Re: [PATCH v3] xfs: test agfl reset on bad list wrapping

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Mar 23, 2018 at 01:26:06PM +0800, Eryu Guan wrote:
> On Wed, Mar 21, 2018 at 09:57:16AM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > From the kernel patch that this test examines ("xfs: detect agfl count
> > corruption and reset agfl"):
> > 
> > "The struct xfs_agfl v5 header was originally introduced with
> > unexpected padding that caused the AGFL to operate with one less
> > slot than intended. The header has since been packed, but the fix
> > left an incompatibility for users who upgrade from an old kernel
> > with the unpacked header to a newer kernel with the packed header
> > while the AGFL happens to wrap around the end. The newer kernel
> > recognizes one extra slot at the physical end of the AGFL that the
> > previous kernel did not. The new kernel will eventually attempt to
> > allocate a block from that slot, which contains invalid data, and
> > cause a crash.
> > 
> > "This condition can be detected by comparing the active range of the
> > AGFL to the count. While this detects a padding mismatch, it can
> > also trigger false positives for unrelated flcount corruption. Since
> > we cannot distinguish a size mismatch due to padding from unrelated
> > corruption, we can't trust the AGFL enough to simply repopulate the
> > empty slot.
> > 
> > "Instead, avoid unnecessarily complex detection logic and and use a
> > solution that can handle any form of flcount corruption that slips
> > through read verifiers: distrust the entire AGFL and reset it to an
> > empty state. Any valid blocks within the AGFL are intentionally
> > leaked. This requires xfs_repair to rectify (which was already
> > necessary based on the state the AGFL was found in). The reset
> > mitigates the side effect of the padding mismatch problem from a
> > filesystem crash to a free space accounting inconsistency."
> > 
> > This test exercises the reset code by mutating a fresh filesystem to
> > contain an agfl with various list configurations of correctly wrapped,
> > incorrectly wrapped, not wrapped, and actually corrupt free lists; then
> > checks the success of the reset operation by fragmenting the free space
> > btrees to exercise the agfl.  Kernels without this reset fix will shut
> > down the filesystem with corruption errors.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > v3: use fallocate instead of dd write, more factoring of common code
> > v2: remove unncessary umounts, refactor long lines into helpers
> > ---
> >  common/rc         |   23 ++++-
> >  tests/xfs/709     |  258 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  tests/xfs/709.out |   13 +++
> >  tests/xfs/group   |    1 
> >  4 files changed, 293 insertions(+), 2 deletions(-)
> >  create mode 100755 tests/xfs/709
> >  create mode 100644 tests/xfs/709.out
> > 
> > diff --git a/common/rc b/common/rc
> > index 2c29d55..f7eb72d 100644
> > --- a/common/rc
> > +++ b/common/rc
> > @@ -3440,6 +3440,26 @@ _get_device_size()
> >  	grep `_short_dev $1` /proc/partitions | awk '{print $3}'
> >  }
> >  
> > +# Make sure we actually have dmesg checking set up.
> > +_require_check_dmesg() {
> > +	test -w /dev/kmsg || \
> > +		_notrun "Test requires writable /dev/kmsg."
> > +}
> > +
> > +# Return the dmesg log since the start of this test.  Caller must ensure that
> > +# /dev/kmsg was writable when the test was started so that we can find the
> > +# beginning of this test's log messages; _require_check_dmesg does this.
> > +_dmesg_since_test_start() {
> > +	dmesg | tac | sed -ne "0,\#run fstests $seqnum at $date_time#p" | \
> > +		tac
> > +}
> > +
> > +# check dmesg log for a specific string, subject to the same requirements as
> > +# _dmesg_since_test_start.
> > +_check_dmesg_for() {
> > +	_dmesg_since_test_start | egrep -q "$1"
> > +}
> > +
> >  # check dmesg log for WARNING/Oops/etc.
> >  _check_dmesg()
> >  {
> > @@ -3455,8 +3475,7 @@ _check_dmesg()
> >  
> >  	# search the dmesg log of last run of $seqnum for possible failures
> >  	# use sed \cregexpc address type, since $seqnum contains "/"
> 
> The comments about sed usage probably should go to
> _dmesg_since_test_start() too.

