Re: [PATCH 1/1] generic: test reads racing with slow reflink operations

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Nov 10, 2023 at 10:40:19PM +0800, Zorro Lang wrote:
> On Wed, Nov 08, 2023 at 01:29:28PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > XFS has a rather slow reflink operation.  While a reflink operation is
> > running, other programs cannot read the contents of the source file,
> > which is causing latency spikes.  Catherine Hoang wrote a patch to
> > permit reads, since the source file contents do not change.  This is a
> > functionality test for that patch.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Reviewed-by: Catherine Hoang <catherine.hoang@oracle.com>
> > ---
> >  configure.ac              |    1 
> >  include/builddefs.in      |    1 
> >  m4/package_libcdev.m4     |   12 ++
> >  src/Makefile              |    4 +
> >  src/t_reflink_read_race.c |  339 +++++++++++++++++++++++++++++++++++++++++++++
> >  tests/generic/1953        |   74 ++++++++++
> >  tests/generic/1953.out    |    6 +
> >  7 files changed, 437 insertions(+)
> >  create mode 100644 src/t_reflink_read_race.c
> >  create mode 100755 tests/generic/1953
> >  create mode 100644 tests/generic/1953.out
> > 
> > 
> > diff --git a/configure.ac b/configure.ac
> > index 4687d8a3c0..7333045330 100644
> > --- a/configure.ac
> > +++ b/configure.ac
> > @@ -71,6 +71,7 @@ AC_HAVE_BMV_OF_SHARED
> >  AC_HAVE_NFTW
> >  AC_HAVE_RLIMIT_NOFILE
> >  AC_HAVE_FIEXCHANGE
> > +AC_HAVE_FICLONE
> >  
> >  AC_CHECK_FUNCS([renameat2])
> >  AC_CHECK_FUNCS([reallocarray])
> > diff --git a/include/builddefs.in b/include/builddefs.in
> > index 969acf0da2..446350d5fc 100644
> > --- a/include/builddefs.in
> > +++ b/include/builddefs.in
> > @@ -73,6 +73,7 @@ HAVE_NFTW = @have_nftw@
> >  HAVE_BMV_OF_SHARED = @have_bmv_of_shared@
> >  HAVE_RLIMIT_NOFILE = @have_rlimit_nofile@
> >  HAVE_FIEXCHANGE = @have_fiexchange@
> > +HAVE_FICLONE = @have_ficlone@
> >  
> >  GCCFLAGS = -funsigned-char -fno-strict-aliasing -Wall
> >  
> > diff --git a/m4/package_libcdev.m4 b/m4/package_libcdev.m4
> > index 7f73104405..91eb64db21 100644
> > --- a/m4/package_libcdev.m4
> > +++ b/m4/package_libcdev.m4
> > @@ -173,4 +173,16 @@ AC_DEFUN([AC_HAVE_FIEXCHANGE],
> >      ]])],[have_fiexchange=yes
> >         AC_MSG_RESULT(yes)],[AC_MSG_RESULT(no)])
> >      AC_SUBST(have_fiexchange)
> > +
> > +# Check if we have FICLONE
> > +AC_DEFUN([AC_HAVE_FICLONE],
> > +  [ AC_MSG_CHECKING([for FICLONE])
> > +    AC_LINK_IFELSE([AC_LANG_PROGRAM([[
> > +#include <sys/ioctl.h>
> > +#include <linux/fs.h>
> > +    ]], [[
> > +	 ioctl(-1, FICLONE, -1);
> > +    ]])],[have_ficlone=yes
> > +       AC_MSG_RESULT(yes)],[AC_MSG_RESULT(no)])
> > +    AC_SUBST(have_ficlone)
> 
> I got below build error:
>   libtoolize: Consider adding '-I m4' to ACLOCAL_AMFLAGS in Makefile.am.
>   cp include/install-sh .
>   aclocal -I m4
>   /usr/bin/m4:m4/package_libcdev.m4:162: ERROR: end of file in string
>   autom4te: error: /usr/bin/m4 failed with exit status: 1
>   aclocal: error: autom4te failed with exit status: 1
>   make: *** [Makefile:66: configure] Error 1
> 
> I think you missed a "])" at here, below "])" belong to last AC_DEFUN.

Yep, that was a porting bug when I reshuffled the patches.

