From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754722AbbHJO6O (ORCPT ); Mon, 10 Aug 2015 10:58:14 -0400 Received: from foss.arm.com ([217.140.101.70]:50199 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754513AbbHJO6J (ORCPT ); Mon, 10 Aug 2015 10:58:09 -0400 Date: Mon, 10 Aug 2015 15:58:04 +0100 From: Catalin Marinas To: Will Deacon Cc: Nathan Lynch , Russell King , "linux-kernel@vger.kernel.org" , John Stultz , Thomas Gleixner , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 2/2] arm64: VDSO: fix coarse clock monotonicity regression Message-ID: <20150810145804.GA15394@e104818-lin.cambridge.arm.com> References: <1438999403-5770-1-git-send-email-nathan_lynch@mentor.com> <1438999403-5770-3-git-send-email-nathan_lynch@mentor.com> <20150810092252.GB1604@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150810092252.GB1604@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 10, 2015 at 10:22:53AM +0100, Will Deacon wrote: > On Sat, Aug 08, 2015 at 03:03:23AM +0100, Nathan Lynch wrote: > > Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the > > real timekeeper last") it has become possible on arm64 to: > > > > - Obtain a CLOCK_MONOTONIC_COARSE or CLOCK_REALTIME_COARSE timestamp > > via syscall. > > - Subsequently obtain a timestamp for the same clock ID via VDSO which > > predates the first timestamp (by one jiffy). > > > > This is because arm64's update_vsyscall is deriving the coarse time > > using the __current_kernel_time interface, when it should really be > > using the timekeeper object provided to it by the timekeeping core. > > It happened to work before only because __current_kernel_time would > > access the same timekeeper object which had been passed to > > update_vsyscall. This is no longer the case. > > > > Signed-off-by: Nathan Lynch > > --- > > arch/arm64/kernel/vdso.c | 7 +++---- > > 1 file changed, 3 insertions(+), 4 deletions(-) > > > > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c > > index ec37ab3f524f..97bc68f4c689 100644 > > --- a/arch/arm64/kernel/vdso.c > > +++ b/arch/arm64/kernel/vdso.c > > @@ -199,16 +199,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, > > */ > > void update_vsyscall(struct timekeeper *tk) > > { > > - struct timespec xtime_coarse; > > u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter"); > > > > ++vdso_data->tb_seq_count; > > smp_wmb(); > > > > - xtime_coarse = __current_kernel_time(); > > vdso_data->use_syscall = use_syscall; > > - vdso_data->xtime_coarse_sec = xtime_coarse.tv_sec; > > - vdso_data->xtime_coarse_nsec = xtime_coarse.tv_nsec; > > + vdso_data->xtime_coarse_sec = tk->xtime_sec; > > + vdso_data->xtime_coarse_nsec = tk->tkr_mono.xtime_nsec >> > > + tk->tkr_mono.shift; > > vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec; > > vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec; > > Looks good, > > Acked-by: Will Deacon > > There's probably still time for Catalin to pick this up for 4.2. Applied, I'll send a pull request today/tomorrow. Thanks. -- Catalin