Re: cpuidle: Kernel panics with AMD Opteron 6300 entering C2 - clock related

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 06/18/2015 01:21 PM, Sebastian Parschauer wrote:
> On 18.06.2015 12:52, Sebastian Parschauer wrote:
>> On 18.06.2015 11:22, Daniel Lezcano wrote:
>>> On 06/17/2015 12:06 PM, Sebastian Parschauer wrote:
>>>> Hi cpuidle maintainers,
>>>>
>>>> we notice kernel panics with CPUs from the AMD Opteron 6300 series and
>>>> kernel 3.12 when entering C2. In that C-state the clock is shut down but
>>>> the flag CPUIDLE_FLAG_TIMER_STOP isn't set. We use the TSC clock source
>>>> for performance as our servers host KVM VMs. During the panics
>>>> interrupts are enabled again and the timer interrupt corrupts the
>>>> instruction pointer and/or the stack pointer.
>>>>
>>>> Would it help to set the flag CPUIDLE_FLAG_TIMER_STOP for C2?
>>>> Or how to fix this?
>>>
>>> Did you try the flag ? Does it fix it ?
>>
>> Thanks for your reply. Unfortunately we can't roll out new kernels fast
>> (VMs have to be migrated). But we've disabled the C2 state via sysfs for
>> all CPU cores and all servers and had one more kernel panic with the
>> same call trace although C2 was (or should have been) disabled. We use
>> the menu governor and a v3.12.40 kernel.
>>
>> It's strange to me coming into the same code path with state index 2 as
>> parameter again. I think I'll prepare a kernel with some debug messages
>> when transitioning from one state to another and deploy it to a test system.
>>
>> Is there any better method to debug the cpuidle driver?
>>
>> How do you guys test it?
>>
>> Can we provide any missing additional information?
>>
>> Maybe something else corrupts the memory in an interrupt and the cpuidle
>> driver is just the one noticing an unrelated problem.
>
> Sorry, I had a closer look at the most recent crash again. It happened
> at entering C1 with disabled C2. So maybe our problem is not cpuidle
> related.

As mentioned in the previous email, disabling the idle state index 2 in 
the kernel does not prevent the firmware to auto-promote to this state.

By the way, I am not sure this is really the C2 state but the idle state 
index 2. Could you give the C state name you have in the sysfs directory ?


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