From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754545AbbHJJW7 (ORCPT ); Mon, 10 Aug 2015 05:22:59 -0400 Received: from foss.arm.com ([217.140.101.70]:48434 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753548AbbHJJW5 (ORCPT ); Mon, 10 Aug 2015 05:22:57 -0400 Date: Mon, 10 Aug 2015 10:22:53 +0100 From: Will Deacon To: Nathan Lynch Cc: "linux-arm-kernel@lists.infradead.org" , Russell King , John Stultz , Thomas Gleixner , "linux-kernel@vger.kernel.org" , catalin.marinas@arm.com Subject: Re: [PATCH 2/2] arm64: VDSO: fix coarse clock monotonicity regression Message-ID: <20150810092252.GB1604@arm.com> References: <1438999403-5770-1-git-send-email-nathan_lynch@mentor.com> <1438999403-5770-3-git-send-email-nathan_lynch@mentor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438999403-5770-3-git-send-email-nathan_lynch@mentor.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 Hi Nathan, 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. Will