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

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

On Thu, Jul 07, 2022 at 08:06:39PM +0800, Zorro Lang wrote:
> 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?

Ok.

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

Oops, will delete.

> > +_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)

Ooh, nice suggestion.  I"ll convert the test.

> > +
> > +# 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?

Nope, that was an oversight on my part.  I'll add
_require_scratch_xfs_crc to the start of the test.

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

Yep.

> > +	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?

Right.  We're setting up the empty leaf block 0 to check that the kernel
and fsck tools do /not/ flag this as corruption.

> Or xfs_repair should blame the empty leaf block?

...though repair run in not-dryrun mode will free the empty leaf block 0
if it finds one.

> > +		-c print >> $seqres.full
> > +}
> > +
> > +make_empty_leaf $e0_ino || exit
> 
> How about call _fail() directly in make_empty_leaf, if [ "$magic" != "0x3bee" ]

_require_scratch_xfs_crc should take care of that.

> > +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?

Correct.

--D

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