Discussion:
[PATCH] fstests: btrfs, add regression test for clone ioctl
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Filipe Manana
2014-10-21 20:43:11 UTC
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Regression test for a btrfs clone ioctl issue where races between
a clone operation and concurrent target file reads would result in
leaving stale data in the page cache. After the clone operation
finished, reading from the clone target file would return the old
and no longer valid data. This affected only buffered reads (i.e.
didn't affect direct IO reads).

This issue was fixed by the following linux kernel patch:

Btrfs: ensure readers see new data after a clone operation
(commit c125b8bff1d9f6c8c91ce4eb8bd5616058c7d510)

Signed-off-by: Filipe Manana <***@suse.com>
---
tests/btrfs/081 | 131 ++++++++++++++++++++++++++++++++++++++++++++++++++++
tests/btrfs/081.out | 4 ++
tests/btrfs/group | 1 +
3 files changed, 136 insertions(+)
create mode 100755 tests/btrfs/081
create mode 100644 tests/btrfs/081.out

diff --git a/tests/btrfs/081 b/tests/btrfs/081
new file mode 100755
index 0000000..d2e3767
--- /dev/null
+++ b/tests/btrfs/081
@@ -0,0 +1,131 @@
+#! /bin/bash
+# FSQA Test No. 081
+#
+# Regression test for a btrfs clone ioctl issue where races between
+# a clone operation and concurrent target file reads would result in
+# leaving stale data in the page cache. After the clone operation
+# finished, reading from the clone target file would return the old
+# and no longer valid data. This affected only buffered reads (i.e.
+# didn't affect direct IO reads).
+#
+# This issue was fixed by the following linux kernel patch:
+#
+# Btrfs: ensure readers see new data after a clone operation
+# (commit c125b8bff1d9f6c8c91ce4eb8bd5616058c7d510)
+#
+#-----------------------------------------------------------------------
+#
+# Copyright (C) 2014 SUSE Linux Products GmbH. All Rights Reserved.
+# Author: Filipe Manana <***@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"
+tmp=/tmp/$$
+status=1 # failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+ rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# real QA test starts here
+_need_to_be_root
+_supported_fs btrfs
+_supported_os Linux
+_require_scratch
+_require_btrfs_cloner
+
+rm -f $seqres.full
+
+num_extents=100
+extent_size=8192
+
+create_source_file()
+{
+ name=$1
+
+ # Create a file with $num_extents extents, each with a size of
+ # $extent_size bytes.
+ touch $SCRATCH_MNT/$name
+ for ((i = 0; i < $num_extents; i++)); do
+ off=$((i * $extent_size))
+ run_check $XFS_IO_PROG \
+ -c "pwrite -S $i -b $extent_size $off $extent_size" \
+ -c "fsync" $SCRATCH_MNT/$name
+ done
+}
+
+create_target_file()
+{
+ name=$1
+ file_size=$(($num_extents * $extent_size))
+
+ run_check $XFS_IO_PROG -f -c "pwrite -S 0xff 0 $file_size" \
+ -c "fsync" $SCRATCH_MNT/$name
+}
+
+reader_loop()
+{
+ name=$1
+
+ while true; do
+ cat $SCRATCH_MNT/$name > /dev/null
+ done
+}
+
+_scratch_mkfs >>$seqres.full 2>&1
+_scratch_mount
+
+create_source_file "foo"
+create_target_file "bar"
+
+reader_loop "bar" &
+reader_pid=$!
+
+$CLONER_PROG -s 0 -d 0 -l $(($num_extents * $extent_size)) \
+ $SCRATCH_MNT/foo $SCRATCH_MNT/bar
+
+kill $reader_pid > /dev/null 2>&1
+
+# Now both foo and bar should have exactly the same content.
+# This didn't use to be the case before the btrfs kernel fix mentioned
+# above. The clone ioctl was racy, as it removed bar's pages from the
+# page cache and only after it would update bar's metadata to point to
+# the same extents that foo's metadata points to - and this was done in
+# an unprotected way, so that a file read request done right after the
+# clone ioctl removed the pages from the page cache and before it updated
+# bar's metadata, would result in populating the page cache with stale
+# data. Therefore a file read after the clone operation finished would
+# not get the cloned data but it would get instead the old and no longer
+# valid data.
+md5sum $SCRATCH_MNT/foo | _filter_scratch
+md5sum $SCRATCH_MNT/bar | _filter_scratch
+
+# Validate the content of bar still matches foo's content even after
+# clearing all of bar's data from the page cache.
+_scratch_remount
+md5sum $SCRATCH_MNT/bar | _filter_scratch
+
+status=0
+exit
diff --git a/tests/btrfs/081.out b/tests/btrfs/081.out
new file mode 100644
index 0000000..3c7c3d2
--- /dev/null
+++ b/tests/btrfs/081.out
@@ -0,0 +1,4 @@
+QA output created by 081
+14968c092c68e32fa35e776392d14523 SCRATCH_MNT/foo
+14968c092c68e32fa35e776392d14523 SCRATCH_MNT/bar
+14968c092c68e32fa35e776392d14523 SCRATCH_MNT/bar
diff --git a/tests/btrfs/group b/tests/btrfs/group
index 801fc73..fc60c63 100644
--- a/tests/btrfs/group
+++ b/tests/btrfs/group
@@ -82,3 +82,4 @@
077 auto quick
078 auto
080 auto
+081 auto quick
--
1.9.1

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