Re: [PATCH 1/2] xfs: make sure that we handle empty xattr leaf blocks ok

[Zorro Lang <zlang@redhat.com>]

On Tue, Jul 05, 2022 at 03:02:28PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Make sure that the kernel can handle empty xattr leaf blocks properly,
> since we've screwed this up enough times.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  tests/xfs/845 |  131 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 131 insertions(+)
>  create mode 100755 tests/xfs/845
> 
> 
> diff --git a/tests/xfs/845 b/tests/xfs/845
> new file mode 100755
> index 00000000..4a846e57
> --- /dev/null
> +++ b/tests/xfs/845
> @@ -0,0 +1,131 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2022 Oracle.  All Rights Reserved.
> +#
> +# FS QA Test 845
> +#
> +# Make sure that XFS can handle empty leaf xattr blocks correctly.  These
> +# blocks can appear in files as a result of system crashes in the middle of
> +# xattr operations, which means that we /must/ handle them gracefully.
> +# Check that read and write verifiers won't trip, that the get/list/setxattr
> +# operations don't stumble over them, and that xfs_repair will offer to remove
> +# the entire xattr fork if the root xattr leaf block is empty.
> +#
> +# Regression test for kernel commit:
> +#
> +# af866926d865 ("xfs: empty xattr leaf header blocks are not corruption")
> +#
> +. ./common/preamble
> +_begin_fstest auto quick attr
> +
> +# Override the default cleanup function.
> +# _cleanup()
> +# {
> +# 	cd /
> +# 	rm -r -f $tmp.*
> +# }

Remove this part directly?

> +
> +# Import common functions.
> +. ./common/filter
> +. ./common/attr
> +
> +# real QA test starts here
> +
> +# Modify as appropriate.
      ^^
      This comment is useless

> +_supported_fs xfs
> +_require_scratch
> +_fixed_by_kernel_commit af866926d865 "xfs: empty xattr leaf header blocks are not corruption"
> +
> +_scratch_mkfs_xfs | _filter_mkfs >$seqres.full 2>$tmp.mkfs
> +cat $tmp.mkfs >> $seqres.full
> +source $tmp.mkfs
> +_scratch_mount
> +
> +$XFS_IO_PROG -f -c 'pwrite -S 0x58 0 64k' $SCRATCH_MNT/largefile >> $seqres.full
> +$XFS_IO_PROG -f -c "pwrite -S 0x58 0 $isize" $SCRATCH_MNT/smallfile >> $seqres.full
> +
> +smallfile_md5=$(md5sum < $SCRATCH_MNT/smallfile)
> +largefile_md5=$(md5sum < $SCRATCH_MNT/largefile)

Hmm... is the tail '-' (printed by md5sum) as you wish? How about use the
_md5_checksum() in common/rc ? (Same as below small_md5 and large_md5 part)

> +
> +# Try to force the creation of a single leaf block in each of three files.
> +# The first one gets a local attr, the second a remote attr, and the third
> +# is left for scrub and repair to find.
> +touch $SCRATCH_MNT/e0
> +touch $SCRATCH_MNT/e1
> +touch $SCRATCH_MNT/e2
> +
> +$ATTR_PROG -s x $SCRATCH_MNT/e0 < $SCRATCH_MNT/smallfile >> $seqres.full
> +$ATTR_PROG -s x $SCRATCH_MNT/e1 < $SCRATCH_MNT/smallfile >> $seqres.full
> +$ATTR_PROG -s x $SCRATCH_MNT/e2 < $SCRATCH_MNT/smallfile >> $seqres.full
> +
> +e0_ino=$(stat -c '%i' $SCRATCH_MNT/e0)
> +e1_ino=$(stat -c '%i' $SCRATCH_MNT/e1)
> +e2_ino=$(stat -c '%i' $SCRATCH_MNT/e2)
> +
> +_scratch_unmount
> +
> +# We used to think that it wasn't possible for empty xattr leaf blocks to
> +# exist, but it turns out that setting a large xattr on a file that has no
> +# xattrs can race with a log flush and crash, which results in an empty
> +# leaf block being logged and recovered.  This is rather hard to trip, so we
> +# use xfs_db to turn a regular leaf block into an empty one.
> +make_empty_leaf() {
> +	local inum="$1"
> +
> +	echo "editing inode $inum" >> $seqres.full
> +
> +	magic=$(_scratch_xfs_get_metadata_field hdr.info.magic "inode $inum" "ablock 0")
> +	if [ "$magic" = "0xfbee" ]; then
> +		_notrun "V4 filesystems deprecated"

