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=-5.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 1FB97C352A3 for ; Thu, 13 Feb 2020 20:44:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2CA7222C2 for ; Thu, 13 Feb 2020 20:44:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="F3ayNW2N" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728100AbgBMUor (ORCPT ); Thu, 13 Feb 2020 15:44:47 -0500 Received: from mail-qk1-f195.google.com ([209.85.222.195]:44968 "EHLO mail-qk1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727927AbgBMUor (ORCPT ); Thu, 13 Feb 2020 15:44:47 -0500 Received: by mail-qk1-f195.google.com with SMTP id v195so7039330qkb.11 for ; Thu, 13 Feb 2020 12:44:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=LGZL8B9m+ilzkwsOKl6SOln5HHutKWEkvqhf7ivBJIk=; b=F3ayNW2NSkM7HnQx4BHPDF7z8ooTocTXqD69VRWsE57xogHS/BREYNTBVqHY7H3a87 UOGnaUaHBjVdApHKjDldpUB8YE9IsS0nv9qubkI7dS8wxE6FLTB6XBGmDcS77vGZzBEl 7SRdTDE06ObZfpOfFFjhMbKqN1psy2ioRSZ8k= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=LGZL8B9m+ilzkwsOKl6SOln5HHutKWEkvqhf7ivBJIk=; b=titR7gpjgXy3s6w0WLXcqx3qWS6BjiU0NoKfeb1I+J3OMwPyIZqZ69fu3dSqd9rXme fx++QtjYVhBY3v14We+ipXl5nmdme5KTV09j7oOAzhlzNYj/WhCCmz5cWDXKs5okQlkY NCk/5dT+CCz6sI5Zsk/T1+DWV0D8CY4py4Lf6WBvgX4wKoOhFKajLiy7iEy67nA45Ocv YmNo6PNTjE7uRvnNpTXgHCprXydx7Bx2pUVgww8tB/pXwUPp082xkVuk/1cUMLKP9Ph7 Mq7y64aWJS5hYGO5Fcb2E75Lx0Cvv+kCfJ3aoROyLEuJJLFYVryF+LGrxG3L59mpsWKQ 93IQ== X-Gm-Message-State: APjAAAWTwKcwIwYrZmI3RvrKOFP200IzocRFNu9Yj0nUrwKlIbEybjoo Y4UEZu/VRsXq/73qGv4TDKFN/w== X-Google-Smtp-Source: APXvYqwv98+xg9XT2ijvAzhSUJJszIibPsO7J7uiDNP2L+pssDhPUOKi/8BDl76wt/Tko/xF9nB/WQ== X-Received: by 2002:a37:6858:: with SMTP id d85mr49814qkc.286.1581626685614; Thu, 13 Feb 2020 12:44:45 -0800 (PST) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id x41sm2183809qtj.52.2020.02.13.12.44.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Feb 2020 12:44:44 -0800 (PST) Date: Thu, 13 Feb 2020 15:44:44 -0500 From: Joel Fernandes To: "Paul E. McKenney" Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Message-ID: <20200213204444.GA94647@google.com> References: <20200212210139.382424693@infradead.org> <20200212210749.971717428@infradead.org> <20200212232005.GC115917@google.com> <20200213082716.GI14897@hirez.programming.kicks-ass.net> <20200213135138.GB2935@paulmck-ThinkPad-P72> <20200213164031.GH14914@hirez.programming.kicks-ass.net> <20200213185612.GG2935@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200213185612.GG2935@paulmck-ThinkPad-P72> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 13, 2020 at 10:56:12AM -0800, Paul E. McKenney wrote: [...] > > > It might well be that I could make these functions be NMI-safe, but > > > rcu_prepare_for_idle() in particular would be a bit ugly at best. > > > So, before looking into that, I have a question. Given these proposed > > > changes, will rcu_nmi_exit_common() and rcu_nmi_enter_common() be able > > > to just use in_nmi()? > > > > That _should_ already be the case today. That is, if we end up in a > > tracer and in_nmi() is unreliable we're already screwed anyway. > > So something like this, then? This is untested, probably doesn't even > build, and could use some careful review from both Peter and Steve, > at least. As in the below is the second version of the patch, the first > having been missing a couple of important "!" characters. I removed the static