From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754387AbbHJJIc (ORCPT ); Mon, 10 Aug 2015 05:08:32 -0400 Received: from foss.arm.com ([217.140.101.70]:48370 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753421AbbHJJIb (ORCPT ); Mon, 10 Aug 2015 05:08:31 -0400 Date: Mon, 10 Aug 2015 10:08:24 +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" Subject: Re: [PATCH 1/2] ARM: VDSO: fix coarse clock monotonicity regression Message-ID: <20150810090824.GA1604@arm.com> References: <1438999403-5770-1-git-send-email-nathan_lynch@mentor.com> <1438999403-5770-2-git-send-email-nathan_lynch@mentor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438999403-5770-2-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 On Sat, Aug 08, 2015 at 03:03:22AM +0100, Nathan Lynch wrote: > Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the > real timekeeper last") it has become possible on ARM 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 ARM'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/arm/kernel/vdso.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c > index efe17dd9b921..c8b243c1aef8 100644 > --- a/arch/arm/kernel/vdso.c > +++ b/arch/arm/kernel/vdso.c > @@ -296,7 +296,6 @@ static bool tk_is_cntvct(const struct timekeeper *tk) > */ > void update_vsyscall(struct timekeeper *tk) > { > - struct timespec xtime_coarse; > struct timespec64 *wtm = &tk->wall_to_monotonic; > > if (!cntvct_ok) { > @@ -308,10 +307,10 @@ void update_vsyscall(struct timekeeper *tk) > > vdso_write_begin(vdso_data); > > - xtime_coarse = __current_kernel_time(); > vdso_data->tk_is_cntvct = tk_is_cntvct(tk); > - 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; Do you need a cast to u32 here? Will