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 D0236C2BA83 for ; Wed, 12 Feb 2020 15:39:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A741D2073C for ; Wed, 12 Feb 2020 15:39:06 +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="1JAp9IgM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728640AbgBLPjG (ORCPT ); Wed, 12 Feb 2020 10:39:06 -0500 Received: from merlin.infradead.org ([205.233.59.134]:33512 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727026AbgBLPjE (ORCPT ); Wed, 12 Feb 2020 10:39:04 -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=eCwIZ8Hf6W398rCvWhZ+i5ZRPRRZxaxzUmzv2wz82pE=; b=1JAp9IgMQN6yuuPOz8FEz6IG3t dc4IWKrCf+0M6ik8hAb2VJ5w1rGW+hPlEqE1EgRVVsrDHmfT5RzRxWfpezdA17dnXPpHUhx3wegav WXX3rtSjqMnUwIqLcHKoSbEV+KQhOXqK3Y1CyxTbiZIig1O8UwHwCNqDPHQczpl2Z5M8MsxJHajj7 JIVjUS1Idgs1ngdUH0ggJeVXNk9nSOwjlEnHMCEYMeYuOQdtar/uXNKDXT+ckjy4Mx4E4As3Tc9AX hl6FdDOeY5a4lOsMkGp51wPs6YElRwxapa/T9tG/XDx6fN9UIVqcpsXNLWfFdvNkVhywgK/aUKuA9 ZuQxRC2w==; 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 1j1u5r-00046F-4s; Wed, 12 Feb 2020 15:38:27 +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 C7E6E300E0C; Wed, 12 Feb 2020 16:36:34 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B17F120149390; Wed, 12 Feb 2020 16:38:23 +0100 (CET) Date: Wed, 12 Feb 2020 16:38:23 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com Subject: Re: [PATCH 4/8] sched,rcu,tracing: Mark preempt_count_{add,sub}() notrace Message-ID: <20200212153823.GW14897@hirez.programming.kicks-ass.net> References: <20200212093210.468391728@infradead.org> <20200212094107.838108888@infradead.org> <20200212092417.04c3da8c@gandalf.local.home> <20200212150211.GS14897@hirez.programming.kicks-ass.net> <20200212101415.3615d66c@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200212101415.3615d66c@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 Wed, Feb 12, 2020 at 10:14:15AM -0500, Steven Rostedt wrote: > > My initial patch has __preempt_count_add/sub() in, but then I figured > > someone would go complain the tracepoint would go missing. > > Fine, but what bug are you trying to fix? I haven't seen one mentioned > yet. Function tracing has recursion protection, and tracing > preempt_count in nmi_enter() causes no problems. What's the problem you > are trying to solve? The same one as yesterday; if we hit a tracer in NMI context, when !rcu_is_watching() and in_nmi() is still 0, we're fucked.