From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id DB7876B0087 for ; Thu, 4 Jun 2009 09:17:10 -0400 (EDT) Date: Thu, 4 Jun 2009 21:16:59 +0800 From: Wu Fengguang 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> Sender: owner-linux-mm@kvack.org To: Andi Kleen Cc: "akpm@linux-foundation.org" , "npiggin@suse.de" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" List-ID: 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org