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

[Ross Zwisler <ross.zwisler@linux.intel.com>]

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 | 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");
+
+	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!");
+
+	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 $seqres.full
+
+# Modify as appropriate.
+_supported_fs generic
+_supported_os Linux
+_require_scratch_dax
+_require_test_program "t_dax_stale_pmd"
+_require_user
+
+# real QA test starts here
+_scratch_mkfs >>$seqres.full 2>&1
+_scratch_mount "-o dax"
+
+$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
+
+_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
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

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