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Message-ID: <1351260672.16863.81.camel@twins>
Subject: Re: [PATCH 26/31] sched, numa, mm: Add fault driven placement and
 migration policy
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>,
        Mel Gorman <mgorman@suse.de>, Johannes Weiner <hannes@cmpxchg.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Date: Fri, 26 Oct 2012 16:11:12 +0200
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On Fri, 2012-10-26 at 15:50 +0200, Ingo Molnar wrote:
> 
> Oh, just found the reason:
> 
> the ptep_modify_prot_start()/modify()/commit() sequence is 
> SMP-unsafe - it has to be done under the mmap_sem write-locked.
> 
> It is safe against *hardware* updates to the PTE, but not safe 
> against itself. 

Shouldn't the pte_lock serialize all that still? All sites that modify
PTE contents should hold the pte_lock (and do afaict).