Re: [tip:x86/urgent] x86/mce: Fix the MCE poll timer logic

From: Chen Gong
Date: Wed Jun 06 2012 - 05:52:11 EST


ä 2012/6/6 17:27, Thomas Gleixner åé:
> On Wed, 6 Jun 2012, Chen Gong wrote:
>> In fact, there still exists another potential issue:
>>
>> static void __mcheck_cpu_init_timer(void)
>> {
>> struct timer_list *t = &__get_cpu_var(mce_timer);
>> unsigned long iv = __this_cpu_read(mce_next_interval);
>>
>> setup_timer(t, mce_timer_fn, smp_processor_id());
>>
>> if (mce_ignore_ce)
>> return;
>>
>> __this_cpu_write(mce_next_interval, iv);
>> if (!iv)
>> return;
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> Because the 2nd patch is not merged yet, so here iv is zero when this
>> function is called, which means at the beginning, the poll timers are
>> not registered until some other conditions trigger *add_timer_on*.
> Dammit. I dropped the
>
> iv = check_interval * HZ;
>
> line before __this_cpu_write() and nobody noticed. :(
>
>> t->expires = round_jiffies(jiffies + iv);
>> add_timer_on(t, smp_processor_id());
>> }
>>
>> Another potential issue is in this function two smp_processor_id()
>> are called. If conext changes during this procedure (I'm not sure
>> if it can hapen, besides secondary_cpu kickoff, online/offline will
> No. This code is always called with preemption disabled.
>
>> call these functions, even in virtualization envrionment, etc.).
> What has virtualization to do with that ?
>
>> So I think it will be better saving the value in the beginning of
>> this function. Make sense?
> No. Otherwise all the __this_cpu_read/write accesses are bogus as
> well.
>
>
Oh, yes, since __this_cpu_read/write can be used here, there no context
issue.
Please ignore my over-thinking.
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