diff mbox

[v2,2/2] dax: add regression test for stale mmap reads

Message ID 20170425205106.20576-2-ross.zwisler@linux.intel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Ross Zwisler April 25, 2017, 8:51 p.m. UTC 
This adds a regression test for the following kernel patch:

  dax: fix data corruption due to stale mmap reads

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 | 59 +++++++++++++++++++++++++++++++++++++++++++++
 tests/generic/427     | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
 tests/generic/427.out |  2 ++
 tests/generic/group   |  1 +
 6 files changed, 131 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

Comments

Eryu Guan April 26, 2017, 7:47 a.m. UTC | #1 
On Tue, Apr 25, 2017 at 02:51:06PM -0600, Ross Zwisler wrote:
> This adds a regression test for the following kernel patch:
> 
>   dax: fix data corruption due to stale mmap reads
> 
> 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>

I reproduced it now with 4.10 kernel, I think it was because I enalbed
KASAN on my 4.11-rc8 kernel. And the special mkfs options for ext4/xfs
are not needed either.

> ---
>  .gitignore            |  1 +
>  src/Makefile          |  2 +-
>  src/t_dax_stale_pmd.c | 59 +++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/427     | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/427.out |  2 ++
>  tests/generic/group   |  1 +
>  6 files changed, 131 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..59fbbe1
> --- /dev/null
> +++ b/src/t_dax_stale_pmd.c
> @@ -0,0 +1,59 @@
> +#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");
> +
> +	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))) {
> +		fprintf(stderr, "strncmp mismatch: '%s' vs '%s'\n", buffer,
> +				data);
> +		exit(1);
> +	}
> +
> +	close(fd);
> +	return 0;
> +}
> diff --git a/tests/generic/427 b/tests/generic/427
> new file mode 100755
> index 0000000..6e265a1
> --- /dev/null
> +++ b/tests/generic/427
> @@ -0,0 +1,67 @@
> +#! /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_test_program "t_dax_stale_pmd"
> +_require_xfs_io_command "falloc"

I'm wondering if falloc is really needed? If not, this test could be run
with ext2/3 too. See below.

> +_require_user

This is not needed anymore.

> +
> +# real QA test starts here
> +
> +# ensure we have no pre-existing block allocations, so we get a hole
> +rm -f $TEST_DIR/testfile
> +$XFS_IO_PROG -f -c "falloc 0 4M" $TEST_DIR/testfile >> $seqres.full 2>&1

I found that 'xfs_io -fc "truncate 4M" $TEST_DIR/testfile' works too,
from the comments in test and kernel patch, if I understand correctly,
we only need to mmap un-allocated blocks, right?

If truncate(2) works too, I think we can move truncate operation to the
t_dax_stale_pmd program too, because the whole truncate && mmap && read
sequence are logically together, this also avoids the confusion on why
testfile is in 4M size.

Thanks,
Eryu

> +chmod 0644 $TEST_DIR/testfile
> +
> +src/t_dax_stale_pmd $TEST_DIR/testfile
> +
> +# success, all done
> +echo "Silence is golden"
> +status=0
> +exit
> diff --git a/tests/generic/427.out b/tests/generic/427.out
> new file mode 100644
> index 0000000..61295e5
> --- /dev/null
> +++ b/tests/generic/427.out
> @@ -0,0 +1,2 @@
> +QA output created by 427
> +Silence is golden
> diff --git a/tests/generic/group b/tests/generic/group
> index f29009c..06f6e9d 100644
> --- a/tests/generic/group
> +++ b/tests/generic/group
> @@ -429,3 +429,4 @@
>  424 auto quick
>  425 auto quick attr
>  426 auto quick exportfs
> +427 auto quick
> -- 
> 2.9.3
>
Murphy Zhou April 26, 2017, 9:09 a.m. UTC | #2 
On Tue, Apr 25, 2017 at 02:51:06PM -0600, Ross Zwisler wrote:
> This adds a regression test for the following kernel patch:
> 
>   dax: fix data corruption due to stale mmap reads
> 
> 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 | 59 +++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/427     | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/427.out |  2 ++
>  tests/generic/group   |  1 +
>  6 files changed, 131 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..59fbbe1
> --- /dev/null
> +++ b/src/t_dax_stale_pmd.c
> @@ -0,0 +1,59 @@
> +#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");
> +
> +	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))) {
> +		fprintf(stderr, "strncmp mismatch: '%s' vs '%s'\n", buffer,
> +				data);
		munmap
		close(fd);
> +		exit(1);
> +	}
> +
	munmap

