linux-kernel - Re: [PATCH 02/16] x86, mce: call-in should be after updating global

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Date:	Mon, 15 Jun 2009 17:40:25 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	huang ying <huang.ying.caritas@...il.com>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <ak@...ux.intel.com>,
	Huang Ying <ying.huang@...el.com>
Subject: Re: [PATCH 02/16] x86, mce: call-in should be after updating 	global_nwo

huang ying wrote:
> 2009/6/15 Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>:
>> At the beginning of Monarch synchronization, processors wait until
>> all of them have entered the exception handler and then check the
>> global_nwo to determine if any of them saw a fatal event.
>>
>> However since current code does call-in before updating global_nwo,
>> it might happen that the global_nwo does not reflect some of local
>> nwo at the time.  This might break printing corrected errors not
>> handled yet on panic.
> 
> This is almost same as the patch that I just posted. I think this is
> because it trigger a failure in mce-test suite, and we both find the
> failure.

That's right.

> But your patch lacks memory barrier between mce_callin and global_nwo
> updating/reading. Atomic operations does not imply memory barrier.

You are right.  I agree that your patch is better fix.

It seems my patch includes cleanup for mce_start(), so I'll extract it
and make another patch soon.


Thanks,
H.Seto

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