Re: [PATCH 2/2] dax: add regression test for stale mmap reads

Eryu Guan
2017-04-26T03:42:25Z

On Tue, Apr 25, 2017 at 02:39:11PM -0600, Ross Zwisler wrote:
> On Tue, Apr 25, 2017 at 07:27:39PM +0800, Eryu Guan wrote:
> > On Mon, Apr 24, 2017 at 11:49:32AM -0600, Ross Zwisler wrote:
> > > This adds a regression test for the following kernel patch:
> > >
> > > dax: fix data corruption due to stale mmap reads
> > >
> >
> > Seems that this patch hasn't been merged into linus tree, thus 4.11-rc8
> > kernel should fail this test, but it passed for me, tested with 4.11-rc8
> > kernel on both ext4 and xfs, with both brd devices and pmem devices
> > created from "memmap=10G!5G memmap=15G!15G" kernel boot command line.
> > Did I miss anything?
> >
> > # ./check -s ext4_pmem_4k generic/427
> > SECTION -- ext4_pmem_4k
>
> Ooh, I didn't add this 'ext4_pmem_4k' section goodness, and it's not present
> in the xfstests/master that I was using. Do you have patches to add that?

That's one of my config sections, it's all user-defined, not committed
to fstests repo :)

You can take a look at README.config-sections for more details. Here is
my local.config file for your reference

[default]
TEST_DEV=/dev/pmem0
SCRATCH_DEV=/dev/pmem1
TEST_DIR=/mnt
SCRATCH_MNT=/scratch

RECREATE_TEST_DEV=true

[xfs_pmem_4k]
FSTYP=xfs
MKFS_OPTIONS="-f -m crc=1 -b size=4k"

[ext4_pmem_4k]
FSTYP=ext4
MKFS_OPTIONS="-b 4096"

>
> > RECREATING -- ext4 on /dev/pmem0
> > FSTYP -- ext4
> > PLATFORM -- Linux/x86_64 hp-dl360g9-15 4.11.0-rc8.kasan
> > MKFS_OPTIONS -- -b 4096 /dev/pmem1
> > MOUNT_OPTIONS -- -o acl,user_xattr -o context=system_u:object_r:root_t:s0 /dev/pmem1 /scratch
> >
> > generic/427 1s ... 1s
> > Ran: generic/427
> > Passed all 1 tests
>
> Your memmap params look fine. I tested with BRD and PMEM, and with EXT4 and
> XFS, and all combinations failed for me as expected with v4.11-rc8.
>
> One issue could have been that the test file already existed when the test was
> run. I wasn't removing it between runs earlier, but I've fixed that for v2.
>
> Another issue I guess could have been that the hole that we got back from the
> filesystem was smaller than 2MiB? Can you try running v2 (which I'll post in
> a second) against a TEST_DEV made with one of the following:
>
> ext4: mkfs.ext4 -b 4096 -E stride=512 -F $TEST_DEV
> xfs: mkfs.xfs -f -d su=2m,sw=1 $TEST_DEV
>
> This helps us get 2MiB sized and aligned allocations so we can fault in PMDs,
> but I'm not sure whether or not it would matter for holes.

I guess that's the point to reproduce the failure, I'll confirm with v2
patches. If these non-default & not widely tested mkfs options are
required to reproduce it, I think we can specify them in the test, as
extra mkfs options to _scratch_mkfs, as what generic/413 does.

