diff --git a/sys/kern/uipc_cow.c b/sys/kern/uipc_cow.c
index dfe2c8690ce3..2258aca7ee56 100644
--- a/sys/kern/uipc_cow.c
+++ b/sys/kern/uipc_cow.c
@@ -77,9 +77,6 @@ struct netsend_cow_stats {
 
 static struct netsend_cow_stats socow_stats = {0,0,0,0,0,0,0,0,0,0,0};
 
-extern struct sf_buf *sf_bufs;
-extern vm_offset_t sf_base;
-#define dtosf(x) (&sf_bufs[((uintptr_t)(x) - (uintptr_t)sf_base) >> PAGE_SHIFT])
 static void socow_iodone(void *addr, void *args);
 
 static void
@@ -89,7 +86,7 @@ socow_iodone(void *addr, void *args)
 	struct sf_buf *sf;
 	vm_page_t pp;
 
-	sf = dtosf(addr);
+	sf = args;
 	pp = sf->m;
 	s = splvm();
 	/* remove COW mapping  */
@@ -98,7 +95,7 @@ socow_iodone(void *addr, void *args)
 	vm_page_unlock_queues();
 	splx(s);
 	/* note that sf_buf_free() unwires the page for us*/
-	sf_buf_free(addr, NULL);
+	sf_buf_free(addr, args);
 	socow_stats.iodone++;
 }
 
@@ -153,7 +150,7 @@ socow_setup(struct mbuf *m0, struct uio *uio)
 	 */
 	m0->m_data = (caddr_t)sf->kva;
 	m0->m_len = PAGE_SIZE;
-	MEXTADD(m0, sf->kva, PAGE_SIZE, socow_iodone, NULL, 0, EXT_SFBUF);
+	MEXTADD(m0, sf->kva, PAGE_SIZE, socow_iodone, sf, 0, EXT_SFBUF);
 	socow_stats.success++;
 
 	iov = uio->uio_iov;
diff --git a/sys/kern/uipc_syscalls.c b/sys/kern/uipc_syscalls.c
index 285eaca82293..67734524c93c 100644
--- a/sys/kern/uipc_syscalls.c
+++ b/sys/kern/uipc_syscalls.c
@@ -1661,8 +1661,6 @@ sf_buf_alloc()
 	return (sf);
 }
 
-#define dtosf(x)	(&sf_bufs[((uintptr_t)(x) - (uintptr_t)sf_base) >> PAGE_SHIFT])
-
 /*
  * Detatch mapped page and release resources back to the system.
  */
@@ -1672,7 +1670,7 @@ sf_buf_free(void *addr, void *args)
 	struct sf_buf *sf;
 	struct vm_page *m;
 
-	sf = dtosf(addr);
+	sf = args;
 	pmap_qremove((vm_offset_t)addr, 1);
 	m = sf->m;
 	vm_page_lock_queues();
@@ -1955,14 +1953,14 @@ retry_lookup:
 		MGETHDR(m, M_TRYWAIT, MT_DATA);
 		if (m == NULL) {
 			error = ENOBUFS;
-			sf_buf_free((void *)sf->kva, NULL);
+			sf_buf_free((void *)sf->kva, sf);
 			sbunlock(&so->so_snd);
 			goto done;
 		}
 		/*
 		 * Setup external storage for mbuf.
 		 */
-		MEXTADD(m, sf->kva, PAGE_SIZE, sf_buf_free, NULL, M_RDONLY,
+		MEXTADD(m, sf->kva, PAGE_SIZE, sf_buf_free, sf, M_RDONLY,
 		    EXT_SFBUF);
 		m->m_data = (char *) sf->kva + pgoff;
 		m->m_pkthdr.len = m->m_len = xfsize;