[Qemu-devel] Re: BUG: soft lockup - CPU#0 stuck for 13s! [swapper:0]

[Anthony Liguori]

On 08/25/2010 08:19 AM, Avi Kivity wrote:
>  On 08/25/2010 04:15 PM, Boris Dolgov wrote:
> > Hello!
> >
> > I try to use KVM on slackware host and centos5 guest with SMP.
> >
> > When the server is idle, I get following errors in /var/log/messages:
> > http://pastebin.com/4RrMVuXq
> >
> > Guest:
> > address@hidden ~]# uname -a
> > Linux centos-5-x64.slave 2.6.18-194.11.1.el5 #1 SMP Tue Aug 10
> > 19:05:06 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux
> >
> > Start command: /usr/local/qemu/bin/qemu-system-x86_64 -name
> > centos-5-x64 -m 384 -smp 2 -cdrom
> > /root/CentOS-5.5-x86_64-netinstall.iso -drive
> > index=0,media=disk,if=virtio,file=/dev/mapper/vgvm-centos5x64,boot=on
> > -vnc 0.0.0.0:1 -net nic,macaddr=fe:e1:de:ad:57:22 -net
> > tap,script=/usr/local/qemu/bin/qemu-ifup -monitor stdio -usb
> > -usbdevice tablet -enable-kvm
> >
> > Host:
> > address@hidden:~# uname -a
> > Linux superserver 2.6.35.3 #4 SMP Mon Aug 23 12:17:01 MSD 2010 x86_64
> > Intel(R) Xeon(R) CPU           X3460  @ 2.80GHz GenuineIntel GNU/Linux
> > address@hidden:~# /usr/local/qemu/bin/qemu-system-x86_64 -version
> > QEMU PC emulator version 0.12.5 (qemu-kvm-0.12.5), Copyright (c)
> > 2003-2008 Fabrice Bellard
> >
> > What does it mean?
>
> Looks like a bug in our USB emulation.  Copying qemu-devel to see if 
> anyone has a clue.

USB tablet emulation would not do anything that causes QEMU to block so 
it seems unlikely to me.

What's more likely is that since USB is polling based, statistically 
speaking it's more likely that a VCPU is executing that call when the 
soft lockup is detected.

Regards,

Anthony Liguori