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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,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 F061BC433DB for ; Fri, 22 Jan 2021 08:35:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 97F1B23381 for ; Fri, 22 Jan 2021 08:35:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727041AbhAVIfC (ORCPT ); Fri, 22 Jan 2021 03:35:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59662 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727010AbhAVIcl (ORCPT ); Fri, 22 Jan 2021 03:32:41 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 21823C06174A for ; Fri, 22 Jan 2021 00:31:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=l1or63vZWLAmnmjTaOxJSexcVLE8UAT7YoDDiA/iMos=; b=m0nbZBt1lHv3C2bHS9svSKWxMQ C3QPGZHuZp/BwawtR4sGVGxdbIsqSqOoqxA/MlrxbEJpUWR7WjglXt+Qb1Oe1gxkGHJId9q+eYlC3 vF8boDyYRxPfAYyG6Djclt9pmbVP5pNStBxfDchFDfpBNpsl23MhD4SWsw20kWE2rqsgoUO2jXiIg dPHWf3lqqesATffitN3A+qfBuoteVfgWQtxjS7iWAJ1L6TLaQzQMO/q7EO7sknePSDR+Wg9cLSP5a xyNaNlNnSBH12A2oE4DwLHpZnUWbSO7Tl8Gci+C2N19Fy9gHQbcDnJGDA99rNGmyiM1tkaOnu8L49 Ql7T5/FA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1l2rr0-000Vxh-F8; Fri, 22 Jan 2021 08:31:40 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 33D383012DF; Fri, 22 Jan 2021 09:31:37 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 1B65F2D54EF7A; Fri, 22 Jan 2021 09:31:37 +0100 (CET) Date: Fri, 22 Jan 2021 09:31:37 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: tglx@linutronix.de, frederic@kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, cai@lca.pw, mgorman@techsingularity.net, joel@joelfernandes.org, valentin.schneider@arm.com Subject: Re: [RFC][PATCH 4/7] smp: Optimize send_call_function_single_ipi() Message-ID: References: <20200526161057.531933155@infradead.org> <20200526161907.953304789@infradead.org> <20200527095645.GH325280@hirez.programming.kicks-ass.net> <20200527101513.GJ325303@hirez.programming.kicks-ass.net> <20200527155656.GU2869@paulmck-ThinkPad-P72> <20200527163543.GA706478@hirez.programming.kicks-ass.net> <20200527171236.GC706495@hirez.programming.kicks-ass.net> <20210122002012.GB2743@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210122002012.GB2743@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 21, 2021 at 04:20:12PM -0800, Paul E. McKenney wrote: > > --- > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 368749008ae8..2c8d4c3e341e 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -445,7 +445,7 @@ static int rcu_is_cpu_rrupt_from_idle(void) > > /* > > * Usually called from the tick; but also used from smp_function_call() > > * for expedited grace periods. This latter can result in running from > > - * the idle task, instead of an actual IPI. > > + * a (usually the idle) task, instead of an actual IPI. > > The story is growing enough hair that we should tell it only once. > So here just where it is called from: > > /* > * Usually called from the tick; but also used from smp_function_call() > * for expedited grace periods. > */ > > > lockdep_assert_irqs_disabled(); > > > > @@ -461,9 +461,14 @@ static int rcu_is_cpu_rrupt_from_idle(void) > > return false; > > > > /* > > - * If we're not in an interrupt, we must be in the idle task! > > + * If we're not in an interrupt, we must be in task context. > > + * > > + * This will typically be the idle task through: > > + * flush_smp_call_function_from_idle(), > > + * > > + * but can also be in CPU HotPlug through smpcfd_dying(). > > */ > > Good, but how about like this? > > /* > * If we are not in an interrupt handler, we must be in > * smp_call_function() handler. > * > * Normally, smp_call_function() handlers are invoked from > * the idle task via flush_smp_call_function_from_idle(). > * However, they can also be invoked from CPU hotplug > * operations via smpcfd_dying(). > */ > > > - WARN_ON_ONCE(!nesting && !is_idle_task(current)); > > + WARN_ON_ONCE(!nesting && !in_task(current)); > > This is used in time-critical contexts, so why not RCU_LOCKDEP_WARN()? > That should also allow checking more closely. Would something like the > following work? > > RCU_LOCKDEP_WARN(!nesting && !is_idle_task(current) && (!in_task(current) || !lockdep_cpus_write_held())); > > Where lockdep_cpus_write_held is defined in kernel/cpu.c: Works for me, except s/in_task(current)/in_task()/ compiles a lot better.