Can _require_scratch_xfs_crc (at beginning) help that? Or is there a way to
get a v4 leaf block when crc isn't enabled?

> +		return 1

I think _notrun will exit directly, this "return 1" never be run.

> +	fi
> +
> +	magic=$(_scratch_xfs_get_metadata_field hdr.info.hdr.magic "inode $inum" "ablock 0")
> +	if [ "$magic" != "0x3bee" ]; then
> +		echo "inode $inum ablock 0 is not a leaf block?"
> +		_scratch_xfs_db -x -c "inode $inum" -c "ablock 0" -c print >> $seqres.full
> +		return 1
> +	fi
> +
> +	base=$(_scratch_xfs_get_metadata_field "hdr.freemap[0].base" "inode $inum" "ablock 0")
> +
> +	_scratch_xfs_db -x -c "inode $inum" -c "ablock 0" \
> +		-c "write -d hdr.count 0" \
> +		-c "write -d hdr.usedbytes 0" \
> +		-c "write -d hdr.firstused $dbsize" \
> +		-c "write -d hdr.freemap[0].size $((dbsize - base))" \

Nice trick:) Do we expect there's not corruption (can be found by xfs_repair)
at here? Or xfs_repair should blame the empty leaf block?

> +		-c print >> $seqres.full
> +}
> +
> +make_empty_leaf $e0_ino || exit

How about call _fail() directly in make_empty_leaf, if [ "$magic" != "0x3bee" ]

> +make_empty_leaf $e1_ino
> +make_empty_leaf $e2_ino
> +
> +_scratch_mount
> +
> +# Check that listxattr/getxattr/removexattr do nothing.
> +$ATTR_PROG -l $SCRATCH_MNT/e0 2>&1 | _filter_scratch
> +$ATTR_PROG -g x $SCRATCH_MNT/e0 2>&1 | _filter_scratch
> +$ATTR_PROG -r x $SCRATCH_MNT/e0 2>&1 | _filter_scratch
> +
> +# Add a small attr to e0
> +$ATTR_PROG -s x $SCRATCH_MNT/e0 < $SCRATCH_MNT/smallfile > /dev/null
> +$ATTR_PROG -l $SCRATCH_MNT/e0 2>&1 | sed -e 's/\([0-9]*\) byte/XXX byte/g' | _filter_scratch
> +small_md5="$($GETFATTR_PROG -n user.x --absolute-names --only-values $SCRATCH_MNT/e0 | md5sum)"
> +test "$small_md5" = "$smallfile_md5" || \
> +	echo "smallfile $smallfile_md5 does not match small attr $small_md5"
> +
> +# Add a large attr to e1
> +$ATTR_PROG -s x $SCRATCH_MNT/e1 < $SCRATCH_MNT/largefile > /dev/null
> +$ATTR_PROG -l $SCRATCH_MNT/e1 2>&1 | _filter_scratch
> +large_md5="$($GETFATTR_PROG -n user.x --absolute-names --only-values $SCRATCH_MNT/e1 | md5sum)"
> +test "$large_md5" = "$largefile_md5" || \
> +	echo "largefile $largefile_md5 does not match large attr $large_md5"
> +
> +
> +# Leave e2 to try to trip the repair tools, since xfs_repair used to flag
> +# empty leaf blocks incorrectly too.

So we expect there's not corruption at here, and the empty leaf block can
be used properly?

Thanks,
Zorro

> +
> +# success, all done
> +status=0
> +exit
>