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 5AB4FEE49A5 for ; Tue, 22 Aug 2023 06:36:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233066AbjHVGf7 (ORCPT ); Tue, 22 Aug 2023 02:35:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51750 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231928AbjHVGf5 (ORCPT ); Tue, 22 Aug 2023 02:35:57 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A693FBC; Mon, 21 Aug 2023 23:35:51 -0700 (PDT) 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 EE0F12F4; Mon, 21 Aug 2023 23:36:31 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.3.221]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5A2D23F740; Mon, 21 Aug 2023 23:35:48 -0700 (PDT) Date: Tue, 22 Aug 2023 07:35:41 +0100 From: Mark Rutland To: Doug Anderson Cc: Catalin Marinas , Will Deacon , Sumit Garg , Daniel Thompson , Marc Zyngier , linux-perf-users@vger.kernel.org, ito-yuichi@fujitsu.com, Chen-Yu Tsai , Ard Biesheuvel , Stephen Boyd , Peter Zijlstra , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, kgdb-bugreport@lists.sourceforge.net, Masayoshi Mizuma , "Rafael J . Wysocki" , Lecopzer Chen , linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 5/7] arm64: ipi_debug: Add support for backtrace using the debug IPI Message-ID: References: <20230601213440.2488667-1-dianders@chromium.org> <20230601143109.v9.5.I65981105e1f62550b0316625dd1e599deaf9e1aa@changeid> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 21, 2023 at 05:06:50PM -0700, Doug Anderson wrote: > On Mon, Aug 7, 2023 at 3:23 AM Mark Rutland wrote: > > On Thu, Jun 01, 2023 at 02:31:49PM -0700, Douglas Anderson wrote: > > > From: Sumit Garg > > > static irqreturn_t ipi_debug_handler(int irq, void *data) > > > { > > > - /* nop, NMI handlers for special features can be added here. */ > > > + irqreturn_t ret = IRQ_NONE; > > > + > > > + /* > > > + * NOTE: Just like in arch_trigger_cpumask_backtrace(), we're calling > > > + * a function with "nmi_" in the name but it works fine even if we > > > + * are using a regulaor IPI. > > > + */ > > > + if (nmi_cpu_backtrace(get_irq_regs())) > > > + ret = IRQ_HANDLED; > > > > > > > Does this need the printk_deferred_{enter,exit}() that 32-bit arm has? > > I don't _think_ so, but I also don't _think_ it's needed for arm32. > ;-) Let me explain my logic and you can tell me if it sounds right to > you. > > If we're doing the backtrace in pseudo-NMI context then we definitely > don't need it. Specifically, the printk_deferred_{enter,exit}() just > manages the per-cpu "printk_context" value. That value doesn't matter > if "in_nmi()" returns true. > > If we're _not_ doing the backtrace in pseudo-NMI context then I think > we also don't need it. After all, if we're not in pseudo-NMI context > then it's perfectly fine to print, right? > > While it's hard to know 100% for sure, my best guess is that in arm > this might have helped prevent stack traces from getting interspersed > among one another. I guess this is no longer needed as of commit > 55d6af1d6688 ("lib/nmi_backtrace: explicitly serialize banner and > regs")? In any case, when I tested this earlier things seemed to > printout fine without it... Thanks for that explanation; that makes sense to me! Looking around a bit I see that x86 doesn't bother either. > That being said, it wouldn't hurt to include it here and I'll do it if you > want. No need -- I'm happy without it. Thanks, Mark.