 #ifdef INVARIANTS
+                if (malloc_trash_free) {
+                        memset(addr, 0xa5, size);
+                }
 		/*
 		 * Cache a pointer to the malloc_type that most recently freed
 		 * this memory here.  This way we know who is most likely to