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

[Anthony Sheetz <sheetzam@xxxxxxxxxxx>]

Is there anything else I can get you at this time to help troubleshoot this?

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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