On Wed, Jun 7, 2023 at 12:38 AM Darrick J. Wong <djwong@xxxxxxxxxx> wrote:
> On Tue, Jun 06, 2023 at 03:35:45PM +0200, Andreas Gruenbacher wrote:
> > This is the same as generic/647, but with an additional test that writes
> > a memory-mapped page onto itself using direct I/O.
> >
> > For direct I/O writes, the kernel will invalidate the page cache before
> > and after carrying out the write. This puts filesystems that fault in
> > pages on demand and then carry out the write with page faults disabled
> > into a position in which they will not be able to make any progress.
> > ---
> > src/mmap-rw-fault.c | 33 ++++++++++++++++++++++++++++++---
> > tests/generic/728 | 41 +++++++++++++++++++++++++++++++++++++++++
> > tests/generic/728.out | 2 ++
> > 3 files changed, 73 insertions(+), 3 deletions(-)
> > create mode 100755 tests/generic/728
> > create mode 100644 tests/generic/728.out
> >
> > diff --git a/src/mmap-rw-fault.c b/src/mmap-rw-fault.c
> > index 82f9d978..161d9f79 100644
> > --- a/src/mmap-rw-fault.c
> > +++ b/src/mmap-rw-fault.c
> > @@ -20,6 +20,7 @@
> > #include <string.h>
> > #include <errno.h>
> > #include <err.h>
> > +#include <getopt.h>
> >
> > char *filename;
> > unsigned int page_size;
> > @@ -109,11 +110,29 @@ static ssize_t do_write(int fd, const void *buf, size_t count, off_t offset)
> > return count2;
> > }
> >
> > +static void usage(const char *argv0)
> > +{
> > + fprintf(stderr, "Usage: %s [-2] {filename}\n", argv0);
> > + exit(2);
> > +}
> > +
> > int main(int argc, char *argv[])
> > {
> > - if (argc != 2)
> > - errx(1, "no test filename argument given");
> > - filename = argv[1];
> > + int opt, opt_2 = 0;
> > +
> > + while ((opt = getopt(argc, argv, "2")) != -1) {
> > + switch(opt) {
> > + case '2':
> > + opt_2 = 1;
> > + break;
> > + default:
> > + usage(argv[0]);
> > + }
> > + }
> > +
> > + if (optind + 1 != argc)
> > + usage(argv[0]);
> > + filename = argv[optind];
> >
> > page_size = ret = sysconf(_SC_PAGE_SIZE);
> > if (ret == -1)
> > @@ -179,6 +198,14 @@ int main(int argc, char *argv[])
> > errx(1, "pread (D_DIRECT) from hole is broken");
> > done();
> >
> > + if (opt_2) {
> > + init('f', O_RDWR | O_DIRECT);
> > + ret = do_write(fd, addr + page_size, page_size, page_size);
> > + if (ret != page_size)
> > + err(1, "pwrite %s (O_DIRECT): %ld != %u", filename, ret, page_size);
> > + done();
> > + }
> > +
> > if (unlink(filename))
> > err(1, "unlink %s", filename);
> >
> > diff --git a/tests/generic/728 b/tests/generic/728
> > new file mode 100755
> > index 00000000..13a88dc0
> > --- /dev/null
> > +++ b/tests/generic/728
> > @@ -0,0 +1,41 @@
> > +#! /bin/bash
> > +# SPDX-License-Identifier: GPL-2.0
> > +# Copyright (c) 2023 Red Hat, Inc. All Rights Reserved.
> > +#
> > +# FS QA Test 728
> > +#
> > +# Trigger page faults in the same file during read and write
> > +#
> > +# This is generic/647 with an additional test that writes a memory-mapped page
> > +# onto itself using direct I/O.
> > +#
> > +# The kernel will invalidate the page cache
> > +# before carrying out the write, so filesystems that fault in the target page before carrying out the direct I/O write will never make any progress.
>
> Oddly linewrapped...
Oops, I'll repost.
> How many filesystems stall when running this? ext4/btrfs/xfs didn't
> when I tried.
gfs2 got this wrong. btrfs also has page faults disabled during direct
writes, but it already fell back to buffered writes when it didn't
make progress (as does gfs2 now).
Thanks,
Andreas
> --D
>
> > +#
> > +. ./common/preamble
> > +_begin_fstest auto quick
> > +
> > +# Override the default cleanup function.
> > +_cleanup()
> > +{
> > + cd /
> > + rm -f $tmp.*
> > + rm -f $TEST_DIR/mmap-rw-fault.tmp
> > +}
> > +
> > +# Import common functions.
> > +. ./common/filter
> > +
> > +# real QA test starts here
> > +
> > +_supported_fs generic
> > +_require_test
> > +_require_odirect
> > +_require_test_program mmap-rw-fault
> > +
> > +echo "Silence is golden"
> > +
> > +$here/src/mmap-rw-fault -2 $TEST_DIR/mmap-rw-fault.tmp
> > +
> > +status=$?
> > +exit
> > diff --git a/tests/generic/728.out b/tests/generic/728.out
> > new file mode 100644
> > index 00000000..ab39f45f
> > --- /dev/null
> > +++ b/tests/generic/728.out
> > @@ -0,0 +1,2 @@
> > +QA output created by 728
> > +Silence is golden
> > --
> > 2.40.0
> >
>
