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

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Message-ID: <851fc09e0906150126x4bb003flbf099aff0eed2a66@mail.gmail.com>
Date:	Mon, 15 Jun 2009 16:26:08 +0800
From:	huang ying <huang.ying.caritas@...il.com>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.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

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.

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

Best Regards,
Huang Ying
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