From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx135.postini.com [74.125.245.135]) by kanga.kvack.org (Postfix) with SMTP id DCFAE6B0033 for ; Mon, 26 Aug 2013 19:40:18 -0400 (EDT) Received: from /spool/local by e23smtp04.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 27 Aug 2013 09:23:03 +1000 Received: from d23relay03.au.ibm.com (d23relay03.au.ibm.com [9.190.235.21]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id 68F362CE8052 for ; Tue, 27 Aug 2013 09:40:11 +1000 (EST) Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay03.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r7QNdxZo41156654 for ; Tue, 27 Aug 2013 09:40:00 +1000 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r7QNe9vs013125 for ; Tue, 27 Aug 2013 09:40:10 +1000 Date: Tue, 27 Aug 2013 07:40:07 +0800 From: Wanpeng Li Subject: Re: [PATCH v4 8/10] mm/hwpoison: fix memory failure still hold reference count after unpoison empty zero page Message-ID: <20130826234007.GA15608@hacker.(null)> Reply-To: Wanpeng Li References: <1377506774-5377-1-git-send-email-liwanp@linux.vnet.ibm.com> <1377506774-5377-8-git-send-email-liwanp@linux.vnet.ibm.com> <1377531937-15nx3q8e-mutt-n-horiguchi@ah.jp.nec.com> <521be416.a5e8420a.6786.09d1SMTPIN_ADDED_BROKEN@mx.google.com> <20130826163150.72bb773c.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130826163150.72bb773c.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Naoya Horiguchi , Andi Kleen , Fengguang Wu , Tony Luck , gong.chen@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Hi Andrew, On Mon, Aug 26, 2013 at 04:31:50PM -0700, Andrew Morton wrote: >On Tue, 27 Aug 2013 07:26:04 +0800 Wanpeng Li wrote: > >> Hi Naoya, >> On Mon, Aug 26, 2013 at 11:45:37AM -0400, Naoya Horiguchi wrote: >> >On Mon, Aug 26, 2013 at 04:46:12PM +0800, Wanpeng Li wrote: >> >> madvise hwpoison inject will poison the read-only empty zero page if there is >> >> no write access before poison. Empty zero page reference count will be increased >> >> for hwpoison, subsequent poison zero page will return directly since page has >> >> already been set PG_hwpoison, however, page reference count is still increased >> >> by get_user_pages_fast. The unpoison process will unpoison the empty zero page >> >> and decrease the reference count successfully for the fist time, however, >> >> subsequent unpoison empty zero page will return directly since page has already >> >> been unpoisoned and without decrease the page reference count of empty zero page. >> >> This patch fix it by decrease page reference count for empty zero page which has >> >> already been unpoisoned and page count > 1. >> > >> >I guess that fixing on the madvise side looks reasonable to me, because this >> >refcount mismatch happens only when we poison with madvise(). The root cause >> >is that we can get refcount multiple times on a page, even if memory_failure() >> >or soft_offline_page() can do its work only once. >> > >> >> I think this just happen in read-only before poison case against empty >> zero page. >> >> Hi Andrew, >> >> I see you have already merged the patch, which method you prefer? >> > >Addressing it within the madvise code does sound more appropriate. The >change which >mm-hwpoison-fix-memory-failure-still-holding-reference-count-after-unpoisoning-empty-zero-page.patch >makes is pretty darn strange-looking at at least needs a comment >telling people what it's doing, and why. Thanks for your great point out. ;-) I will address it within the madvise code and resend patch 8/10 ~ patch 10/10. Regards, Wanpeng Li -- 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