Re: [PATCH 1/6] hfsplus: prevent btree data loss on root split

From: "Ernesto A. Fernández" <ernesto.mnd.fernandez@gmail.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/6] hfsplus: prevent btree data loss on root split
Date: Sun, 2 Sep 2018 21:06:03 -0300	[thread overview]
Message-ID: <20180903000603.bm333cbkdgyi2nox@eaf> (raw)
In-Reply-To: <20180902233236.GA27618@dastard>

On Mon, Sep 03, 2018 at 09:32:36AM +1000, Dave Chinner wrote:
> On Sun, Sep 02, 2018 at 01:33:09AM -0300, Ernesto A. Fernández wrote:
> > On Sat, Sep 01, 2018 at 02:49:26PM +1000, Dave Chinner wrote:
> > > On Fri, Aug 31, 2018 at 11:55:54AM -0300, Ernesto A. Fernández wrote:
> > > > On Thu, Aug 30, 2018 at 10:36:42PM -0700, Christoph Hellwig wrote:
> > > > > On Fri, Aug 31, 2018 at 12:58:19AM -0300, Ernesto A. Fernández wrote:
> > > > > > Creating, renaming or deleting a file may cause catalog corruption and
> > > > > > data loss.  This bug is randomly triggered by xfstests generic/027, but
> > > > > > here is a faster reproducer:
> > > > > > 
> > > > > >   truncate -s 50M fs.iso
> > > > > >   mkfs.hfsplus fs.iso
> > > > > >   mount fs.iso /mnt
> > > > > >   i=100
> > > > > >   while [ $i -le 150 ]; do
> > > > > >     touch /mnt/$i &>/dev/null
> > > > > >     ((++i))
> > > > > >   done
> > > > > >   i=100
> > > > > >   while [ $i -le 150 ]; do
> > > > > >     mv /mnt/$i /mnt/$(perl -e "print $i x82") &>/dev/null
> > > > > >     ((++i))
> > > > > >   done
> > > > > >   umount /mnt
> > > > > >   fsck.hfsplus -n fs.iso
> > > > > 
> > > > > It would be good to wire up this short reproducer as well for xfstests.
> > > > 
> > > > Yes, that's my intention. The problem is that mkfs.hfsplus does not allow
> > > > setting the size of the filesystem for scratch_mkfs_sized(); you need a
> > > > workaround with the device mapper. I think I should submit that patch first
> > > > and see if there is a problem with it.
> > > 
> > > You don't need to do that. We use loop devices like this w/ mkfs_dev
> > > quite a lot in fstests. For example, generic/361 has pretty much the
> > > exact code pattern you need....
> > 
> > I see what you mean in this case, but I really want to run every test that
> > uses _scratch_mkfs_sized(); generic/027 in particular, since it's the one
> > that found these bugs for me.
> 
> Trying to hack around SCRATCH_DEV to be some other device set up by
> _scratch_mkfs_sized is likely to break things in unexpected ways.
> Lots of library routines directly access SCRATCH_DEV or manipulate
> it in interesting ways (e.g. build their own dm constructs on it).
> 

I wasn't changing SCRATCH_DEV, the device mapper was only used briefly
on _scratch_mkfs_sized, and then again on _check_scratch_fs. Still your
point stands, Eryu already found problems with my patch.

> IMO the right thing to do is implement the size parameter in
> mkfs.hfsplus. I note that it has a dry-run capability (-N <size>)
> already allows it to simulate making a filesystem of any size, so it
> looks to me that most of what you need it to do is already in the
> mkfs code. Then you can test for the mkfs parameter in
> _scratch_mkfs_sized....

I'll look into it. I will also need to change fsck.hfsplus, since it
claims it found corruption when the filesystem doesn't fill the device.

Thanks.

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com