generic: test a deadlock in xfs_rename when whiteing out files

wenli xie reported a buffer cache deadlock when an overlayfs is mounted
atop xfs and overlayfs tries to replace a single-nlink file with a
whiteout file.  This test reproduces that deadlock.

Reported-by: wenli xie <wlxie7296@gmail.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/631

@@ -0,0 +1,108 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (c) 2021 Oracle.  All Rights Reserved.
+#
+# FS QA Test No. 631
+#
+# Reproducer for a deadlock in xfs_rename reported by Wenli Xie.
+#
+# When overlayfs is running on top of xfs and the user unlinks a file in the
+# overlay, overlayfs will create a whiteout inode and ask us to "rename" the
+# whiteout file atop the one being unlinked.  If the file being unlinked loses
+# its one nlink, we then have to put the inode on the unlinked list.
+#
+# This requires us to grab the AGI buffer of the whiteout inode to take it
+# off the unlinked list (which is where whiteouts are created) and to grab
+# the AGI buffer of the file being deleted.  If the whiteout was created in
+# a higher numbered AG than the file being deleted, we'll lock the AGIs in
+# the wrong order and deadlock.
+#
+# Note that this test doesn't do anything xfs-specific so it's a generic test.
+# This is a regression test for commit 6da1b4b1ab36 ("xfs: fix an ABBA deadlock
+# in xfs_rename").
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1    # failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	stop_workers
+	cd /
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+
+# real QA test starts here
+_supported_fs generic
+_require_scratch
+test "$FSTYP" = "overlay" && _notrun "Test does not apply to overlayfs."
+_require_extra_fs overlay
+
+rm -f $seqres.full
+
+_scratch_mkfs >> $seqres.full
+_scratch_mount
+_supports_filetype $SCRATCH_MNT || _notrun "overlayfs test requires d_type"
+
+mkdir $SCRATCH_MNT/lowerdir
+mkdir $SCRATCH_MNT/lowerdir1
+mkdir $SCRATCH_MNT/lowerdir/etc
+mkdir $SCRATCH_MNT/workers
+echo salts > $SCRATCH_MNT/lowerdir/etc/access.conf
+touch $SCRATCH_MNT/running
+
+stop_workers() {
+	test -e $SCRATCH_MNT/running || return
+	rm -f $SCRATCH_MNT/running
+
+	while [ "$(ls $SCRATCH_MNT/workers/ | wc -l)" -gt 0 ]; do
+		wait
+	done
+}
+
+worker() {
+	local tag="$1"
+	local mergedir="$SCRATCH_MNT/merged$tag"
+	local l="lowerdir=$SCRATCH_MNT/lowerdir:$SCRATCH_MNT/lowerdir1"
+	local u="upperdir=$SCRATCH_MNT/upperdir$tag"
+	local w="workdir=$SCRATCH_MNT/workdir$tag"
+	local i="index=off,nfs_export=off"
+
+	touch $SCRATCH_MNT/workers/$tag
+	while test -e $SCRATCH_MNT/running; do
+		rm -rf $SCRATCH_MNT/merged$tag
+		rm -rf $SCRATCH_MNT/upperdir$tag
+		rm -rf $SCRATCH_MNT/workdir$tag
+		mkdir $SCRATCH_MNT/merged$tag
+		mkdir $SCRATCH_MNT/workdir$tag
+		mkdir $SCRATCH_MNT/upperdir$tag
+
+		mount -t overlay overlay -o "$l,$u,$w,$i" $mergedir
+		mv $mergedir/etc/access.conf $mergedir/etc/access.conf.bak
+		touch $mergedir/etc/access.conf
+		mv $mergedir/etc/access.conf $mergedir/etc/access.conf.bak
+		touch $mergedir/etc/access.conf
+		umount $mergedir
+	done
+	rm -f $SCRATCH_MNT/workers/$tag
+}
+
+for i in $(seq 0 $((4 + LOAD_FACTOR)) ); do
+	worker $i &
+done
+
+sleep $((30 * TIME_FACTOR))
+stop_workers
+
+echo Silence is golden.
+# success, all done
+status=0
+exit

tests/generic/631.out

@@ -0,0 +1,2 @@
+QA output created by 631
+Silence is golden.

tests/generic/group

@@ -633,3 +633,4 @@
 628 auto quick rw clone
 629 auto quick rw copy_range
 630 auto quick rw dedupe clone
+631 auto rw overlay rename