From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932146AbcHFUxG (ORCPT ); Sat, 6 Aug 2016 16:53:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60650 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751601AbcHFUxF (ORCPT ); Sat, 6 Aug 2016 16:53:05 -0400 From: Kyle Walker To: john.stultz@linaro.org, tglx@linutronix.de, schwidefsky@de.ibm.com, linux-kernel@vger.kernel.org Cc: kwalker@redhat.com Subject: [PATCH v2] clocksource: Defer override invalidation unless clock is unstable Date: Sat, 6 Aug 2016 12:07:30 -0400 Message-Id: <1470499650-14701-1-git-send-email-kwalker@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Sat, 06 Aug 2016 16:07:53 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Clocksources don't get the VALID_FOR_HRES flag until they have been checked by a watchdog. However, when using an override, the clocksource_select logic will clear the override value if the clocksource is not marked VALID_FOR_HRES during that inititial check. When using the boot arguments clocksource=, this selection can run before the watchdog, and can cause the override to be incorrectly cleared. To address this condition, the override_name is only invalidated for unstable clocksources. Otherwise, the override is left intact until after the watchdog has validated the clocksource as stable/unstable. Signed-off-by: Kyle Walker Cc: John Stultz Cc: Thomas Gleixner Cc: Martin Schwidefsky Cc: linux-kernel@vger.kernel.org --- Notes: Changes from v1: * Altered changelog description, many thanks to John Stultz for the assist! kernel/time/clocksource.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 56ece14..4c1bb2a 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -600,9 +600,18 @@ static void __clocksource_select(bool skipcur) */ if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { /* Override clocksource cannot be used. */ - pr_warn("Override clocksource %s is not HRT compatible - cannot switch while in HRT/NOHZ mode\n", - cs->name); - override_name[0] = 0; + if (cs->flags & CLOCK_SOURCE_UNSTABLE) { + pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", + cs->name); + override_name[0] = 0; + } else { + /* + * The override cannot be currently verified. + * Deferring to let the watchdog check. + */ + pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", + cs->name); + } } else /* Override clocksource can be used. */ best = cs; -- 2.5.5