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Date: Wed, 19 Jun 2013 10:06:56 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Stanislav Meduna <stano@meduna.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
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        the arch/x86 maintainers <x86@kernel.org>,
        Hai Huang <hhuang@redhat.com>
Subject: Re: [PATCH] mm: fix up a spurious page fault whenever it happens
Message-ID: <20130619080656.GF16094@twins.programming.kicks-ass.net>
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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.