[CentOS-virt] BUG: soft lockup detected on CPU#?

Ross S. W. Walker rwalker at medallion.com
Tue Jan 22 17:58:42 UTC 2008

Brett Worth wrote:
> Hello All.
> I've just started looking into Xen and have a test 
> environment in place.  I'm seeing an
> annoying problem that I thought worthy of a post.
> Config:
> I have 2 x HP DL585 servers each with 4 Dual core Opterons 
> (non-vmx) and 16GB RAM
> configured as Xen servers.  These run CentOS 5.1 with the 
> latest updates applied.  These
> system both attach to an iSCSI target which is an HP DL385 
> running ietd and serving SAN
> based storage.
> I have a test VM running CentOS 5.1 also updated.
> Problem:
> If I run the VM on a single server everything is OK.  If I do 
> a migrate of the VM to the
> other server I start getting random "BUG: soft lockup 
> detected on CPU#?" messages on the
> VM console.  The messages seem to happen with IO but not 
> every time.  A reboot of the VM
> on the new server will stop these messages.
> I've also left the VM running overnight a couple of times and 
> when I do I find that any
> external sessions (ssh) are hung in the morning but the 
> console session is not.  New ssh
> sessions can be started and seem to work.
> After much googling it looks like the kernel messages can 
> occur if dom0 is very busy but
> mine is not.
> Any suggestions?

The soft lockup is technically not a BUG.

You will see these errors if an IRQ takes more then 10 seconds
to respond.

In your case I would take a look at your iSCSI setup and the
time it takes to migrate the VM from one node to another along
with SCSI reserve/release setup on the iSCSI target.

I also have been using the Xen 3.2 RPMs off xen.org to CentOS
5.1 which good results, the VM migration may run smoother and
quicker in Xen 3.2, but in doing so you take Xen off the
reservation, if your OK with that it may fix your issues.


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