From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A779DC4361B for ; Thu, 4 Mar 2021 01:09:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 848E464E99 for ; Thu, 4 Mar 2021 01:09:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1452190AbhCDBH0 (ORCPT ); Wed, 3 Mar 2021 20:07:26 -0500 Received: from mail.kernel.org ([198.145.29.99]:57392 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354723AbhCDAyE (ORCPT ); Wed, 3 Mar 2021 19:54:04 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id F3D3364FED; Thu, 4 Mar 2021 00:53:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1614819202; bh=k3BIxfi+L1YBlW8Mtw5C8sYz1WXfklRN1Yk9lexwAH0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cnP7jgpY5bzMScON1VlS9N+UWFfUqfEzAbQxpiTBJU2pk3kyF/pxB0mCOH5sPZUpb BY0luTQ71VQ/s+hU0JriNIm9RC7odDzFJnCraDj669G7OatvVNohjPKeAHOQwJi47o uypiACueXrdKTeBFRDsftJUeVuIn/4UNXLN8Z1Z3C8FwbyPc80MYbk20xRZtb7Rj/9 jGbTmAvjeCUpNfh/N52yK/Iyynp342TURgtR3TNmiqAYO8MEQEN+kZvwVWhRe6qN6x TgLgh0pclTmTllOOKDC4RqmPJjz4a4oBVI4dC/Nxop1AmkXutWxNhoH24gHJyGL4vQ U2WxC4cChYLnA== From: paulmck@kernel.org To: linux-kernel@vger.kernel.org Cc: john.stultz@linaro.org, tglx@linutronix.de, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@fb.com, neeraju@codeaurora.org, ak@linux.intel.com, "Paul E. McKenney" Subject: [PATCH kernel/time 1/5] clocksource: Provide module parameters to inject delays in watchdog Date: Wed, 3 Mar 2021 16:53:16 -0800 Message-Id: <20210304005320.25834-1-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20210304004931.GA25461@paulmck-ThinkPad-P72> References: <20210304004931.GA25461@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" When the clocksource watchdog marks a clock as unstable, this might be due to that clock being unstable or it might be due to delays that happen to occur between the reads of the two clocks. Yes, interrupts are disabled across those two reads, but there are no shortage of things that can delay interrupts-disabled regions of code ranging from SMI handlers to vCPU preemption. It would be good to have some indication as to why the clock was marked unstable. The first step is a way of injecting such delays, and this commit therefore provides a clocksource.inject_delay_freq and clocksource.inject_delay_run kernel boot parameters that specify that sufficient delay be injected to cause the clocksource_watchdog() function to mark a clock unstable. This delay is injected every Nth set of M calls to clocksource_watchdog(), where N is the value specified for the inject_delay_freq boot parameter and M is the value specified for the inject_delay_run boot parameter. Values of zero or less for either parameter disable delay injection, and the default for clocksource.inject_delay_freq is zero, that is, disabled. The default for clocksource.inject_delay_run is the value one, that is single-call runs. This facility is intended for diagnostic use only, and should be avoided on production systems. Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd Cc: Jonathan Corbet Cc: Mark Rutland Cc: Marc Zyngier Cc: Andi Kleen [ paulmck: Apply Rik van Riel feedback. ] Reported-by: Chris Mason Signed-off-by: Paul E. McKenney --- Documentation/admin-guide/kernel-parameters.txt | 22 ++++++++++++++++++++ kernel/time/clocksource.c | 27 +++++++++++++++++++++++++ 2 files changed, 49 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 0454572..fc57952 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -583,6 +583,28 @@ loops can be debugged more effectively on production systems. + clocksource.inject_delay_freq= [KNL] + Number of runs of calls to clocksource_watchdog() + before delays are injected between reads from the + two clocksources. Values less than or equal to + zero disable this delay injection. These delays + can cause clocks to be marked unstable, so use + of this parameter should therefore be avoided on + production systems. Defaults to zero (disabled). + + clocksource.inject_delay_run= [KNL] + Run lengths of clocksource_watchdog() delay + injections. Specifying the value 8 will result + in eight consecutive delays followed by eight + times the value specified for inject_delay_freq + of consecutive non-delays. + + clocksource.max_read_retries= [KNL] + Number of clocksource_watchdog() retries due to + external delays before the clock will be marked + unstable. Defaults to three retries, that is, + four attempts to read the clock under test. + clearcpuid=BITNUM[,BITNUM...] [X86] Disable CPUID feature X for the kernel. See arch/x86/include/asm/cpufeatures.h for the valid bit diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index cce484a..4be4391 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -14,6 +14,7 @@ #include /* for spin_unlock_irq() using preempt_count() m68k */ #include #include +#include #include "tick-internal.h" #include "timekeeping_internal.h" @@ -184,6 +185,31 @@ void clocksource_mark_unstable(struct clocksource *cs) spin_unlock_irqrestore(&watchdog_lock, flags); } +static int inject_delay_freq; +module_param(inject_delay_freq, int, 0644); +static int inject_delay_run = 1; +module_param(inject_delay_run, int, 0644); +static int max_read_retries = 3; +module_param(max_read_retries, int, 0644); + +static void clocksource_watchdog_inject_delay(void) +{ + int i; + static int injectfail = -1; + + if (inject_delay_freq <= 0 || inject_delay_run <= 0) + return; + if (injectfail < 0 || injectfail > INT_MAX / 2) + injectfail = inject_delay_run; + if (!(++injectfail / inject_delay_run % inject_delay_freq)) { + pr_warn("%s(): Injecting delay.\n", __func__); + for (i = 0; i < 2 * WATCHDOG_THRESHOLD / NSEC_PER_MSEC; i++) + udelay(1000); + pr_warn("%s(): Done injecting delay.\n", __func__); + } + WARN_ON_ONCE(injectfail < 0); +} + static void clocksource_watchdog(struct timer_list *unused) { struct clocksource *cs; @@ -208,6 +234,7 @@ static void clocksource_watchdog(struct timer_list *unused) local_irq_disable(); csnow = cs->read(cs); + clocksource_watchdog_inject_delay(); wdnow = watchdog->read(watchdog); local_irq_enable(); -- 2.9.5