On Mon, Jan 14, 2019 at 05:30:36PM +0800, Eryu Guan wrote: > On Fri, Jan 11, 2019 at 08:31:24AM -0500, Brian Foster wrote: > > XFS has a bug where page writeback can end up sending data to the > > wrong location due to a stale, cached file mapping. Add a test to > > trigger this problem by racing background writeback with a > > truncate/rewrite of the final page of the file. > > > > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx> > > --- > > > > Hi all, > > > > This is a resend of an old post[1] that never quite made it upstream. It > > wasn't a big deal at the time because we didn't really have a proper fix > > for the problem. I'm resending now because there is a proposed fix[2]. > > Thanks for the resending! > > > > > I've verified that this still reproduces the problem and no longer fails > > with the fix applied (in hundreds of iters). Note that reproduction may > > require many iterations. It took me anywhere from 5 to 30 or so on the > > box I tested, which I think is reasonable for the tradeoff of a fairly > > quick test. There was some discussion on the original post around making > > the test run longer for a more reliable reproducer, but I'm not sure how > > valuable that is given this is a targeted regression test. Thoughts > > appreciated. > > It took me around 5 iterations to hit the corruption, I think it's fine. > > But a couple of things changed over the years :) > Indeed, these changes all sound good. I'll include them in v2, thanks! Brian > > > > Brian > > > > [1] https://marc.info/?l=fstests&m=150902929900510&w=2 > > [2] https://marc.info/?l=linux-xfs&m=154721212321112&w=2 > > > > tests/generic/999 | 94 +++++++++++++++++++++++++++++++++++++++++++ > > tests/generic/999.out | 2 + > > tests/generic/group | 1 + > > 3 files changed, 97 insertions(+) > > create mode 100755 tests/generic/999 > > create mode 100644 tests/generic/999.out > > > > diff --git a/tests/generic/999 b/tests/generic/999 > > new file mode 100755 > > index 00000000..9e56a1e0 > > --- /dev/null > > +++ b/tests/generic/999 > > @@ -0,0 +1,94 @@ > > +#! /bin/bash > > +# FS QA Test 999 > > +# > > +# Test XFS page writeback code for races with the cached file mapping. XFS > > +# caches the file -> block mapping for a full extent once it is initially looked > > +# up. The cached mapping is used for all subsequent pages in the same writeback > > +# cycle that cover the associated extent. Under certain conditions, it is > > +# possible for concurrent operations on the file to invalidate the cached > > +# mapping without the knowledge of writeback. Writeback ends up sending I/O to a > > +# partly stale mapping and potentially leaving delalloc blocks in the current > > +# mapping unconverted. > > +# > > +#----------------------------------------------------------------------- > > +# Copyright (c) 2017 Red Hat, Inc. All Rights Reserved. > ^^^^ 2019? > > +# > > +# 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 > > +#----------------------------------------------------------------------- > > And please change this to SPDX-License-Identifier. > > > +# > > + > > +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 > > + > > +# remove previous $seqres.full before test > > +rm -f $seqres.full > > + > > +# real QA test starts here > > + > > +# Modify as appropriate. > > +_supported_fs generic > > +_supported_os Linux > > +_require_scratch > > +_require_test_program "feature" > > _require_xfs_io_command "sync_range" > > > + > > +_scratch_mkfs >> $seqres.full 2>&1 || _fail "mkfs failed" > > +_scratch_mount || _fail "mount failed" > > _scratch_mount will _fail the test on failure now :) > > > + > > +file=$SCRATCH_MNT/file > > +filesize=$((1024 * 1024 * 32)) > > +pagesize=`src/feature -s` > > +truncsize=$((filesize - pagesize)) > > + > > +for i in $(seq 0 15); do > > + # Truncate the file and fsync to persist the final size on-disk. This is > > + # required so the subsequent truncate will not wait on writeback. > > + $XFS_IO_PROG -fc "truncate 0" $file > > + $XFS_IO_PROG -c "truncate $filesize" -c fsync $file > > + > > + # create a small enough delalloc extent to likely be contiguous > > + $XFS_IO_PROG -c "pwrite 0 $filesize" $file >> $seqres.full 2>&1 > > + > > + # Start writeback and a racing truncate and rewrite of the final page. > > + $XFS_IO_PROG -c "sync_range -w 0 0" $file & > > + sync_pid=$! > > + $XFS_IO_PROG -c "truncate $truncsize" \ > > + -c "pwrite $truncsize $pagesize" $file >> $seqres.full 2>&1 > > + > > + # If the test fails, the most likely outcome is an sb_fdblocks mismatch > > + # and/or an associated delalloc assert failure on inode reclaim. Cycle > > + # the mount to trigger detection. > > + wait $sync_pid > > + _scratch_cycle_mount || _fail "mount failed" > > And _scratch_cycle_mount will exit the test on failure as well. > > Thanks, > Eryu > > > +done > > + > > +echo Silence is golden > > + > > +# success, all done > > +status=0 > > +exit > > diff --git a/tests/generic/999.out b/tests/generic/999.out > > new file mode 100644 > > index 00000000..3b276ca8 > > --- /dev/null > > +++ b/tests/generic/999.out > > @@ -0,0 +1,2 @@ > > +QA output created by 999 > > +Silence is golden > > diff --git a/tests/generic/group b/tests/generic/group > > index ea5aa7aa..ce165981 100644 > > --- a/tests/generic/group > > +++ b/tests/generic/group > > @@ -525,3 +525,4 @@ > > 520 auto quick log > > 521 soak long_rw > > 522 soak long_rw > > +999 auto quick > > -- > > 2.17.2 > >
