Re: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks on v3.6

[John Stultz]

On 08/06/2012 11:28 AM, Sasha Levin wrote:
> On 08/06/2012 08:20 PM, John Stultz wrote:
> > On 08/06/2012 10:21 AM, John Stultz wrote:
> > > On 08/05/2012 09:55 AM, Sasha Levin wrote:
> > > > On 07/30/2012 03:17 PM, Avi Kivity wrote:
> > > > > Possible causes:
> > > > >    - the APIC calibration in the guest failed, so it is programming too
> > > > > low values into the timer
> > > > >    - it actually needs 1 us wakeups and then can't keep up (esp. as kvm
> > > > > interrupt injection is slowing it down)
> > > > >
> > > > > You can try to find out by changing
> > > > > arch/x86/kvm/lapic.c:start_lapic_timer() to impose a minimum wakeup of
> > > > > (say) 20 microseconds which will let the guest live long enough for you
> > > > > to ftrace it and see what kind of timers it is programming.
> > > > I've kept trying to narrow it down, and found out It's triggerable using adjtimex().
> > Sorry, one more question: Could you provide details on how is it trigger-able using adjtimex?
> It triggers after a while of fuzzing using trinity of just adjtimex ('./trinity --quiet -l off -cadjtimex').
>
> Trinity is available here: http://git.codemonkey.org.uk/?p=trinity.git .
>
> Let me know if I can help further with reproducing this, I can probably copy over my testing environment to some other host if you'd like.
So far no luck. Dmesg mostly just gets filled up with trinity-child 
OOMs.   How much memory are you running with?

Are you running trinity as root or as some user that has CAP_SYS_TIME 
and can actually change values via adjtimex? Or does it trip just by 
reading the values?

thanks
-john


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