linux-kernel - Re: mm: OS boot failed when set command-line kmemcheck=1

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Date:	Wed, 26 Feb 2014 09:43:04 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Xishi Qiu <qiuxishi@...wei.com>, Robert Richter <rric@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: mm: OS boot failed when set command-line kmemcheck=1

On Wed, Feb 19, 2014 at 02:24:41PM -0800, David Rientjes wrote:
> On Wed, 19 Feb 2014, Xishi Qiu wrote:
> 
> > Here is a warning, I don't whether it is relative to my hardware.
> > If set "kmemcheck=1 nowatchdog", it can boot.
> > 
> > code:
> > 	...
> > 	pte = kmemcheck_pte_lookup(address);
> > 	if (!pte)
> > 		return false;
> > 
> > 	WARN_ON_ONCE(in_nmi());
> > 
> > 	if (error_code & 2)
> > 	...

That code seems to assume NMI context cannot fault; this is false since
a while back (v3.9 or thereabouts).

> > [   10.920757]  [<ffffffff810452c1>] kmemcheck_fault+0xb1/0xc0
> > [   10.920760]  [<ffffffff814d262b>] __do_page_fault+0x39b/0x4c0
> > [   10.920763]  [<ffffffff814d2829>] do_page_fault+0x9/0x10
> > [   10.920765]  [<ffffffff814cf222>] page_fault+0x22/0x30
> > [   10.920774]  [<ffffffff8101eb02>] intel_pmu_handle_irq+0x142/0x3a0
> > [   10.920777]  [<ffffffff814d0655>] perf_event_nmi_handler+0x35/0x60
> > [   10.920779]  [<ffffffff814cfe83>] nmi_handle+0x63/0x150
> > [   10.920782]  [<ffffffff814cffd3>] default_do_nmi+0x63/0x290
> > [   10.920784]  [<ffffffff814d02a8>] do_nmi+0xa8/0xe0
> > [   10.920786]  [<ffffffff814cf527>] end_repeat_nmi+0x1e/0x2e

And this does indeed show a fault from NMI context; which is totally
expected.

kmemcheck needs to be fixed; but I've no clue how any of that works.
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