linux-kernel - Re: [PATCH v2 4/5] x86/mce: Simplify flow when handling recoverable memory errors

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Date:	Tue, 11 Nov 2014 09:15:18 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Chen Gong <gong.chen@...ux.intel.com>, X86 ML <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/5] x86/mce: Simplify flow when handling recoverable
 memory errors

On Tue, Nov 11, 2014 at 8:30 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Tue, Nov 11, 2014 at 08:22:45AM -0800, Andy Lutomirski wrote:
>> I think it's okay-ish, but only if it's necessary, and I still don't
>> see why it's necessary.
>>
>> Can't you just remove TIF_MCE_NOTIFY entirely and just do all the
>> mce_notify_process work directly in do_machine_check?  IOW, why do you
>> need to store any state per-task when it's already on the stack
>> anyway.
>
> I wish but memory_failure() can't run in #MC context as it noodles
> quite a lot and grabs all kinds of locks and does a bunch of other
> atomit-context-unsafe things.

Oh -- does it need to sleep?

I find myself wondering whether a much cleaner solution might be to
sync regs and switch stacks before invoking do_machine_check rather
than afterwards.  Then do_machine_check would really be completely
non-atomic.  It would add a few lines of asm, though.

--Andy

>
> And it needs to run *before* the process is killed as it looks at its
> pages.
>
> --
> Regards/Gruss,
>     Boris.
>
> Sent from a fat crate under my desk. Formatting is fine.
> --



-- 
Andy Lutomirski
AMA Capital Management, LLC
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