From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751820AbdILTto (ORCPT ); Tue, 12 Sep 2017 15:49:44 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:36283 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751529AbdILTtT (ORCPT ); Tue, 12 Sep 2017 15:49:19 -0400 Message-Id: <20170912194147.377182587@linutronix.de> User-Agent: quilt/0.63-1 Date: Tue, 12 Sep 2017 21:37:10 +0200 From: Thomas Gleixner To: LKML Cc: Ingo Molnar , Peter Zijlstra , Borislav Petkov , Andrew Morton , Sebastian Siewior , Nicholas Piggin , Don Zickus , Chris Metcalf , Ulrich Obergfell Subject: [patch V2 16/29] lockup_detector: Create new thread handling infrastructure References: <20170912193654.321505854@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=lockup_detector_Create_new_thread_handling_infrastructure.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The lockup detector reconfiguration tears down all watchdog threads when the watchdog is disabled and sets them up again when its enabled. That's a pointless exercise. The watchdog threads are not consuming an insane amount of resources, so it's enough to set them up at init time and keep them in parked position when the watchdog is disabled and unpark them when it is reenabled. The smpboot thread infrastructure takes care of keeping the force parked threads in place even across cpu hotplug. Another horrible mechanism are the open coded park/unpark loops which are used for reconfiguration of the watchdog. The smpboot infrastructure allows exactly the same via smpboot_update_cpumask_thread_percpu(), which is cpu hotplug safe. Using that instead of the open coded loops allows to get rid of the hotplug locking mess in the watchdog code. Implement a clean infrastructure which allows to replace the open coded nonsense. Signed-off-by: Thomas Gleixner Cc: Don Zickus Cc: Chris Metcalf Cc: Peter Zijlstra Cc: Sebastian Siewior Cc: Nicholas Piggin Cc: Ulrich Obergfell Cc: Borislav Petkov Cc: Andrew Morton Link: http://lkml.kernel.org/r/20170831073054.260048944@linutronix.de --- kernel/watchdog.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -139,6 +139,9 @@ unsigned int __read_mostly softlockup_pa CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE; int __read_mostly soft_watchdog_enabled; +struct cpumask watchdog_allowed_mask __read_mostly; +static bool softlockup_threads_initialized __read_mostly; + static u64 __read_mostly sample_period; static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts); @@ -584,12 +587,84 @@ static void watchdog_disable_all_cpus(vo } } +static void softlockup_update_smpboot_threads(void) +{ + lockdep_assert_held(&watchdog_mutex); + + if (!softlockup_threads_initialized) + return; + + smpboot_update_cpumask_percpu_thread(&watchdog_threads, + &watchdog_allowed_mask); + __lockup_detector_cleanup(); +} + +/* Temporarily park all watchdog threads */ +static void softlockup_park_all_threads(void) +{ + cpumask_clear(&watchdog_allowed_mask); + softlockup_update_smpboot_threads(); +} + +/* + * Park threads which are not longer enabled and unpark threads which have + * been newly enabled. + */ +static void softlockup_update_threads(void) +{ + cpumask_copy(&watchdog_allowed_mask, &watchdog_cpumask); + softlockup_update_smpboot_threads(); +} + +static void softlockup_reconfigure_threads(bool enabled) +{ + softlockup_park_all_threads(); + set_sample_period(); + if (enabled) + softlockup_update_threads(); +} + +/* + * Create the watchdog thread infrastructure. + * + * The threads are not unparked as watchdog_allowed_mask is empty. When + * the threads are sucessfully initialized, take the proper locks and + * unpark the threads in the watchdog_cpumask if the watchdog is enabled. + */ +static __init void softlockup_init_threads(void) +{ + int ret; + + /* + * If sysctl is off and watchdog got disabled on the command line, + * nothing to do here. + */ + if (!IS_ENABLED(CONFIG_SYSCTL) && + !(watchdog_enabled && watchdog_thresh)) + return; + + ret = smpboot_register_percpu_thread_cpumask(&watchdog_threads, + &watchdog_allowed_mask); + if (ret) { + pr_err("Failed to initialize soft lockup detector threads\n"); + return; + } + + mutex_lock(&watchdog_mutex); + softlockup_threads_initialized = true; + softlockup_reconfigure_threads(watchdog_enabled && watchdog_thresh); + mutex_unlock(&watchdog_mutex); +} + #else /* CONFIG_SOFTLOCKUP_DETECTOR */ static inline int watchdog_park_threads(void) { return 0; } static inline void watchdog_unpark_threads(void) { } static inline int watchdog_enable_all_cpus(void) { return 0; } static inline void watchdog_disable_all_cpus(void) { } static inline void set_sample_period(void) { } +static inline void softlockup_init_threads(void) { } +static inline void softlockup_update_threads(void) { } +static inline void softlockup_reconfigure_threads(bool enabled) { } #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */ static void __lockup_detector_cleanup(void)