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Re: [Qemu-devel] race between kvm-kmod-3.0 and kvm-kmod-3.3 // was: race

From: Peter Lieven
Subject: Re: [Qemu-devel] race between kvm-kmod-3.0 and kvm-kmod-3.3 // was: race condition in qemu-kvm-1.0.1
Date: Wed, 04 Jul 2012 16:57:04 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20111108 Thunderbird/3.1.16

On 07/03/12 15:25, Avi Kivity wrote:
On 07/03/2012 04:15 PM, Peter Lieven wrote:
On 03.07.2012 15:13, Avi Kivity wrote:
On 07/03/2012 04:01 PM, Peter Lieven wrote:
Further output from my testing.

Linux 2.6.38 with included kvm module
Linux 3.0.0 with included kvm module

Linux 3.2.0 with included kvm module
Linux 2.6.28 with kvm-kmod 3.4
Linux 3.0.0 with kvm-kmod 3.4
Linux 3.2.0 with kvm-kmod 3.4

I can trigger the race with any of qemu-kvm 0.12.5, 1.0 or 1.0.1.
It might be that the code was introduced somewhere between 3.0.0
and 3.2.0 in the kvm kernel module and that the flaw is not
in qemu-kvm.

Any hints?

A bisect could tell us where the problem is.

To avoid bisecting all of linux, try

     git bisect v3.2 v3.0 virt/kvm arch/x86/kvm

would it also be ok to bisect kvm-kmod?
Yes, but note that kvm-kmod is spread across two repositories which are
not often tested out of sync, so you may get build failures.

ok, i just started with this with a 3.0 (good) and 3.2 (bad) vanilla kernel. i can confirm the bug and i am no starting to bisect. it will take while with my equipment if anyone
has a powerful testbed to run this i would greatly appreciate help.

if anyone wants to reproduce:

a) v3.2 from git.kernel.org
b) qemu-kvm 1.0.1 from sourceforge
c) ubuntu 64-bit 12.04 server cd
d) empty (e.g. all zero) hard disk image

./qemu-system-x86_64 -m 512 -cdrom /home/lieven/Downloads/ubuntu-12.04-server-amd64.iso -hda /dev/hd1/vmtest -vnc :1 -monitor stdio -boot dc

then choose boot from first harddisk and try to quit the qemu monitor with 'quit'. -> hypervisor hangs.


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