Re: BUG: ext3 corruption in domU

["Roger Pau Monné" <roger.pau@citrix.com>]

On 17/04/13 15:00, Ian Campbell 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@hellion.org.uk 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?)
> 
> The issue was initially reported with Squeeze (Jeremy 2.6.32 tree) domU
> on a Wheezy (mainline 3.2) dom0 but IIRC has also been repeated with
> Wheezy on Wheezy now so this isn't cross version confusion about barrier
> semantics AFAICT.

Hello,

I've been trying to reproduce this issue, but so far I haven't been able
to. I guess I'm missing something, so here are the steps I followed:

First, I've created a primary partition in my HDD, it's sda3, and then
I've executed the following in order to encrypt it and setup the lvm:

# cryptsetup luksFormat /dev/sda3
# cryptsetup luksOpen /dev/sda3 crypt
# pvcreate /dev/mapper/crypt
# vgcreate crypt /dev/mapper/crypt
# lvcreate -L 20G crypt -n debian

That gives me a block device /dev/crypt/debian, that I'm attaching to a
Debian DomU as xvdb, I've created a partition to fill the whole disk and
formatted it inside the guest using mkfs.ext3.

Then, inside the guest, I've scp'ed a 10G file from a remote host, and
checked the checksum, everything OK. So far, I've tested with a Dom0
kernel 3.2.0-0.bpo.4-amd64 and a DomU kernel 3.2.0-0.bpo.4-amd64 and
2.6.32-5-xen-amd64, both tests where OK.

Regards, Roger.