linux-kernel - Re: [PATCH] mm: fix up a spurious page fault whenever it happens

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Message-ID: <20130619080656.GF16094@twins.programming.kicks-ass.net>
Date:	Wed, 19 Jun 2013 10:06:56 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stanislav Meduna <stano@...una.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Hai Huang <hhuang@...hat.com>
Subject: Re: [PATCH] mm: fix up a spurious page fault whenever it happens

On Wed, Jun 19, 2013 at 09:36:39AM +0200, Stanislav Meduna wrote:
> On 19.06.2013 07:20, Linus Torvalds wrote:
> 
> >> No crash in 2 days running with preempt none...
> > 
> > Is this UP?
> 
> Yes it is.
> 
> > There's the fast_tlb race that Peter fixed in commit 29eb77825cc7
> > ("arch, mm: Remove tlb_fast_mode()"). I'm not seeing how it would
> > cause infinite TLB faults, but it definitely causes potentially
> > incoherent TLB contents. And afaik it only happens with
> > CONFIG_PREEMPT, and on UP systems. Which sounds like it might match
> > your setup...
> 
> Oh, thank you for the pointer, this indeed looks interesting.
> 
> Unfortunately the patch massively does not apply to 3.4 which
> I am using and I know too little what all is involved here
> to backport it. I will test it when (if) it gets to the 3.4(-rt)
> (or when I find some spare time to play with the newer kernel
> on that system).

The easiest way to test for your system is to ensure tlb_fast_mode()
return an unconditional 0.
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