>
> > Some comments inline.
> >
> > > The above patch fixes an issue where users of DAX can suffer data
> > > corruption from stale mmap reads via the following sequence:
> > >
> > > - open an mmap over a 2MiB hole
> > >
> > > - read from a 2MiB hole, faulting in a 2MiB zero page
> > >
> > > - write to the hole with write(3p). The write succeeds but we incorrectly
> > > leave the 2MiB zero page mapping intact.
> > >
> > > - via the mmap, read the data that was just written. Since the zero page
> > > mapping is still intact we read back zeroes instead of the new data.
> > >
> > > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> > > ---
> > > .gitignore | 1 +
> > > src/Makefile | 2 +-
> > > src/t_dax_stale_pmd.c | 56 ++++++++++++++++++++++++++++++++++++++++++
> > > tests/generic/427 | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++
> > > tests/generic/427.out | 2 ++
> > > tests/generic/group | 1 +
> > > 6 files changed, 129 insertions(+), 1 deletion(-)
> > > create mode 100644 src/t_dax_stale_pmd.c
> > > create mode 100755 tests/generic/427
> > > create mode 100644 tests/generic/427.out
> > >
> > > diff --git a/.gitignore b/.gitignore
> > > index ded4a61..9664dc9 100644
> > > --- a/.gitignore
> > > +++ b/.gitignore
> > > @@ -134,6 +134,7 @@
> > > /src/renameat2
> > > /src/t_rename_overwrite
> > > /src/t_mmap_dio
> > > +/src/t_dax_stale_pmd
> > >
> > > # dmapi/ binaries
> > > /dmapi/src/common/cmd/read_invis
> > > diff --git a/src/Makefile b/src/Makefile
> > > index abfd873..7e22b50 100644
> > > --- a/src/Makefile
> > > +++ b/src/Makefile
> > > @@ -12,7 +12,7 @@ TARGETS = dirstress fill fill2 getpagesize holes lstat64 \
> > > godown resvtest writemod makeextents itrash rename \
> > > multi_open_unlink dmiperf unwritten_sync genhashnames t_holes \
> > > t_mmap_writev t_truncate_cmtime dirhash_collide t_rename_overwrite \
> > > - holetest t_truncate_self t_mmap_dio af_unix
> > > + holetest t_truncate_self t_mmap_dio af_unix t_dax_stale_pmd
> > >
> > > LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
> > > preallo_rw_pattern_writer ftrunc trunc fs_perms testx looptest \
> > > diff --git a/src/t_dax_stale_pmd.c b/src/t_dax_stale_pmd.c
> > > new file mode 100644
> > > index 0000000..d0016eb
> > > --- /dev/null
> > > +++ b/src/t_dax_stale_pmd.c
> > > @@ -0,0 +1,56 @@
> > > +#include <errno.h>
> > > +#include <fcntl.h>
> > > +#include <libgen.h>
> > > +#include <stdio.h>
> > > +#include <stdlib.h>
> > > +#include <string.h>
> > > +#include <sys/mman.h>
> > > +#include <sys/stat.h>
> > > +#include <sys/types.h>
> > > +#include <unistd.h>
> > > +
> > > +#define MiB(a) ((a)*1024*1024)
> > > +
> > > +void err_exit(char *op)
> > > +{
> > > + fprintf(stderr, "%s: %s\n", op, strerror(errno));
> > > + exit(1);
> > > +}
> > > +
> > > +int main(int argc, char *argv[])
> > > +{
> > > + volatile int a __attribute__((__unused__));
> > > + char *buffer = "HELLO WORLD!";
> > > + char *data;
> > > + int fd;
> > > +
> > > + if (argc < 2) {
> > > + printf("Usage: %s <pmem file>\n", basename(argv[0]));
> > > + exit(0);
> > > + }
> > > +
> > > + fd = open(argv[1], O_RDWR);
> > > + if (fd < 0)
> > > + err_exit("fd");
> > ^^^^ Nitpick, the "op" should be "open"?
> > > +
> > > + data = mmap(NULL, MiB(2), PROT_READ, MAP_SHARED, fd, MiB(2));
> > > +
> > > + /*
> > > + * This faults in a 2MiB zero page to satisfy the read.
> > > + * 'a' is volatile so this read doesn't get optimized out.
> > > + */
> > > + a = data[0];
> > > +
> > > + pwrite(fd, buffer, strlen(buffer), MiB(2));
> > > +
> > > + /*
> > > + * Try and use the mmap to read back the data we just wrote with
> > > + * pwrite(). If the kernel bug is present the mapping from the 2MiB
> > > + * zero page will still be intact, and we'll read back zeros instead.
> > > + */
> > > + if (strncmp(buffer, data, strlen(buffer)))
> > > + err_exit("strncmp mismatch!");
> >
> > strncmp doesn't set errno, this err_exit message might be confusing:
> > "strncmp mismatch!: Success"
>
> Ah, thanks, fixed in v2.
>
> > > +
> > > + close(fd);
> > > + return 0;
> > > +}
> > > diff --git a/tests/generic/427 b/tests/generic/427
> > > new file mode 100755
> > > index 0000000..baf1099
> > > --- /dev/null
> > > +++ b/tests/generic/427
> > > @@ -0,0 +1,68 @@
> > > +#! /bin/bash
> > > +# FS QA Test 427
> > > +#
> > > +# This is a regression test for kernel patch:
> > > +# dax: fix data corruption due to stale mmap reads
> > > +# created by Ross Zwisler <ross.zwisler@linux.intel.com>
> > > +#
> > > +#-----------------------------------------------------------------------
> > > +# Copyright (c) 2017 Intel Corporation. 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 /
> > > + rm -f $tmp.*
> > > +}
> > > +
> > > +# get standard environment, filters and checks
> > > +. ./common/rc
> > > +. ./common/filter
> > > +
> > > +# remove previous $seqres.full before test
> > > +rm -f $seqres.full
> > > +
> > > +# Modify as appropriate.
> > > +_supported_fs generic
> > > +_supported_os Linux
> > > +_require_scratch_dax
> >
> > I don't think dax is a requirement here, this test could run on normal
> > block device without "-o dax" option too. It won't hurt to run with more
> > test configurations. And test on nvdimm device with dax mount option
> > could be one of the test configs, e.g.
> >
> > TEST_DEV=/dev/pmem0
> > SCRATCH_DEV=/dev/pmem1
> > MOUNT_OPTIONS="-o dax"
> > ...
>
> Yep, agreed, fixed in v2.

Then perhaps the test program should be renamed? As no dax is required.
How about t_mmap_stale_pmd?

>
> > > +_require_test_program "t_dax_stale_pmd"
> > > +_require_user
> >
> > _require_xfs_io_command "falloc"
> >
> > So test _notrun on ext2/3.
>
> Fixed in v2.
>
> > > +
> > > +# real QA test starts here
> > > +_scratch_mkfs >>$seqres.full 2>&1
> > > +_scratch_mount "-o dax"
> >
> > Same here, dax is not required.
>
> Fixed in v2.
>
> >
> > > +
> > > +$XFS_IO_PROG -f -c "falloc 0 4M" $SCRATCH_MNT/testfile >> $seqres.full 2>&1
> > > +chmod 0644 $SCRATCH_MNT/testfile
> > > +chown $qa_user $SCRATCH_MNT/testfile
> >
> > Any specific reason to use $qa_user to run this test? Comments would be
> > great.
>
> Nope, just cargo-culting my way through my first xfstest. :) I've removed
> this for v2.

I think it's in a pretty good shape for "first fstests test" :)

>
> > Thanks,
> > Eryu
>
> Thanks for the review!

Thanks for adding new test!

Eryu

>
> > > +
> > > +_user_do "src/t_dax_stale_pmd $SCRATCH_MNT/testfile"
> > > +
> > > +# success, all done
> > > +echo "Silence is golden"
> > > +status=0
> > > +exit
> > > diff --git a/tests/generic/427.out b/tests/generic/427.out
> --
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