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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 73B91C433EF for ; Thu, 9 Sep 2021 01:10:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5A45661167 for ; Thu, 9 Sep 2021 01:10:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348941AbhIIBLS (ORCPT ); Wed, 8 Sep 2021 21:11:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:60488 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232144AbhIIBLR (ORCPT ); Wed, 8 Sep 2021 21:11:17 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0A4FD6115B; Thu, 9 Sep 2021 01:10:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1631149809; bh=jX/+qe+mshe9NQpY4nv0hiSuyosD7KUERle9R5zkFIM=; h=Date:From:To:Subject:In-Reply-To:From; b=RLch+0XeeuFu40/c2xQWm/8lmGUT5b8L93bgKIn7LyGAgi0pAxqR3e7sQgy87s8xZ XIbE+VfeQgzoauSJs4syOtBqif3uY/SVedTQ5hV/W8SBQZjNfCgQYoL/yCER66P2yP uiPiNHfPuBFgnRVmNEK4pXJYYBiG3PLcGX+eeltg= Date: Wed, 08 Sep 2021 18:10:08 -0700 From: Andrew Morton To: akpm@linux-foundation.org, chris@chrisdown.name, guro@fb.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, riel@surriel.com, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 3/8] mm,vmscan: fix divide by zero in get_scan_count Message-ID: <20210909011008.OFzJhcuDA%akpm@linux-foundation.org> In-Reply-To: <20210908180859.d523d4bb4ad8eec11c61500d@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Rik van Riel Subject: mm,vmscan: fix divide by zero in get_scan_count Changeset f56ce412a59d ("mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim") introduced a divide by zero corner case when oomd is being used in combination with cgroup memory.low protection. When oomd decides to kill a cgroup, it will force the cgroup memory to be reclaimed after killing the tasks, by writing to the memory.max file for that cgroup, forcing the remaining page cache and reclaimable slab to be reclaimed down to zero. Previously, on cgroups with some memory.low protection that would result in the memory being reclaimed down to the memory.low limit, or likely not at all, having the page cache reclaimed asynchronously later. With f56ce412a59d the oomd write to memory.max tries to reclaim all the way down to zero, which may race with another reclaimer, to the point of ending up with the divide by zero below. This patch implements the obvious fix. Link: https://lkml.kernel.org/r/20210826220149.058089c6@imladris.surriel.com Fixes: f56ce412a59d ("mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim") Signed-off-by: Rik van Riel Acked-by: Roman Gushchin Acked-by: Michal Hocko Acked-by: Johannes Weiner Acked-by: Chris Down Cc: Signed-off-by: Andrew Morton --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/vmscan.c~mmvmscan-fix-divide-by-zero-in-get_scan_count +++ a/mm/vmscan.c @@ -2715,7 +2715,7 @@ out: cgroup_size = max(cgroup_size, protection); scan = lruvec_size - lruvec_size * protection / - cgroup_size; + (cgroup_size + 1); /* * Minimally target SWAP_CLUSTER_MAX pages to keep _