--- /dev/null
+#! /bin/bash
+# FS QA Test 034
+#
+# Test overlay nlink when adding lower hardlinks.
+#
+# nlink of overlay inode could be dropped indefinitely by adding
+# unaccounted lower hardlinks underneath a mounted overlay and
+# trying to remove them.
+#
+# The simplest way to understand this test is this:
+# Imagine that you have a tool (e.g. xfs_db) with which you can add
+# hardlinks, without changing the value of nlink stored on-disk for the
+# inode. This is exactly what this test does when it adds lower hardlinks
+# underneath a mounted overlay.
+#
+# Commit 5f8415d6b87e ("ovl: persistent overlay inode nlink for indexed
+# inodes") fixes this issue, although the issue was never exposed in any
+# released kernel.
+#
+# With overlayfs indexed copy up and without the fix, the test triggers
+# WARN_ON(inode->i_nlink == 0) in drop_link().
+#
+#-----------------------------------------------------------------------
+# Copyright (C) 2017 CTERA Networks. All Rights Reserved.
+# Author: Amir Goldstein <amir73il@gmail.com>
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it would be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write the Free Software Foundation,
+# Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+#-----------------------------------------------------------------------
+#
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+tmp=/tmp/$$
+status=1 # failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+ cd /
+ rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+_supported_fs overlay
+_supported_os Linux
+_require_scratch
+
+# Remove all files from previous tests
+_scratch_mkfs
+
+# Create lower hardlink
+lowerdir=$OVL_BASE_SCRATCH_MNT/$OVL_LOWER
+mkdir -p $lowerdir
+touch $lowerdir/0
+ln $lowerdir/0 $lowerdir/1
+
+_scratch_mount
+
+# Copy up lower hardlink - overlay inode nlink 2 is copied from lower
+touch $SCRATCH_MNT/0
+
+# Add lower hardlinks while overlay is mounted - overlay inode nlink
+# is not being updated
+ln $lowerdir/0 $lowerdir/2
+ln $lowerdir/0 $lowerdir/3
+
+# Unlink the 2 un-accounted lower hardlinks - overlay inode nlinks
+# drops 2 and may reach 0 if the situation is not detected
+rm $SCRATCH_MNT/2
+rm $SCRATCH_MNT/3
+
+# Check if getting ENOENT when trying to link !I_LINKABLE with nlink 0
+ln $SCRATCH_MNT/0 $SCRATCH_MNT/4
+
+# Unlink all hardlinks - if overlay inode nlink is 0, this will trigger
+# WARN_ON() in drop_nlink()
+rm $SCRATCH_MNT/0
+rm $SCRATCH_MNT/1
+rm $SCRATCH_MNT/4
+
+# Verify that orphan index is cleaned on mount
+_scratch_cycle_mount
+ls $OVL_BASE_SCRATCH_MNT/$OVL_WORK/index 2>/dev/null
+
+echo "Silence is golden"
+status=0
+exit