From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753122Ab0DKVrA (ORCPT <rfc822;w@1wt.eu>);
	Sun, 11 Apr 2010 17:47:00 -0400
Received: from mx1.redhat.com ([209.132.183.28]:46630 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752895Ab0DKVq7 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Sun, 11 Apr 2010 17:46:59 -0400
Message-ID: <4BC24309.7060004@redhat.com>
Date: Sun, 11 Apr 2010 17:45:45 -0400
From: Rik van Riel <riel@redhat.com>
User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.7) Gecko/20100120 Fedora/3.0.1-1.fc12 Lightning/1.0b2pre Thunderbird/3.0.1
MIME-Version: 1.0
To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Borislav Petkov <bp@alien8.de>, Johannes Weiner <hannes@cmpxchg.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Minchan Kim <minchan.kim@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Lee Schermerhorn <Lee.Schermerhorn@hp.com>,
       Nick Piggin <npiggin@suse.de>, Andrea Arcangeli <aarcange@redhat.com>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>, sgunderson@bigfoot.com
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas
 of a mergeable VMA
References: <alpine.LFD.2.00.1004101101180.3558@i5.linux-foundation.org> <20100410185145.GB28952@a1.tnic> <20100410185839.GA32035@a1.tnic> <alpine.LFD.2.00.1004101234210.3558@i5.linux-foundation.org> <alpine.LFD.2.00.1004101308250.3618@i5.linux-foundation.org> <20100410203628.GB32035@a1.tnic> <alpine.LFD.2.00.1004101336440.3618@i5.linux-foundation.org> <20100410212555.GA1797@a1.tnic> <alpine.LFD.2.00.1004101427090.3618@i5.linux-foundation.org> <20100410215115.GA2599@a1.tnic> <20100411130801.GA7189@a1.tnic> <alpine.LFD.2.00.1004110938570.3514@i5.linux-foundation.org> <alpine.LFD.2.00.1004111010280.3514@i5.linux-foundation.org>
In-Reply-To: <alpine.LFD.2.00.1004111010280.3514@i5.linux-foundation.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 04/11/2010 01:16 PM, Linus Torvalds wrote:

> Actually, so if it's that race, then we might get rid of the oops with
> this total hack.

Another thing I just thought of.

The anon_vma struct will not be reused for something completely
different due to the SLAB_DESTROY_BY_RCU flag that the anon_vma_cachep
is created with.

The anon_vma_chain structs are allocated from a slab without that
flag, so they can be reused for something else in the middle of
an RCU section.

Is that something worth fixing, or is this so subtle that we'd
rather not have the code rely on this kind of behaviour at all?