Index: arm/arm/busdma_machdep-v6.c
===================================================================
--- arm/arm/busdma_machdep-v6.c	(revision 252497)
+++ arm/arm/busdma_machdep-v6.c	(working copy)
@@ -192,14 +192,26 @@
 static void
 busdma_init(void *dummy)
 {
+	int uma_flags;
 
+	uma_flags = 0;
+
 	/* Create a cache of buffers in standard (cacheable) memory. */
 	standard_allocator = busdma_bufalloc_create("buffer", 
 	    arm_dcache_align,	/* minimum_alignment */
 	    NULL,		/* uma_alloc func */ 
 	    NULL,		/* uma_free func */
-	    0);			/* uma_zcreate_flags */
+	    uma_flags);		/* uma_zcreate_flags */
 
+#ifdef INVARIANTS
+	/* 
+	 * Force UMA zone to allocate service structures like
+	 * slabs using own allocator. uma_debug code performs
+	 * atomic ops on uma_slab_t fields and safety of this
+	 * operation is not guaranteed for write-back caches
+	 */
+	uma_flags = UMA_ZONE_OFFPAGE;
+#endif
 	/*
 	 * Create a cache of buffers in uncacheable memory, to implement the
 	 * BUS_DMA_COHERENT (and potentially BUS_DMA_NOCACHE) flag.
@@ -208,7 +220,7 @@
 	    arm_dcache_align,	/* minimum_alignment */
 	    busdma_bufalloc_alloc_uncacheable, 
 	    busdma_bufalloc_free_uncacheable, 
-	    0);			/* uma_zcreate_flags */
+	    uma_flags);	/* uma_zcreate_flags */
 }
 
 /*