Index: sys/ufs/ffs/ffs_vfsops.c
===================================================================
--- sys/ufs/ffs/ffs_vfsops.c
+++ sys/ufs/ffs/ffs_vfsops.c
@@ -461,6 +461,29 @@
 	mp->mnt_kern_flag &= ~MNTK_FPLOOKUP;
 	mp->mnt_flag |= mntorflags;
 	MNT_IUNLOCK(mp);
+	/*
+	 * Must not call namei() while owning busy ref.
+	 */
+	if ((mp->mnt_flag & MNT_UPDATE) != 0)
+		vfs_unbusy(mp);
+	/*
+	 * Not an update, or updating the name: look up the name
+	 * and verify that it refers to a sensible disk device.
+	 */
+	NDINIT(&ndp, LOOKUP, FOLLOW, UIO_SYSSPACE, fspec, td);
+	error = namei(&ndp);
+	if ((mp->mnt_flag & MNT_UPDATE) != 0) {
+		/*
+		 * Unmount does not start if MNT_UPDATE is set.  Mount
+		 * update busies mp before setting MNT_UPDATE.  We
+		 * must be able to retain our busy ref successfully,
+		 * without sleep.
+		 */
+		error1 = vfs_busy(mp, MBF_NOWAIT);
+		MPASS(error1 == 0);
+	}
+	error1 = error;
+
 	/*
 	 * If updating, check whether changing from read-only to
 	 * read/write; if there is no device name, that's all we do.
@@ -567,7 +590,7 @@
 		if ((mp->mnt_flag & MNT_RELOAD) &&
 		    (error = ffs_reload(mp, td, 0)) != 0)
 			return (error);
-		if (fs->fs_ronly &&
+		if (fs->fs_ronly && error1 == 0 &&
 		    !vfs_flagopt(mp->mnt_optnew, "ro", NULL, 0)) {
 			/*
 			 * If we are running a checker, do not allow upgrade.
@@ -725,33 +748,14 @@
 		 */
 		if (mp->mnt_flag & MNT_SNAPSHOT)
 			return (ffs_snapshot(mp, fspec));
-
-		/*
-		 * Must not call namei() while owning busy ref.
-		 */
-		vfs_unbusy(mp);
 	}
 
-	/*
-	 * Not an update, or updating the name: look up the name
-	 * and verify that it refers to a sensible disk device.
-	 */
-	NDINIT(&ndp, LOOKUP, FOLLOW | LOCKLEAF, UIO_SYSSPACE, fspec, td);
-	error = namei(&ndp);
-	if ((mp->mnt_flag & MNT_UPDATE) != 0) {
-		/*
-		 * Unmount does not start if MNT_UPDATE is set.  Mount
-		 * update busies mp before setting MNT_UPDATE.  We
-		 * must be able to retain our busy ref succesfully,
-		 * without sleep.
-		 */
-		error1 = vfs_busy(mp, MBF_NOWAIT);
-		MPASS(error1 == 0);
-	}
-	if (error != 0)
-		return (error);
+	if (error1 != 0)
+		return (error1);
 	NDFREE(&ndp, NDF_ONLY_PNBUF);
 	devvp = ndp.ni_vp;
+	if ((error = vget(devvp, LK_EXCLUSIVE | LK_RETRY)) != 0)
+		return (error);
 	if (!vn_isdisk_error(devvp, &error)) {
 		vput(devvp);
 		return (error);