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,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 3CED8C433ED for ; Wed, 14 Apr 2021 04:36:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 13F69613CC for ; Wed, 14 Apr 2021 04:36:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230490AbhDNEg0 (ORCPT ); Wed, 14 Apr 2021 00:36:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:42798 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230315AbhDNEgZ (ORCPT ); Wed, 14 Apr 2021 00:36:25 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 67C10611F2; Wed, 14 Apr 2021 04:36:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1618374964; bh=61bJm5ufCHY2CsWGgDxPaswGMEVaByntw0Gga0y1nRc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YRYUqWMIGrB5ED+YlTr/+AynalmS4ggwnkSJLJRSEnhe82iKzebDHlPbzmfMXQZwO uP1becoLIbyHDqFPq/ouYGTl0lyh6UyMCB9XuOx2M6qeYOvaye3HCTGOq0mus1qQLi YrhA0B472iD5TG4q53SyJ5J8B3g8No7m5Gh3m2EKTZA8pxC4IOxAZl/Y6nUBZA/JJn f2JweE4Ixm3LFPwKgV8YvRPj0tpzKTXDT5BY7jKaXY1x2poyd113AfC/L/GnJU9drB ZxIk5el4KrCLln8qZN3dWAe/F6EKk4iQ2vsaSl1gaadD7eT+mSyzQb6mfZZhe6dD+G 9ZTKYqgZYj4BA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 365405C23F6; Tue, 13 Apr 2021 21:36:04 -0700 (PDT) From: "Paul E. McKenney" To: tglx@linutronix.de Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org, 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" , Chris Mason Subject: [PATCH v8 clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog Date: Tue, 13 Apr 2021 21:35:58 -0700 Message-Id: <20210414043602.2812981-1-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20210414043435.GA2812539@paulmck-ThinkPad-P17-Gen-1> References: <20210414043435.GA2812539@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Therefore, provide 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 --- .../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 04545725f187..fc57952dcba0 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 cce484a2cc7c..4be4391aa72f 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(); -- 2.25.1