Re: [PATCH 09/10] generic: test a deadlock in xfs_rename when whiteing out files

Eryu Guan
2021-03-14T18:07:45Z

On Mon, Mar 08, 2021 at 08:40:53PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
>
> 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>
> ---
> tests/generic/1300 | 109 ++++++++++++++++++++++++++++++++++++++++++++++++
> tests/generic/1300.out | 2 +
> tests/generic/group | 1
> 3 files changed, 112 insertions(+)
> create mode 100755 tests/generic/1300
> create mode 100644 tests/generic/1300.out
>
>
> diff --git a/tests/generic/1300 b/tests/generic/1300
> new file mode 100755
> index 00000000..10df44e3
> --- /dev/null
> +++ b/tests/generic/1300
> @@ -0,0 +1,109 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +# Copyright (c) 2021 Oracle. All Rights Reserved.
> +#
> +# FS QA Test No. 1300
> +#
> +# 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."
> +
> +modprobe -q overlay
> +grep -q overlay /proc/filesystems || _notrun "Test requires overlayfs."

We have _require_ext2() and _require_tmpfs(), I think it's time to
refactor them into a new _require_filesystem() helper?

> +
> +rm -f $seqres.full
> +
> +_scratch_mkfs >> $seqres.full
> +_scratch_mount

Also, doing overlay mount requires the underlying to export d_type,
perhaps we should do '_supports_filetype $SCRATCH_MNT' here, otherwise
filesystems like nfs would fail the test.

> +
> +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
> diff --git a/tests/generic/1300.out b/tests/generic/1300.out
> new file mode 100644
> index 00000000..5805d30d
> --- /dev/null
> +++ b/tests/generic/1300.out
> @@ -0,0 +1,2 @@
> +QA output created by 1300
> +Silence is golden.
> diff --git a/tests/generic/group b/tests/generic/group
> index 778aa8c4..2233a59d 100644
> --- a/tests/generic/group
> +++ b/tests/generic/group
> @@ -631,3 +631,4 @@
> 947 auto quick rw clone
> 948 auto quick rw copy_range
> 949 auto quick rw dedupe clone
> +1300 auto rw overlay

Also add 'rename' group?

Thanks,
Eryu