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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Date:	Wed, 21 May 2014 10:03:02 +0800
From:	Chen Yucong <slaoub@...il.com>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	tony.luck@...el.com, bp@...en8.de, ak@...ux.intel.com,
	ying.huang@...el.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 Wed, 2014-05-21 at 10:40 +0900, Hidetoshi Seto wrote:
> (2014/05/20 11:11), 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.
> 
> I don't think it should be local.
> Originally what we want to have here is memory to save mces_seen for each online cpus,
> such as a global array like mces_seen[cpus]. But at same time we don't want to preallocate
> big array enough for max possible cpus. So we use per-cpu store instead. 
> 
But mces_seen will just be updated by Per-CPU rather than monarch CPU.
It is only read by 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.
> 
> In case if we decide panic in mce path, uncleared mces_seen can be referred from memory dump.
> I suppose it will help trouble investigation.
> 
> > 
> > Based on the above reasons, this patch distirbute the clear operation of mces_seen to Per-CPU
> > rather than only monarch CPU.
> 
> "local" "occurs" "result" "distribute"
> I recommend you to use spell-checker for your postings...
Thanks very much for your suggestion, I will use a spell-cheker for my
carelessness. 

thx!
cyc

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