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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 BDE1FC43142 for ; Fri, 22 Jun 2018 14:34:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7271E243BB for ; Fri, 22 Jun 2018 14:34:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7271E243BB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-m68k.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933603AbeFVOeF (ORCPT ); Fri, 22 Jun 2018 10:34:05 -0400 Received: from albert.telenet-ops.be ([195.130.137.90]:44640 "EHLO albert.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751551AbeFVOeD (ORCPT ); Fri, 22 Jun 2018 10:34:03 -0400 Received: from ayla.of.borg ([84.194.111.163]) by albert.telenet-ops.be with bizsmtp id 1qa21y0083XaVaC06qa2Gs; Fri, 22 Jun 2018 16:34:02 +0200 Received: from rox.of.borg ([192.168.97.57]) by ayla.of.borg with esmtp (Exim 4.86_2) (envelope-from ) id 1fWN8U-00055H-1q; Fri, 22 Jun 2018 16:34:02 +0200 Received: from geert by rox.of.borg with local (Exim 4.90_1) (envelope-from ) id 1fWN8T-0001xf-W1; Fri, 22 Jun 2018 16:34:02 +0200 From: Geert Uytterhoeven To: John Stultz , Thomas Gleixner , Stephen Boyd Cc: Arnd Bergmann , linux-alpha@vger.kernel.org, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, Geert Uytterhoeven , stable@vger.kernel.org Subject: [PATCH v3] time: Make sure jiffies_to_msecs() preserves non-zero time periods Date: Fri, 22 Jun 2018 16:33:57 +0200 Message-Id: <20180622143357.7495-1-geert@linux-m68k.org> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For the common cases where 1000 is a multiple of HZ, or HZ is a multiple of 1000, jiffies_to_msecs() never returns zero when passed a non-zero time period. However, if HZ > 1000 and not an integer multiple of 1000 (e.g. 1024 or 1200, as used on alpha and DECstation), jiffies_to_msecs() may return zero for small non-zero time periods. This may break code that relies on receiving back a non-zero value. jiffies_to_usecs() does not need such a fix: one jiffy can only be less than one µs if HZ > 1000000, and such large values of HZ are already rejected at build time, twice: - include/linux/jiffies.h does #error if HZ >= 12288, - kernel/time/time.c has BUILD_BUG_ON(HZ > USEC_PER_SEC). Signed-off-by: Geert Uytterhoeven Reviewed-by: Arnd Bergmann Cc: stable@vger.kernel.org --- Broken since forever. v3: - Add Reviewed-by, - Cc stable, - Explain better why jiffies_to_usecs() does not need a fix, v2: - Add examples of affected systems, - Use DIV_ROUND_UP(). --- kernel/time/time.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/time/time.c b/kernel/time/time.c index 6fa99213fc720e4b..2b41e8e2d31db26f 100644 --- a/kernel/time/time.c +++ b/kernel/time/time.c @@ -28,6 +28,7 @@ */ #include +#include #include #include #include @@ -314,9 +315,10 @@ unsigned int jiffies_to_msecs(const unsigned long j) return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC); #else # if BITS_PER_LONG == 32 - return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32; + return (HZ_TO_MSEC_MUL32 * j + (1ULL << HZ_TO_MSEC_SHR32) - 1) >> + HZ_TO_MSEC_SHR32; # else - return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN; + return DIV_ROUND_UP(j * HZ_TO_MSEC_NUM, HZ_TO_MSEC_DEN); # endif #endif } -- 2.17.1