Ok

> > -	dmesg | tac | sed -ne "0,\#run fstests $seqnum at $date_time#p" | \
> > -		tac | $filter >$seqres.dmesg
> > +	_dmesg_since_test_start | $filter >$seqres.dmesg
> >  	egrep -q -e "kernel BUG at" \
> >  	     -e "WARNING:" \
> >  	     -e "BUG:" \
> > diff --git a/tests/xfs/709 b/tests/xfs/709
> > new file mode 100755
> > index 0000000..78cefe5
> > --- /dev/null
> > +++ b/tests/xfs/709
> > @@ -0,0 +1,258 @@
> > +#! /bin/bash
> > +# FS QA Test No. 709
> > +#
> > +# Make sure XFS can fix a v5 AGFL that wraps over the last block.
> > +# Refer to commit 96f859d52bcb ("libxfs: pack the agfl header structure so
> > +# XFS_AGFL_SIZE is correct") for details on the original on-disk format error
> > +# and the patch "xfs: detect agfl count corruption and reset agfl") for details
> > +# about the fix.
> > +#
> > +#-----------------------------------------------------------------------
> > +# Copyright (c) 2018 Oracle, Inc.
> > +#
> > +# 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"
> > +
> > +here=`pwd`
> > +tmp=/tmp/$$
> > +status=1
> > +trap "_cleanup; rm -f $tmp.*; exit \$status" 0 1 2 3 15
> > +
> > +_cleanup()
> > +{
> > +	cd /
> > +	rm -f $tmp.*
> > +}
> > +
> > +rm -f $seqres.full
> > +
> > +# get standard environment, filters and checks
> > +. ./common/rc
> > +. ./common/filter
> > +
> > +# real QA test starts here
> > +_supported_fs xfs
> > +_supported_os Linux
> > +
> > +_require_check_dmesg
> > +_require_scratch
> > +_require_test_program "punch-alternating"
> > +
> > +# This is only a v5 filesystem problem
> > +_require_scratch_xfs_crc
> > +
> > +mount_loop() {
> > +	if ! _try_scratch_mount >> $seqres.full 2>&1; then
> > +		echo "scratch mount failed" >> $seqres.full
> > +		return
> > +	fi
> > +
> > +	# Trigger agfl fixing by fragmenting free space enough to cause
> > +	# a bnobt split
> > +	blksz=$(_get_file_block_size ${SCRATCH_MNT})
> > +	bno_maxrecs=$(( blksz / 8 ))
> > +	filesz=$((bno_maxrecs * 3 * blksz))
> > +	rm -rf $SCRATCH_MNT/a
> > +	$XFS_IO_PROG -f -c "falloc 0 $filesz" $SCRATCH_MNT/a
> 
> And I noticed test failure with patch "xfs: detect agfl count corruption
> and reset agfl" applied on top of 4.16-rc5 kernel. Looks like we should
> dump xfs_io output to $seqres.full, as in v2 patch
> 
> dd if=/dev/zero of=$SCRATCH_MNT/a bs=8192k >> $seqres.full 2>&1

Yep.

In the bad_start case the fs checks every agfl and refuses to mount...
if your kernel has CONFIG_XFS_DEBUG=y.

> --- tests/xfs/709.out   2018-03-23 12:45:16.831011711 +0800
> +++ /root/workspace/xfstests/results//xfs_4k_crc/xfs/709.out.bad        2018-03-23 13:12:10.083980820 +0800
> @@ -7,6 +7,7 @@
>  TEST good_start
>  TEST good_wrap
>  TEST bad_start
> +fallocate: Structure needs cleaning
>  ASSERT flfirst < good_agfl_size - 1
>  ASSERT flfirst < fllast
>  TEST no_move
> 
> > +	test -e $SCRATCH_MNT/a && ./src/punch-alternating $SCRATCH_MNT/a
> > +	rm -rf $SCRATCH_MNT/a
> > +
> > +	_scratch_unmount 2>&1 | _filter_scratch
> > +}
> > +
> > +dump_ag0() {
> > +	_scratch_xfs_db -c 'sb 0' -c 'p' -c 'agf 0' -c 'p' -c 'agfl 0' -c 'p'
> > +}
> > +
> > +runtest() {
> > +	cmd="$1"
> > +
> > +	# Format filesystem
> > +	echo "TEST $cmd" | tee /dev/ttyprintk
> 
> What's the purpose of writing to /dev/ttyprintk? I don't see how it's
> used in the test.

It makes it easy to tell which kernel messages came from which runtest()
invocation so that we can tell if a particular agfl mutation test
actually triggered the fixup.

--D

> Thanks,
> Eryu
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