From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753129AbcERKL3 (ORCPT ); Wed, 18 May 2016 06:11:29 -0400 Received: from TYO201.gate.nec.co.jp ([210.143.35.51]:34876 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752603AbcERKL2 convert rfc822-to-8bit (ORCPT ); Wed, 18 May 2016 06:11:28 -0400 From: Naoya Horiguchi To: Vlastimil Babka CC: Mel Gorman , Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "Naoya Horiguchi" Subject: [PATCH v2] mm: check_new_page_bad() directly returns in __PG_HWPOISON case Thread-Topic: [PATCH v2] mm: check_new_page_bad() directly returns in __PG_HWPOISON case Thread-Index: AQHRsO1pxuDdArEpD0aQuTi4ZRbbJw== Date: Wed, 18 May 2016 10:09:50 +0000 Message-ID: <20160518100949.GA17299@hori1.linux.bs1.fc.nec.co.jp> References: <1463470975-29972-1-git-send-email-n-horiguchi@ah.jp.nec.com> <20160518092100.GB2527@techsingularity.net> <573C365B.6020807@suse.cz> In-Reply-To: <573C365B.6020807@suse.cz> Accept-Language: en-US, ja-JP Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.128.101.5] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 18, 2016 at 11:31:07AM +0200, Vlastimil Babka wrote: > On 05/18/2016 11:21 AM, Mel Gorman wrote: > > On Tue, May 17, 2016 at 04:42:55PM +0900, Naoya Horiguchi wrote: > > > There's a race window between checking page->flags and unpoisoning, which > > > taints kernel with "BUG: Bad page state". That's overkill. It's safer to > > > use bad_flags to detect hwpoisoned page. > > > > > > > I'm not quite getting this one. Minimally, instead of = __PG_HWPOISON, it > > should have been (bad_flags & __PG_POISON). As Vlastimil already pointed > > out, __PG_HWPOISON can be 0. What I'm not getting is why this fixes the > > race. The current race is > > > > 1. Check poison, set bad_flags > > 2. poison clears in parallel > > 3. Check page->flag state in bad_page and trigger warning > > > > The code changes it to > > > > 1. Check poison, set bad_flags > > 2. poison clears in parallel > > 3. Check bad_flags and trigger warning > > I think you got step 3 here wrong. It's "skip the warning since we have set > bad_flags to hwpoison and bad_flags didn't change due to parallel unpoison". > > Perhaps the question is why do we need to split the handling between > check_new_page_bad() and bad_page() like this? It might have been different > in the past, but seems like at this point we only look for hwpoison from > check_new_page_bad(). But a cleanup can come later. Thanks for clarification. check_new_page_bad() is the only function interested in hwpoison flag, so we had better move the hwpoison related code in bad_page() to check_new_page_bad(). Thanks, Naoya Horiguchi --- >>From c600b1ee6c36b3df6973f5365b4179c92f3c08e3 Mon Sep 17 00:00:00 2001 From: Naoya Horiguchi Date: Wed, 18 May 2016 18:42:57 +0900 Subject: [PATCH v2] mm: check_new_page_bad() directly returns in __PG_HWPOISON case Currently we check page->flags twice for "HWPoisoned" case of check_new_page_bad(), which can cause a race with unpoisoning. This race unnecessarily taints kernel with "BUG: Bad page state". check_new_page_bad() is the only caller of bad_page() which is interested in __PG_HWPOISON, so let's move the hwpoison related code in bad_page() to it. Signed-off-by: Naoya Horiguchi --- mm/page_alloc.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5b269bc3eca7..59b938ddfb2d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -522,12 +522,6 @@ static void bad_page(struct page *page, const char *reason, static unsigned long nr_shown; static unsigned long nr_unshown; - /* Don't complain about poisoned pages */ - if (PageHWPoison(page)) { - page_mapcount_reset(page); /* remove PageBuddy */ - return; - } - /* * Allow a burst of 60 reports, then keep quiet for that minute; * or allow a steady drip of one report per second. @@ -1654,6 +1648,9 @@ static void check_new_page_bad(struct page *page) if (unlikely(page->flags & __PG_HWPOISON)) { bad_reason = "HWPoisoned (hardware-corrupted)"; bad_flags = __PG_HWPOISON; + /* Don't complain about hwpoisoned pages */ + page_mapcount_reset(page); /* remove PageBuddy */ + return; } if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) { bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set"; -- 2.5.5