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

[Brian Foster <bfoster@redhat.com>]

On Sun, Sep 15, 2019 at 11:34:35AM +0800, Eryu Guan wrote:
> On Fri, Sep 13, 2019 at 01:36:24PM -0400, 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.
> 
> There was a comment in v1, but not in this v2, we should keep that
> comment.
> 
> > 
> > > +_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.
> 
> Agreed, but looks like echo (which is a bash builtin) is faster than
> touch (which requires forking new process every loop).
> 

Ah, interesting. I suppose that makes sense if there's tangible benefit.
Would that benefit stand if we created an internal _touch helper or some
such instead of open-coding it everywhere?

> > 
> > > +}
> > > +
> > > +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 $(seq 0 245); do echo -n a; done`
> 
> Or
> 
> 	prefix=`$PERL_PROG -e 'print "a"x256;'`
> 
> ? Which seems a bit simpler to me.
> 
> > 
> > > +	# 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).
> > 
> > > +
> > > +_scratch_mkfs_xfs -bsize=1024 -dagcount=1 >> $seqres.full 2>&1 ||
> > > +	_fail "mkfs failed"
> > 
> > Why -bsize=1k? Does that make the reproducer more effective?
> > 
> > > +_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?
> > 
> > > +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.
> 
> The deadlock has been fixed, so I think it's fine to leave dangerous
> group.
> 

Do you mean to leave it in or out?

In general, what's the approach for dealing with dangerous tests that
are no longer dangerous? Leave them indefinitely or remove them after a
period of time? I tend to skip dangerous tests on regression runs just
because I'm not looking for a deadlock or crash to disrupt a long
running test.

Brian

> > 
> > Brian
> 
> Thanks a lot for the review!
> 
> Eryu
> 
> > 
> > > +# 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