From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f200.google.com (mail-lb0-f200.google.com [209.85.217.200]) by kanga.kvack.org (Postfix) with ESMTP id 4BB666B025E for ; Wed, 18 May 2016 05:21:05 -0400 (EDT) Received: by mail-lb0-f200.google.com with SMTP id ne4so20698388lbc.1 for ; Wed, 18 May 2016 02:21:05 -0700 (PDT) Received: from outbound-smtp07.blacknight.com (outbound-smtp07.blacknight.com. [46.22.139.12]) by mx.google.com with ESMTPS id n124si9825287wma.8.2016.05.18.02.21.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 18 May 2016 02:21:03 -0700 (PDT) Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp07.blacknight.com (Postfix) with ESMTPS id 966B81C1832 for ; Wed, 18 May 2016 10:21:02 +0100 (IST) Date: Wed, 18 May 2016 10:21:01 +0100 From: Mel Gorman Subject: Re: [PATCH v1] mm: bad_page() checks bad_flags instead of page->flags for hwpoison page Message-ID: <20160518092100.GB2527@techsingularity.net> References: <1463470975-29972-1-git-send-email-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1463470975-29972-1-git-send-email-n-horiguchi@ah.jp.nec.com> Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Andrew Morton , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Naoya Horiguchi 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 There is warning either way. What did I miss? -- Mel Gorman SUSE Labs -- 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