linux-kernel - Re: [PATCH v3] x86/mce: Try printing all machine check banks known before panic

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Message-ID: <20141121164140.GA4274@pd.tnic>
Date:	Fri, 21 Nov 2014 17:41:40 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	rui wang <ruiv.wang@...il.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gong.chen@...ux.intel.com" <gong.chen@...ux.intel.com>,
	"Wang, Rui Y" <rui.y.wang@...el.com>
Subject: Re: [PATCH v3] x86/mce: Try printing all machine check banks known
 before panic

On Fri, Nov 21, 2014 at 09:20:59AM +0800, rui wang wrote:
> We've found there are cases after mce_log() has been called, we then
> decide to panic, but print_mce() can't find anything in the mcelog
> buffer. I think the mcelog buffer can be consumed by the user space
> daemon (possibly on a different CPU). We may end up seeing the "panic
> from unknown source" message without printing any mca banks, which is
> one of the cases where this bug was originated.

Ok, so modify the mcelog buffer to not zero out its entries when they're
being read out in userspace through mce_chrdev_read() but simply to
leave them in. Then you can read them out again on panic time. The mce
log buffer will have to become a circular buffer or something like that.

-- 
Regards/Gruss,
    Boris.

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