Re: [PATCH] fstests: btrfs: Test if btrfs will corrupt nodatasum compressed extent when replacing device

Eryu Guan
2018-06-07T06:21:29Z

On Fri, Jun 01, 2018 at 09:34:48AM +0800, Qu Wenruo wrote:
> This is a long existing bug (from 2012) but exposed by a reporter
> recently, that when compressed extent without data csum get written to
> device-replace target device, the written data is in fact uncompressed data
> other than the original compressed data.
>
> And since btrfs still consider the data is compressed and will try to read it
> as compressed, it can cause read error.
>
> The root cause is located, and one RFC patch already sent to fix it,
> titled "[PATCH RFC] btrfs: scrub: Don't use inode pages for device replace".
> (The RFC is only for the extra possible way to fix the bug, the fix
> itself should work without problem)
>
> Reported-by: James Harvey <jamespharvey20@gmail.com>
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Looks fine to me overall, some minor issues inline. But I'd really like
an explicit ACK from btrfs folks.

> ---
> tests/btrfs/161 | 91 +++++++++++++++++++++++++++++++++++++++++++++
> tests/btrfs/161.out | 2 +
> tests/btrfs/group | 1 +
> 3 files changed, 94 insertions(+)
> create mode 100755 tests/btrfs/161
> create mode 100644 tests/btrfs/161.out
>
> diff --git a/tests/btrfs/161 b/tests/btrfs/161
> new file mode 100755
> index 00000000..d4a2b474
> --- /dev/null
> +++ b/tests/btrfs/161
> @@ -0,0 +1,91 @@
> +#! /bin/bash
> +# FS QA Test 161
> +#
> +# Test if btrfs will corrupt compressed data extent without data csum
> +# by replacing it with uncompressed data, when doing replacing device.
> +#
> +# This could be fixed by the following RFC patch:
> +# "[PATCH RFC] btrfs: scrub: Don't use inode pages for device replace"
> +#
> +#-----------------------------------------------------------------------
> +# Copyright (C) 2018 SUSE Linux Products GmbH. All Rights Reserved.
> +#
> +# 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 # 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
> +
> +# Modify as appropriate.
> +_supported_fs btrfs
> +_supported_os Linux
> +_require_test

This is not needed, there's no point running fsck on $TEST_DEV after
test when it's not used at all.

> +_require_scratch_dev_pool 2
> +_require_scratch_dev_pool_equal_size
> +
> +
> +_scratch_dev_pool_get 1
> +_spare_dev_get
> +_scratch_pool_mkfs >> $seqres.full 2>&1
> +
> +# Create nodatasum inode
> +_scratch_mount "-o nodatasum"
> +touch $SCRATCH_MNT/nodatasum_file
> +_scratch_remount "datasum,compress"
> +_pwrite_byte 0xcd 0 128K $SCRATCH_MNT/nodatasum_file > /dev/null
> +
> +# Write the compressed data back to disk
> +sync
> +
> +# Replace the device
> +_run_btrfs_util_prog replace start -Bf 1 $SPARE_DEV $SCRATCH_MNT
> +
> +_scratch_unmount
> +
> +_mount $SPARE_DEV $SCRATCH_MNT

Better to explain the cycle mount with comments.

> +
> +# Since now the compressed extent contains *UNCOMPRESSED* data, reading it will
> +# easily trigger a EIO error
> +cat $SCRATCH_MNT/nodatasum_file > /dev/null
> +
> +_scratch_unmount
> +_spare_dev_put
> +_scratch_dev_pool_put
> +
> +echo "Silence is golden"
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/btrfs/161.out b/tests/btrfs/161.out
> new file mode 100644
> index 00000000..1752a243
> --- /dev/null
> +++ b/tests/btrfs/161.out
> @@ -0,0 +1,2 @@
> +QA output created by 161
> +Silence is golden
> diff --git a/tests/btrfs/group b/tests/btrfs/group
> index f04ee8d5..f900b3d0 100644
> --- a/tests/btrfs/group
> +++ b/tests/btrfs/group
> @@ -163,3 +163,4 @@
> 158 auto quick raid scrub
> 159 auto quick
> 160 auto quick
> +161 auto quick replace

Anand introduced a new 'volume' group in commit 144c8463d38b ("btrfs:
introduce btrfs/volume group"), all 'replace' tests should be in
'volume' group now.

Thanks,
Eryu

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> 2.17.0
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