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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 70326C00449 for ; Fri, 5 Oct 2018 06:00:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2BB6320834 for ; Fri, 5 Oct 2018 06:00:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2BB6320834 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de 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 S1727667AbeJEM5g (ORCPT ); Fri, 5 Oct 2018 08:57:36 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:37345 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726979AbeJEM5g (ORCPT ); Fri, 5 Oct 2018 08:57:36 -0400 Received: from tmo-101-17.customers.d1-online.com ([80.187.101.17] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1g8JA0-0003YZ-Hm; Fri, 05 Oct 2018 08:00:24 +0200 Date: Fri, 5 Oct 2018 08:00:23 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski cc: x86@kernel.org, LKML Subject: Re: [PATCH 2/3] x86/vdso: Rearrange do_hres() to improve code generation In-Reply-To: <99e93a6be59916959ad259482f4cf347e8af9bac.1538689401.git.luto@kernel.org> Message-ID: References: <99e93a6be59916959ad259482f4cf347e8af9bac.1538689401.git.luto@kernel.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 4 Oct 2018, Andy Lutomirski wrote: > index 18c8a78d1ec9..419de7552c2f 100644 > --- a/arch/x86/entry/vdso/vclock_gettime.c > +++ b/arch/x86/entry/vdso/vclock_gettime.c > @@ -147,10 +147,9 @@ notrace static int do_hres(clockid_t clk, struct timespec *ts) > > do { > seq = gtod_read_begin(gtod); > - ts->tv_sec = base->sec; > + cycles = vgetcyc(gtod->vclock_mode); > ns = base->nsec; > last = gtod->cycle_last; > - cycles = vgetcyc(gtod->vclock_mode); > if (unlikely((s64)cycles < 0)) > return vdso_fallback_gettime(clk, ts); > if (cycles > last) > @@ -158,7 +157,7 @@ notrace static int do_hres(clockid_t clk, struct timespec *ts) > ns >>= gtod->shift; > } while (unlikely(gtod_read_retry(gtod, seq))); > > - ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns); > + ts->tv_sec = base->sec + __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns); You cannot access base->sec outside of the seqcount protected region. It might have been incremented by now and you'll get a time jump by a full second. Thanks, tglx