Re: 2.6.35-rc1 regression with pvclock and smp guests

Avi Kivity
2010-07-25T08:44:30Z

On 07/22/2010 03:53 PM, Andre Przywara wrote:
> Hi,
>
> I found a regression with pvclock and SMP KVM _guests_.
> PVCLOCK enabled guest kernels boot with qemu-kvm.git and with smp=1,
> but with smp=2 halt at:
>
> Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
> (last line shown)
>
> I bisected this down to:
> commit 489fb490dbf8dab0249ad82b56688ae3842a79e8
> Author: Glauber Costa <glommer@redhat.com>
> Date: Tue May 11 12:17:40 2010 -0400
>
> x86, paravirt: Add a global synchronization point for pvclock
>
> One commit before works, smp=1 always works, disabling PVCLOCK works.
> Using qemu-kvm-0.12.4 works, too.
> Having PVCLOCK enabled and with smp=2 the kernel halts without any
> further message.
> This is still the case with the lastest tip.
> Even pinning both VCPU threads to the same host core show the bug.
> The bug triggers on all hosts I tested, an single socket quadcore
> Athlon, a dual socket dualcore K8-Opteron and a quad socket 12core
> Opteron.
>
> Please note that this is the guest kernel, the host kernel does not
> matter.
>
> I have no idea (and don't feel like ;-) debugging this, so I hope
> someone will find and fix the bug.

Does this go away with CONFIG_DEBUG_RODATA=n? If so, it's a known bug
in the atomic_*() clobber lists.

--
error compiling committee.c: too many arguments to function