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 08D36C352A3 for ; Tue, 11 Feb 2020 15:31:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D25262082F for ; Tue, 11 Feb 2020 15:31:43 +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="XVWLVjn3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729318AbgBKPbn (ORCPT ); Tue, 11 Feb 2020 10:31:43 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:40148 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728294AbgBKPbm (ORCPT ); Tue, 11 Feb 2020 10:31:42 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=VWBCOELY6rkhccDCqlZILUKA2AGhvyeFtdMCkPYvY6Q=; b=XVWLVjn3Xk2wUFZvXsV0Bhod4q eCRC8Jl3We+M4z+VhaSGOYs5+vyaXFvVoqzeieN+007vOuR/HlarbmEZJbXAdEJfgZ8KsoGHWFR55 vx/pTW4fsq05srqrFTy2XKi8NlRj29xWp1aj/ZrJl4pW3tjPX8SKDU7miwyoXPHk1DmmQe1z+18s1 RAjbh+C58Hf1hhYmakUN/VMa/TO16k/Ky38tfmfqA/o+Ez+Iu2gx7/rqmfFUY42/3HkbneD6jVl5c 7ujvZ8VUPsQgoN8px3oh1i3S+JkD/pzbrUrzMZJhB2jzI14pXUvoBs3FscWVQrNVdSJxoWGtiSpwk MDalKZCw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j1XVW-0004uo-1e; Tue, 11 Feb 2020 15:31:26 +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 6E8AC300739; Tue, 11 Feb 2020 16:29:35 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2362120148940; Tue, 11 Feb 2020 16:31:24 +0100 (CET) Date: Tue, 11 Feb 2020 16:31:24 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Steven Rostedt , LKML , Ingo Molnar , "Joel Fernandes (Google)" , Greg Kroah-Hartman , "Gustavo A. R. Silva" , Thomas Gleixner , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan Subject: Re: [PATCH] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook Message-ID: <20200211153124.GV14914@hirez.programming.kicks-ass.net> References: <20200210170643.3544795d@gandalf.local.home> <20200211114954.GK14914@hirez.programming.kicks-ass.net> <20200211090503.68c0d70f@gandalf.local.home> <20200211150615.GK2935@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200211150615.GK2935@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 Tue, Feb 11, 2020 at 07:06:15AM -0800, Paul E. McKenney wrote: > And I have to ask... What happens if we are very early in from-idle > NMI entry (or very late in NMI exit), such that both in_nmi() and > rcu_is_watching() are returning false? Or did I miss a turn somewhere? We must, by very careful inspection, ensure that doesn't happen. No tracing must happen before preempt_count increment / after preempt_count decrement. Otherwise we can no longer recover.