Re: [PATCH] generic/033: add xfs delalloc indirect block depletion reproducer

[Brian Foster <bfoster@redhat.com>]

On Thu, Sep 25, 2014 at 11:54:16AM +0800, Eryu Guan wrote:
> On Wed, Sep 24, 2014 at 02:47:05PM -0400, Brian Foster wrote:
> > XFS allocates extra indirect blocks for delayed allocation extents at
> > write time. When delalloc extents are split, the existing indirect block
> > reservation was historically divided up evenly among the new extents
> > even though the overall requirement for two extents could exceed the
> > requirement for the original. Repeated delalloc extent splits ultimately
> > leads to extents with 0 indirect blocks and in turn leads to assert
> > failures in XFS.
> > 
> > Add a test to stress indirect block reservation for delayed allocation
> > extents. The test converts a single delalloc extent to many and operates
> > on the remaining extents to detect or trigger potential problems.
> > 
> > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > ---
> > 
> > Here's a simple reproducer for the indirect block reservation problem
> > called out here:
> > 
> > http://oss.sgi.com/archives/xfs/2014-09/msg00337.html
> > 
> > It reproduces the assert failures described therein:
> > 
> > XFS: Assertion failed: startblockval(del.br_startblock) > 0, file: fs/xfs/libxfs/xfs_bmap.c, line: 5281
> > 
> > Note that this test also unintentionally fails on XFS. The test file
> > ends up zero-sized after the remount and thus hexdump doesn't produce
> > any output. This doesn't occur on ext4, I suspect due to the fact that
> > the range being zeroed is flushed beforehand, though I could be wrong
> > about that.
> 
> Tested with ext4 and xfs, and ext4 passes/xfs fails the test as
> described here.
> 
> Reviewed-by: Eryu Guan <eguan@redhat.com>
> 
> With one nitpick below..
> 
> > 
> > In any event, this calls out a separate bug in XFS where if appending
> > data is chucked from cache by zero range before written back (eof is
> > page aligned), we lose the on-disk inode size update and the inode size
> > changes unexpectedly across the remount (assuming nothing else changes
> > the size, of course).
> > 
> > Brian
> > 
> >  tests/generic/033     | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++
> >  tests/generic/033.out |  4 +++
> >  tests/generic/group   |  1 +
> >  3 files changed, 93 insertions(+)
> >  create mode 100755 tests/generic/033
> >  create mode 100644 tests/generic/033.out
> > 
> > diff --git a/tests/generic/033 b/tests/generic/033
> > new file mode 100755
> > index 0000000..41198b7
> > --- /dev/null
> > +++ b/tests/generic/033
> > @@ -0,0 +1,88 @@
> > +#! /bin/bash
> > +# FS QA Test No. 033
> > +#
> > +# This test stresses indirect block reservation for delayed allocation extents.
> > +# XFS reserves extra blocks for deferred allocation of delalloc extents. These
> > +# reserved blocks can be divided among more extents than anticipated if the
> > +# original extent for which the blocks were reserved is split into multiple
> > +# delalloc extents. If this scenario repeats, eventually some extents are left
> > +# without any indirect block reservation whatsoever. This leads to assert
> > +# failures and possibly other problems in XFS.
> > +#
> > +#-----------------------------------------------------------------------
> > +# Copyright (c) 2014 Red Hat, Inc.  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
> > +
> > +# real QA test starts here
> > +rm -f $seqres.full
> > +
> > +# Modify as appropriate.
> > +_supported_fs generic
> > +_supported_os Linux
> > +_require_scratch
> > +_require_xfs_io_command "fzero"
> > +
> > +_scratch_mkfs >/dev/null 2>&1
> > +_scratch_mount
> > +
> > +file=$SCRATCH_MNT/file.$seq
> > +bytes=$((64 * 1024))
> > +
> > +# create sequential delayed allocation
> > +$XFS_IO_PROG -f -c "pwrite 0 $bytes" $file | _filter_xfs_io \
> > +	>> $seqres.full 2>&1
> 
> The output of xfs_io is redirected to $seqres.full, so it's not
> necessary to be filtered, for debug purpose.
> 
> And the following two xfs_io calls.
> 

Indeed, I'll post v2. Thanks for the review.

Brian

> Thanks,
> Eryu
> 
> > +
> > +# Zero every other 4k range to split the larger delalloc extent into many more
> > +# smaller extents. Use zero instead of hole punch because the former does not
> > +# force writeback (and hence delalloc conversion). It can simply discard
> > +# delalloc blocks and convert the ranges to unwritten.
> > +endoff=$((bytes - 4096))
> > +for i in $(seq 0 8192 $endoff); do
> > +	$XFS_IO_PROG -c "fzero -k $i 4k" $file | _filter_xfs_io \
> > +		>> $seqres.full 2>&1
> > +done
> > +
> > +# now zero the opposite set to remove remaining delalloc extents
> > +for i in $(seq 4096 8192 $endoff); do
> > +	$XFS_IO_PROG -c "fzero -k $i 4k" $file | _filter_xfs_io	\
> > +		>> $seqres.full 2>&1
> > +done
> > +
> > +_scratch_remount
> > +hexdump $file
> > +
> > +status=0
> > +exit
> > diff --git a/tests/generic/033.out b/tests/generic/033.out
> > new file mode 100644
> > index 0000000..419d831
> > --- /dev/null
> > +++ b/tests/generic/033.out
> > @@ -0,0 +1,4 @@
> > +QA output created by 033
> > +0000000 0000 0000 0000 0000 0000 0000 0000 0000
> > +*
> > +0010000
> > diff --git a/tests/generic/group b/tests/generic/group
> > index 8e0c22a..1227408 100644
> > --- a/tests/generic/group
> > +++ b/tests/generic/group
> > @@ -32,6 +32,7 @@
> >  027 auto enospc
> >  028 auto quick
> >  032 auto quick rw
> > +033 auto quick rw
> >  053 acl repair auto quick
> >  062 attr udf auto quick
> >  068 other auto freeze dangerous stress
> > -- 
> > 1.8.3.1
> > 
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