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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 BD38BC352A3 for ; Tue, 11 Feb 2020 11:50:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87B3F2086A for ; Tue, 11 Feb 2020 11:50:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="D2a6GjUK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728624AbgBKLuw (ORCPT ); Tue, 11 Feb 2020 06:50:52 -0500 Received: from merlin.infradead.org ([205.233.59.134]:53110 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728009AbgBKLuw (ORCPT ); Tue, 11 Feb 2020 06:50:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=y67BwQMxRYM3PjeNYdtynviH/nF5k899kzzr0M34J3E=; b=D2a6GjUK41it4NsOtJ7f5KRfMr PNF+xhX+Z+sgjso57V+MQ6YauMkNsAC9IsiKN9fBnl7JV13BXgksYnZmpjvEG5+WxAILBwayynov6 OQNHBMClv3xJEwNNXW+dFt8AmwY55F07VIA1Qe1s/ieRvSTGhY3QFMLjTQnCgiCwqFLtlis8vl4Se spnT1fKOnUbVoGSsbcgQDos5uey52EyeRDGLGHQAPY/taOmj5ud95qVa8MqLUTcCLM59/nNiRFLNN wASswfi4R6GXaE0UX89wPFamBTyg+OT7tzMq1sxgIm4pGB0cb7vuqtelZWit8Bei0ENu2GgPygqbG jrj0RANw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j1U3B-0002TI-FS; Tue, 11 Feb 2020 11:49:57 +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 867D3300739; Tue, 11 Feb 2020 12:48:05 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2810B2B88D75C; Tue, 11 Feb 2020 12:49:54 +0100 (CET) Date: Tue, 11 Feb 2020 12:49:54 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: LKML , Ingo Molnar , "Joel Fernandes (Google)" , Greg Kroah-Hartman , "Gustavo A. R. Silva" , Thomas Gleixner , "Paul E. McKenney" , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan Subject: Re: [PATCH] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook Message-ID: <20200211114954.GK14914@hirez.programming.kicks-ass.net> References: <20200210170643.3544795d@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200210170643.3544795d@gandalf.local.home> 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 Mon, Feb 10, 2020 at 05:06:43PM -0500, Steven Rostedt wrote: > + if (!rcu_watching) { \ > + /* Can not use RCU if rcu is not watching and in NMI */ \ > + if (in_nmi()) \ > + return; \ > + rcu_irq_enter_irqson(); \ > + } \ I saw the same weirdness in __trace_stack(), and I'm confused by it. How can we ever get to: in_nmi() && !rcu_watching() ? That should be a BUG. In particular, nmi_enter() has rcu_nmi_enter(). Paul, can that really happen?