Odd hang in the Ubuntu installer

Odd hang in the Ubuntu installer

[Soren Hansen]

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Hi guys.

I'm trying to figure out what's going on with this bug:

   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/217815

The short version of the problem is that it seems that if the console is
left alone for an extended period of time, everything seems to stall
until something (moving the mouse around, pressing a key, whatever)
awakens it again.  It usually shows itself when you choose the
"Encrypted LVM" option in our installer (this process wipes the drive,
which is a rather lenghty process), since that's probably the only place
where you'd leave the console alone for a while, while still getting
some UI feedback (and suddenly lack of feedback, obviously).

It started when I backported this to the kvm version in our archive:

commit d2668b3fd41f88c18a7f9c4f1d024f0e5d9f64cf
Author: Marcelo Tosatti <mtosatti@redhat.com>
Date:   Wed Apr 2 20:20:14 2008 -0300
Subject: kvm: qemu: separate thread for IO handling


While trying to solve this problem, I noticed that that commit was just
one of a set of three patches. Applying those two:

commit 1743ef816b6cd22d100ccb80e542b8ca19c75392
Author: Marcelo Tosatti <mtosatti@redhat.com>
Date:   Wed Apr 2 20:20:15 2008 -0300
Subject: kvm: qemu: add function to handle signals

commit d84f71afaafec49e0ab3aa7a33518df04c14f38a
Author: Marcelo Tosatti <mtosatti@redhat.com>
Date:   Wed Apr 2 20:20:16 2008 -0300
Subject: kvm: qemu: notify IO thread of pending bhs

...makes it take a bit longer before it happens, but it's still very
much reproducable. Reverting those changes fixes it completely.

We've tried with kvm 66, which also exhibits this behaviour, so I'm
fairly confident I didn't mess up the patch while backporting it. In
case you're interested, the backported patch is here:

   http://people.ubuntu.com/~soren/virtio_hang.patch

The latter two commits applied without changes (with a bit of fuzz,
though).

I'm hoping one of you guys could give me a hint (or perhaps even a
patch)?

-- 
Soren Hansen               | 
Virtualisation specialist  | Ubuntu Server Team
Canonical Ltd.             | http://www.ubuntu.com/

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