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

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Message-ID: <50202987.80409@us.ibm.com>
Date:	Mon, 06 Aug 2012 13:31:03 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Sasha Levin <levinsasha928@...il.com>
CC:	Avi Kivity <avi@...hat.com>, paulmck@...ux.vnet.ibm.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	mingo@...nel.org, a.p.zijlstra@...llo.nl, prarit@...hat.com,
	tglx@...utronix.de, Dave Jones <davej@...hat.com>
Subject: Re: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks on v3.6

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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