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Re: [Xen-API] XCP 1.0-beta: md on dom0 kernel causes kernel oops

To: Simon Rowe <simon.rowe@xxxxxxxxxxxxx>
Subject: Re: [Xen-API] XCP 1.0-beta: md on dom0 kernel causes kernel oops
From: Tomoe Sugihara <sugihara@xxxxxxxxxxxxx>
Date: Fri, 03 Dec 2010 08:03:35 +0900
Cc: Jonathan Ludlam <Jonathan.Ludlam@xxxxxxxxxxxxx>, "xen-api@xxxxxxxxxxxxxxxxxxx" <xen-api@xxxxxxxxxxxxxxxxxxx>
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On 12/02/2010 05:50 PM, Simon Rowe wrote:
On Wednesday 01 Dec 2010 23:03:48 Tomoe Sugihara wrote:

I tried the following two and both ended up with Oops.

1. just two regular HDDs --- /dev/sdc and /dev/sde or whatever.

     Here's how I reproduced just now.Very soon after dd, kernel panics.

      $ mdadm --create /dev/md0 --level=mirror --raid-devices=2 /dev/sdc
/dev/sde mdadm: /dev/sdc appears to be part of a raid array:
          level=raid1 devices=2 ctime=Mon Nov 29 15:52:53 2010
      mdadm: /dev/sde appears to be part of a raid array:
          level=raid1 devices=2 ctime=Mon Nov 29 09:34:34 2010
      Continue creating array? y
      mdadm: array /dev/md0 started.
      $ dd if=/dev/zero of=/dev/md0 bs=1M



2. dm linear devices which are on top of iscsi

    mdadm --create /dev/mirror/000008bc --auto=md --bitmap=internal
--metadata=0 --run --bitmap-chunk=65536 --delay=5   --level=1
--assume-clean --raid-devices=3 /dev/mapper/00000001-00000003
/dev/mapper/00000002-000002d7 /dev/mapper/00000003-0000050a

     Interestingly, his doesn't cause kernel panic; similar stack trace
shows up in dmsg and mdadm stalls.

We don't support (and therefore test) software RAID in XenServer. I'll some of
our kernel guys if there's anything obvious.

        Simon


Could you see the email that I reported the issue? Here's a link to the post:
http://www.mail-archive.com/xen-api@xxxxxxxxxxxxxxxxxxx/msg02151.html

As I said, the issue is introduced by dom0 custom patch, which I put a link to 
the repository below,
therefor it is not there in vanilla kernel.

http://xenbits.xen.org/XCP/linux-2.6.32.pq.hg?diff/2d68a42120cf/blktap2-ioc.diff

I would really want it to be addressed not only for our SM backend plugin but 
also for the sake
of removing the vulnerability.

Best,
Tomoe

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