diff --git a/sys/alpha/alpha/busdma_machdep.c b/sys/alpha/alpha/busdma_machdep.c
index c48016be2fb3..bd127a1f9ad2 100644
--- a/sys/alpha/alpha/busdma_machdep.c
+++ b/sys/alpha/alpha/busdma_machdep.c
@@ -367,10 +367,12 @@ bus_dmamem_alloc_size(bus_dma_tag_t dmat, void** vaddr, int flags,
 		 *     and handles multi-seg allocations.  Nobody is doing
 		 *     multi-seg allocations yet though.
 		 */
+		mtx_lock(&Giant);
 		*vaddr = contigmalloc(size, M_DEVBUF,
 		    (flags & BUS_DMA_NOWAIT) ? M_NOWAIT : M_WAITOK,
 		    0ul, dmat->lowaddr, dmat->alignment? dmat->alignment : 1ul,
 		    dmat->boundary);
+		mtx_unlock(&Giant);
 	}
 	if (*vaddr == NULL)
 		return (ENOMEM);
@@ -400,8 +402,11 @@ bus_dmamem_free_size(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map,
 		panic("bus_dmamem_free: Invalid map freed\n");
 	if ((size <= PAGE_SIZE) && dmat->lowaddr >= ptoa(Maxmem))
 		free(vaddr, M_DEVBUF);
-	else
+	else {
+		mtx_lock(&Giant);
 		contigfree(vaddr, size, M_DEVBUF);
+		mtx_unlock(&Giant);
+	}
 }
 
 void
@@ -842,11 +847,13 @@ alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages)
 
 		if (bpage == NULL)
 			break;
+		mtx_lock(&Giant);
 		bpage->vaddr = (vm_offset_t)contigmalloc(PAGE_SIZE, M_DEVBUF,
 							 M_NOWAIT, 0ul,
 							 dmat->lowaddr,
 							 PAGE_SIZE,
 							 dmat->boundary);
+		mtx_unlock(&Giant);
 		if (bpage->vaddr == NULL) {
 			free(bpage, M_DEVBUF);
 			break;
diff --git a/sys/amd64/amd64/busdma_machdep.c b/sys/amd64/amd64/busdma_machdep.c
index 2ce359b0a795..270d22269914 100644
--- a/sys/amd64/amd64/busdma_machdep.c
+++ b/sys/amd64/amd64/busdma_machdep.c
@@ -348,10 +348,12 @@ bus_dmamem_alloc_size(bus_dma_tag_t dmat, void** vaddr, int flags,
 		 *     and handles multi-seg allocations.  Nobody is doing
 		 *     multi-seg allocations yet though.
 		 */
+		mtx_lock(&Giant);
 		*vaddr = contigmalloc(size, M_DEVBUF,
 		    (flags & BUS_DMA_NOWAIT) ? M_NOWAIT : M_WAITOK,
 		    0ul, dmat->lowaddr, dmat->alignment? dmat->alignment : 1ul,
 		    dmat->boundary);
+		mtx_unlock(&Giant);
 	}
 	if (*vaddr == NULL)
 		return (ENOMEM);
@@ -381,8 +383,11 @@ bus_dmamem_free_size(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map,
 		panic("bus_dmamem_free: Invalid map freed\n");
 	if ((size <= PAGE_SIZE) && dmat->lowaddr >= ptoa(Maxmem))
 		free(vaddr, M_DEVBUF);
-	else
+	else {
+		mtx_lock(&Giant);
 		contigfree(vaddr, size, M_DEVBUF);
+		mtx_unlock(&Giant);
+	}
 }
 
 void
@@ -793,11 +798,13 @@ alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages)
 
 		if (bpage == NULL)
 			break;
+		mtx_lock(&Giant);
 		bpage->vaddr = (vm_offset_t)contigmalloc(PAGE_SIZE, M_DEVBUF,
 							 M_NOWAIT, 0ul,
 							 dmat->lowaddr,
 							 PAGE_SIZE,
 							 0);
+		mtx_unlock(&Giant);
 		if (bpage->vaddr == 0) {
 			free(bpage, M_DEVBUF);
 			break;
diff --git a/sys/i386/i386/busdma_machdep.c b/sys/i386/i386/busdma_machdep.c
index 2ce359b0a795..270d22269914 100644
--- a/sys/i386/i386/busdma_machdep.c
+++ b/sys/i386/i386/busdma_machdep.c
@@ -348,10 +348,12 @@ bus_dmamem_alloc_size(bus_dma_tag_t dmat, void** vaddr, int flags,
 		 *     and handles multi-seg allocations.  Nobody is doing
 		 *     multi-seg allocations yet though.
 		 */
+		mtx_lock(&Giant);
 		*vaddr = contigmalloc(size, M_DEVBUF,
 		    (flags & BUS_DMA_NOWAIT) ? M_NOWAIT : M_WAITOK,
 		    0ul, dmat->lowaddr, dmat->alignment? dmat->alignment : 1ul,
 		    dmat->boundary);
+		mtx_unlock(&Giant);
 	}
 	if (*vaddr == NULL)
 		return (ENOMEM);
@@ -381,8 +383,11 @@ bus_dmamem_free_size(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map,
 		panic("bus_dmamem_free: Invalid map freed\n");
 	if ((size <= PAGE_SIZE) && dmat->lowaddr >= ptoa(Maxmem))
 		free(vaddr, M_DEVBUF);
-	else
+	else {
+		mtx_lock(&Giant);
 		contigfree(vaddr, size, M_DEVBUF);
+		mtx_unlock(&Giant);
+	}
 }
 
 void
@@ -793,11 +798,13 @@ alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages)
 
