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

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Date:	Wed, 06 Jun 2012 17:52:11 +0800
From:	Chen Gong <gong.chen@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"Luck, Tony" <tony.luck@...el.com>, "bp@...64.org" <bp@...64.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [tip:x86/urgent] x86/mce: Fix the MCE poll timer logic

于 2012/6/6 17:27, Thomas Gleixner 写道:
> 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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