Date: Thu, 16 Jun 2016 13:29:52 -0400
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-nfs@vger.kernel.org
Subject: Re: odd sillyrename bug in 4.6 / 4.7-rc
Message-ID: <20160616172952.GA17604@fieldses.org>
References: <20160616150146.GA14015@infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <20160616150146.GA14015@infradead.org>
From: bfields@fieldses.org (J. Bruce Fields)
Sender: linux-nfs-owner@vger.kernel.org

On Thu, Jun 16, 2016 at 08:01:47AM -0700, Christoph Hellwig wrote:
> I've run into an odd bug when testing the clone / reflink functionality,
> and managed to isolate a testcase not relying on clones.  The issue is
> that after a lot of direct I/O hitting ENOSPC on a NFS mount I run
> into a silly rename that never gets cleaned up after cleaning up the
> directory.

I have a redhat bug for what sounds like the same behavior.  I spent
some time looking at it but I don't think I got anywere.

	https://bugzilla.redhat.com/show_bug.cgi?id=1132610

(But you probably can't see that right now; I'll see if I can open it.)

--b.

> 
> Note that so far I've only managed to reproduce it against a Linux
> server running XFS (ext4 and btrfs seem fine) despite looking like
> a client bug, and although once in a while a single run of the testcase
> cause the bug I usually need a few iterations.
> 
> All over it seems like some odd dentry refcount race where we see
> a spurious reference for one reason or another.
> 
> 
> Below is a patch to xfstests to add this reproducer:
> 
> 
> diff --git a/tests/generic/700 b/tests/generic/700
> new file mode 100755
> index 0000000..33505b0
> --- /dev/null
> +++ b/tests/generic/700
> @@ -0,0 +1,130 @@
> +#! /bin/bash
> +# FS QA Test No. 700
> +#
> +# Dumbed down Copy of the original version of generic/187 that reproduced
> +# NFS silly rename issues.
> +#-----------------------------------------------------------------------
> +# Copyright (c) 2015, Oracle and/or its affiliates.  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 -rf $tmp.* $testdir
> +}
> +
> +# get standard environment, filters and checks
> +. ./common/rc
> +. ./common/filter
> +
> +# real QA test starts here
> +_supported_os Linux
> +_require_xfs_io_command "falloc"
> +_require_xfs_io_command "fpunch"
> +test $FSTYP = "btrfs" && _notrun "Can't fragment free space on btrfs."
> +_require_odirect
> +
> +rm -f $seqres.full
> +
> +_fragment_freesp()
> +{
> +	file=$1
> +
> +	# consume nearly all available space (leave ~1MB)
> +	avail=`_get_available_space $SCRATCH_MNT`
> +	echo "$avail bytes left"
> +	filesize=$((avail - 1048576))
> +	$XFS_IO_PROG -fc "truncate $filesize" $file
> +
> +	chunks=20
> +	chunksizemb=$((filesize / chunks / 1048576))
> +	seq 1 $chunks | while read f; do
> +		echo "$((f * chunksizemb)) file size $f / 20"
> +		$XFS_IO_PROG -fc "falloc -k $(( (f - 1) * chunksizemb))m ${chunksizemb}m" $file
> +	done
> +
> +	chunks=100
> +	chunksizemb=$((filesize / chunks / 1048576))
> +	seq 80 $chunks | while read f; do
> +		echo "$((f * chunksizemb)) file size $f / $chunks"
> +		$XFS_IO_PROG -fc "falloc -k $(( (f - 1) * chunksizemb))m ${chunksizemb}m" $file
> +	done
> +
> +	filesizemb=$((filesize / 1048576))
> +	$XFS_IO_PROG -fc "falloc -k 0 ${filesizemb}m" $file
> +
> +	# Try again anyway
> +	avail=`_get_available_space $SCRATCH_MNT`
> +	$XFS_IO_PROG -fc "pwrite -S 0x65 0 $avail" ${file}.${i}
> +
> +	# Punch out whatever we need
> +	seq 1 $((nr * 4)) | while read f; do
> +		$XFS_IO_PROG -f -c "fpunch $((f * 2 * blksz)) $blksz" $file
> +	done
> +}
> +
> +echo "Format and mount"
> +_scratch_mkfs > $seqres.full 2>&1
> +_scratch_mount >> $seqres.full 2>&1
> +
> +testdir=$SCRATCH_MNT/test-$seq
> +mkdir $testdir
> +
> +echo "Create the original files"
> +blksz=65536
> +nr=1024
> +filesize=$((blksz * nr))
> +_pwrite_byte 0x61 0 $filesize $testdir/file1 >> $seqres.full
> +_pwrite_byte 0x62 0 $filesize $testdir/file2 >> $seqres.full
> +seq 0 2 $((nr-1)) | while read f; do
> +#	_reflink_range $testdir/file1 $((blksz * f)) $testdir/file3 $((blksz * f)) $blksz >> $seqres.full
> +	touch $testdir/file3
> +	_pwrite_byte 0x61 $((blksz * f)) $blksz $testdir/file3.chk >> $seqres.full
> +done
> +seq 1 2 $((nr-1)) | while read f; do
> +	touch $testdir/file3
> +#	_reflink_range $testdir/file2 $((blksz * f)) $testdir/file3 $((blksz * f)) $blksz >> $seqres.full
> +	_pwrite_byte 0x62 $((blksz * f)) $blksz $testdir/file3.chk >> $seqres.full
> +done
> +_scratch_cycle_mount
> +_fragment_freesp $testdir/bigfile >> $seqres.full 2>&1
> +filesize=$((blksz * nr))
> +_scratch_cycle_mount
> +
> +echo "Overwrite"
> +cowoff=$((filesize / 4))
> +cowsz=$((filesize / 2))
> +$XFS_IO_PROG -d -f -c "pwrite -S 0x63 -b $cowsz $cowoff $cowsz" $testdir/file3 >> $seqres.full
> +_pwrite_byte 0x63 $cowoff $cowsz $testdir/file3.chk >> $seqres.full
> +
> +# mount / unmount
> +_scratch_cycle_mount
> +
> +echo "Deleting"
> +rm -r $testdir
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/generic/700.out b/tests/generic/700.out
> new file mode 100644
> index 0000000..9f7ce0f
> --- /dev/null
> +++ b/tests/generic/700.out
> @@ -0,0 +1,5 @@
> +QA output created by 700
> +Format and mount
> +Create the original files
> +Overwrite
> +Deleting
> diff --git a/tests/generic/group b/tests/generic/group
> index 2bd40a1..46a796a 100644
> --- a/tests/generic/group
> +++ b/tests/generic/group
> @@ -354,6 +354,7 @@
>  349 blockdev quick rw
>  350 blockdev quick rw
>  351 blockdev quick rw
> +700 auto nfs
>  923 auto quick clone
>  924 auto quick clone
>  925 auto quick clone
> --
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