Thanks, :)
--
Xiong
> +	close(fd);
> +	return 0;
> +}
> diff --git a/tests/generic/427 b/tests/generic/427
> new file mode 100755
> index 0000000..6e265a1
> --- /dev/null
> +++ b/tests/generic/427
> @@ -0,0 +1,67 @@
> +#! /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_test_program "t_dax_stale_pmd"
> +_require_xfs_io_command "falloc"
> +_require_user
> +
> +# real QA test starts here
> +
> +# ensure we have no pre-existing block allocations, so we get a hole
> +rm -f $TEST_DIR/testfile
> +$XFS_IO_PROG -f -c "falloc 0 4M" $TEST_DIR/testfile >> $seqres.full 2>&1
> +chmod 0644 $TEST_DIR/testfile
> +
> +src/t_dax_stale_pmd $TEST_DIR/testfile
> +
> +# success, all done
> +echo "Silence is golden"
> +status=0
> +exit
> diff --git a/tests/generic/427.out b/tests/generic/427.out
> new file mode 100644
> index 0000000..61295e5
> --- /dev/null
> +++ b/tests/generic/427.out
> @@ -0,0 +1,2 @@
> +QA output created by 427
> +Silence is golden
> diff --git a/tests/generic/group b/tests/generic/group
> index f29009c..06f6e9d 100644
> --- a/tests/generic/group
> +++ b/tests/generic/group
> @@ -429,3 +429,4 @@
>  424 auto quick
>  425 auto quick attr
>  426 auto quick exportfs
> +427 auto quick
> -- 
> 2.9.3
>
Ross Zwisler April 26, 2017, 5:50 p.m. UTC | #3 
On Wed, Apr 26, 2017 at 03:47:27PM +0800, Eryu Guan wrote:
> On Tue, Apr 25, 2017 at 02:51:06PM -0600, Ross Zwisler wrote:
<>
> > diff --git a/tests/generic/427 b/tests/generic/427
> > new file mode 100755
> > index 0000000..6e265a1
> > --- /dev/null
> > +++ b/tests/generic/427
> > @@ -0,0 +1,67 @@
> > +#! /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_test_program "t_dax_stale_pmd"
> > +_require_xfs_io_command "falloc"
> 
> I'm wondering if falloc is really needed? If not, this test could be run
> with ext2/3 too. See below.
> 
> > +_require_user
> 
> This is not needed anymore.

Fixed in v3.

> > +
> > +# real QA test starts here
> > +
> > +# ensure we have no pre-existing block allocations, so we get a hole
> > +rm -f $TEST_DIR/testfile
> > +$XFS_IO_PROG -f -c "falloc 0 4M" $TEST_DIR/testfile >> $seqres.full 2>&1
> 
> I found that 'xfs_io -fc "truncate 4M" $TEST_DIR/testfile' works too,
> from the comments in test and kernel patch, if I understand correctly,
> we only need to mmap un-allocated blocks, right?
> 
> If truncate(2) works too, I think we can move truncate operation to the
> t_dax_stale_pmd program too, because the whole truncate && mmap && read
> sequence are logically together, this also avoids the confusion on why
> testfile is in 4M size.

Yep, that works.  In v3 I've moved to using only ftruncate so we can enable
ext2/3, and I've moved those calls into the C file with comments explaining
why we're doing things.
Ross Zwisler April 26, 2017, 6 p.m. UTC | #4 
On Wed, Apr 26, 2017 at 05:09:07PM +0800, Xiong Zhou wrote:
> On Tue, Apr 25, 2017 at 02:51:06PM -0600, Ross Zwisler wrote:
<>
> > +	/*
> > +	 * 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))) {
> > +		fprintf(stderr, "strncmp mismatch: '%s' vs '%s'\n", buffer,
> > +				data);
> 		munmap
> 		close(fd);
> > +		exit(1);
> > +	}
> > +
> 	munmap

Yep, thanks, fixed in v3.
diff mbox

Patch

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..59fbbe1
--- /dev/null
+++ b/src/t_dax_stale_pmd.c
@@ -0,0 +1,59 @@ 
+#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");
+
+	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))) {
+		fprintf(stderr, "strncmp mismatch: '%s' vs '%s'\n", buffer,
+				data);
+		exit(1);
+	}
+
+	close(fd);
+	return 0;
+}
diff --git a/tests/generic/427 b/tests/generic/427
new file mode 100755
index 0000000..6e265a1
--- /dev/null
+++ b/tests/generic/427
@@ -0,0 +1,67 @@ 
+#! /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_test_program "t_dax_stale_pmd"
+_require_xfs_io_command "falloc"
+_require_user
+
+# real QA test starts here
+
+# ensure we have no pre-existing block allocations, so we get a hole
+rm -f $TEST_DIR/testfile
+$XFS_IO_PROG -f -c "falloc 0 4M" $TEST_DIR/testfile >> $seqres.full 2>&1
+chmod 0644 $TEST_DIR/testfile
+
+src/t_dax_stale_pmd $TEST_DIR/testfile
+
+# success, all done
+echo "Silence is golden"
+status=0
+exit
diff --git a/tests/generic/427.out b/tests/generic/427.out
new file mode 100644
index 0000000..61295e5
--- /dev/null
+++ b/tests/generic/427.out
@@ -0,0 +1,2 @@ 
+QA output created by 427
+Silence is golden
diff --git a/tests/generic/group b/tests/generic/group
index f29009c..06f6e9d 100644
--- a/tests/generic/group
+++ b/tests/generic/group
@@ -429,3 +429,4 @@ 
 424 auto quick
 425 auto quick attr
 426 auto quick exportfs
+427 auto quick