diff --git a/tools/test/stress2/misc/all.exclude b/tools/test/stress2/misc/all.exclude
index d4a57af4d559..5106478ff2d0 100644
--- a/tools/test/stress2/misc/all.exclude
+++ b/tools/test/stress2/misc/all.exclude
@@ -1,104 +1,106 @@
 # List of tests not to run, unless the '-a' option is used with run.sh
 # Exclude names must start in column 1
 
 backingstore.sh		g_vfs_done():md6a[WRITE(offset=...)]error = 28			20111220
 backingstore2.sh	panic: 43 vncache entries remaining				20111220
 backingstore3.sh	g_vfs_done():md6a[WRITE(offset=...)]error = 28			20111230
 dd.sh			CAM stuck in vmwait						20200116
 devfs4.sh		Hang seen							20210210
 force4.sh		https://people.freebsd.org/~pho/stress/log/log0082.txt		20210328
 fsync.sh		panic: Journal overflow						20190208
 fuse.sh			Memory corruption seen in log file kostik734.txt		20141114
 fuse2.sh		Deadlock seen							20121129
 fuse3.sh		Deadlock seen							20141120
 getrandom.sh		Known DoS issue							20201107
 getrandom2.sh		Known DoS issue							20200302
 gjournal.sh		panic: Journal overflow						20190626
 gjournal2.sh		panic: Journal overflow						20180125
 gjournal3.sh		panic: Bio not on queue						20171225
 gjournal4.sh		CAM stuck in vmwait						20180517
 gnop7.sh		Waiting for patch commit					20190820
 gnop8.sh		Waiting for patch commit					20201214
 gnop9.sh		Waiting for patch commit					20201214
 gnop10.sh		Waiting for patch commit					20210105
 graid1_8.sh		Known issue							20170909
 graid1_9.sh		panic: Bad effnlink						20180212
 lockf5.sh		Spinning threads seen						20160718
 ifconfig.sh		Bug 253824							20210322
 ifconfig2.sh		https://people.freebsd.org/~pho/stress/log/log0051.txt		20210210
 maxvnodes2.sh		https://people.freebsd.org/~pho/stress/log/log0083.txt		20210329
 memguard.sh		https://people.freebsd.org/~pho/stress/log/log0088.txt		20210402
 memguard2.sh		Waiting for fix commit
 memguard3.sh		Waiting for fix commit
 memsetdomain.sh		May change policy for random threads to to domainset_fixed	20210104
 mlockall2.sh		Unrecoverable OOM killing seen					20190203
 mlockall7.sh		Needs further investigation					20210123
 nfs15lockd.sh		panic: Assertion td->td_realucred == td->td_ucred failed ...	20210211
 newfs4.sh		watchdog fired. newbuf						20190225
 nfs10.sh		Double fault							20151013
 nfs13.sh		mount_nfs hangs in mntref					20191007
 nfs16.sh		panic: Failed to register NFS lock locally - error=11		20160608
 oom2.sh			Hang in pfault							20180324
 overcommit2.sh		CAM stuck in vmwait seen					20200112
 pageout.sh		panic: handle_written_filepage: not started			20190218
 pmc8.sh			panic: [pmc,2749] (ri21, rc1) waiting too long for pmc to ...	20210621
 quota10.sh		people.freebsd.org/~pho/stress/log/quota10-2.txt		20200525
 quota2.sh		panic: dqflush: stray dquot					20120221
 quota3.sh		panic: softdep_deallocate_dependencies: unrecovered ...		20111222
 quota7.sh		panic: dqflush: stray dquot					20120221
 sctp3.sh		panic: Queues are not empty when handling SHUTDOWN-COMPLETE	20210211
 sendfile25.sh		WiP								20200611
 signal.sh		Timing issues. Needs fixing					20171116
 swapoff2.sh		swap_pager_force_pagein: read from swap failed			20171223
 swapoff5.sh		log0005.txt, known issue					20210111
 systrace.sh		WiP								20200227
 systrace2.sh		WiP								20200227
 syzkaller11.sh		WiP								20200721
 syzkaller15.sh		WiP								20200712
 syzkaller16.sh		WiP								20210722
 syzkaller19.sh		WiP								20200712
 syzkaller25.sh		WiP								20201116
 syzkaller28.sh		WiP								20201120
 syzkaller29.sh		May change policy for random threads to to domainset_fixed	20210104
 syzkaller30.sh		May change policy for random threads to to domainset_fixed	20210104
 syzkaller31.sh		panic: Bad tailq NEXT(0xfffffe0079608f00->tqh_last) != NULL	20210322
 syzkaller32.sh		Fatal trap 18: integer divide fault while in kernel mode	20210322
 syzkaller33.sh		Fatal trap 18: integer divide fault while in kernel mode	20210418
 syzkaller39.sh		WiP								20210607
 syzkaller40.sh		WiP								20210607
 syzkaller41.sh		WiP								20210607
 syzkaller42.sh		WiP								20210613
 syzkaller43.sh		WiP								20210906
 truss3.sh		WiP								20200915
 unionfs.sh		insmntque: non-locked vp: xx is not exclusive locked...		20130909
 unionfs2.sh		insmntque: mp-safe fs and non-locked vp is not ...		20111219
 unionfs3.sh		insmntque: mp-safe fs and non-locked vp is not ...		20111216
+unionfs4.sh		WiP								20210916
+unionfs5.sh		WiP								20210916
 
