qemu-kvm 0.12.4 hanging forever

qemu-kvm 0.12.4 hanging forever

[Zach Carter]

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'

Re: qemu-kvm 0.12.4 hanging forever

[Brian Jackson]

On Thursday, July 01, 2010 05:37:29 pm Zach Carter wrote:
> 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.


That's pretty well known. Use a newer kernel with a newer qemu-kvm, or use the 
packages that come with CentOS.


> 
> 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.


There's a reason Redhat disables scsi support in their kvm... it's not really 
suggested to use it.


> 
> 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'
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Re: qemu-kvm 0.12.4 hanging forever

[Zach Carter]

On Thursday 01 July 2010 16:02:26 Brian Jackson wrote:
> > 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.
> 
> That's pretty well known. Use a newer kernel with a newer qemu-kvm, or use
> the  packages that come with CentOS.

I looked though mail lists and searched with google for quite a while and 
didn't anything that sounded the same.  Is there a bug reference or some other 
search term I could use to find others discussing this issue?

> > 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.
> 
> There's a reason Redhat disables scsi support in their kvm... it's not
> really  suggested to use it.

What specific reason is that?  The kvm.spec %changelog references RedHat 
bugzilla 512837, however I am not authorized to access it.

scsi is a hard requirement for us, even if we have to stay on the old kernel 
module.  

Any additional insight would be much appreciated.

thanks,

-Zach

Re: qemu-kvm 0.12.4 hanging forever

[David S. Ahern]

On 07/02/10 11:28, Zach Carter wrote:
> On Thursday 01 July 2010 16:02:26 Brian Jackson wrote:

>>> 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.
>>
>> There's a reason Redhat disables scsi support in their kvm... it's not
>> really  suggested to use it.
> 
> What specific reason is that?  The kvm.spec %changelog references RedHat 
> bugzilla 512837, however I am not authorized to access it.
> 
> scsi is a hard requirement for us, even if we have to stay on the old kernel 
> module.  
> 
> Any additional insight would be much appreciated.

I've used SCSI for RHEL3 and RHEL4 guests for years. Performance is
significantly better than IDE. I have yet to have a guest crash because
of it.

David


> 
> thanks,
> 
> -Zach
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