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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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?)

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.

Ian.

> First, I'm happy to provide more information about this bug as
> requsted. I recognize not all relevant data has
> been collected yet.
> 
> Detailed information about this bug can be found at
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=705124.
> 
> The executive summary is: Using Debian Testing (7.0, wheezy) dom0 with
> LVM and full disk encryption with
> Debian Stable (6.0, Squeeze) domU, transferring large files via scp or
> rsync over openswan results in data corruption, with
> eventual file system corruption. The culprit appears to be full disk
> encryption, however that evidence may not be conclusive.
> 
> While I don't mind providing additional information, I'd hate to have
> to repeat the information I've provided to the Debian bug hunting
> folks.
> 
> Thanks in advance for any help you can provide.
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel



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