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 0E346C352A3 for ; Thu, 13 Feb 2020 22:58:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BE44F2168B for ; Thu, 13 Feb 2020 22:58:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="kWOo8uCe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727964AbgBMW64 (ORCPT ); Thu, 13 Feb 2020 17:58:56 -0500 Received: from mail-qt1-f196.google.com ([209.85.160.196]:37929 "EHLO mail-qt1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727347AbgBMW6z (ORCPT ); Thu, 13 Feb 2020 17:58:55 -0500 Received: by mail-qt1-f196.google.com with SMTP id f3so5638115qtc.5 for ; Thu, 13 Feb 2020 14:58:54 -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=QQ8aqjci/Lwyw9q7suLzZpcUN0T/hD2Iv8u4ubfdK48=; b=kWOo8uCeKieahZ+ybYWZM3x7RVS4A2jmbvaRDycQFoBM9+9Ymq8sa6dSYezmrHTjYC FymL8ax9jbhLxDqkYKcdWgFPi+MOzVMCCEo4g3+/1YvGCxVYb0+Vgav4U0OURgSFH3c2 7m1AJUdWUEUBYvo7+W1HDemO8Wf9+jYkUEuiI= 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=QQ8aqjci/Lwyw9q7suLzZpcUN0T/hD2Iv8u4ubfdK48=; b=SjuuvJt0WK6s5sNcx8kqlVMBJMgW7tNOm2es16Frt6NkC74LxFfLLu3WRe1pZF7qYN WDZua10khQQ5l5f9mB0/+rt50uQCtaxqJ2J3/x2Xpuc1LcIxCbafBkVM0XZ9mf8/jlf9 n3GIO793HOL1Xxy1ixwzF3cTCTbMz5NCoszd4dIeEeSWispxPs39D2AZl9ykef8Zwv1A i8g/soghbtoIJssfvBlxnqwoxKu5xGS3pcicgAEybhs5o/2Itz3XpHgykaRsxTeifyw7 teE/xAUR1rsP3hIzGCWYZ5eAHflkpSiiI8y+22L/6ncV0y4DRvKhQ3twd6H/e0YSFTv0 /d0w== X-Gm-Message-State: APjAAAUUzenM8zA92Kvapc5ClkkkM0Eu0yOzd0aRjDW31oe17W9s6+ox pebjGfxuGXYUHr5+lCw6/fhmbA== X-Google-Smtp-Source: APXvYqwhCRC/g7GQf6Y2QhfsSs4pBHwdi/mReCnFduCOhskIwE3bDHjtCmPLxLOm+JQ/BbHZzN8Bdg== X-Received: by 2002:ac8:7b9b:: with SMTP id p27mr369676qtu.2.1581634734355; Thu, 13 Feb 2020 14:58:54 -0800 (PST) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id a13sm2139459qkh.123.2020.02.13.14.58.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Feb 2020 14:58:53 -0800 (PST) Date: Thu, 13 Feb 2020 17:58:53 -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: <20200213225853.GB112239@google.com> References: <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> <20200213204444.GA94647@google.com> <20200213205442.GK2935@paulmck-ThinkPad-P72> <20200213211930.GG170680@google.com> <20200213214859.GL2935@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200213214859.GL2935@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 01:48:59PM -0800, Paul E. McKenney wrote: > On Thu, Feb 13, 2020 at 04:19:30PM -0500, Joel Fernandes wrote: > > On Thu, Feb 13, 2020 at 12:54:42PM -0800, Paul E. McKenney wrote: > > > On Thu, Feb 13, 2020 at 03:44:44PM -0500, Joel Fernandes wrote: > > > > 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. > > > > > > My compiler complained about the static and the __always_inline, so I > > > fixed those. But please help me out on adding the NOKPROBE_SYMBOL() > > > to rcu_nmi_exit(). What bad thing happens if we leave this on only > > > rcu_nmi_enter()? > > > > It seemed odd to me we were not allowing kprobe on the rcu_nmi_enter() but > > allowing it on exit (from a code reading standpoint) so my reaction was to > > add it to both, but we could probably keep that as a separate > > patch/discussion since it is slightly unrelated to the patch.. Sorry to > > confuse the topic. > > Actually and perhaps unusually, I was not being sarcastic, but was instead > asking a serious question. Is the current code correct? Should the > current NOKPROBE_SYMBOL() be removed? Should the other NOKPROBE_SYMBOL() > be added? Something else? And either way, why? Oh ok, it was a fair question. Seems Steve nailed it, only the rcu_nmi_enter() needs NOKPROBE, although as you mentioned in the other thread, it would be good to get Masami's eyes on it since he introduced the NOKPROBE. thanks, - Joel > Thanx, Paul > > > thanks, > > > > - Joel > > > > > > > Thanx, Paul > > > > > > > ---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(); > > > > } > > > > > > > > /*