Date: Thu, 4 Jun 2009 21:16:59 +0800
From: Wu Fengguang <fengguang.wu@intel.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
       "npiggin@suse.de" <npiggin@suse.de>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH] [6/16] HWPOISON: Add various poison checks in
	mm/memory.c
Message-ID: <20090604131659.GB29103@localhost>
References: <20090603846.816684333@firstfloor.org> <20090603184639.1933B1D028F@basil.firstfloor.org> <20090604042603.GA15682@localhost> <20090604051915.GN1065@one.firstfloor.org> <20090604115533.GB22118@localhost> <20090604125228.GZ1065@one.firstfloor.org> <20090604125026.GA29026@localhost> <20090604130255.GB1065@one.firstfloor.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20090604130255.GB1065@one.firstfloor.org>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2224
Lines: 48

On Thu, Jun 04, 2009 at 09:02:55PM +0800, Andi Kleen wrote:
> On Thu, Jun 04, 2009 at 08:50:26PM +0800, Wu Fengguang wrote:
> > On Thu, Jun 04, 2009 at 08:52:28PM +0800, Andi Kleen wrote:
> > > On Thu, Jun 04, 2009 at 07:55:33PM +0800, Wu Fengguang wrote:
> > > > On Thu, Jun 04, 2009 at 01:19:15PM +0800, Andi Kleen wrote:
> > > > > On Thu, Jun 04, 2009 at 12:26:03PM +0800, Wu Fengguang wrote:
> > > > > > On Thu, Jun 04, 2009 at 02:46:38AM +0800, Andi Kleen wrote:
> > > > > > >
> > > > > > > Bail out early when hardware poisoned pages are found in page fault handling.
> > > > > >
> > > > > > I suspect this patch is also not absolutely necessary: the poisoned
> > > > > > page will normally have been isolated already.
> > > > >
> > > > > It's needed to prevent new pages comming in when there is a parallel
> > > > > fault while the memory failure handling is in process.
> > > > > Otherwise the pages could get remapped in that small window.
> > > > 
> > > > This patch makes no difference at least for file pages, including tmpfs.
> > > 
> > > I was more thinking of anonymous pages with multiple mappers (e.g.
> > > COW after fork)
> > 
> > I guess they are handled by do_anonymous_page() or do_wp_page(),
> > instead of do_linear_fault()/do_nonlinear_fault()?
> 
> You're right. Sorry was a little confused in my earlier reply.
> 
> I think what I meant is: what happens during the window
> when the page has just the poison bit set, but is not isolated/unmapped yet.
> During that window I want new mappers to not come in.
> That is why that check is there.

As soon as the poisoned page is locked, it is in safe hand - the new
mappers will have to wait, and then find it either truncated (mapping
== NULL) for file pages, or its PTE updated through the pte_same()
checks in do_wp_page().  do_anonymous_page() is safe because it
allocates the good new page.

We lock the page immediately after setting PG_hwpoison, so the window
is small enough :)

Thanks,
Fengguang
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/