--- sys/mount.h.sav	2013-08-29 15:19:40.000000000 -0400
+++ sys/mount.h	2013-08-29 15:23:59.000000000 -0400
@@ -609,6 +609,7 @@ typedef int vfs_sysctl_t(struct mount *m
 		    struct sysctl_req *req);
 typedef void vfs_susp_clean_t(struct mount *mp);
 typedef void vfs_notify_lowervp_t(struct mount *mp, struct vnode *lowervp);
+typedef void vfs_killio_t(struct mount *mp);
 
 struct vfsops {
 	vfs_mount_t		*vfs_mount;
@@ -628,6 +629,7 @@ struct vfsops {
 	vfs_susp_clean_t	*vfs_susp_clean;
 	vfs_notify_lowervp_t	*vfs_reclaim_lowervp;
 	vfs_notify_lowervp_t	*vfs_unlink_lowervp;
+	vfs_killio_t		*vfs_killio;
 };
 
 vfs_statfs_t	__vfs_statfs;
@@ -756,6 +758,14 @@ vfs_statfs_t	__vfs_statfs;
 	}								\
 } while (0)
 
+#define	VFS_KILLIO(MP) do {						\
+	if (*(MP)->mnt_op->vfs_killio != NULL) {			\
+		VFS_PROLOGUE(MP);					\
+		(*(MP)->mnt_op->vfs_killio)(MP);			\
+		VFS_EPILOGUE(MP);					\
+	}								\
+} while (0)
+
 #define VFS_KNOTE_LOCKED(vp, hint) do					\
 {									\
 	if (((vp)->v_vflag & VV_NOKNOTE) == 0)				\
--- kern/vfs_mount.c.sav	2013-08-29 15:24:36.000000000 -0400
+++ kern/vfs_mount.c	2013-08-29 17:22:51.000000000 -0400
@@ -1269,8 +1269,16 @@ dounmount(mp, flags, td)
 	}
 	mp->mnt_kern_flag |= MNTK_UNMOUNT | MNTK_NOINSMNTQ;
 	/* Allow filesystems to detect that a forced unmount is in progress. */
-	if (flags & MNT_FORCE)
+	if (flags & MNT_FORCE) {
 		mp->mnt_kern_flag |= MNTK_UNMOUNTF;
+		MNT_IUNLOCK(mp);
+		/*
+		 * Must be done after setting MNTK_UNMOUNTF and before
+		 * waiting for mnt_lockref to become 0.
+		 */
+		VFS_KILLIO(mp);
+		MNT_ILOCK(mp);
+	}
 	error = 0;
 	if (mp->mnt_lockref) {
 		mp->mnt_kern_flag |= MNTK_DRAINING;
--- fs/nfsclient/nfs_clvfsops.c.sav	2013-08-29 15:30:50.000000000 -0400
+++ fs/nfsclient/nfs_clvfsops.c	2013-08-29 16:52:54.000000000 -0400
@@ -120,6 +120,7 @@ static vfs_root_t nfs_root;
 static vfs_statfs_t nfs_statfs;
 static vfs_sync_t nfs_sync;
 static vfs_sysctl_t nfs_sysctl;
+static vfs_killio_t nfs_killio;
 
 /*
  * nfs vfs operations.
@@ -134,6 +135,7 @@ static struct vfsops nfs_vfsops = {
 	.vfs_uninit =		ncl_uninit,
 	.vfs_unmount =		nfs_unmount,
 	.vfs_sysctl =		nfs_sysctl,
+	.vfs_killio =		nfs_killio,
 };
 VFS_SET(nfs_vfsops, nfs, VFCF_NETWORK | VFCF_SBDRY);
 
@@ -1676,6 +1678,19 @@ nfs_sysctl(struct mount *mp, fsctlop_t o
 }
 
 /*
+ * Kill off any RPCs in progress, so that they will all return errors.
+ * This allows dounmount() to continue as far as VFS_UNMOUNT() for a
+ * forced dismount.
+ */
+static void
+nfs_killio(struct mount *mp)
+{
+	struct nfsmount *nmp = VFSTONFS(mp);
+
+	newnfs_nmcancelreqs(nmp);
+}
+
+/*
  * Extract the information needed by the nlm from the nfs vnode.
  */
 static void