Re: [Xen-devel] BUG: ext3 corruption in domU

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, May 29, 2013 at 07:53:39AM -0400, Anthony Sheetz wrote:
> Is there anything else I can get you at this time to help troubleshoot this?

Well, this reminds me of a ext3 bug in the 2.6.32 stable tree that 
the maintainer of ext3 would not want to backport the fix. It was an
bug that caused corruption.

If I could just remember the email thread about it. 
> 
> On Fri, May 24, 2013 at 10:20 AM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> > On Thu, May 23, 2013 at 02:19:50PM -0400, Anthony Sheetz wrote:
> >> On Wed, May 22, 2013 at 4:10 PM, Konrad Rzeszutek Wilk
> >> <konrad.wilk@xxxxxxxxxx> wrote:
> >> > On Mon, Apr 22, 2013 at 01:26:34PM +0100, Ian Campbell wrote:
> >> >> Konrad is on vacation this week, so it'll probably be next week before
> >> >> this gets looked at by him.
> >> >
> >> > And I finally got to this email in my 'vacation-mbox'
> >> >>
> >> >> Ian.
> >> >>
> >> >> On Mon, 2013-04-22 at 13:22 +0100, Anthony Sheetz wrote:
> >> >> > I realize folks are pretty busy, but we're still interested in getting
> >> >> > this problem solved, and I want to be sure it's not lost in the
> >> >> > shuffle.
> >> >> > Any chance of getting some attention for it?
> >> >> >
> >> >> > On Wed, Apr 17, 2013 at 9:00 AM, Ian Campbell 
> >> >> > <Ian.Campbell@xxxxxxxxxx> wrote:
> >> >> > > On Tue, 2013-04-16 at 18:39 +0100, Anthony Sheetz wrote:
> >> >> > >> (re-sending, first message seems to have gotten lost)
> >> >> > >>
> >> >> > >> I was referred here by Ian Campbell ijc@xxxxxxxxxxxxxx from 
> >> >> > >> bugs.debian.org.
> >> >> > >
> >> >> > > I'm here too (different hat ;-)), thanks for posting it here. I've 
> >> >> > > added
> >> >> > > some people who know about the block stuff to the CC.
> >> >> > >
> >> >> > > Guys, my suspicion is that the issue is that barriers issued by ext3
> >> >> > > inside the guest aren't making it all the way down the
> >> >> > > ext3->blkfront->blkback->lvm->dm-crypt->disk chain leading the
> >> >> > > filesystem to eventually corrupt itself.
> >> >> > >
> >> >> > > The issue seems to relate to the use of dm-crypt since
> >> >> > > ext3->blkfront->blkback->lvm->disk is reported work fine.
> >> >> > >
> >> >> > > However there is no problem with the local dom0 ext3 root filesystem
> >> >> > > which is also in the same lvm VG on the crypt device (i.e.
> >> >> > > ext3->lvm->dm-crypt->disk), so its not purely a dm-crypt issue. I 
> >> >> > > figure
> >> >> > > something is up at the blkfront->back link which causes the barriers
> >> >> > > which blkback is injecting into the block subsystem either don't 
> >> >> > > make it
> >> >> > > to the dm-crypt layer or do not DTRT once they arrive.
> >> >> > >
> >> >> > > I'm not really sure with how to proceed (or how to ask Anthony to
> >> >> > > proceed) with verifying any part of that hypothesis though.
> >> >> > >
> >> >> > > ISTR issues with old vs new style barriers or barriers with no data 
> >> >> > > in
> >> >> > > them or something, could this be related to that? (or am I thinking 
> >> >> > > of
> >> >> > > DISCARD?)
> >> >
> >> > You are using two different kernel versions. The 2.6.32 domU is only 
> >> > using
> >> > WRITE_BARRIERs, while in the 3.2 kernels that have been completly 
> >> > eliminated.
> >> > The mechanism they use is called 'WRITE_FLUSH'. The 3.2 kernel has a 
> >> > patch:
> >> > ommit 29bde093787f3bdf7b9b4270ada6be7c8076e36b
> >> > Author: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> >> > Date:   Mon Oct 10 00:42:22 2011 -0400
> >> >
> >> >     xen/blkback: Support 'feature-barrier' aka old-style BARRIER 
> >> > requests.
> >> >
> >> >
> >> > which emulates the barrier request by draining all of the oustanding 
> >> > I/Os and then
> >> > sending the WRITE_FLUSH.
> >> >
> >> > But it looks like you are hitting an issue here. Just to make sure
> >> > that is the case, what happens if you use the _same_ kernel in both dom0 
> >> > and
> >> > domU? Does it work then?
> >> >
> >>
> >> First, thank you so much for getting back to me, it's really appreciated.
> >> At this point I've forgotten if I did this with Wheezy on Wheezy, and
> >> what the result was.
> >> I'll have to test using the 3.2 kernel on the domU Debian Squeeze and
> >> get back to you. I should be able to do that early next week.
> >
> > Thank you. Also when you do this test, could you also provide the 
> > 'xenstore-ls'
> > output from dom0? And the 'dmesg' output from the guest (or at least
> > the 'xl console <guest> | tee /tmp/log' ? That would give me and idea if
> > the frontend/backend have the right negotiation parameters.
> >
> > Have a good weekend!
> 
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