From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma() Date: Thu, 08 Apr 2010 16:50:55 -0400 Message-ID: <4BBE41AF.5050807@redhat.com> References: <20100408191737.296180458@chello.nl> <20100408192722.687144862@chello.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:26522 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933241Ab0DHUv7 (ORCPT ); Thu, 8 Apr 2010 16:51:59 -0400 In-Reply-To: <20100408192722.687144862@chello.nl> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Andrea Arcangeli , Avi Kivity , Thomas Gleixner , Ingo Molnar , akpm@linux-foundation.org, Linus Torvalds , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Benjamin Herrenschmidt , David Miller , Hugh Dickins , Mel Gorman , Nick Piggin On 04/08/2010 03:17 PM, Peter Zijlstra wrote: > There is nothing preventing the anon_vma from being detached while we > are spinning to acquire the lock. Most (all?) current users end up > calling something like vma_address(page, vma) on it, which has a > fairly good chance of weeding out wonky vmas. > > However suppose the anon_vma got freed and re-used while we were > waiting to acquire the lock, and the new anon_vma fits with the > page->index (because that is the only thing vma_address() uses to > determine if the page fits in a particular vma, we could end up > traversing faulty anon_vma chains. > > Close this hole for good by re-validating that page->mapping still > holds the very same anon_vma pointer after we acquire the lock, if not > be utterly paranoid and retry the whole operation (which will very > likely bail, because it's unlikely the page got attached to a different > anon_vma in the meantime). > > Signed-off-by: Peter Zijlstra > Cc: Hugh Dickins > Cc: Linus Torvalds Reviewed-by: Rik van Riel