[PATCH v2] generic/032: add xfs unwritten extent data corruption reproducer

Brian Foster
2014-09-22T19:40:40Z

XFS had a data corruption problem where writeback of pages to unwritten
extents would fail to run unwritten extent conversion at I/O completion.
This causes subsequent reads of written, but unconverted regions to
return zeroes. This occurs on sub-page block size filesystems when
writeback contends for the inode lock (e.g., with a file writer).

Add a test that creates the conditions to reproduce the data corruption
and detect it by looking for unwritten extents after all said extents
have been overwritten.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---

v2:
- Converted to generic test.
- Use fiemap instead of xfs_bmap.
- Added to rw group.
- Various fixups: init/clean $tmp, loop syntax, redirect output to
$seqres.full, use _scratch_remount.
v1: http://oss.sgi.com/archives/xfs/2014-09/msg00296.html

tests/generic/032 | 119 ++++++++++++++++++++++++++++++++++++++++++++++++++
tests/generic/032.out | 5 +++
tests/generic/group | 1 +
3 files changed, 125 insertions(+)
create mode 100755 tests/generic/032
create mode 100644 tests/generic/032.out

diff --git a/tests/generic/032 b/tests/generic/032
new file mode 100755
index 0000000..deaeba8
--- /dev/null
+++ b/tests/generic/032
@@ -0,0 +1,119 @@
+#! /bin/bash
+# FS QA Test No. 032
+#
+# This test implements a data corruption scenario on XFS filesystems with
+# sub-page sized blocks and unwritten extents. Inode lock contention during
+# writeback of pages to unwritten extents leads to failure to convert those
+# extents on I/O completion. This causes data corruption as unwritten extents
+# are always read back as zeroes.
+#
+#-----------------------------------------------------------------------
+# 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 /
+ kill -9 $syncpid > /dev/null 2>&1
+ wait
+ rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/punch
+
+# real QA test starts here
+rm -f $seqres.full
+
+_syncloop()
+{
+ while [ true ]; do
+ sync
+ done
+}
+
+# Modify as appropriate.
+_supported_fs generic
+_supported_os Linux
+_require_scratch
+_require_xfs_io_command "falloc"
+_require_xfs_io_command "fiemap"
+
+_scratch_mkfs >/dev/null 2>&1
+_scratch_mount
+
+# run background sync thread
+_syncloop &
+syncpid=$!
+
+for iters in $(seq 1 100)
+do
+ rm -f $SCRATCH_MNT/file
+
+ # create a delalloc block in each page of the first 64k of the file
+ for pgoff in $(seq 0 0x1000 0xf000); do
+ offset=$((pgoff + 0xc00))
+ $XFS_IO_PROG -f \
+ -c "pwrite $offset 0x1" \
+ $SCRATCH_MNT/file >> $seqres.full 2>&1
+ done
+
+ # preallocate the first 64k and overwite, writing past 64k to contend
+ # with writeback
+ $XFS_IO_PROG \
+ -c "falloc 0 0x10000" \
+ -c "pwrite 0 0x100000" \
+ -c "fsync" \
+ $SCRATCH_MNT/file >> $seqres.full 2>&1
+
+ # Check for unwritten extents. We should have none since we wrote over
+ # the entire preallocated region and ran fsync.
+ $XFS_IO_PROG \
+ -c "fiemap -v" \
+ $SCRATCH_MNT/file | _filter_fiemap | \
+ grep unwritten >> $seqres.full 2>&1
+ if [ $? == 0 ]; then
+ # data corruption! dump the extent list and break out to dump
+ # the file content
+ $XFS_IO_PROG -c "fiemap -v" $SCRATCH_MNT/file
+ break
+ fi
+done
+
+echo $iters iterations
+
+kill $syncpid
+wait
+
+# clear page cache and dump the file
+_scratch_remount
+hexdump $SCRATCH_MNT/file
+
+_scratch_unmount
+
+status=0
+exit
diff --git a/tests/generic/032.out b/tests/generic/032.out
new file mode 100644
index 0000000..ca5376d
--- /dev/null
+++ b/tests/generic/032.out
@@ -0,0 +1,5 @@
+QA output created by 032
+100 iterations
+0000000 cdcd cdcd cdcd cdcd cdcd cdcd cdcd cdcd
+*
+0100000
diff --git a/tests/generic/group b/tests/generic/group
index bdcfd9d..8e0c22a 100644
--- a/tests/generic/group
+++ b/tests/generic/group
@@ -31,6 +31,7 @@
026 acl quick auto
027 auto enospc
028 auto quick
+032 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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