Re: [PATCH] generic: test pagecache invalidation after direct write

Eryu Guan
2017-03-21T15:52:22Z

On Tue, Mar 21, 2017 at 11:11:52AM -0400, Brian Foster wrote:
> On Mon, Mar 13, 2017 at 02:50:05PM +0800, Eryu Guan wrote:
> > Test if direct write invalidates pagecache correctly, so that subsequent
> > buffer read reads the correct data from disk.
> >
> > This test is inspired LTP tests dio29, and serves as a regression test
> > for the bug found by it, see kernel commit c771c14baa33 ("iomap:
> > invalidate page caches should be after iomap_dio_complete() in direct
> > write").
> >
> > The test can be easily expanded to other write/read combinations, e.g.
> > buffer write + direct read and direct write + direct read, so they are
> > also being tested.
> >
> > Signed-off-by: Eryu Guan <eguan@redhat.com>
> > ---
>
> Hi Eryu,
>
> This mostly looks Ok to me. I notice the test takes just over 2m on a
> test vm and seems to reproduce less than 50% of the time (only in a
> handful of tries). Then again, it only requires 10s or so on a more high
> end system, so that's pretty good. Either way, have you played around
> with the tunables to either speed up the test and/or improve the
> reproducibility?

Yes, the original reproducer for the bug is quick and almost always
reproduces for me on my test vm.

runtest $((10 * LOAD_FACTOR)) -b $sectorsize -n 3 -i 1

I tuned the second test config, which adds more stress. I think current
config works best for me. It takes me around 3 minutes to finish and
doesn't lose too much stress.

runtest $((5 * LOAD_FACTOR)) -b $sectorsize -n 8 -i 4

>
> Mostly nits and minor comments to follow...
>
> > .gitignore | 1 +
> > src/Makefile | 3 +-
> > src/dio-invalidate-cache.c | 335 +++++++++++++++++++++++++++++++++++++++++++++
> > tests/generic/418 | 122 +++++++++++++++++
> > tests/generic/418.out | 2 +
> > tests/generic/group | 1 +
> > 6 files changed, 463 insertions(+), 1 deletion(-)
> > create mode 100644 src/dio-invalidate-cache.c
> > create mode 100755 tests/generic/418
> > create mode 100644 tests/generic/418.out
> >
> > diff --git a/.gitignore b/.gitignore
> > index 48a40a0..1ed2a92 100644
> > --- a/.gitignore
> > +++ b/.gitignore
> > @@ -45,6 +45,7 @@
> > /src/dbtest
> > /src/devzero
> > /src/dio-interleaved
> > +/src/dio-invalidate-cache
> > /src/dirperf
> > /src/dirstress
> > /src/dmiperf
> > diff --git a/src/Makefile b/src/Makefile
> > index eb5a56c..a7f27f0 100644
> > --- a/src/Makefile
> > +++ b/src/Makefile
> > @@ -21,7 +21,8 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
> > stale_handle pwrite_mmap_blocked t_dir_offset2 seek_sanity_test \
> > seek_copy_test t_readdir_1 t_readdir_2 fsync-tester nsexec cloner \
> > renameat2 t_getcwd e4compact test-nextquota punch-alternating \
> > - attr-list-by-handle-cursor-test listxattr dio-interleaved t_dir_type
> > + attr-list-by-handle-cursor-test listxattr dio-interleaved t_dir_type \
> > + dio-invalidate-cache
> >
> > SUBDIRS =
> >
> > diff --git a/src/dio-invalidate-cache.c b/src/dio-invalidate-cache.c
> > new file mode 100644
> > index 0000000..4fd72ab
> > --- /dev/null
> > +++ b/src/dio-invalidate-cache.c
> > @@ -0,0 +1,335 @@
> > +/*
> > + * Copyright (c) 2017 Red Hat Inc. 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
> > + */
> > +
> > +/*
> > + * Fork N children, each child writes to and reads from its own region of the
> > + * same test file, and check if what it reads is what it writes. The test
> > + * region is determined by N * blksz. Write and read operation can be either
> > + * direct or buffered.
> > + */
> > +
> > +#ifndef _GNU_SOURCE
> > +#define _GNU_SOURCE
> > +#endif
> > +#include <sys/file.h>
> > +#include <sys/types.h>
> > +#include <sys/wait.h>
> > +#include <errno.h>
> > +#include <fcntl.h>
> > +#include <signal.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <unistd.h>
> > +
> > +#define DEF_BLKSZ 4096
> > +
> > +int verbose = 0;
> > +
> > +static void usage(const char *prog)
> > +{
> > + fprintf(stderr, "Usage: %s [-Fhptrwv] [-b blksz] [-n nr_child] [-i iterations] [-o offset] <-f filename>\n", prog);
> > + fprintf(stderr, "\t-F\tPreallocate all blocks by writing them before test\n");
> > + fprintf(stderr, "\t-p\tPreallocate all blocks using fallocate(2) before test\n");
> > + fprintf(stderr, "\t-t\tTruncate test file to largest size before test\n");
> > + fprintf(stderr, "\t-r\tDo direct read\n");
> > + fprintf(stderr, "\t-w\tDo direct write\n");
> > + fprintf(stderr, "\t-v\tBe verbose\n");
> > + fprintf(stderr, "\t-h\tshow this help message\n");
> > + exit(EXIT_FAILURE);
> > +}
> > +
> > +static int cmpbuf(char *b1, char *b2, int bsize)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < bsize; i++) {
> > + if (strncmp(&b1[i], &b2[i], 1)) {
>
> If you're going to iterate the buffer a byte at a time, shouldn't
> something like 'if (b1[1] != b2[i]) ...' be sufficient here?