from rcu_nmi_enter()/exit() as it is called from outside, that makes it build now. Updated below is Paul's diff. I also added NOKPROBE_SYMBOL() to rcu_nmi_exit() to match rcu_nmi_enter() since it seemed asymmetric. ---8<----------------------- diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d91c9156fab2e..bbcc7767f18ee 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -614,16 +614,18 @@ void rcu_user_enter(void) } #endif /* CONFIG_NO_HZ_FULL */ -/* +/** + * rcu_nmi_exit - inform RCU of exit from NMI context + * * If we are returning from the outermost NMI handler that interrupted an * RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting * to let the RCU grace-period handling know that the CPU is back to * being RCU-idle. * - * If you add or remove a call to rcu_nmi_exit_common(), be sure to test + * If you add or remove a call to rcu_nmi_exit(), be sure to test * with CONFIG_RCU_EQS_DEBUG=y. */ -static __always_inline void rcu_nmi_exit_common(bool irq) +__always_inline void rcu_nmi_exit(void) { struct rcu_data *rdp = this_cpu_ptr(&rcu_data); @@ -651,25 +653,15 @@ static __always_inline void rcu_nmi_exit_common(bool irq) trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks)); WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ - if (irq) + if (!in_nmi()) rcu_prepare_for_idle(); rcu_dynticks_eqs_enter(); - if (irq) + if (!in_nmi()) rcu_dynticks_task_enter(); } - -/** - * rcu_nmi_exit - inform RCU of exit from NMI context - * - * If you add or remove a call to rcu_nmi_exit(), be sure to test - * with CONFIG_RCU_EQS_DEBUG=y. - */ -void rcu_nmi_exit(void) -{ - rcu_nmi_exit_common(false); -} +NOKPROBE_SYMBOL(rcu_nmi_exit); /** * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle @@ -693,7 +685,7 @@ void rcu_nmi_exit(void) void rcu_irq_exit(void) { lockdep_assert_irqs_disabled(); - rcu_nmi_exit_common(true); + rcu_nmi_exit(); } /* @@ -777,7 +769,7 @@ void rcu_user_exit(void) #endif /* CONFIG_NO_HZ_FULL */ /** - * rcu_nmi_enter_common - inform RCU of entry to NMI context + * rcu_nmi_enter - inform RCU of entry to NMI context * @irq: Is this call from rcu_irq_enter? * * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and @@ -786,10 +778,10 @@ void rcu_user_exit(void) * long as the nesting level does not overflow an int. (You will probably * run out of stack space first.) * - * If you add or remove a call to rcu_nmi_enter_common(), be sure to test + * If you add or remove a call to rcu_nmi_enter(), be sure to test * with CONFIG_RCU_EQS_DEBUG=y. */ -static __always_inline void rcu_nmi_enter_common(bool irq) +__always_inline void rcu_nmi_enter(void) { long incby = 2; struct rcu_data *rdp = this_cpu_ptr(&rcu_data); @@ -807,12 +799,12 @@ static __always_inline void rcu_nmi_enter_common(bool irq) */ if (rcu_dynticks_curr_cpu_in_eqs()) { - if (irq) + if (!in_nmi()) rcu_dynticks_task_exit(); rcu_dynticks_eqs_exit(); - if (irq) + if (!in_nmi()) rcu_cleanup_after_idle(); incby = 1; @@ -834,14 +826,6 @@ static __always_inline void rcu_nmi_enter_common(bool irq) rdp->dynticks_nmi_nesting + incby); barrier(); } - -/** - * rcu_nmi_enter - inform RCU of entry to NMI context - */ -void rcu_nmi_enter(void) -{ - rcu_nmi_enter_common(false); -} NOKPROBE_SYMBOL(rcu_nmi_enter); /** @@ -869,7 +853,7 @@ NOKPROBE_SYMBOL(rcu_nmi_enter); void rcu_irq_enter(void) { lockdep_assert_irqs_disabled(); - rcu_nmi_enter_common(true); + rcu_nmi_enter(); } /*