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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 116DCC4332F for ; Tue, 22 Nov 2022 17:46:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234607AbiKVRq2 (ORCPT ); Tue, 22 Nov 2022 12:46:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59596 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234517AbiKVRpo (ORCPT ); Tue, 22 Nov 2022 12:45:44 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 85AC782BC3; Tue, 22 Nov 2022 09:45:08 -0800 (PST) Message-ID: <20221122173648.849454220@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1669139105; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=FhfrDrd2SIdwsUU/mnu4VC/j8yhsPAhYg8PH8x3o4f8=; b=h3OzbbsnMY4WNTR5FAlmXYF3ZNnCD+EoUf+SIaR/RJ+zceXB7RwDR1GVgOsDYFiD5+GNQg 0hRhNcwGp2q0wDxf8rLFKPzFykNuzCpuMZ9pzMkkcVphJYINcpVT8RDBNAb5VUXSiMRLqc xSac9Ufm311E13DVjcT5RSbMpADzuf4ffSxL8RfhAKnDsAscOiUe9jpRU0LjjRLFp3o0Wr FRMsJckn5xLvVZeqhIvioGh4vrcWXmbHObObkzaOvD/rAcP3lE+oTl0vjaC+p/nhv2D/Rr EMI81eh3bdvvOcRZuaBjEzkO837ywnYxRm8tXliLIgYHzElF+JvPIK3g9otuNg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1669139105; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=FhfrDrd2SIdwsUU/mnu4VC/j8yhsPAhYg8PH8x3o4f8=; b=ms+XQH5b7Yjshnr/nlQBJV0Zwry/ked33KWOhWX6J0W5ARgT/K4i7lNc1T9FW3Nw/2oiq/ L5ux23S1X8+1KrAw== From: Thomas Gleixner To: LKML Cc: Linus Torvalds , Steven Rostedt , Anna-Maria Behnsen , Peter Zijlstra , Stephen Boyd , Guenter Roeck , Andrew Morton , Julia Lawall , Arnd Bergmann , Viresh Kumar , Marc Zyngier , Marcel Holtmann , Johan Hedberg , Luiz Augusto von Dentz , linux-bluetooth@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org Subject: [patch V2 13/17] timers: Split [try_to_]del_timer[_sync]() to prepare for shutdown mode References: <20221122171312.191765396@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Date: Tue, 22 Nov 2022 18:45:05 +0100 (CET) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Tearing down timers which have circular dependencies to other functionality, e.g. workqueues, where the timer can schedule work and work can arm timers is not trivial. In those cases it is desired to shutdown the timer in a way which prevents rearming of the timer. The mechanism to do so it to set timer->function to NULL and use this as an indicator for the timer arming functions to ignore the (re)arm request. Split the inner workings of try_do_del_timer_sync(), del_timer_sync() and del_timer() into helper functions to prepare for implementing the shutdown functionality. No functional change. Co-developed-by: Steven Rostedt Signed-off-by: Steven Rostedt Signed-off-by: Thomas Gleixner Tested-by: Guenter Roeck Link: https://lore.kernel.org/all/20220407161745.7d6754b3@gandalf.local.home Link: https://lore.kernel.org/all/20221110064101.429013735@goodmis.org --- kernel/time/timer.c | 143 +++++++++++++++++++++++++++++++++------------------- 1 file changed, 92 insertions(+), 51 deletions(-) --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1297,20 +1297,14 @@ void add_timer_on(struct timer_list *tim EXPORT_SYMBOL_GPL(add_timer_on); /** - * timer_delete - Deactivate a timer. + * __timer_delete - Internal function: Deactivate a timer. * @timer: The timer to be deactivated * - * The function only deactivates a pending timer, but contrary to - * timer_delete_sync() it does not take into account whether the timers - * callback function is concurrently executed on a different CPU or not. - * It neither prevents rearming of the timer. If @timer can be rearmed - * concurrently then the return value of this function is meaningless. - * * Return: * * %0 - The timer was not pending * * %1 - The timer was pending and deactivated */ -int timer_delete(struct timer_list *timer) +static int __timer_delete(struct timer_list *timer) { struct timer_base *base; unsigned long flags; @@ -1326,25 +1320,37 @@ int timer_delete(struct timer_list *time return ret; } -EXPORT_SYMBOL(timer_delete); /** - * try_to_del_timer_sync - Try to deactivate a timer - * @timer: Timer to deactivate + * timer_delete - Deactivate a timer. + * @timer: The timer to be deactivated * - * This function tries to deactivate a timer. On success the timer is not - * queued and the timer callback function is not running on any CPU. + * The function only deactivates a pending timer, but contrary to + * timer_delete_sync() it does not take into account whether the timers + * callback function is concurrently executed on a different CPU or not. + * It neither prevents rearming of the timer. If @timer can be rearmed + * concurrently then the return value of this function is meaningless. * - * This function does not guarantee that the timer cannot be rearmed right - * after dropping the base lock. That needs to be prevented by the calling - * code if necessary. + * Return: + * * %0 - The timer was not pending + * * %1 - The timer was pending and deactivated + */ +int timer_delete(struct timer_list *timer) +{ + return __timer_delete(timer); +} +EXPORT_SYMBOL(timer_delete); + +/** + * __try_to_del_timer_sync - Internal function: Try to deactivate a