Random Kernel Panic on Dreamplug (FS related)

[Ian Lepore]

On Tue, 2014-09-30 at 04:34 -0700, John-Mark Gurney wrote:
> Ian Lepore wrote this message on Mon, Sep 29, 2014 at 07:49 -0600:
> > On Sun, 2014-09-28 at 21:01 -0700, John-Mark Gurney wrote:
> > > Mattia Rossi wrote this message on Fri, Sep 26, 2014 at 14:19 +0200:
> > > > This might be part of the weird FFS issues the Dreamplug has and no-one 
> > > > knows why they're happening.
> > > 
> > > Are you running w/ FFS journaling?  If so, try turning it off, but
> > > keeping softupdates on..
> > > 
> > 
> > It's not an SU+J problem, or even an SU problem.  fsck finds
> > non-existant errors on filesystems known to be clean, and if
> > write-enabled it will corrupt the good filesystem when attempting to
> > correct those "errors".  This is on armv4 only, not v6.  I tested with
> > and without softupdates on.  I tested with UFS1 and UFS2 filesystems.
> > You can even do a newfs followed immediately by an fsck on it and it
> > will corrupt the fs.
> > 
> > The one thing I haven't done is opened a PR for this.
> 
> Hmm... I just tested this on my AVILA board, and I don't see this on
> either UFS1 or UFS2...  Are you doing this via HD or md?  My testing was
> via a 64MB md as I don't have a good way to attach external storage to
> my board...
> 
> If you really are seeing immediate corruption to an SD card, then I'd
> make sure that the card is getting the correct data written to it...
> 

There isn't actually any corruption on the filesystem until fsck starts
trying to fix what it thinks is wrong.  That is, fsck -n will report
problems, you then move that drive to a non-armv4 system and fsck there
reports no problems.  If you let armv4 fsck "fix" problems then move the
drive to another system and re-check, the filesystem IS corrupted at
that point.

> I'd suggest trying to run ZFS since it checksums everything it writes,
> but not sure if it'd run, and if so, how well...
> 

afaik, nobody has ever tried zfs on any arm platform.  Maybe it just
works.  I'd love to hear from someone about it.  I don't have time
myself to learn to configure and administer it.

-- Ian