From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4CC5AC282C2 for ; Wed, 13 Feb 2019 13:19:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 17694222B1 for ; Wed, 13 Feb 2019 13:19:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390476AbfBMNT2 (ORCPT ); Wed, 13 Feb 2019 08:19:28 -0500 Received: from outbound-smtp26.blacknight.com ([81.17.249.194]:44862 "EHLO outbound-smtp26.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730377AbfBMNT1 (ORCPT ); Wed, 13 Feb 2019 08:19:27 -0500 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp26.blacknight.com (Postfix) with ESMTPS id A5B90B890C for ; Wed, 13 Feb 2019 13:19:25 +0000 (GMT) Received: (qmail 25019 invoked from network); 13 Feb 2019 13:19:25 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[37.228.225.79]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 13 Feb 2019 13:19:25 -0000 Date: Wed, 13 Feb 2019 13:19:23 +0000 From: Mel Gorman To: Andrew Morton Cc: Yury Norov , Vlastimil Babka , Andrea Arcangeli , David Rientjes , Michal Hocko , Will Deacon , Catalin Marinas , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Subject: [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks Message-ID: <20190213131923.GQ9565@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Yury Norov reported that an arm64 KVM instance could not boot since after v5.0-rc1 and could addressed by reverting the patches 1c30844d2dfe272d58c ("mm: reclaim small amounts of memory when an external 73444bc4d8f92e46a20 ("mm, page_alloc: do not wake kswapd with zone lock held") The problem is that a division by zero error is possible if boosting occurs either very early in boot or if the high watermark is very small. This patch checks for the conditions and avoids boosting in those cases. Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs") Reported-and-tested-by: Yury Norov Signed-off-by: Mel Gorman --- mm/page_alloc.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d295c9bc01a8..ae7e4ba5b9f5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2170,6 +2170,11 @@ static inline void boost_watermark(struct zone *zone) max_boost = mult_frac(zone->_watermark[WMARK_HIGH], watermark_boost_factor, 10000); + + /* high watermark be be uninitialised or very small */ + if (!max_boost) + return; + max_boost = max(pageblock_nr_pages, max_boost); zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages, -- Mel Gorman SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 820A9C282C2 for ; 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13 Feb 2019 13:19:25 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[37.228.225.79]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 13 Feb 2019 13:19:25 -0000 Date: Wed, 13 Feb 2019 13:19:23 +0000 From: Mel Gorman To: Andrew Morton Subject: [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks Message-ID: <20190213131923.GQ9565@techsingularity.net> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190213_051931_147166_98A3C94A X-CRM114-Status: GOOD ( 10.86 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrea Arcangeli , Yury Norov , Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, Michal Hocko , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, David Rientjes , Vlastimil Babka Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Yury Norov reported that an arm64 KVM instance could not boot since after v5.0-rc1 and could addressed by reverting the patches 1c30844d2dfe272d58c ("mm: reclaim small amounts of memory when an external 73444bc4d8f92e46a20 ("mm, page_alloc: do not wake kswapd with zone lock held") The problem is that a division by zero error is possible if boosting occurs either very early in boot or if the high watermark is very small. This patch checks for the conditions and avoids boosting in those cases. Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs") Reported-and-tested-by: Yury Norov Signed-off-by: Mel Gorman --- mm/page_alloc.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d295c9bc01a8..ae7e4ba5b9f5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2170,6 +2170,11 @@ static inline void boost_watermark(struct zone *zone) max_boost = mult_frac(zone->_watermark[WMARK_HIGH], watermark_boost_factor, 10000); + + /* high watermark be be uninitialised or very small */ + if (!max_boost) + return; + max_boost = max(pageblock_nr_pages, max_boost); zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages, -- Mel Gorman SUSE Labs _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel