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=-20.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS 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 D7924C432C3 for ; Wed, 17 Mar 2021 15:49:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9077564FA7 for ; Wed, 17 Mar 2021 15:49:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232598AbhCQPtf (ORCPT ); Wed, 17 Mar 2021 11:49:35 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:51080 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232286AbhCQPsz (ORCPT ); Wed, 17 Mar 2021 11:48:55 -0400 Date: Wed, 17 Mar 2021 15:48:53 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1615996134; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6hjnE+IA5FQLSR7yfiBz2zi672OXi5zkFX5blMDwTGA=; b=T5fAQtABS4T/H8qNHVGAc7IDh78t1HEFG0glrjidC3L1fdWgIAIaK0g0y5huVuKf2wvDSz vaaIw6CWJfwWv6PDCjp4NqnEFEw5Qkf1XogZxMh0iIDpdrTalEMbe9klvJhMMt9Q4El+Cx wWWEiypy1h9elNnT44xwDKkqypkPLNfA340n3RftakvsOgIn6r6qqz62SnApz/sJeHZ7sC zi/EMLuNo8leGoTw8kXHHvvSqyj9Hnkp6ps8vPxm6dfkOiweHrdn1n4/M27KoxEvdIvUsl kYsmN5SWuzIDDiynmkVE8xQRutjSxx0GuFhbPniB4qIy1llai/U/ax36TgCcNQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1615996134; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6hjnE+IA5FQLSR7yfiBz2zi672OXi5zkFX5blMDwTGA=; b=/GT0gRXpSSj6tZMIKk1mfmb7+1KoZd2gjsFnYZfGEJu9Xt0Qo+ta12BUPdBZQI3uGBErP9 ho6f6jVniLtu/4BA== From: "tip-bot2 for Thomas Gleixner" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: irq/core] softirq: Make softirq control and processing RT aware Cc: Thomas Gleixner , Sebastian Andrzej Siewior , "Paul E. McKenney" , Frederic Weisbecker , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org In-Reply-To: <20210309085727.426370483@linutronix.de> References: <20210309085727.426370483@linutronix.de> MIME-Version: 1.0 Message-ID: <161599613356.398.2321779206858751256.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the irq/core branch of tip: Commit-ID: 8b1c04acad082dec76f3f8f7e1fa13493d6cbb79 Gitweb: https://git.kernel.org/tip/8b1c04acad082dec76f3f8f7e1fa13493d6cbb79 Author: Thomas Gleixner AuthorDate: Tue, 09 Mar 2021 09:55:56 +01:00 Committer: Thomas Gleixner CommitterDate: Wed, 17 Mar 2021 16:34:10 +01:00 softirq: Make softirq control and processing RT aware Provide a local lock based serialization for soft interrupts on RT which allows the local_bh_disabled() sections and servicing soft interrupts to be preemptible. Provide the necessary inline helpers which allow to reuse the bulk of the softirq processing code. Signed-off-by: Thomas Gleixner Tested-by: Sebastian Andrzej Siewior Tested-by: Paul E. McKenney Reviewed-by: Frederic Weisbecker Acked-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20210309085727.426370483@linutronix.de --- include/linux/bottom_half.h | 2 +- kernel/softirq.c | 188 +++++++++++++++++++++++++++++++++-- 2 files changed, 182 insertions(+), 8 deletions(-) diff --git a/include/linux/bottom_half.h b/include/linux/bottom_half.h index a19519f..e4dd613 100644 --- a/include/linux/bottom_half.h +++ b/include/linux/bottom_half.h @@ -4,7 +4,7 @@ #include -#ifdef CONFIG_TRACE_IRQFLAGS +#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_TRACE_IRQFLAGS) extern void __local_bh_disable_ip(unsigned long ip, unsigned int cnt); #else static __always_inline void __local_bh_disable_ip(unsigned long ip, unsigned int cnt) diff --git a/kernel/softirq.c b/kernel/softirq.c index eaca333..1ed1c55 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -13,6 +13,7 @@ #include #include #include +#include #include #include #include @@ -103,20 +104,189 @@ EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context); #endif /* - * preempt_count and SOFTIRQ_OFFSET usage: - * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving - * softirq processing. - * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET) + * SOFTIRQ_OFFSET usage: + * + * On !RT kernels 'count' is the preempt counter, on RT kernels this applies + * to a per CPU counter and to task::softirqs_disabled_cnt. + * + * - count is changed by SOFTIRQ_OFFSET on entering or leaving softirq + * processing. + * + * - count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET) * on local_bh_disable or local_bh_enable. + * * This lets us distinguish between whether we are currently processing * softirq and whether we just have bh disabled. */ +#ifdef CONFIG_PREEMPT_RT -#ifdef CONFIG_TRACE_IRQFLAGS /* - * This is for softirq.c-internal use, where hardirqs are disabled + * RT accounts for BH disabled sections in task::softirqs_disabled_cnt and + * also in per CPU softirq_ctrl::cnt. This is necessary to allow tasks in a + * softirq disabled section to be