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

Ross Zwisler
2017-04-24T17:49:44Z

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