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

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(a)linux.intel.com&gt; --- .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(a)linux.intel.com&gt; +# +#----------------------------------------------------------------------- +# 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