linux-kernel - RE: [RFC 0/9] mce recovery for Sandy Bridge server

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Date:	Tue, 24 May 2011 09:57:46 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mauro Carvalho Chehab <mchehab@...hat.com>
Subject: RE: [RFC 0/9] mce recovery for Sandy Bridge server

Other points noted - I'll go look at the previous discussion threads
you gave me links to.

I do want to comment on this point:
> Creating a callback there would be a good place to do the TIF_MCE work and also 
> to extract any events that got queued by other NMIs. Note that more events 
> might be queued by further NMIs while we are processing the MCE path - while 
> with the task->mce_error_pfn hack we are limited to a single pending event only 
> and subsequent NMIs will overwrite this value!

I wasn't very happy with task->mce_error_pfn either - but being overwritten
is not one of its flaws.  The task that stumbled on the error must not be
run until the error is dealt with - any other NMIs for other errors must
be happening to other tasks (who have their own task->mce_error_pfn).

> A happy side effect is that the TIF_MCE_NOTIFY hack could go away as well.

We need some way to stop the task that found the error dead in its
tracks - if it tripped over a data error, then running it will just trip
over the same error again. If it had a memory error during an instruction
fetch we have no place to return to.

So can we talk about this part for a while before returning to the
"how to report this" discussion?

So here's the situation - we are in the NMI handler when we find from
looking at the machine check bank registers that we have a recoverable
error. We know the physical address, and we know the task (which might
have been in user or kernel context). I can package that information
into a perf/event ... but then how can I mark the current task as
not-fit-for-execution?

-Tony

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