diff --git a/sys/alpha/alpha/busdma_machdep.c b/sys/alpha/alpha/busdma_machdep.c
index 2075053e597..0b9ed6d5184 100644
--- a/sys/alpha/alpha/busdma_machdep.c
+++ b/sys/alpha/alpha/busdma_machdep.c
@@ -42,6 +42,7 @@
 #include <vm/vm_page.h>
 #include <vm/vm_map.h>
 
+#include <machine/atomic.h>
 #include <machine/bus.h>
 #include <machine/sgmap.h>
 #include <machine/md_var.h>
@@ -179,9 +180,8 @@ bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
 			newtag->filterarg = parent->filterarg;
 			newtag->parent = parent->parent;
 		}
-		if (newtag->parent != NULL) {
-			parent->ref_count++;
-		}
+		if (newtag->parent != NULL)
+			atomic_add_int(&parent->ref_count, 1);
 	}
 	
 	if (newtag->lowaddr < ptoa(Maxmem) && (flags & BUS_DMA_ALLOCNOW) != 0) {
@@ -228,7 +228,7 @@ bus_dma_tag_destroy(bus_dma_tag_t dmat)
 			bus_dma_tag_t parent;
 
 			parent = dmat->parent;
-			dmat->ref_count--;
+			atomic_subtract_int(&dmat->ref_count, 1);
 			if (dmat->ref_count == 0) {
 				free(dmat, M_DEVBUF);
 			}
diff --git a/sys/amd64/amd64/busdma_machdep.c b/sys/amd64/amd64/busdma_machdep.c
index d431ea079e4..4fe748c8d23 100644
--- a/sys/amd64/amd64/busdma_machdep.c
+++ b/sys/amd64/amd64/busdma_machdep.c
@@ -42,6 +42,7 @@
 #include <vm/vm_page.h>
 #include <vm/vm_map.h>
 
+#include <machine/atomic.h>
 #include <machine/bus.h>
 #include <machine/md_var.h>
 
@@ -186,9 +187,8 @@ bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
 			newtag->filterarg = parent->filterarg;
 			newtag->parent = parent->parent;
 		}
-		if (newtag->parent != NULL) {
-			parent->ref_count++;
-		}
+		if (newtag->parent != NULL)
+			atomic_add_int(&parent->ref_count, 1);
 	}
 	
 	if (newtag->lowaddr < ptoa(Maxmem) && (flags & BUS_DMA_ALLOCNOW) != 0) {
@@ -235,7 +235,7 @@ bus_dma_tag_destroy(bus_dma_tag_t dmat)
 			bus_dma_tag_t parent;
 
 			parent = dmat->parent;
-			dmat->ref_count--;
+			atomic_subtract_int(&dmat->ref_count, 1);
 			if (dmat->ref_count == 0) {
 				free(dmat, M_DEVBUF);
 				/*
diff --git a/sys/i386/i386/busdma_machdep.c b/sys/i386/i386/busdma_machdep.c
index d431ea079e4..4fe748c8d23 100644
--- a/sys/i386/i386/busdma_machdep.c
+++ b/sys/i386/i386/busdma_machdep.c
@@ -42,6 +42,7 @@
 #include <vm/vm_page.h>
 #include <vm/vm_map.h>
 
+#include <machine/atomic.h>
 #include <machine/bus.h>
 #include <machine/md_var.h>
 
@@ -186,9 +187,8 @@ bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
 			newtag->filterarg = parent->filterarg;
 			newtag->parent = parent->parent;
 		}
-		if (newtag->parent != NULL) {
-			parent->ref_count++;
-		}
+		if (newtag->parent != NULL)
+			atomic_add_int(&parent->ref_count, 1);
 	}
 	
 	if (newtag->lowaddr < ptoa(Maxmem) && (flags & BUS_DMA_ALLOCNOW) != 0) {
@@ -235,7 +235,7 @@ bus_dma_tag_destroy(bus_dma_tag_t dmat)
 			bus_dma_tag_t parent;
 
 			parent = dmat->parent;
-			dmat->ref_count--;
+			atomic_subtract_int(&dmat->ref_count, 1);
 			if (dmat->ref_count == 0) {
 				free(dmat, M_DEVBUF);
 				/*
diff --git a/sys/ia64/ia64/busdma_machdep.c b/sys/ia64/ia64/busdma_machdep.c
index 9b70d6c488b..3feacca4fba 100644
--- a/sys/ia64/ia64/busdma_machdep.c
+++ b/sys/ia64/ia64/busdma_machdep.c
@@ -41,6 +41,7 @@
 #include <vm/vm_page.h>
 #include <vm/vm_map.h>
 
