Re: [PATCH v1.1 8/8] xfs: test for premature ENOSPC with large cow delalloc extents

Zorro Lang
2024-03-02T20:51:06Z

On Fri, Mar 01, 2024 at 09:52:02AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
>
> On a higly fragmented filesystem a Direct IO write can fail with -ENOSPC error
> even though the filesystem has sufficient number of free blocks.
>
> This occurs if the file offset range on which the write operation is being
> performed has a delalloc extent in the cow fork and this delalloc extent
> begins much before the Direct IO range.
>
> In such a scenario, xfs_reflink_allocate_cow() invokes xfs_bmapi_write() to
> allocate the blocks mapped by the delalloc extent. The extent thus allocated
> may not cover the beginning of file offset range on which the Direct IO write
> was issued. Hence xfs_reflink_allocate_cow() ends up returning -ENOSPC.
>
> This test addresses this issue.
>
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
> v1.1: address some missing bits and remove extraneous code
> ---
> common/rc | 14 ++++++++
> tests/xfs/1923 | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> tests/xfs/1923.out | 8 +++++
> 3 files changed, 108 insertions(+)
> create mode 100755 tests/xfs/1923
> create mode 100644 tests/xfs/1923.out
>
> diff --git a/common/rc b/common/rc
> index 30c44dddd9..d3a2a0718b 100644
> --- a/common/rc
> +++ b/common/rc
> @@ -1873,6 +1873,20 @@ _require_scratch_delalloc()
> _scratch_unmount
> }
>
> +# Require test fs supports delay allocation.
> +_require_test_delalloc()
> +{
> + _require_command "$FILEFRAG_PROG" filefrag
> +
> + rm -f $TEST_DIR/testy
> + $XFS_IO_PROG -f -c 'pwrite 0 64k' $TEST_DIR/testy &> /dev/null
> + $FILEFRAG_PROG -v $TEST_DIR/testy 2>&1 | grep -q delalloc
> + res=$?
> + rm -f $TEST_DIR/testy
> + test $res -eq 0 || \
> + _notrun "test requires delayed allocation buffered writes"
> +}
> +
> # this test needs a test partition - check we're ok & mount it
> #
> _require_test()
> diff --git a/tests/xfs/1923 b/tests/xfs/1923
> new file mode 100755
> index 0000000000..7068fda64c
> --- /dev/null
> +++ b/tests/xfs/1923
> @@ -0,0 +1,86 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2022-2024 Oracle. All Rights Reserved.
> +#
> +# FS QA Test No. 1923
> +#
> +# This is a regression test for "xfs: Fix false ENOSPC when performing direct
> +# write on a delalloc extent in cow fork". If there is a lot of free space but
> +# it is very fragmented, it's possible that a very large delalloc reservation
> +# could be created in the CoW fork by a buffered write. If a directio write
> +# tries to convert the delalloc reservation to a real extent, it's possible
> +# that the allocation will succeed but fail to convert even the first block of
> +# the directio write range. In this case, XFS will return ENOSPC even though
> +# all it needed to do was to keep converting until the allocator returns ENOSPC
> +# or the first block of the direct write got some space.
> +#
> +. ./common/preamble
> +_begin_fstest auto quick clone
> +
> +_cleanup()
> +{
> + cd /
> + rm -f $file1 $file2 $fragmentedfile
> +}
> +
> +# Import common functions.
> +. ./common/reflink
> +. ./common/inject
> +
> +# real QA test starts here
> +_fixed_by_kernel_commit d62113303d69 \
> + "xfs: Fix false ENOSPC when performing direct write on a delalloc extent in cow fork"
> +
> +# Modify as appropriate.
> +_supported_fs xfs
> +_require_test_program "punch-alternating"
> +_require_test_reflink
> +_require_xfs_io_error_injection "bmap_alloc_minlen_extent"
> +_require_test_delalloc
> +
> +file1=$TEST_DIR/file1.$seq
> +file2=$TEST_DIR/file2.$seq
> +fragmentedfile=$TEST_DIR/fragmentedfile.$seq
> +
> +rm -f $file1 $file2 $fragmentedfile
> +
> +# COW operates on pages, so we must not perform operations in units smaller
> +# than a page.
> +blksz=$(_get_file_block_size $TEST_DIR)
> +pagesz=$(_get_page_size)
> +if (( $blksz < $pagesz )); then
> + blksz=$pagesz
> +fi
> +
> +echo "Create source file"
> +$XFS_IO_PROG -f -c "pwrite 0 $((blksz * 256))" $file1 >> $seqres.full
> +
> +sync
> +
> +echo "Create Reflinked file"
> +_cp_reflink $file1 $file2 >> $seqres.full
> +
> +echo "Set cowextsize"
> +$XFS_IO_PROG -c "cowextsize $((blksz * 128))" -c stat $file1 >> $seqres.full
> +
> +echo "Fragment FS"
> +$XFS_IO_PROG -f -c "pwrite 0 $((blksz * 512))" $fragmentedfile >> $seqres.full
> +sync
> +$here/src/punch-alternating $fragmentedfile
> +
> +echo "Allocate block sized extent from now onwards"
> +_test_inject_error bmap_alloc_minlen_extent 1
> +
> +echo "Create big delalloc extent in CoW fork"
> +$XFS_IO_PROG -c "pwrite 0 $blksz" $file1 >> $seqres.full
> +
> +sync
> +
> +$XFS_IO_PROG -c 'bmap -elpv' -c 'bmap -celpv' $file1 >> $seqres.full

The "-c" option might get:

$ xfs_io -c "bmap -celpv" testfile
xfs_io: xfsctl(XFS_IOC_GETBMAPX) iflags=0x28 ["testfile"]: Invalid argument

It will break the golden image, can we redirect stderr to $seqres.full,
as it's just for debug? If you agree, I can help to change that by adding
"2>&1" at the end. Or you hope to deal with it by other method?

Thanks,
Zorro

> +
> +echo "Direct I/O write at offset 3FSB"
> +$XFS_IO_PROG -d -c "pwrite $((blksz * 3)) $((blksz * 2))" $file1 >> $seqres.full
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/xfs/1923.out b/tests/xfs/1923.out
> new file mode 100644
> index 0000000000..a0553cf3ee
> --- /dev/null
> +++ b/tests/xfs/1923.out
> @@ -0,0 +1,8 @@
> +QA output created by 1923
> +Create source file
> +Create Reflinked file
> +Set cowextsize
> +Fragment FS
> +Allocate block sized extent from now onwards
> +Create big delalloc extent in CoW fork
> +Direct I/O write at offset 3FSB
>