> >    ])
> > diff --git a/src/Makefile b/src/Makefile
> > index 2815f919b2..49dd2f6c1e 100644
> > --- a/src/Makefile
> > +++ b/src/Makefile
> > @@ -94,6 +94,10 @@ ifeq ($(HAVE_SEEK_DATA), yes)
> >   endif
> >  endif
> >  
> > +ifeq ($(HAVE_FICLONE),yes)
> > +     TARGETS += t_reflink_read_race
> > +endif
> > +
> >  CFILES = $(TARGETS:=.c)
> >  LDIRT = $(TARGETS) fssum
> >  
> 
> [snip]
> 
> > diff --git a/tests/generic/1953 b/tests/generic/1953
> > new file mode 100755
> > index 0000000000..058538e6fe
> > --- /dev/null
> > +++ b/tests/generic/1953
> > @@ -0,0 +1,74 @@
> > +#! /bin/bash
> > +# SPDX-License-Identifier: GPL-2.0
> > +# Copyright (c) 2023, Oracle and/or its affiliates.  All Rights Reserved.
> > +#
> > +# FS QA Test No. 1953
> > +#
> > +# Race file reads with a very slow reflink operation to see if the reads
> > +# actually complete while the reflink is ongoing.  This is a functionality
> > +# test for XFS commit f3ba4762fa56 "xfs: allow read IO and FICLONE to run
> > +# concurrently".
> > +#
> > +. ./common/preamble
> > +_begin_fstest auto clone punch
> > +
> > +# Import common functions.
> > +. ./common/filter
> > +. ./common/attr
> > +. ./common/reflink
> > +
> > +# real QA test starts here
> > +_require_scratch_reflink
> > +_require_cp_reflink
> > +_require_xfs_io_command "fpunch"
> > +_require_test_program "punch-alternating"
> > +_require_test_program "t_reflink_read_race"
> > +
> > +rm -f "$seqres.full"
> > +
> > +echo "Format and mount"
> > +_scratch_mkfs > "$seqres.full" 2>&1
> > +_scratch_mount >> "$seqres.full" 2>&1
> > +
> > +testdir="$SCRATCH_MNT/test-$seq"
> > +mkdir "$testdir"
> > +
> > +calc_space() {
> > +	blocks_needed=$(( 2 ** (fnr + 1) ))
> > +	space_needed=$((blocks_needed * blksz * 5 / 4))
> > +}
> > +
> > +# Figure out the number of blocks that we need to get the reflink runtime above
> > +# 1 seconds
> > +echo "Create a many-block file"
> > +for ((fnr = 1; fnr < 40; fnr++)); do
> > +	free_blocks=$(stat -f -c '%a' "$testdir")
> > +	blksz=$(_get_file_block_size "$testdir")
> > +	space_avail=$((free_blocks * blksz))
> > +	calc_space
> > +	test $space_needed -gt $space_avail && \
> > +		_notrun "Insufficient space for stress test; would only create $blocks_needed extents."
> > +
> > +	off=$(( (2 ** fnr) * blksz))
> > +	$XFS_IO_PROG -f -c "pwrite -S 0x61 -b 4194304 $off $off" "$testdir/file1" >> "$seqres.full"
> > +	"$here/src/punch-alternating" "$testdir/file1" >> "$seqres.full"
> > +
> > +	timeout 1s cp --reflink=always "$testdir/file1" "$testdir/garbage" || break
> 
> To make sure we have this program:
>   _require_command "$TIMEOUT_PROG" timeout
> then use $TIMEOUT_PROG at here.

<shrug> timeout is in coreutils, is that not a requirement?

Will add anyway.

> Others looks good to me, if it expects to get below failure on linux 6.6.0-rc6+.
> 
> # ./check generic/1953
> FSTYP         -- xfs (debug)
> PLATFORM      -- Linux/x86_64 hp-dl380pg8-01 6.6.0-rc6-mainline+ #7 SMP PREEMPT_DYNAMIC Thu Oct 19 22:34:28 CST 2023
> MKFS_OPTIONS  -- -f /dev/loop0
> MOUNT_OPTIONS -- -o context=system_u:object_r:root_t:s0 /dev/loop0 /mnt/scratch
> 
> generic/1953       - output mismatch (see /root/git/xfstests/results//generic/1953.out.bad)
>     --- tests/generic/1953.out  2023-11-10 22:22:12.379185281 +0800
>     +++ /root/git/xfstests/results//generic/1953.out.bad        2023-11-10 22:28:27.041801352 +0800
>     @@ -3,4 +3,4 @@
>      Create a many-block file
>      Reflink the big file
>      Terminated
>     -test completed successfully
>     +clone finished before any reads
>     ...
>     (Run 'diff -u /root/git/xfstests/tests/generic/1953.out /root/git/xfstests/results//generic/1953.out.bad'  to see the entire diff)
> Ran: generic/1953
> Failures: generic/1953
> Failed 1 of 1 tests

This output is correct for 6.6; the functionality examined by this test
was merged for 6.7-rc1.

--D

> 
> Thanks,
> Zorro
> 
> > +done
> > +echo "fnr=$fnr" >> $seqres.full
> > +
> > +echo "Reflink the big file"
> > +$here/src/t_reflink_read_race "$testdir/file1" "$testdir/file2" \
> > +	"$testdir/outcome" &>> $seqres.full
> > +
> > +if [ ! -e "$testdir/outcome" ]; then
> > +	echo "Could not set up program"
> > +elif grep -q "finished read early" "$testdir/outcome"; then
> > +	echo "test completed successfully"
> > +else
> > +	cat "$testdir/outcome"
> > +fi
> > +
> > +# success, all done
> > +status=0
> > +exit
> > diff --git a/tests/generic/1953.out b/tests/generic/1953.out
> > new file mode 100644
> > index 0000000000..8eaacb7ff0
> > --- /dev/null
> > +++ b/tests/generic/1953.out
> > @@ -0,0 +1,6 @@
> > +QA output created by 1953
> > +Format and mount
> > +Create a many-block file
> > +Reflink the big file
> > +Terminated
> > +test completed successfully
> > 
> 
>