linux-kernel - Re: [patch] mm: xip fix fault vs sparse page invalidate race

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Date:	Mon, 18 Aug 2008 12:50:40 +0200
From:	Carsten Otte <cotte@...ibm.com>
To:	Nick Piggin <npiggin@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	borntrae@...ux.vnet.ibm.com, Jared Hulbert <jaredeh@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch] mm: xip fix fault vs sparse page invalidate race

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@...e.de>
Ouch.
Acked-by: Carsten Otte <cotte@...ibm.com>
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