Re: mm: OS boot failed when set command-line kmemcheck=1

[Xishi Qiu]

On 2014/2/26 18:14, Vegard Nossum wrote:

> On 26 February 2014 09:43, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> On Wed, Feb 19, 2014 at 02:24:41PM -0800, David Rientjes wrote:
>>> On Wed, 19 Feb 2014, Xishi Qiu wrote:
>>>
>>>> Here is a warning, I don't whether it is relative to my hardware.
>>>> If set "kmemcheck=1 nowatchdog", it can boot.
>>>>
>>>> code:
>>>>     ...
>>>>     pte = kmemcheck_pte_lookup(address);
>>>>     if (!pte)
>>>>             return false;
>>>>
>>>>     WARN_ON_ONCE(in_nmi());
>>>>
>>>>     if (error_code & 2)
>>>>     ...
>>
>> That code seems to assume NMI context cannot fault; this is false since
>> a while back (v3.9 or thereabouts).
>>
>>>> [   10.920757]  [<ffffffff810452c1>] kmemcheck_fault+0xb1/0xc0
>>>> [   10.920760]  [<ffffffff814d262b>] __do_page_fault+0x39b/0x4c0
>>>> [   10.920763]  [<ffffffff814d2829>] do_page_fault+0x9/0x10
>>>> [   10.920765]  [<ffffffff814cf222>] page_fault+0x22/0x30
>>>> [   10.920774]  [<ffffffff8101eb02>] intel_pmu_handle_irq+0x142/0x3a0
>>>> [   10.920777]  [<ffffffff814d0655>] perf_event_nmi_handler+0x35/0x60
>>>> [   10.920779]  [<ffffffff814cfe83>] nmi_handle+0x63/0x150
>>>> [   10.920782]  [<ffffffff814cffd3>] default_do_nmi+0x63/0x290
>>>> [   10.920784]  [<ffffffff814d02a8>] do_nmi+0xa8/0xe0
>>>> [   10.920786]  [<ffffffff814cf527>] end_repeat_nmi+0x1e/0x2e
>>
>> And this does indeed show a fault from NMI context; which is totally
>> expected.
>>
>> kmemcheck needs to be fixed; but I've no clue how any of that works.
> 
> IIRC the reason we don't support page faults in NMI context is that we
> may already be handling an existing fault (or trap) when the NMI hits.
> So that would mess up kmemcheck's working state. I don't really see
> that anything has changed in this respect lately, so it could always
> have been broken.
> 
> I think the way we dealt with this before was just to make sure than
> NMI handlers don't access any kmemcheck-tracked memory (i.e. to make
> sure that all memory touched by NMI handlers has been marked NOTRACK).
> And the purpose of this warning is just to tell us that something
> inside an NMI triggered a page fault (in this specific case, it seems
> to be intel_pmu_handle_irq).
> 
> I guess there are two ways forward:
> 
>  - create a stack of things that kmemcheck is working on, so that we
> handle recursive page faults
>  - try to figure out why intel_pmu_handle_irq() faults and add a
> (kmemcheck-specific) workaround for it
> 
> Incidentally, do you remember what exactly changed wrt page faults in
> NMI context?
> 
> 
> Vegard
> 
> .
> 

Hi Vegardï

I use PERF_COUNT_HW_CACHE_MISSES instead of PERF_COUNT_HW_CPU_CYCLESï
and change watchdog_thresh to a large value, then OS boot successfully. 
I don't know why.

static struct perf_event_attr wd_hw_attr = {
	.type		= PERF_TYPE_HARDWARE,
	.config		= PERF_COUNT_HW_CPU_CYCLES, -> change to PERF_COUNT_HW_CACHE_MISSES
	.size		= sizeof(struct perf_event_attr),
	.pinned		= 1,
	.disabled	= 1,
};

Thanks,
Xishi Qiu

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