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: <537C040E.3040901@jp.fujitsu.com>
Date:	Wed, 21 May 2014 10:40:30 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Chen Yucong <slaoub@...il.com>, tony.luck@...el.com
CC:	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

(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. 

> 
> 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,
H.Seto

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