From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from psmtp.com (na3sys010amx138.postini.com [74.125.245.138])
	by kanga.kvack.org (Postfix) with SMTP id 53B1C6B004D
	for <linux-mm@kvack.org>; Wed,  1 Aug 2012 04:20:40 -0400 (EDT)
Date: Wed, 1 Aug 2012 10:20:36 +0200
From: Michal Hocko <mhocko@suse.cz>
Subject: Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown
 of hugetlbfs shared page tables V2 (resend)
Message-ID: <20120801082036.GC4436@tiehlicka.suse.cz>
References: <20120720145121.GJ9222@suse.de>
 <alpine.LSU.2.00.1207222033030.6810@eggly.anvils>
 <50118E7F.8000609@redhat.com>
 <50120FA8.20409@redhat.com>
 <20120727102356.GD612@suse.de>
 <5016DC5F.7030604@redhat.com>
 <20120731124650.GO612@suse.de>
 <50181AA1.0@redhat.com>
 <20120731200650.GB19524@tiehlicka.suse.cz>
 <50189857.4000501@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <50189857.4000501@redhat.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Larry Woodman <lwoodman@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>, Linux-MM <linux-mm@kvack.org>, David Gibson <david@gibson.dropbear.id.au>, Ken Chen <kenchen@google.com>, Cong Wang <xiyou.wangcong@gmail.com>, LKML <linux-kernel@vger.kernel.org>

On Tue 31-07-12 22:45:43, Larry Woodman wrote:
> On 07/31/2012 04:06 PM, Michal Hocko wrote:
> >On Tue 31-07-12 13:49:21, Larry Woodman wrote:
> >>On 07/31/2012 08:46 AM, Mel Gorman wrote:
> >>>Fundamentally I think the problem is that we are not correctly detecting
> >>>that page table sharing took place during huge_pte_alloc(). This patch is
> >>>longer and makes an API change but if I'm right, it addresses the underlying
> >>>problem. The first VM_MAYSHARE patch is still necessary but would you mind
> >>>testing this on top please?
> >>Hi Mel, yes this does work just fine.  It ran for hours without a panic so
> >>I'll Ack this one if you send it to the list.
> >Hi Larry, thanks for testing! I have a different patch which tries to
> >address this very same issue. I am not saying it is better or that it
> >should be merged instead of Mel's one but I would be really happy if you
> >could give it a try. We can discuss (dis)advantages of both approaches
> >later.
> >
> >Thanks!
> 
> Hi Michal, the system hung when I tested this patch on top of the
> latest 3.5 kernel.  I wont have AltSysrq access to the system until
> tomorrow AM.  

Please hold on. The patch is crap. I forgot about 
if (!vma_shareable(vma, addr))
	return;

case so somebody got an uninitialized pmd. The patch bellow handles
that.

Sorry about that and thanks to Mel to notice this.
---