linux-kernel - Re: [PATCH v2] x86/mce: Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU

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Message-ID: <20140520173308.GE16428@pd.tnic>
Date:	Tue, 20 May 2014 19:33:08 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Chen Yucong <slaoub@...il.com>
Cc:	tony.luck@...el.com, ak@...ux.intel.com, ying.huang@...el.com,
	seto.hidetoshi@...fujitsu.com, linux-kernel@...r.kernel.org,
	linux-edac@...r.kernel.org
Subject: Re: [PATCH v2] x86/mce: Distirbute the clear operation of mces_seen
 to Per-CPU rather than only monarch CPU

On Tue, May 20, 2014 at 10:11:25AM +0800, Chen Yucong wrote:
> mces_seen is a Per-CPU variable which should only be accessed by
> Per-CPU as possible. So the clear operation of mces_seen should also
> be lcoal to Per-CPU rather than monarch CPU.
>
> Meanwhile, there is also a potential risk that mces_seen will not
> be be cleared if a timeout occors in mce_end for monarch CPU. As a
> reuslt, the stale value of mces_seen will reappear on the next mce.

I don't know how many times I have to tell you this already: if we reach
the timeout, we have a much bigger friggin' problem!

What you could do instead is make the machine panic in the tolerant==1,
i.e., the default case, in mce_timed_out().

Basically, in the case any core is stuck and we reach a timeout, we want
to panic the whole box immediately. There's a very little chance we can
recover so panic is the only sane thing left to do.

Ok?

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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