You're right, I must have copied this pattern from ltp test and
didn't think more about it.

>
> > + fprintf(stderr, "cmpbuf: offset %d: Expected: 0x%x,"
> > + " got 0x%x\n", i, b1[i], b2[i]);
> > + return 1;
> > + }
> > + }
> > + return 0;
> > +}
> > +
> > +static void kill_children(pid_t *pids, int nr_child)
> > +{
> > + int i;
> > + pid_t pid;
> > +
> > + for (i = 0; i < nr_child; i++) {
> > + pid = *(pids + i);
>
> pids[i] ?

Sure.

>
> > + if (pid == 0)
> > + continue;
> > + kill(pid, SIGTERM);
> > + }
> > + return;
> > +}
> > +
> > +static int wait_children(pid_t *pids, int nr_child)
> > +{
> > + int i, status, ret = 0;
> > + pid_t pid;
> > +
> > + for (i = 0; i < nr_child; i++) {
> > + pid = *(pids + i);
> > + if (pid == 0)
> > + continue;
> > + waitpid(pid, &status, 0);
> > + ret += WEXITSTATUS(status);
> > + }
> > + return ret;
> > +}
> > +
> > +static void dumpbuf(char *buf, int size, int blksz)
> > +{
> > + int i;
> > +
> > + printf("dumping buffer content\n");
> > + for (i = 0; i < size; i++) {
> > + if (((i % blksz) == 0) || ((i % 64) == 0))
> > + putchar('\n');
> > + fprintf(stderr, "%x", buf[i]);
>
> Hmm.. is it intentional to write the buf data to stderr and the newlines
> to stdout? What does this look like if stderr is redirected?

No.. they both should go to stdout.