 		if (bpage == NULL)
 			break;
+		mtx_lock(&Giant);
 		bpage->vaddr = (vm_offset_t)contigmalloc(PAGE_SIZE, M_DEVBUF,
 							 M_NOWAIT, 0ul,
 							 dmat->lowaddr,
 							 PAGE_SIZE,
 							 0);
+		mtx_unlock(&Giant);
 		if (bpage->vaddr == 0) {
 			free(bpage, M_DEVBUF);
 			break;
diff --git a/sys/ia64/ia64/busdma_machdep.c b/sys/ia64/ia64/busdma_machdep.c
index e7c38bee1209..80f350b98f10 100644
--- a/sys/ia64/ia64/busdma_machdep.c
+++ b/sys/ia64/ia64/busdma_machdep.c
@@ -354,10 +354,12 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
 		 *     and handles multi-seg allocations.  Nobody is doing
 		 *     multi-seg allocations yet though.
 		 */
+		mtx_lock(&Giant);
 		*vaddr = contigmalloc(dmat->maxsize, M_DEVBUF,
 		    (flags & BUS_DMA_NOWAIT) ? M_NOWAIT : M_WAITOK,
 		    0ul, dmat->lowaddr, dmat->alignment? dmat->alignment : 1ul,
 		    dmat->boundary);
+		mtx_unlock(&Giant);
 	}
 	if (*vaddr == NULL)
 		return (ENOMEM);
@@ -379,8 +381,11 @@ bus_dmamem_free(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map)
 		panic("bus_dmamem_free: Invalid map freed\n");
 	if ((dmat->maxsize <= PAGE_SIZE) && dmat->lowaddr >= ptoa(Maxmem))
 		free(vaddr, M_DEVBUF);
-	else
+	else {
+		mtx_lock(&Giant);
 		contigfree(vaddr, dmat->maxsize, M_DEVBUF);
+		mtx_unlock(&Giant);
+	}
 }
 
 #define BUS_DMAMAP_NSEGS ((64 * 1024 / PAGE_SIZE) + 1)
@@ -817,11 +822,13 @@ alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages)
 
 		if (bpage == NULL)
 			break;
+		mtx_lock(&Giant);
 		bpage->vaddr = (vm_offset_t)contigmalloc(PAGE_SIZE, M_DEVBUF,
 							 M_NOWAIT, 0ul,
 							 dmat->lowaddr,
 							 PAGE_SIZE,
 							 0);
+		mtx_unlock(&Giant);
 		if (bpage->vaddr == NULL) {
 			free(bpage, M_DEVBUF);
 			break;
diff --git a/sys/powerpc/powerpc/busdma_machdep.c b/sys/powerpc/powerpc/busdma_machdep.c
index b7ff1de17c0e..6c6dd36421da 100644
--- a/sys/powerpc/powerpc/busdma_machdep.c
+++ b/sys/powerpc/powerpc/busdma_machdep.c
@@ -217,10 +217,12 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
                  *     and handles multi-seg allocations.  Nobody is doing
                  *     multi-seg allocations yet though.
                  */
+		mtx_lock(&Giant);
                 *vaddr = contigmalloc(dmat->maxsize, M_DEVBUF,
                     (flags & BUS_DMA_NOWAIT) ? M_NOWAIT : M_WAITOK,
                     0ul, dmat->lowaddr, dmat->alignment? dmat->alignment : 1ul,
                     dmat->boundary);
+		mtx_unlock(&Giant);
         }
 
         if (*vaddr == NULL)
@@ -240,8 +242,11 @@ bus_dmamem_free(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map)
                 panic("bus_dmamem_free: Invalid map freed\n");
         if (dmat->maxsize <= PAGE_SIZE)
 		free(vaddr, M_DEVBUF);
-        else
+        else {
+		mtx_lock(&Giant);
 		contigfree(vaddr, dmat->maxsize, M_DEVBUF);
+		mtx_unlock(&Giant);
+	}
 }
 
 /*
diff --git a/sys/sparc64/sparc64/bus_machdep.c b/sys/sparc64/sparc64/bus_machdep.c
index 71e1d0b8f967..4d825f76329f 100644
--- a/sys/sparc64/sparc64/bus_machdep.c
+++ b/sys/sparc64/sparc64/bus_machdep.c
@@ -630,11 +630,13 @@ nexus_dmamem_alloc_size(bus_dma_tag_t pdmat, bus_dma_tag_t ddmat, void **vaddr,
 		 * and handles multi-seg allocations.  Nobody is doing multi-seg
 		 * allocations yet though.
 		 */
+		mtx_lock(&Giant);
 		*vaddr = contigmalloc(size, M_DEVBUF,
 		    (flags & BUS_DMA_NOWAIT) ? M_NOWAIT : M_WAITOK,
 		    0ul, ddmat->dt_lowaddr,
 		    ddmat->dt_alignment ? ddmat->dt_alignment : 1UL,
 		    ddmat->dt_boundary);
+		mtx_unlock(&Giant);
 	}
 	if (*vaddr == NULL) {
 		free(*mapp, M_DEVBUF);
@@ -663,8 +665,11 @@ nexus_dmamem_free_size(bus_dma_tag_t pdmat, bus_dma_tag_t ddmat, void *vaddr,
 	sparc64_dmamem_free_map(ddmat, map);
 	if ((size <= PAGE_SIZE))
 		free(vaddr, M_DEVBUF);
-	else
+	else {
+		mtx_lock(&Giant);
 		contigfree(vaddr, size, M_DEVBUF);
+		mtx_unlock(&Giant);
+	}
 }
 
 static void