From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753501AbbHJPsD (ORCPT ); Mon, 10 Aug 2015 11:48:03 -0400 Received: from relay1.mentorg.com ([192.94.38.131]:43304 "EHLO relay1.mentorg.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751955AbbHJPsA (ORCPT ); Mon, 10 Aug 2015 11:48:00 -0400 From: Nathan Lynch To: CC: Russell King , John Stultz , Will Deacon , Thomas Gleixner , Subject: [PATCH v2] ARM: VDSO: fix coarse clock monotonicity regression Date: Mon, 10 Aug 2015 10:46:32 -0500 Message-ID: <1439221592-31875-1-git-send-email-nathan_lynch@mentor.com> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1438999403-5770-1-git-send-email-nathan_lynch@mentor.com> References: <1438999403-5770-1-git-send-email-nathan_lynch@mentor.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- Changes since v1: - Add u32 cast to nsec calculation. 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..54a5aeab988d 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 = (u32)(tk->tkr_mono.xtime_nsec >> + tk->tkr_mono.shift); vdso_data->wtm_clock_sec = wtm->tv_sec; vdso_data->wtm_clock_nsec = wtm->tv_nsec; -- 2.1.0