>
> > + }
> > + putchar('\n');
> > +}
> > +
> > +static int run_test(const char *filename, int n_child, int blksz, off_t offset,
> > + int nr_iter, int flag_rd, int flag_wr)
> > +{
> > + char *buf_rd;
> > + char *buf_wr;
> > + off_t seekoff;
> > + int fd_rd, fd_wr;
> > + int i, ret;
> > + long page_size;
> > +
> > + seekoff = offset + blksz * n_child;
> > +
> > + page_size = sysconf(_SC_PAGESIZE);
> > + ret = posix_memalign((void **)&buf_rd, (size_t)page_size,
> > + blksz > page_size ? blksz : (size_t)page_size);
> > + if (ret) {
> > + fprintf(stderr, "posix_memalign(buf_rd, %d, %d) failed: %d\n",
> > + blksz, blksz, ret);
> > + exit(EXIT_FAILURE);
> > + }
> > + memset(buf_rd, 0, blksz);
> > + ret = posix_memalign((void **)&buf_wr, (size_t)page_size,
> > + blksz > page_size ? blksz : (size_t)page_size);
> > + if (ret) {
> > + fprintf(stderr, "posix_memalign(buf_wr, %d, %d) failed: %d\n",
> > + blksz, blksz, ret);
> > + exit(EXIT_FAILURE);
> > + }
> > + memset(buf_wr, 0, blksz);
> > +
> > + fd_rd = open(filename, flag_rd);
> > + if (fd_rd < 0) {
> > + perror("open readonly for read");
> > + exit(EXIT_FAILURE);
> > + }
> > +
> > + fd_wr = open(filename, flag_wr);
> > + if (fd_wr < 0) {
> > + perror("open writeonly for direct write");
> > + exit(EXIT_FAILURE);
> > + }
> > +
> > +#define log(format, ...) \
> > + if (verbose) { \
> > + printf("[%d:%d] ", n_child, i); \
> > + printf(format, __VA_ARGS__); \
> > + }
> > +
> > +
> > + /* seek, write, read and verify */
> > + ret = 0;
> > + for (i = 0; i < nr_iter; i++) {
> > + memset(buf_wr, n_child + i + 1, blksz);
>
> Why use n_child? It doesn't help us differentiate from other threads if
> the values are incremented. Might be more simple to just use i + 1.

Sure, will fix it.

>
> > + if (lseek(fd_wr, seekoff, SEEK_SET) < 0) {
> > + perror("lseek for write");
> > + exit(EXIT_FAILURE);
> > + }
> > + log("write(fd_wr, %p, %d)\n", buf_wr, blksz);
> > + if (write(fd_wr, buf_wr, blksz) < 0) {
> > + perror("direct write");
> > + exit(EXIT_FAILURE);
> > + }
>
> pwrite()/pread() could eliminate the need for the lseek() calls. Also,
> we probably want to check for short writes as well.

OK.

>
> > +
> > + /* make sure buffer write hit disk before direct read */
> > + if (!(flag_wr & O_DIRECT)) {
> > + if (fsync(fd_wr) < 0) {
> > + perror("fsync(fd_wr)");
> > + exit(EXIT_FAILURE);
> > + }
> > + }
> > +
> > + if (lseek(fd_rd, seekoff, SEEK_SET) < 0) {
> > + perror("lseek for read");
> > + exit(EXIT_FAILURE);
> > + }
> > + log("read(fd_rd, %p, %d)\n", buf_rd, blksz);
> > + if (read(fd_rd, buf_rd, blksz) != blksz) {
> > + perror("buffer read");
> > + exit(EXIT_FAILURE);
> > + }
> > + if (cmpbuf(buf_wr, buf_rd, blksz) != 0) {
> > + fprintf(stderr, "[%d:%d] FAIL - comparsion failed, "
>
> Typo: comparison

Will fix.

>
> > + "offset %d\n", n_child, i, (int)seekoff);
> > + ret += 1;
>
> ret doesn't appear to be used after this.

Originally there was no exit call in this error case, but I forgot to
remove the "ret += 1" when adding exit. Will fix it.