+#include <machine/atomic.h>
 #include <machine/bus.h>
 #include <machine/md_var.h>
 
@@ -175,9 +176,8 @@ bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
 			newtag->filterarg = parent->filterarg;
 			newtag->parent = parent->parent;
 		}
-		if (newtag->parent != NULL) {
-			parent->ref_count++;
-		}
+		if (newtag->parent != NULL)
+			atomic_add_int(&parent->ref_count, 1);
 	}
 	
 	if (newtag->lowaddr < ptoa(Maxmem) && (flags & BUS_DMA_ALLOCNOW) != 0) {
@@ -224,7 +224,7 @@ bus_dma_tag_destroy(bus_dma_tag_t dmat)
 			bus_dma_tag_t parent;
 
 			parent = dmat->parent;
-			dmat->ref_count--;
+			atomic_subtract_int(&dmat->ref_count, 1);
 			if (dmat->ref_count == 0) {
 				free(dmat, M_DEVBUF);
 			}
diff --git a/sys/powerpc/powerpc/busdma_machdep.c b/sys/powerpc/powerpc/busdma_machdep.c
index 6c6dd36421d..63fdf71c8d3 100644
--- a/sys/powerpc/powerpc/busdma_machdep.c
+++ b/sys/powerpc/powerpc/busdma_machdep.c
@@ -51,6 +51,7 @@ static const char rcsid[] =
 #include <vm/vm_page.h>
 #include <vm/vm_map.h>
 
+#include <machine/atomic.h>
 #include <machine/bus.h>
 #include <machine/cpufunc.h>
 
@@ -133,9 +134,8 @@ bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
                         newtag->filterarg = parent->filterarg;
                         newtag->parent = parent->parent;
 		}
-                if (newtag->parent != NULL) {
-                        parent->ref_count++;
-		}
+		if (newtag->parent != NULL)
+			atomic_add_int(&parent->ref_count, 1);
 	}
 
 	*dmat = newtag;
@@ -154,7 +154,7 @@ bus_dma_tag_destroy(bus_dma_tag_t dmat)
                         bus_dma_tag_t parent;
 			
                         parent = dmat->parent;
-                        dmat->ref_count--;
+                        atomic_subtract_int(&dmat->ref_count, 1);
                         if (dmat->ref_count == 0) {
                                 free(dmat, M_DEVBUF);
                                 /*
diff --git a/sys/sparc64/sparc64/bus_machdep.c b/sys/sparc64/sparc64/bus_machdep.c
index 588fc8c108a..11f7b78fc5f 100644
--- a/sys/sparc64/sparc64/bus_machdep.c
+++ b/sys/sparc64/sparc64/bus_machdep.c
@@ -128,6 +128,7 @@
 #include <vm/vm_map.h>
 
 #include <machine/asi.h>
+#include <machine/atomic.h>
 #include <machine/bus.h>
 #include <machine/bus_private.h>
 #include <machine/cache.h>
@@ -246,7 +247,7 @@ bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
 		newtag->dt_boundary = ulmin(parent->dt_boundary,
 		    newtag->dt_boundary);
 	}
-	newtag->dt_parent->dt_ref_count++;
+	atomic_add_int(&newtag->dt_parent->dt_ref_count, 1);
 
 	*dmat = newtag;
 	return (0);
@@ -262,7 +263,7 @@ bus_dma_tag_destroy(bus_dma_tag_t dmat)
 			return (EBUSY);
 		while (dmat != NULL) {
 			parent = dmat->dt_parent;
-			dmat->dt_ref_count--;
+			atomic_subtract_int(&dmat->dt_ref_count, 1);
 			if (dmat->dt_ref_count == 0) {
 				free(dmat, M_DEVBUF);
 				/*