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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 121D2C64E69 for ; Fri, 20 Nov 2020 00:26:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C6B522224D for ; Fri, 20 Nov 2020 00:26:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="1MQ/TLTB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727115AbgKTA0Z (ORCPT ); Thu, 19 Nov 2020 19:26:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:52716 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726192AbgKTA0Z (ORCPT ); Thu, 19 Nov 2020 19:26:25 -0500 Received: from localhost (can06-h06-176-173-97-249.dsl.sta.abo.bbox.fr [176.173.97.249]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 699D022240; Fri, 20 Nov 2020 00:26:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605831984; bh=6woHDUK2/w8uiImED2aQVgFB0Ty6xMl7PTbicL5V8n8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1MQ/TLTB/sfVDGEUi5EE96UXmn32gYFCJXyhx5o7RiYtnWl5g3a8Z+HpnmS7ma79q SvuhIQc1+KjQYV10qbpkVFr05sQcuR0MhBZbn5ofyYBvuRres4RWbWUUyIOtnxtW2J t2dqcm8d6MHYZP4b0NxIQFM4HllUcqRbeeowffpw= Date: Fri, 20 Nov 2020 01:26:21 +0100 From: Frederic Weisbecker To: Thomas Gleixner Cc: LKML , Peter Zijlstra , Paul McKenney , Sebastian Andrzej Siewior , Arnd Bergmann , "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Yoshinori Sato , Rich Felker , linux-sh@vger.kernel.org, Jeff Dike , Richard Weinberger , Anton Ivanov , linux-um@lists.infradead.org, Russell King , Marc Zyngier , Valentin Schneider , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon Subject: Re: [patch 14/19] softirq: Make softirq control and processing RT aware Message-ID: <20201120002621.GA32792@lothringen> References: <20201113140207.499353218@linutronix.de> <20201113141734.324061522@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201113141734.324061522@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org On Fri, Nov 13, 2020 at 03:02:21PM +0100, Thomas Gleixner wrote: > +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); > + rcu_read_lock(); Ah you lock RCU because local_bh_disable() implies it and since it doesn't disable preemption anymore, you must do it explicitly? Perhaps local_lock() should itself imply rcu_read_lock() ? > + } else { > + DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt)); > + } > + } > + > + preempt_disable(); Do you really need to disable preemption here? Migration is disabled by local_lock() and I can't figure out a scenario where the below can conflict with a preempting task. > + /* > + * 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); __this_cpu_add_return() ? > + /* > + * 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); > + } > + preempt_enable(); > +} > +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)); __this_cpu_read() ? Although that's lockdep only so not too important. > + > + preempt_disable(); Same question about preempt_disable(). > + 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); __this_cpu_sub_return? > + current->softirq_disable_cnt = newcnt; > + preempt_enable(); > + > + if (!newcnt && unlock) { > + rcu_read_unlock(); > + local_unlock(&softirq_ctrl.lock); > + } > +} Thanks.