From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx178.postini.com [74.125.245.178]) by kanga.kvack.org (Postfix) with SMTP id 7A8EE6B0033 for ; Mon, 26 Aug 2013 21:48:29 -0400 (EDT) Received: from /spool/local by e23smtp06.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 27 Aug 2013 11:39:54 +1000 Received: from d23relay03.au.ibm.com (d23relay03.au.ibm.com [9.190.235.21]) by d23dlp03.au.ibm.com (Postfix) with ESMTP id 773D9357804E for ; Tue, 27 Aug 2013 11:48:24 +1000 (EST) Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay03.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r7R1mDNP43581454 for ; Tue, 27 Aug 2013 11:48:13 +1000 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r7R1mMYK007875 for ; Tue, 27 Aug 2013 11:48:23 +1000 Date: Tue, 27 Aug 2013 09:48:20 +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: <20130827014820.GA1051@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> <20130826232604.GA12498@hacker.(null)> <1377562349-97tgdeoj-mutt-n-horiguchi@ah.jp.nec.com> <521bf0fc.4950320a.76ab.0f2dSMTPIN_ADDED_BROKEN@mx.google.com> <1377564414-igez3xdx-mutt-n-horiguchi@ah.jp.nec.com> <521bfe37.83892b0a.1b94.2e7cSMTPIN_ADDED_BROKEN@mx.google.com> <1377567253-wwcptjmf-mutt-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1377567253-wwcptjmf-mutt-n-horiguchi@ah.jp.nec.com> Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Andrew Morton , Andi Kleen , Fengguang Wu , Tony Luck , gong.chen@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Mon, Aug 26, 2013 at 09:34:13PM -0400, Naoya Horiguchi wrote: >On Tue, Aug 27, 2013 at 09:17:29AM +0800, Wanpeng Li wrote: >> On Mon, Aug 26, 2013 at 08:46:54PM -0400, Naoya Horiguchi wrote: >> >On Tue, Aug 27, 2013 at 08:21:05AM +0800, Wanpeng Li wrote: >> >> Hi Naoya, >> >> On Mon, Aug 26, 2013 at 08:12:29PM -0400, Naoya Horiguchi wrote: >> >> >Hi Wanpeng, >> >> > >> >> >On Tue, Aug 27, 2013 at 07:26:04AM +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. >> >> > >> >> >OK. I agree. >> >> > >> >> >> Hi Andrew, >> >> >> >> >> >> I see you have already merged the patch, which method you prefer? >> >> >> >> >> >> >How about making madvise_hwpoison() put a page and return immediately >> >> >> >(without calling memory_failure() or soft_offline_page()) when the page >> >> >> >is already hwpoisoned? >> >> >> >I hope it also helps us avoid meaningless printk flood. >> >> >> > >> >> >> >> >> >> Btw, Naoya, how about patch 10/10, any input are welcome! ;-) >> >> > >> >> >No objection if you (and Andrew) decide to go with current approach. >> >> >> >> Andrew prefer your method, I will resend the patch w/ your suggested-by. ;-) >> > >> >Thanks you :) >> > >> >> >But I think that if we shift to fix this problem in madvise(), >> >> >we don't need 10/10 any more. So it looks simpler to me. >> >> >> >> I don't think it's same issue. There is just one page in my test case. >> >> #define PAGES_TO_TEST 1 >> >> If I miss something? >> > >> >Ah, OK. >> >> I complete do it in madvise codes, however, the bug mentioned in patch >> 10/10 is still there. ;-) >> >> > >> >BTW, in my understanding, zero pages are not exist physically (I mean that >> >no real page is allocated to store 4096 bytes of 0.) So there can't happen >> >any real MCE SRAO on zero page. So one possible solution might be that we >> >completely ignore all of madvise(MADV_HWPOISON) over zero pages. >> >> What's the userland visible difference against mmap w/o write access before poison >> you expect? > >In this case the userland is a test program like mce-test, so my expectation >is that the test program shouldn't detect false test failures when it >accidentally calls madvise(MADV_HWPOISON) on zero pages, because there's no >real test target associated with such testcases. So I think just returning >with success return code without doing anything looks good. Ok, I will fix it in this way. ;-) Regards, Wanpeng Li > >Thanks, >Naoya Horiguchi -- 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