Re: [PATCH 2/2] xfs: test the deadlock between the AGI and AGF with RENAME_WHITEOUT

[kaixuxia <xiakaixu1987@gmail.com>]

On 2019/9/14 1:36, Brian Foster wrote:
> On Wed, Sep 11, 2019 at 09:17:08PM +0800, kaixuxia wrote:
>> There is ABBA deadlock bug between the AGI and AGF when performing
>> rename() with RENAME_WHITEOUT flag, and add this testcase to make
>> sure the rename() call works well.
>>
>> Signed-off-by: kaixuxia <kaixuxia@tencent.com>
>> ---
>>  tests/xfs/512     | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  tests/xfs/512.out |  2 ++
>>  tests/xfs/group   |  1 +
>>  3 files changed, 102 insertions(+)
>>  create mode 100755 tests/xfs/512
>>  create mode 100644 tests/xfs/512.out
>>
>> diff --git a/tests/xfs/512 b/tests/xfs/512
>> new file mode 100755
>> index 0000000..754f102
>> --- /dev/null
>> +++ b/tests/xfs/512
>> @@ -0,0 +1,99 @@
>> +#! /bin/bash
>> +# SPDX-License-Identifier: GPL-2.0
>> +# Copyright (c) 2019 Tencent.  All Rights Reserved.
>> +#
>> +# FS QA Test 512
>> +#
>> +# Test the ABBA deadlock case between the AGI and AGF When performing
>> +# rename operation with RENAME_WHITEOUT flag.
>> +#
>> +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
>> +. ./common/renameat2
>> +
>> +rm -f $seqres.full
>> +
>> +# real QA test starts here
>> +_supported_fs xfs
>> +_supported_os Linux
>> +_require_scratch_nocheck
> 
> Why _nocheck? AFAICT the filesystem shouldn't end up intentionally
> corrupted.

Will add the comment in the next version.
> 
>> +_requires_renameat2 whiteout
>> +
>> +prepare_file()
>> +{
>> +	# create many small files for the rename with RENAME_WHITEOUT
>> +	i=0
>> +	while [ $i -le $files ]; do
>> +		file=$SCRATCH_MNT/f$i
>> +		echo > $file >/dev/null 2>&1
>> +		let i=$i+1
>> +	done
> 
> Something like the following is a bit more simple, IMO:
> 
> 	for i in $(seq 1 $files); do
> 		touch $SCRATCH_MNT/f.$i
> 	done
> 
> The same goes for the other while loops below that increment up to
> $files.
> 
>> +}
>> +
>> +rename_whiteout()
>> +{
>> +	# create the rename targetdir
>> +	renamedir=$SCRATCH_MNT/renamedir
>> +	mkdir $renamedir
>> +
>> +	# a long filename could increase the possibility that target_dp
>> +	# allocate new blocks(acquire the AGF lock) to store the filename
>> +	longnamepre=FFFsafdsagafsadfagasdjfalskdgakdlsglkasdg
>> +
> 
> The max filename length is 256 bytes. You could do something like the
> following to increase name length (leaving room for the file index and
> terminating NULL) if it helps the test:
> 
> 	prefix=`for i in $(seq 0 245); do echo -n a; done`
> 
>> +	# now try to do rename with RENAME_WHITEOUT flag
>> +	i=0
>> +	while [ $i -le $files ]; do
>> +		src/renameat2 -w $SCRATCH_MNT/f$i $renamedir/$longnamepre$i >/dev/null 2>&1
>> +		let i=$i+1
>> +	done
>> +}
>> +
>> +create_file()
>> +{
>> +	# create the targetdir
>> +	createdir=$SCRATCH_MNT/createdir
>> +	mkdir $createdir
>> +
>> +	# try to create file at the same time to hit the deadlock
>> +	i=0
>> +	while [ $i -le $files ]; do
>> +		file=$createdir/f$i
>> +		echo > $file >/dev/null 2>&1
>> +		let i=$i+1
>> +	done
>> +}
> 
> You could generalize this function to take a target directory parameter
> and just call it twice (once to prepare and again for the create
> workload).

Right.
> 
>> +
>> +_scratch_mkfs_xfs -bsize=1024 -dagcount=1 >> $seqres.full 2>&1 ||
>> +	_fail "mkfs failed"
> 
> Why -bsize=1k? Does that make the reproducer more effective?
> 
The smaller block size, the more frequently that the blocks are allocated
when creating files...
>> +_scratch_mount
>> +
>> +files=250000
>> +
> 
> Have you tested effectiveness of reproducing the issue with smaller file
> counts? A brief comment here to document where the value comes from
> might be useful. Somewhat related, how long does this test take on fixed
> kernels?

Hmm, 250000 is just a random number big enough for this test. The smaller
file counts maybe is enough. Actually, the create_file() call run fast
than the rename_whiteout() call, so we can choose two different file
counts for them. Anyway, I would address the file counts problem in V3...
> 
>> +prepare_file
>> +rename_whiteout &
>> +create_file &
>> +
>> +wait
>> +echo Silence is golden
>> +
>> +# Failure comes in the form of a deadlock.
>> +
> 
> I wonder if this should be in the dangerous group as well. I go back and
> forth on that though because I tend to filter out dangerous tests and
> the test won't be so risky once the fix proliferates. Perhaps that's
> just a matter of removing it from the dangerous group after a long
> enough period of time.
> 
> Brian
> 
>> +# success, all done
>> +status=0
>> +exit
>> diff --git a/tests/xfs/512.out b/tests/xfs/512.out
>> new file mode 100644
>> index 0000000..0aabdef
>> --- /dev/null
>> +++ b/tests/xfs/512.out
>> @@ -0,0 +1,2 @@
>> +QA output created by 512
>> +Silence is golden
>> diff --git a/tests/xfs/group b/tests/xfs/group
>> index a7ad300..ed250d6 100644
>> --- a/tests/xfs/group
>> +++ b/tests/xfs/group
>> @@ -509,3 +509,4 @@
>>  509 auto ioctl
>>  510 auto ioctl quick
>>  511 auto quick quota
>> +512 auto rename
>> -- 
>> 1.8.3.1
>>
>> -- 
>> kaixuxia

-- 
kaixuxia