preempted. + * + * The per task counter is used for softirq_count(), in_softirq() and + * in_serving_softirqs() because these counts are only valid when the task + * holding softirq_ctrl::lock is running. + * + * The per CPU counter prevents pointless wakeups of ksoftirqd in case that + * the task which is in a softirq disabled section is preempted or blocks. + */ +struct softirq_ctrl { + local_lock_t lock; + int cnt; +}; + +static DEFINE_PER_CPU(struct softirq_ctrl, softirq_ctrl) = { + .lock = INIT_LOCAL_LOCK(softirq_ctrl.lock), +}; + +void __local_bh_disable_ip(unsigned long ip, unsigned int cnt) +{ + unsigned long flags; + int newcnt; + + WARN_ON_ONCE(in_hardirq()); + + /* First entry of a task into a BH disabled section? */ + if (!current->softirq_disable_cnt) { + if (preemptible()) { + local_lock(&softirq_ctrl.lock); + /* Required to meet the RCU bottomhalf requirements. */ + rcu_read_lock(); + } else { + DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt)); + } + } + + /* + * Track the per CPU softirq disabled state. On RT this is per CPU + * state to allow preemption of bottom half disabled sections. + */ + newcnt = __this_cpu_add_return(softirq_ctrl.cnt, cnt); + /* + * Reflect the result in the task state to prevent recursion on the + * local lock and to make softirq_count() & al work. + */ + current->softirq_disable_cnt = newcnt; + + if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && newcnt == cnt) { + raw_local_irq_save(flags); + lockdep_softirqs_off(ip); + raw_local_irq_restore(flags); + } +} +EXPORT_SYMBOL(__local_bh_disable_ip); + +static void __local_bh_enable(unsigned int cnt, bool unlock) +{ + unsigned long flags; + int newcnt; + + DEBUG_LOCKS_WARN_ON(current->softirq_disable_cnt != + this_cpu_read(softirq_ctrl.cnt)); + + if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && softirq_count() == cnt) { + raw_local_irq_save(flags); + lockdep_softirqs_on(_RET_IP_); + raw_local_irq_restore(flags); + } + + newcnt = __this_cpu_sub_return(softirq_ctrl.cnt, cnt); + current->softirq_disable_cnt = newcnt; + + if (!newcnt && unlock) { + rcu_read_unlock(); + local_unlock(&softirq_ctrl.lock); + } +} + +void __local_bh_enable_ip(unsigned long ip, unsigned int cnt) +{ + bool preempt_on = preemptible(); + unsigned long flags; + u32 pending; + int curcnt; + + WARN_ON_ONCE(in_irq()); + lockdep_assert_irqs_enabled(); + + local_irq_save(flags); + curcnt = __this_cpu_read(softirq_ctrl.cnt); + + /* + * If this is not reenabling soft interrupts, no point in trying to + * run pending ones. + */ + if (curcnt != cnt) + goto out; + + pending = local_softirq_pending(); + if (!pending || ksoftirqd_running(pending)) + goto out; + + /* + * If this was called from non preemptible context, wake up the + * softirq daemon. + */ + if (!preempt_on) { + wakeup_softirqd(); + goto out; + } + + /* + * Adjust softirq count to SOFTIRQ_OFFSET which makes + * in_serving_softirq() become true. + */ + cnt = SOFTIRQ_OFFSET; + __local_bh_enable(cnt, false); + __do_softirq(); + +out: + __local_bh_enable(cnt, preempt_on); + local_irq_restore(flags); +} +EXPORT_SYMBOL(__local_bh_enable_ip); + +/* + * Invoked from ksoftirqd_run() outside of the interrupt disabled section + * to acquire the per CPU local lock for reentrancy protection. + */ +static inline void ksoftirqd_run_begin(void) +{ + __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET); + local_irq_disable(); +} + +/* Counterpart to ksoftirqd_run_begin() */ +static inline void ksoftirqd_run_end(void) +{ + __local_bh_enable(SOFTIRQ_OFFSET, true); + WARN_ON_ONCE(in_interrupt()); + local_irq_enable(); +} + +static inline void softirq_handle_begin(void) { } +static inline void softirq_handle_end(void) { } + +static inline bool should_wake_ksoftirqd(void) +{ + return !this_cpu_read(softirq_ctrl.cnt); +} + +static inline void invoke_softirq(void) +{ + if (should_wake_ksoftirqd()) + wakeup_softirqd(); +} + +#else /* CONFIG_PREEMPT_RT */ + +/* + * This one is for softirq.c-internal use, where hardirqs are disabled * legitimately: */ +#ifdef CONFIG_TRACE_IRQFLAGS void __local_bh_disable_ip(unsigned long ip, unsigned int cnt) { unsigned long flags; @@ -277,6 +447,8 @@ asmlinkage __visible void do_softirq(void) local_irq_restore(flags); } +#endif /* !CONFIG_PREEMPT_RT */ + /* * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times, * but break the loop if need_resched() is set or after 2 ms. @@ -381,8 +553,10 @@ restart: pending >>= softirq_bit; } - if (__this_cpu_read(ksoftirqd) == current) + if (!IS_ENABLED(CONFIG_PREEMPT_RT) && + __this_cpu_read(ksoftirqd) == current) rcu_softirq_qs(); + local_irq_disable(); pending = local_softirq_pending();