timer + * @timer: Timer to deactivate * * Return: * * %0 - The timer was not pending * * %1 - The timer was pending and deactivated * * %-1 - The timer callback function is running on a different CPU */ -int try_to_del_timer_sync(struct timer_list *timer) +static int __try_to_del_timer_sync(struct timer_list *timer) { struct timer_base *base; unsigned long flags; @@ -1361,6 +1367,27 @@ int try_to_del_timer_sync(struct timer_l return ret; } + +/** + * try_to_del_timer_sync - Try to deactivate a timer + * @timer: Timer to deactivate + * + * This function tries to deactivate a timer. On success the timer is not + * queued and the timer callback function is not running on any CPU. + * + * This function does not guarantee that the timer cannot be rearmed right + * after dropping the base lock. That needs to be prevented by the calling + * code if necessary. + * + * Return: + * * %0 - The timer was not pending + * * %1 - The timer was pending and deactivated + * * %-1 - The timer callback function is running on a different CPU + */ +int try_to_del_timer_sync(struct timer_list *timer) +{ + return __try_to_del_timer_sync(timer); +} EXPORT_SYMBOL(try_to_del_timer_sync); #ifdef CONFIG_PREEMPT_RT @@ -1437,45 +1464,15 @@ static inline void del_timer_wait_runnin #endif /** - * timer_delete_sync - Deactivate a timer and wait for the handler to finish. + * __timer_delete_sync - Internal function: Deactivate a timer and wait + * for the handler to finish. * @timer: The timer to be deactivated * - * Synchronization rules: Callers must prevent restarting of the timer, - * otherwise this function is meaningless. It must not be called from - * interrupt contexts unless the timer is an irqsafe one. The caller must - * not hold locks which would prevent completion of the timer's callback - * function. The timer's handler must not call add_timer_on(). Upon exit - * the timer is not queued and the handler is not running on any CPU. - * - * For !irqsafe timers, the caller must not hold locks that are held in - * interrupt context. Even if the lock has nothing to do with the timer in - * question. Here's why:: - * - * CPU0 CPU1 - * ---- ---- - * - * call_timer_fn(); - * base->running_timer = mytimer; - * spin_lock_irq(somelock); - * - * spin_lock(somelock); - * timer_delete_sync(mytimer); - * while (base->running_timer == mytimer); - * - * Now timer_delete_sync() will never return and never release somelock. - * The interrupt on the other CPU is waiting to grab somelock but it has - * interrupted the softirq that CPU0 is waiting to finish. - * - * This function cannot guarantee that the timer is not rearmed again by - * some concurrent or preempting code, right after it dropped the base - * lock. If there is the possibility of a concurrent rearm then the return - * value of the function is meaningless. - * * Return: * * %0 - The timer was not pending * * %1 - The timer was pending and deactivated */ -int timer_delete_sync(struct timer_list *timer) +static int __timer_delete_sync(struct timer_list *timer) { int ret; @@ -1505,7 +1502,7 @@ int timer_delete_sync(struct timer_list lockdep_assert_preemption_enabled(); do { - ret = try_to_del_timer_sync(timer); + ret = __try_to_del_timer_sync(timer); if (unlikely(ret < 0)) { del_timer_wait_running(timer); @@ -1515,6 +1512,50 @@ int timer_delete_sync(struct timer_list return ret; } + +/** + * timer_delete_sync - Deactivate a timer and wait for the handler to finish. + * @timer: The timer to be deactivated + * + * Synchronization rules: Callers must prevent restarting of the timer, + * otherwise this function is meaningless. It must not be called from + * interrupt contexts unless the timer is an irqsafe one. The caller must + * not hold locks which would prevent completion of the timer's callback + * function. The timer's handler must not call add_timer_on(). Upon exit + * the timer is not queued and the handler is not running on any CPU. + * + * For !irqsafe timers, the caller must not hold locks that are held in + * interrupt context. Even if the lock has nothing to do with the timer in + * question. Here's why:: + * + * CPU0 CPU1 + * ---- ---- + * + * call_timer_fn(); + * base->running_timer = mytimer; + * spin_lock_irq(somelock); + * + * spin_lock(somelock); + * timer_delete_sync(mytimer); + * while (base->running_timer == mytimer); + * + * Now timer_delete_sync() will never return and never release somelock. + * The interrupt on the other CPU is waiting to grab somelock but it has + * interrupted the softirq that CPU0 is waiting to finish. + * + * This function cannot guarantee that the timer is not rearmed again by + * some concurrent or preempting code, right after it dropped the base + * lock. If there is the possibility of a concurrent rearm then the return + * value of the function is meaningless. + * + * Return: + * * %0 - The timer was not pending + * * %1 - The timer was pending and deactivated + */ +int timer_delete_sync(struct timer_list *timer) +{ + return __timer_delete_sync(timer); +} EXPORT_SYMBOL(timer_delete_sync); static void call_timer_fn(struct timer_list *timer,