 # Test not to run for other reasons:
 
 fuzz.sh			A know issue
 marcus3.sh		OK, but runs for a long time
 statfs.sh		Not very interesting
 vunref.sh		No problems ever seen
 vunref2.sh		No problems ever seen
 
 # Snapshots has been disabled on SU+J
 suj15.sh
 suj16.sh
 suj19.sh
 suj20.sh
 suj21.sh
 suj22.sh
 suj24.sh
 suj25.sh
 suj26.sh
 suj27.sh
 suj28.sh
 
 # Exclude NFS loopback tests
 nfs2.sh			panic: wrong diroffset						20140219
 nfs5.sh
 nfs6.sh
 nfs11.sh		vmwait deadlock							20151004
 nullfs8.sh
 tmpfs18.sh		mntref hang seen						20191019
diff --git a/tools/test/stress2/misc/unionfs4.sh b/tools/test/stress2/misc/unionfs4.sh
new file mode 100755
index 000000000000..557cead66389
--- /dev/null
+++ b/tools/test/stress2/misc/unionfs4.sh
@@ -0,0 +1,77 @@
+#!/bin/sh
+
+#
+# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+#
+# Copyright (c) 2021 Peter Holm
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+
+# "mkdir: mkdir(d2), level 2. mkdir.c:96: No such file or directory" seen
+# with a non debug kernel.
+
+[ `id -u ` -ne 0 ] && echo "Must be root!" && exit 1
+. ../default.cfg
+
+# unionfs usage example from the man page:
+#	   mount -t cd9660 -o ro /dev/cd0 /usr/src
+#	   mount -t unionfs -o noatime /var/obj	/usr/src
+
+md1=$mdstart
+md2=$((md1 + 1))
+mp1=/mnt$md1
+mp2=/mnt$md2
+mkdir -p $mp1 $mp2
+set -e
+for i in $mp1 $mp2; do
+	mount | grep -q "on $i " && umount -f $i
+done
+for i in $md1 $md2; do
+	mdconfig -l | grep -q md$i && mdconfig -d -u $i
+done
+
+mdconfig -a -t swap -s 2g -u $md1
+mdconfig -a -t swap -s 2g -u $md2
+newfs $newfs_flags -n md$md1 > /dev/null
+newfs $newfs_flags -n md$md2 > /dev/null
+mount /dev/md$md1 $mp1
+mount /dev/md$md2 $mp2
+
+mount -t unionfs -o noatime $mp1 $mp2
+set +e
+mount | grep -E "$mp1|$mp2"
+
+export RUNDIR=$mp2/stressX
+export runRUNTIME=2m 
+
+(cd ..; ./run.sh marcus.cfg)
+
+../tools/killall.sh
+umount $mp2	# The unionfs mount
+umount $mp2
+n=`find $mp1/stressX | wc -l`
+[ $n -eq 1 ] && s=0 || { find $mp1/stressX -ls | head -12; s=1; }
+umount $mp1
+mdconfig -d -u $md2
+mdconfig -d -u $md1
+exit $s
diff --git a/tools/test/stress2/misc/unionfs5.sh b/tools/test/stress2/misc/unionfs5.sh
new file mode 100755
index 000000000000..ba00fa2b5258
--- /dev/null
+++ b/tools/test/stress2/misc/unionfs5.sh
@@ -0,0 +1,83 @@
+#!/bin/sh
+
+#
+# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+#
+# Copyright (c) 2021 Peter Holm
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+
+# "mkdir: mkdir(d2), level 2. mkdir.c:96: No such file or directory" seen
+# with a non debug kernel.
+
+[ `id -u ` -ne 0 ] && echo "Must be root!" && exit 1
+. ../default.cfg
+
+# unionfs usage example from the man page:
+#	   mount -t cd9660 -o ro /dev/cd0 /usr/src
+#	   mount -t unionfs -o noatime /var/obj	/usr/src
+
+md1=$mdstart
+md2=$((md1 + 1))
+mp1=/mnt$md1
+mp2=/mnt$md2
+mkdir -p $mp1 $mp2
+set -e
+for i in $mp1 $mp2; do
+	mount | grep -q "on $i " && umount -f $i
+done
+for i in $md1 $md2; do
+	mdconfig -l | grep -q md$i && mdconfig -d -u $i
+done
+
+mdconfig -a -t swap -s 2g -u $md1
+mdconfig -a -t swap -s 2g -u $md2
+newfs $newfs_flags -n md$md1 > /dev/null
+newfs $newfs_flags -n md$md2 > /dev/null
+mount /dev/md$md1 $mp1
+mount /dev/md$md2 $mp2
+
+mount -t unionfs -o noatime $mp1 $mp2
+set +e
+mount | grep -E "$mp1|$mp2"
+
+if [ $# -eq 0 ]; then
+	echo "Using unionfs"
+	export RUNDIR=$mp2/stressX
+else
+	echo "Using FFS"
+	export RUNDIR=$mp1/stressX
+fi
+export runRUNTIME=2m 
+
+(cd ../testcases/mkdir; ./mkdir -t 2m -i 20)
+
+find $RUNDIR -ls
+umount $mp2	# The unionfs mount
+umount $mp2
+n=`find $mp1/stressX | wc -l`
+[ $n -eq 1 ] && s=0 || s=1
+umount $mp1
+mdconfig -d -u $md2
+mdconfig -d -u $md1
+exit $s