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 D808DC61D97 for ; Tue, 24 Jan 2023 17:12:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234593AbjAXRMZ (ORCPT ); Tue, 24 Jan 2023 12:12:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234142AbjAXRMX (ORCPT ); Tue, 24 Jan 2023 12:12:23 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 996E42D72; Tue, 24 Jan 2023 09:12:22 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 122154B3; Tue, 24 Jan 2023 09:13:04 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.11.85]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 119773F64C; Tue, 24 Jan 2023 09:12:16 -0800 (PST) Date: Tue, 24 Jan 2023 17:12:14 +0000 From: Mark Rutland To: Peter Zijlstra 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 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(). > 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? Thanks, Mark.