qemu-kvm 0.12.4 hanging forever

[Zach Carter <z.carter@f5.com>]

Hi:

Under certain 100% reproducible circumstances, when I try to run qemu-kvm, it 
completely hangs without appearing to do anything

I have tried this with qemu-kvm 0.12.4 and with the latest code from the git 
repository. 

Here are some more interesting details.  The 64 bit host, kernel, and kvm 
kernel module are all vanilla CentOS 5.4.  If I use the kmod-
kvm-83-105.el5_4.9 version of the kernel module, it works fine.  Yum update to 
anything past that and the hang occurs 100% of the time.  Update all the way 
to the very latest CentOS 5.5 packages, and I still get the hang.  Downgrade 
just the kvm kernel modules and it starts working again.

I'm sure I could use the qemu-kvm that ships from CentOS with the 
corresponding kernel module, however that lacks certain essential features, 
including support for scsi disk drive emulation.

After messing around with gdb and some printf statements, it looks to me like 
it just loops forever and ever in the "while (1)" loop on about line 1710 of 
qemu-kvm.c.   Killing it and grabbing a backtrace shows that it is spending 
its time mostly sitting in the "select" system call on about line 1288 in 
vt.c.  Maybe its normal to sit in that loop and poll for events, but something 
else should happen eventually.  What is it waiting for?

If I add the -no-kvm option to the command line, it works fine.

Any ideas on how to further troubleshoot?

thanks!

-Zach

My command line:

/opt/qemu-git/bin/qemu-system-x86_64 -drive 
file=my.vmdk,if=scsi,cache=writeback -cdrom my.iso -boot d -nographic -m 1024 -
no-kvm-irqchip -kernel my.vmlinuz -initrd my.initrd.img -append 
'initrd=initrd.img root=/dev/ram0 console=tty0 console=ttyS0,19200 quiet 
action=install mode=silent ramdisk_size=147169 mkvm_cpu_lm 
mkvm_device=/dev/sda mkvm'