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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 01360C61D9D for ; Wed, 25 Jan 2023 09:37:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235273AbjAYJhe (ORCPT ); Wed, 25 Jan 2023 04:37:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232745AbjAYJhc (ORCPT ); Wed, 25 Jan 2023 04:37:32 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E7FEE3AAB; Wed, 25 Jan 2023 01:37:31 -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=ZUwU0WfkKuo04fSMmIA984hyf8mGmOMaibahgi/MR9o=; b=VjGhy5k2GGPJtyEAcXhtVe1y86 YWkKQl2Dj9L5P8Bop7IG+5350+plG+8Yt9TqP4lJ/9AfCFbWi7xMhyicDB1SQHl5gRoQ0QKz6XO0s Ui98kZYYu090lV1JgqytIPzdA4qH+PdegoNvxmwB/Wi8MKeJ8rJmwKgh/E6kaMTyryv+Ete23mmCW lZmY1xIdXKXVwGhdRpOSVuzfNMWoTqc2PporOHz67C2dvoKVcNodvHZjpBgImidwaiMvFbEqXvOy1 boagX1cr+WFtT34yyhHqvTZ2mQ2WF7yOM+/gRoZFispOjoh7wYvJWQFfpqCbOEavg0/xtYpe5KcxV GZV7RTAA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1pKcDF-005odN-75; Wed, 25 Jan 2023 09:37:01 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id A8C37300137; Wed, 25 Jan 2023 10:37:00 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 91F8820774388; Wed, 25 Jan 2023 10:37:00 +0100 (CET) Date: Wed, 25 Jan 2023 10:37:00 +0100 From: Peter Zijlstra To: Mark Rutland Cc: Steven Rostedt , mingo@kernel.org, will@kernel.org, boqun.feng@gmail.com, tglx@linutronix.de, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, seanjc@google.com, pbonzini@redhat.com, jgross@suse.com, srivatsa@csail.mit.edu, amakhalov@vmware.com, pv-drivers@vmware.com, mhiramat@kernel.org, wanpengli@tencent.com, vkuznets@redhat.com, boris.ostrovsky@oracle.com, rafael@kernel.org, daniel.lezcano@linaro.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-trace-kernel@vger.kernel.org, linux-pm@vger.kernel.org Subject: Re: [PATCH 3/6] ftrace/x86: Warn and ignore graph tracing when RCU is disabled Message-ID: References: <20230123205009.790550642@infradead.org> <20230123205515.059999893@infradead.org> <20230123165304.370121e7@gandalf.local.home> <20230123170753.7ac9419e@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 24, 2023 at 05:12:14PM +0000, Mark Rutland wrote: > On Tue, Jan 24, 2023 at 03:44:35PM +0100, Peter Zijlstra wrote: > > On Mon, Jan 23, 2023 at 05:07:53PM -0500, Steven Rostedt wrote: > > > > > Actually, perhaps we can just add this, and all you need to do is create > > > and set CONFIG_NO_RCU_TRACING (or some other name). > > > > Elsewhere I've used CONFIG_ARCH_WANTS_NO_INSTR for this. > > Yes please; if we use CONFIG_ARCH_WANTS_NO_INSTR then arm64 will get this "for > free" once we add the missing checks (which I assume we need) in our ftrace_prepare_return(). Aye. > > Anyway, I took it for a spin and it .... doesn't seems to do the job. > > > > With my patch the first splat is > > > > "RCU not on for: cpuidle_poll_time+0x0/0x70" > > > > While with yours I seems to get the endless: > > > > "WARNING: suspicious RCU usage" > > > > thing. Let me see if I can figure out where it goes side-ways. > > Hmmm... for WARN_ONCE() don't we need to wake RCU first also? I thought we > needed that at least for the printk machinery? Yeah, I'm currently running with a hacked up printk that redirects everything into early_printk() but it still trips up lots. I was just about to go stick on RCU magic into WARN itself, this isn't going to be the only site triggering this fail-cascade.