linux-kernel - lguest, virtio_blk, id is not a head!

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Date:	Fri, 12 Dec 2008 20:47:28 +0100
From:	Andre Grueneberg <list.lguest@...eneberg.de>
To:	lguest@...abs.org
Cc:	linux-kernel@...r.kernel.org
Subject: lguest, virtio_blk, id is not a head!

Hi,

[I'm not regularly reading lkml, but I do read lguest, so please include
me in CC]
I'm using lguest and thus virtio_blk.
Lately I upgraded my host and guest from kernel 2.6.25 (Debian) to
vanilla 2.6.27.8. I have two virtual machines and in both I recognised
the same issue after a while.

After running for some hours the first guest showed the following
message on the console:
virtio_blk virtio1: id 1 is not a head!

Afterwards I was not able to log in to the guest anymore, so I had to
kill it. The kernel was still running -- ping was answered. Only the 
block device (with / on it) seems to have went unresponsive.

A few days later the other guest "crashed" with a similar message
(different id). Another two days later, the same happened.

I do not (yet) know how to reproduce this issue, but it seems to happen
more often. I've never seen this happen with 2.6.25, which ran for ~3
months without stop.

I'm thankful for any idea how to hunt this issue. Especially I wonder
under what (practical) circumstances one can trigger the respective code
in drivers/virtio/virtio_ring.c vring_get_buf().

Thanks,
Andre

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