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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 06794C10F0E for ; Thu, 18 Apr 2019 15:43:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC2092083D for ; Thu, 18 Apr 2019 15:43:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389529AbfDRPni (ORCPT ); Thu, 18 Apr 2019 11:43:38 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:36803 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731317AbfDRPni (ORCPT ); Thu, 18 Apr 2019 11:43:38 -0400 Received: from pd9ef12d2.dip0.t-ipconnect.de ([217.239.18.210] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hH9Bh-0004nI-GJ; Thu, 18 Apr 2019 17:42:57 +0200 Date: Thu, 18 Apr 2019 17:42:55 +0200 (CEST) From: Thomas Gleixner To: Josh Poimboeuf cc: LKML , x86@kernel.org, Andy Lutomirski , Steven Rostedt , Alexander Potapenko , linux-arch@vger.kernel.org, Alexey Dobriyan , Andrew Morton , Pekka Enberg , linux-mm@kvack.org, David Rientjes , Christoph Lameter , Catalin Marinas , Dmitry Vyukov , Andrey Ryabinin , kasan-dev@googlegroups.com, Mike Rapoport , Akinobu Mita , iommu@lists.linux-foundation.org, Robin Murphy , Christoph Hellwig , Marek Szyprowski , Johannes Thumshirn , David Sterba , Chris Mason , Josef Bacik , linux-btrfs@vger.kernel.org, dm-devel@redhat.com, Mike Snitzer , Alasdair Kergon , intel-gfx@lists.freedesktop.org, Joonas Lahtinen , Maarten Lankhorst , dri-devel@lists.freedesktop.org, David Airlie , Jani Nikula , Daniel Vetter , Rodrigo Vivi Subject: Re: [patch V2 28/29] stacktrace: Provide common infrastructure In-Reply-To: <20190418145201.mjzyqbmkjcghqzex@treble> Message-ID: References: <20190418084119.056416939@linutronix.de> <20190418084255.652003111@linutronix.de> <20190418145201.mjzyqbmkjcghqzex@treble> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 18 Apr 2019, Josh Poimboeuf wrote: > On Thu, Apr 18, 2019 at 10:41:47AM +0200, Thomas Gleixner wrote: > > All architectures which support stacktrace carry duplicated code and > > do the stack storage and filtering at the architecture side. > > > > Provide a consolidated interface with a callback function for consuming the > > stack entries provided by the architecture specific stack walker. This > > removes lots of duplicated code and allows to implement better filtering > > than 'skip number of entries' in the future without touching any > > architecture specific code. > > > > Signed-off-by: Thomas Gleixner > > Cc: linux-arch@vger.kernel.org > > This is a step in the right direction, especially if it allows us to get > rid of the 'skip' stuff. But I'm not crazy about the callbacks. > > Another idea I had (but never got a chance to work on) was to extend the > x86 unwind interface to all arches. So instead of the callbacks, each > arch would implement something like this API: > > > struct unwind_state state; > > void unwind_start(struct unwind_state *state, struct task_struct *task, > struct pt_regs *regs, unsigned long *first_frame); > > bool unwind_next_frame(struct unwind_state *state); > > inline bool unwind_done(struct unwind_state *state); > > > Not only would it avoid the callbacks (which is a nice benefit already), > it would also allow the interfaces to be used outside of the > stack_trace_*() interfaces. That would come in handy in cases like the > ftrace stack tracer code, which needs more than the stack_trace_*() API > can give. I surely thought about that, but after staring at all incarnations of arch/*/stacktrace.c I just gave up. Aside of that quite some archs already have callback based unwinders because they use them for more than stacktracing and just have a single implementation of that loop. I'm fine either way. We can start with x86 and then let archs convert over their stuff, but I wouldn't hold my breath that this will be completed in the forseeable future. > Of course, this may be more work than what you thought you signed up for > ;-) I did not sign up for anything. I tripped over that mess by accident and me being me hated it strong enough to give it at least an initial steam blast. Thanks, tglx