Re: [PATCH v2] common/xfs: wipe the XFS superblock of each AGs

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Sun, Sep 22, 2019 at 07:25:12PM +0800, Zorro Lang wrote:
> On Fri, Sep 20, 2019 at 08:34:43AM -0700, Darrick J. Wong wrote:
> > On Fri, Sep 20, 2019 at 02:23:27PM +0800, Zorro Lang wrote:
> > > xfs/030 always fails after d0e484ac699f ("check: wipe scratch devices
> > > between tests") get merged.
> > > 
> > > Due to xfs/030 does a sized(100m) mkfs. Before we merge above commit,
> > > mkfs.xfs detects an old primary superblock, it will write zeroes to
> > > all superblocks before formatting the new filesystem. But this won't
> > > be done if we wipe the first superblock(by merging above commit).
> > > 
> > > That means if we make a (smaller) sized xfs after wipefs, those *old*
> > > superblocks which created by last time mkfs.xfs will be left on disk.
> > > Then when we do xfs_repair, if xfs_repair can't find the first SB, it
> > > will go to find those *old* SB at first. When it finds them,
> > > everyting goes wrong.
> > > 
> > > So I try to get XFS AG geometry(by default) and then try to erase all
> > > superblocks. Thanks Darrick J. Wong helped to analyze this issue.
> > > 
> > > Reported-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com>
> > > Signed-off-by: Zorro Lang <zlang@redhat.com>
> > > ---
> > > 
> > > Hi,
> > > 
> > > V2 did below changes:
> > > 1) Use xfs_db to detect the real xfs geometry
> > > 2) Do a $FSTYP specified wipe before trying to wipefs all scratch devices
> > > 
> > > Thanks,
> > > Zorro
> > > 
> > >  common/rc  |  8 ++++++++
> > >  common/xfs | 20 ++++++++++++++++++++
> > >  2 files changed, 28 insertions(+)
> > > 
> > > diff --git a/common/rc b/common/rc
> > > index 66c7fd4d..56329747 100644
> > > --- a/common/rc
> > > +++ b/common/rc
> > > @@ -4045,6 +4045,14 @@ _try_wipe_scratch_devs()
> > >  {
> > >  	test -x "$WIPEFS_PROG" || return 0
> > >  
> > > +	# Do specified filesystem wipe at first
> > > +	case "$FSTYP" in
> > > +	"xfs")
> > > +		_try_wipe_scratch_xfs
> > > +		;;
> > > +	esac
> > > +
> > > +	# Then do wipefs on all scratch devices
> > >  	for dev in $SCRATCH_DEV_POOL $SCRATCH_DEV $SCRATCH_LOGDEV $SCRATCH_RTDEV; do
> > >  		test -b $dev && $WIPEFS_PROG -a $dev
> > >  	done
> > > diff --git a/common/xfs b/common/xfs
> > > index 1bce3c18..082a1744 100644
> > > --- a/common/xfs
> > > +++ b/common/xfs
> > > @@ -884,3 +884,23 @@ _xfs_mount_agcount()
> > >  {
> > >  	$XFS_INFO_PROG "$1" | grep agcount= | sed -e 's/^.*agcount=\([0-9]*\),.*$/\1/g'
> > >  }
> > > +
> > > +# Wipe the superblock of each XFS AGs
> > > +_try_wipe_scratch_xfs()
> > > +{
> > > +	local num='^[0-9]+$'
> > > +	local agcount
> > > +	local agsize
> > > +	local dbsize
> > > +
> > > +	agcount=`_scratch_xfs_get_sb_field agcount 2>/dev/null`
> > > +	agsize=`_scratch_xfs_get_sb_field agblocks 2>/dev/null`
> > > +	dbsize=`_scratch_xfs_get_sb_field blocksize 2>/dev/null`
> > > +
> > > +	if [[ $agcount =~ $num && $agsize =~ $num && $dbsize =~ $num ]];then
> > > +		for ((i = 0; i < agcount; i++)); do
> > > +			$XFS_IO_PROG -c "pwrite $((i * dbsize * agsize)) $dbsize" \
> > > +				$SCRATCH_DEV >/dev/null;
> > > +		done
> > > +	fi
> > 
> > What happened to the loop that simulates a _scratch_mkfs_xfs run (to get
> > the AG geometry) and then zaps that too?  You need both zeroing loops to
> > make sure xfs/030 doesn't trip over old superblocks, right?
> 
> Hi,
> 
> Sorry I'm not sure what you mean. Do you mean I'd better to do two zeroing
> loops, one is as above, the other is for default mkfs.xfs geometry as
> below[1]?

Yes.

--D

> Thanks,
> Zorro
> 
> [1]
>   local tmp=`mktemp -u`
>   _scratch_mkfs_xfs -N 2>/dev/null | perl -ne '
>     if (/^meta-data=.*\s+agcount=(\d+), agsize=(\d+) blks/) {
>       print STDOUT "agcount=$1\nagsize=$2\n";
>     }
>     if (/^data\s+=\s+bsize=(\d+)\s/) {
>       print STDOUT "dbsize=$1\n";
>     }' > $tmp.mkfs
> 
>   . $tmp.mkfs
>   if [ -n "$agcount" -a -n "$agsize" -a -n "$dbsize" ];then
>     for ((i = 0; i < agcount; i++)); do
>       $XFS_IO_PROG -c "pwrite $((i * dbsize * agsize)) $dbsize" \
>          $SCRATCH_DEV >/dev/null;
>     done
>   fi
>   rm -f $tmp.mkfs
> 
> 
> 
> > 
> > --D
> > 
> > > +}
> > > -- 
> > > 2.20.1
> > >