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

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

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 ?

> ==========
> Additional debug info:
>
> BUG: unable to handle kernel NULL pointer dereference at           (null)
> IP: [<          (null)>]           (null)
> ...
> Call trace:
> [<ffffffff815af9b5>] cpuidle_idle_call+0xc5/0x150
> [<ffffffff8100b529>] arch_cpu_idle+0x9/0x20
> [<ffffffff81092e6f>] cpu_startup_entry+0xaf/0x240
> [<ffffffff8102df4b>] start_secondary+0x1db/0x240
>
> The CPUs provide three C-states:
> 0: POLL
> 1: C1
> 2: C2
>
> C2 information from the crash dump:
>
>> {
>>        name = "C2\000\000\000\000\000\000\000\000\000\000\000\000\000",
>>        desc = "ACPI IOPORT 0x815\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
>>        flags = 1,
>>        exit_latency = 100,
>>        power_usage = 0,
>>        target_residency = 200,
>>        disabled = false,
>>        enter = 0xffffffffa00ab026 <acpi_idle_enter_simple>,
>>        enter_dead = 0xffffffffa00aa39c <acpi_idle_play_dead>
>> }
>
> Assembly level analysis:
>
>> RDX: 0000000225c17d03
>
> So EDX is 00000002 and that's the entered state C2.
>
>> RDI: ffffffff81c15540
>> ..
>> crash> info symbol 0xffffffff81c15540
>> clocksource_tsc in section .data
>>
>> crash> disassemble cpuidle_enter_state
>> ...
>>     0xffffffff815af5fc <+60>:    callq  0xffffffff8109b360 <ktime_get>
>>     0xffffffff815af601 <+65>:    sti
>>     0xffffffff815af602 <+66>:    sub    %r13,%rax <- here rdi still points to clocksource_tsc
>>     0xffffffff815af605 <+69>:    mov    %rax,%rdi <- rdi is overwritten by the ktime_get return address


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