Re: KVM bug, git bisected

[Rik van Riel]

On 03/29/2010 12:11 PM, Rik van Riel wrote:
> On 03/27/2010 08:43 AM, Kent Overstreet wrote:
> > commit 5beb49305251e5669852ed541e8e2f2f7696c53e
> > Author: Rik van Riel <riel@xxxxxxxxxx>
> > Date: Fri Mar 5 13:42:07 2010 -0800
> >
> > mm: change anon_vma linking to fix multi-process server scalability issue
> >
> > I get this when starting kvm. The warning hasn't caused me problems, but
> > I've also been getting a scheduling while atomic panic when I start kvm
> > that I can only reproduce when I don't want to. It's definitely config
> > dependent, I'd guess preempt might have something to do with it.
>
>  From your trace, it looks like mm_take_all_locks is taking close
> to 256 locks, which is where the preempt_count could overflow into
> the softirq count.
>
> Since kvm-qemu is exec'd, I am guessing you have a very large
> number of VMAs in your qemu process. Is that correct?

I just took a look at a qemu-kvm process on my own system.

It has a staggering 385 VMAs!

That definately has the potential of overflowing PREEMPT_BITS
when undergoing mm_take_all_locks...

> Peter, would it be safe to increase PREEMPT_BITS to eg. 10?

Looks like we'll have to.   At least on 64 bits...
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/