Re: [PATCH] Generic test for file fsync after moving files across directories

["Lukáš Czerner" <lczerner@redhat.com>]

On Thu, 26 Feb 2015, Filipe Manana wrote:

> Date: Thu, 26 Feb 2015 19:53:14 +0000
> From: Filipe Manana <fdmanana@suse.com>
> To: fstests@vger.kernel.org
> Cc: linux-btrfs@vger.kernel.org, Filipe Manana <fdmanana@suse.com>
> Subject: [PATCH] Generic test for file fsync after moving files across
>     directories
> 
> Test file fsync after moving one file between directories and fsyncing the
> old parent directory before fsyncing the file. Verify that after a crash the
> file data we fsynced is available.
> 
> This test is motivated by an issue discovered in btrfs which caused the file
> data to be lost (despite fsync returning success to user space). That btrfs
> bug is fixed by the following linux kernel patch:
> 
>    Btrfs: fix data loss in the fast fsync path

Hi,

some comments below.

> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>  tests/generic/067     | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/067.out |  11 +++++
>  tests/generic/group   |   1 +
>  3 files changed, 125 insertions(+)
>  create mode 100755 tests/generic/067
>  create mode 100644 tests/generic/067.out
> 
> diff --git a/tests/generic/067 b/tests/generic/067
> new file mode 100755
> index 0000000..90f26b2
> --- /dev/null
> +++ b/tests/generic/067
> @@ -0,0 +1,113 @@
> +#! /bin/bash
> +# FS QA Test No. 067
> +#
> +# Test file fsync after moving one file between directories and fsyncing the
> +# old parent directory before fsyncing the file. Verify that after a crash the
> +# file data we fsynced is available.
> +#
> +# This test is motivated by an issue discovered in btrfs which caused the file
> +# data to be lost (despite fsync returning success to user space). That btrfs
> +# bug was fixed by the following linux kernel patch:
> +#
> +#   Btrfs: fix data loss in the fast fsync path
> +#
> +#-----------------------------------------------------------------------
> +# Copyright (C) 2015 SUSE Linux Products GmbH. All Rights Reserved.
> +# Author: Filipe Manana <fdmanana@suse.com>
> +#
> +# 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!
> +
> +_cleanup()
> +{
> +	_cleanup_flakey
> +	rm -f $tmp.*
> +}
> +trap "_cleanup; exit \$status" 0 1 2 3 15
> +
> +# get standard environment, filters and checks
> +. ./common/rc
> +. ./common/filter
> +. ./common/dmflakey
> +
> +# real QA test starts here
> +_supported_fs generic
> +_supported_os Linux
> +_need_to_be_root
> +_require_scratch
> +_require_dm_flakey
> +_require_metadata_journaling $SCRATCH_DEV
> +
> +rm -f $seqres.full
> +
> +_scratch_mkfs >> $seqres.full 2>&1
> +_init_flakey
> +_mount_flakey
> +
> +# Create our main test file 'foo', the one we check for data loss.
> +# By doing an fsync against our file, it makes btrfs clear the 'needs_full_sync'
> +# bit from its flags (btrfs inode specific flags).


I am not sure we need that last sentence, it's btrfs specific and I am sure
it has been already explained in detail in the btrfs commit
description.


> +$XFS_IO_PROG -f -c "pwrite -S 0xaa 0 8K" \
> +		-c "fsync" $SCRATCH_MNT/foo | _filter_xfs_io
> +
> +# Now create one other file and 2 directories. We will move this second file
> +# from one directory to the other later because it forces btrfs to commit its
> +# currently open transaction if we fsync the old parent directory. This is
> +# necessary to trigger the data loss bug that affected btrfs.
> +mkdir $SCRATCH_MNT/testdir_1
> +touch $SCRATCH_MNT/testdir_1/bar
> +mkdir $SCRATCH_MNT/testdir_2
> +
> +# Make sure everything is durably persisted.
> +sync
> +
> +# Write more 8Kb of data to our file.
> +$XFS_IO_PROG -c "pwrite -S 0xbb 8K 8K" $SCRATCH_MNT/foo | _filter_xfs_io
> +
> +# Move our 'bar' file into a new directory.
> +mv $SCRATCH_MNT/testdir_1/bar $SCRATCH_MNT/testdir_2/bar
> +
> +# Fsync our first directory. Because it had a file moved into some other
> +# directory, this made btrfs commit the currently open transaction. This is
> +# a condition necessary to trigger the data loss bug.
> +$XFS_IO_PROG -c "fsync" $SCRATCH_MNT/testdir_1
> +
> +# Now fsync our main test file. If the fsync succeeds, we expect the 8Kb of
> +# data we wrote previously to be persisted and available if a crash happens.
> +# This did not happen with btrfs, because of the transaction commit that
> +# happened when we fsynced the parent directory.
> +$XFS_IO_PROG -c "fsync" $SCRATCH_MNT/foo

Ok, so from the description of the test I though that the data loss
will happen on the file we're moving, but apparently its about a
different unrelated file.

Otherwise the test looks fine.

Reviewed-by: Lukas Czerner <lczerner@redhat.com>

Thanks!
-Lukas

> +
> +# Simulate a crash/power loss.
> +_load_flakey_table $FLAKEY_DROP_WRITES
> +_unmount_flakey
> +
> +_load_flakey_table $FLAKEY_ALLOW_WRITES
> +_mount_flakey
> +
> +# Now check that all data we wrote before are available.
> +echo "File content after log replay:"
> +od -t x1 $SCRATCH_MNT/foo
> +
> +status=0
> +exit
> diff --git a/tests/generic/067.out b/tests/generic/067.out
> new file mode 100644
> index 0000000..f30f6ef
> --- /dev/null
> +++ b/tests/generic/067.out
> @@ -0,0 +1,11 @@
> +QA output created by 067
> +wrote 8192/8192 bytes at offset 0
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +wrote 8192/8192 bytes at offset 8192
> +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +File content after log replay:
> +0000000 aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa
> +*
> +0020000 bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> +*
> +0040000
> diff --git a/tests/generic/group b/tests/generic/group
> index e5db772..05cc6a9 100644
> --- a/tests/generic/group
> +++ b/tests/generic/group
> @@ -69,6 +69,7 @@
>  064 auto quick prealloc
>  065 metadata auto quick
>  066 metadata auto quick
> +067 metadata auto quick
>  068 other auto freeze dangerous stress
>  069 rw udf auto quick
>  070 attr udf auto quick stress
>