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#! /bin/bash
# SPDX-License-Identifier: GPL-2.0
# Copyright (C) 2014 SUSE Linux Products GmbH. All Rights Reserved.
#
# 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# and no longer valid data.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)
#
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
_supported_fs btrfs
_supported_os Linux
_require_scratch
_require_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))
$XFS_IO_PROG \
-c "pwrite -S $i -b $extent_size $off $extent_size" \
-c "fsync" $SCRATCH_MNT/$name | _filter_xfs_io
done
}
create_target_file()
{
name=$1
file_size=$(($num_extents * $extent_size))
$XFS_IO_PROG -f -c "pwrite -S 0xff 0 $file_size" \
-c "fsync" $SCRATCH_MNT/$name | _filter_xfs_io
}
reader_loop()
{
name=$1
while true; do
cat $SCRATCH_MNT/$name > /dev/null
done
}
_scratch_mkfs >>$seqres.full 2>&1
_scratch_mount
echo "Creating source file..."
create_source_file "foo"
echo "Creating target file..."
create_target_file "bar"
reader_loop "bar" &
reader_pid=$!
$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.
echo "Verifying file digests after cloning"
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_cycle_mount
echo "Verifying target file digest after umount + mount"
md5sum $SCRATCH_MNT/bar | _filter_scratch
status=0
exit
|