>
> > + if (verbose)
> > + dumpbuf(buf_rd, blksz, blksz);
> > + exit(EXIT_FAILURE);
> > + }
> > + }
> > + exit(ret);
> > +}
> > +
> > +int main(int argc, char *argv[])
> > +{
> > + int nr_iter = 1;
> > + int nr_child = 1;
> > + int blksz = DEF_BLKSZ;
> > + int fd, i, ret = 0;
> > + int flag_rd = O_RDONLY;
> > + int flag_wr = O_WRONLY;
> > + int do_trunc = 0;
> > + int pre_fill = 0;
> > + int pre_alloc = 0;
> > + pid_t pid;
> > + pid_t *pids;
> > + off_t offset = 0;
> > + char *filename = NULL;
> > +
> > + while ((i = getopt(argc, argv, "b:i:n:f:Fpo:tvrw")) != -1) {
> > + switch (i) {
> > + case 'b':
> > + if ((blksz = atoi(optarg)) <= 0) {
> > + fprintf(stderr, "blksz must be > 0\n");
> > + exit(EXIT_FAILURE);
> > + }
> > + if (blksz % 512 != 0) {
> > + fprintf(stderr, "blksz must be multiple of 512\n");
> > + exit(EXIT_FAILURE);
> > + }
> > + break;
> > + case 'i':
> > + if ((nr_iter = atoi(optarg)) <= 0) {
> > + fprintf(stderr, "iterations must be > 0\n");
> > + exit(EXIT_FAILURE);
> > + }
> > + break;
> > + case 'n':
> > + if ((nr_child = atoi(optarg)) <= 0) {
> > + fprintf(stderr, "no of children must be > 0\n");
> > + exit(EXIT_FAILURE);
> > + }
> > + break;
> > + case 'f':
> > + filename = optarg;
> > + break;
> > + case 'F':
> > + pre_fill = 1;
> > + break;
> > + case 'p':
> > + pre_alloc = 1;
> > + break;
> > + case 'r':
> > + flag_rd |= O_DIRECT;
> > + break;
> > + case 'w':
> > + flag_wr |= O_DIRECT;
> > + break;
> > + case 't':
> > + do_trunc = 1;
> > + break;
> > + case 'o':
> > + if ((offset = atol(optarg)) < 0) {
> > + fprintf(stderr, "offset must be >= 0\n");
> > + exit(EXIT_FAILURE);
> > + }
> > + break;
> > + case 'v':
> > + verbose = 1;
> > + break;
> > + case 'h': /* fall through */
> > + default:
> > + usage(argv[0]);
> > + }
> > + }
> > +
> > + if (filename == NULL)
> > + usage(argv[0]);
> > + if (pre_fill && pre_alloc) {
> > + fprintf(stderr, "Error: -F and -p are both specified\n");
> > + exit(EXIT_FAILURE);
> > + }
> > +
> > + pids = malloc(nr_child * sizeof(pid_t));
> > + if (!pids) {
> > + fprintf(stderr, "failed to malloc memory for pids\n");
> > + exit(EXIT_FAILURE);
> > + }
> > + memset(pids, 0, nr_child * sizeof(pid_t));
> > +
> > + /* create & truncate testfile first */
> > + fd = open(filename, O_CREAT | O_TRUNC | O_RDWR, 0600);
> > + if (fd < 0) {
> > + perror("create & truncate testfile");
> > + free(pids);
> > + exit(EXIT_FAILURE);
> > + }
> > + if (do_trunc && (ftruncate(fd, blksz * nr_child) < 0)) {
> > + perror("ftruncate failed");
> > + free(pids);
> > + exit(EXIT_FAILURE);
> > + }
> > + if (pre_fill) {
> > + char *buf;
> > + buf = malloc(blksz * nr_child);
> > + memset(buf, 's', blksz * nr_child);
> > + write(fd, buf, blksz * nr_child);
> > + free(buf);
> > + }
> > + if (pre_alloc) {
> > + fallocate(fd, 0, 0, blksz * nr_child);
> > + }
> > + close(fd);
> > + sync();
>
> Is sync() really necessary here? I'd expect fsync(fd) to be sufficient.

Sure, will fix.

>
> > +
> > + /* fork workers */
> > + for (i = 0; i < nr_child; i++) {
> > + pid = fork();
> > + if (pid < 0) {
> > + perror("fork");
> > + kill_children(pids, nr_child);
> > + free(pids);
> > + exit(EXIT_FAILURE);
> > + } else if (pid == 0) {
>
> /* never returns */

OK.

>
> > + run_test(filename, i, blksz, offset, nr_iter,
> > + flag_rd, flag_wr);
> > + } else {
> > + *(pids + i) = pid;
>
> How about: pids[i] = pid;

Will fix.

