From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 23C026B0055 for ; Thu, 4 Jun 2009 07:55:44 -0400 (EDT) Date: Thu, 4 Jun 2009 19:55:33 +0800 From: Wu Fengguang Subject: Re: [PATCH] [6/16] HWPOISON: Add various poison checks in mm/memory.c Message-ID: <20090604115533.GB22118@localhost> References: <20090603846.816684333@firstfloor.org> <20090603184639.1933B1D028F@basil.firstfloor.org> <20090604042603.GA15682@localhost> <20090604051915.GN1065@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090604051915.GN1065@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 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. In filemap_fault(), it will first do find_lock_page(), which will lock the page and then double check if the page->mapping is NULL. If so, it drops that page and re-find/re-create one in the radix tree. That logic automatically avoids the poisoned page that is being processed, because the poisoned page is now being locked, and when find_lock_page() eventually is able to lock it, its page->mapping will be NULL. So the PageHWPoison(vmf.page) test will never be true for filemap_fault. shmem_fault() calls shmem_getpage() to get the page, which will return EIO on !uptodate page. It then returns VM_FAULT_SIGBUS on its own. > > > --- linux.orig/mm/memory.c 2009-06-03 19:36:23.000000000 +0200 > > > +++ linux/mm/memory.c 2009-06-03 19:36:23.000000000 +0200 > > > @@ -2797,6 +2797,9 @@ > > > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) > > > return ret; > > > > > > + if (unlikely(PageHWPoison(vmf.page))) > > > + return VM_FAULT_HWPOISON; > > > + > > > > Direct return with locked page could lockup someone later. > > Either drop this patch or fix it with this check? > > Fair point. Fixed. OK, 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