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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=no 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 04E61C2D0DD for ; Thu, 2 Jan 2020 08:15:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C5025215A4 for ; Thu, 2 Jan 2020 08:15:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727813AbgABIPF (ORCPT ); Thu, 2 Jan 2020 03:15:05 -0500 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:50424 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727714AbgABIPF (ORCPT ); Thu, 2 Jan 2020 03:15:05 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07417;MF=wenyang@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0TmarSI6_1577952893; Received: from localhost(mailfrom:wenyang@linux.alibaba.com fp:SMTPD_---0TmarSI6_1577952893) by smtp.aliyun-inc.com(127.0.0.1); Thu, 02 Jan 2020 16:15:02 +0800 From: Wen Yang To: Andrew Morton , Qian Cai Cc: xlpang@linux.alibaba.com, Wen Yang , Tejun Heo , Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 0/3] use div64_ul() instead of div_u64() if the divisor is unsigned long Date: Thu, 2 Jan 2020 16:14:39 +0800 Message-Id: <20200102081442.8273-1-wenyang@linux.alibaba.com> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We were first inspired by commit b0ab99e7736a ("sched: Fix possible divide by zero in avg_atom () calculation"), then refer to the recently analyzed mm code, we found this suspicious place. 201 if (min) { 202 min *= this_bw; 203 do_div(min, tot_bw); 204 } And we also disassembled and confirmed it: /usr/src/debug/kernel-4.9.168-016.ali3000/linux-4.9.168-016.ali3000.alios7.x86_64/mm/page-writeback.c: 201 0xffffffff811c37da <__wb_calc_thresh+234>: xor %r10d,%r10d 0xffffffff811c37dd <__wb_calc_thresh+237>: test %rax,%rax 0xffffffff811c37e0 <__wb_calc_thresh+240>: je 0xffffffff811c3800 <__wb_calc_thresh+272> /usr/src/debug/kernel-4.9.168-016.ali3000/linux-4.9.168-016.ali3000.alios7.x86_64/mm/page-writeback.c: 202 0xffffffff811c37e2 <__wb_calc_thresh+242>: imul %r8,%rax /usr/src/debug/kernel-4.9.168-016.ali3000/linux-4.9.168-016.ali3000.alios7.x86_64/mm/page-writeback.c: 203 0xffffffff811c37e6 <__wb_calc_thresh+246>: mov %r9d,%r10d ---> truncates it to 32 bits here 0xffffffff811c37e9 <__wb_calc_thresh+249>: xor %edx,%edx 0xffffffff811c37eb <__wb_calc_thresh+251>: div %r10 0xffffffff811c37ee <__wb_calc_thresh+254>: imul %rbx,%rax 0xffffffff811c37f2 <__wb_calc_thresh+258>: shr $0x2,%rax 0xffffffff811c37f6 <__wb_calc_thresh+262>: mul %rcx 0xffffffff811c37f9 <__wb_calc_thresh+265>: shr $0x2,%rdx 0xffffffff811c37fd <__wb_calc_thresh+269>: mov %rdx,%r10 This series use div64_ul() instead of div_u64() if the divisor is unsigned long, to avoid truncation to 32-bit on 64-bit platforms. Cc: Andrew Morton Cc: Qian Cai Cc: Tejun Heo Cc: Jens Axboe Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Wen Yang (3): mm/page-writeback.c: avoid potential division by zero in wb_min_max_ratio() mm/page-writeback.c: use div64_ul() for u64-by-unsigned-long divide mm/page-writeback.c: improve arithmetic divisions mm/page-writeback.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) -- 1.8.3.1