>
> > + }
> > + }
> > +
> > + ret = wait_children(pids, nr_child);
> > + free(pids);
> > + exit(ret);
> > +}
> > diff --git a/tests/generic/418 b/tests/generic/418
> > new file mode 100755
> > index 0000000..2d56cf0
> > --- /dev/null
> > +++ b/tests/generic/418
> > @@ -0,0 +1,122 @@
> > +#! /bin/bash
> > +# FS QA Test 418
> > +#
> > +# Test pagecache invalidation in buffer/direct write/read combination.
> > +#
> > +# Fork N children, each child writes to and reads from its own region of the
> > +# same test file, and check if what it reads is what it writes. The test region
> > +# is determined by N * blksz. Write and read operation can be either direct or
> > +# buffered.
> > +#
> > +# Regression test for commit c771c14baa33 ("iomap: invalidate page caches
> > +# should be after iomap_dio_complete() in direct write")
> > +#
> > +#-----------------------------------------------------------------------
> > +# Copyright (c) 2017 Red Hat Inc. 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
> > +
> > +# real QA test starts here
> > +_supported_fs generic
> > +_supported_os Linux
> > +_require_test
> > +_require_odirect
> > +_require_block_device $TEST_DEV
> > +_require_test_program "dio-invalidate-cache"
> > +_require_test_program "feature"
> > +
> > +diotest=$here/src/dio-invalidate-cache
> > +testfile=$TEST_DIR/$seq-diotest
> > +sectorsize=`blockdev --getss $TEST_DEV`
> > +pagesize=`src/feature -s`
> > +
> > +# test case array, test different write/read combinations
> > +# -r: use direct read
> > +# -w: use direct write
> > +# -t: truncate file to final size before test, i.e. write to hole
> > +# -p: fallocate whole file before test, i.e. write to allocated but unwritten extents
> > +# -F: fulfill whole file before test, i.e. write to alloated & written extents
>
> Typo: allocated

Will fix.

Thanks a lot for the review! I'll probably send v2 tomorrow.

Thanks,
Eryu

>
> Brian
>
> > +t_cases=(
> > + "-w"
> > + "-wt"
> > + "-wp"
> > + "-wF"
> > + "-r"
> > + "-rt"
> > + "-rp"
> > + "-rF"
> > + "-rw"
> > + "-rwt"
> > + "-rwp"
> > + "-rwF"
> > +)
> > +
> > +runtest()
> > +{
> > + local i=0
> > + local tc=""
> > + local loop=$1
> > + shift
> > +
> > + for tc in ${t_cases[*]}; do
> > + echo "diotest $tc $*" >> $seqres.full
> > + i=0
> > + while [ $i -lt $loop ]; do
> > + $diotest $tc $* -f $testfile
> > + if [ $? -ne 0 ]; then
> > + echo "diotest $tc $* failed at loop $i" | \
> > + tee -a $seqres.full
> > + break
> > + fi
> > + let i=i+1
> > + done
> > + done
> > +}
> > +
> > +while [ $sectorsize -le $((pagesize * 2)) ]; do
> > + # reproducer for the original bug
> > + runtest $((10 * LOAD_FACTOR)) -b $sectorsize -n 3 -i 1
> > + # try more processes and iterations
> > + runtest $((5 * LOAD_FACTOR)) -b $sectorsize -n 8 -i 4
> > + sectorsize=$((sectorsize * 2))
> > +done
> > +echo "Silence is golden"
> > +
> > +# success, all done
> > +status=0
> > +exit
> > diff --git a/tests/generic/418.out b/tests/generic/418.out
> > new file mode 100644
> > index 0000000..954de31
> > --- /dev/null
> > +++ b/tests/generic/418.out
> > @@ -0,0 +1,2 @@
> > +QA output created by 418
> > +Silence is golden
> > diff --git a/tests/generic/group b/tests/generic/group
> > index f0096bb..0a272b7 100644
> > --- a/tests/generic/group
> > +++ b/tests/generic/group
> > @@ -420,3 +420,4 @@
> > 415 auto clone
> > 416 auto enospc
> > 417 auto quick shutdown log
> > +418 auto rw
> > --
> > 2.9.3
> >
> > --
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