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

Qu Wenruo
2018-06-05T11:39:34Z

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On 2018年06月05日 18:42, Anand Jain wrote:
>
>
> On 06/01/2018 09:34 AM, 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>
>> ---
>>   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
>> +_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
>> +
>> +# Since now the compressed extent contains *UNCOMPRESSED* data,
>> reading it will
>> +# easily trigger a EIO error
>
>  This sentence is confusing. Are you referring to the bug?

Yes.

>  what is compressed extent containing uncompressed data?

The data extent has lzo compression flag.
While its on-disk data is in fact the uncompressed data.

With the test case, just check the on-disk data extent, you'll find
that's all 0xcd, other the lzo compressed data.

Thanks,
Qu

>
> Thanks, Anand
>
>> +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
>>
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