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Date: Mon, 18 Aug 2008 12:50:40 +0200
From: Carsten Otte <cotte@de.ibm.com>
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To: Nick Piggin <npiggin@suse.de>
CC: Andrew Morton <akpm@linux-foundation.org>, borntrae@linux.vnet.ibm.com,
       Jared Hulbert <jaredeh@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Linux Memory Management List <linux-mm@kvack.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Hugh Dickins <hugh@veritas.com>
Subject: Re: [patch] mm: xip fix fault vs sparse page invalidate race
References: <20080818053821.GA3011@wotan.suse.de> <20080818054409.GB3011@wotan.suse.de>
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Nick Piggin wrote:
> XIP has a race between sparse pages being inserted into page tables, and
> sparse pages being zapped when its time to put a non-sparse page in.
> 
> What can happen is that a process can be left with a dangling sparse page
> in a MAP_SHARED mapping, while the rest of the world sees the non-sparse
> version. Ie. data corruption. 
> 
> Guard these operations with a seqlock, making fault-in-sparse-pages
> the slowpath, and try-to-unmap-sparse-pages the fastpath.
> 
> Signed-off-by: Nick Piggin <npiggin@suse.de>
Ouch.
Acked-by: Carsten Otte <cotte@de.ibm.com>