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=-14.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 BE1C9C4707D for ; Fri, 21 May 2021 17:23:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 961F061183 for ; Fri, 21 May 2021 17:23:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231441AbhEURZS (ORCPT ); Fri, 21 May 2021 13:25:18 -0400 Received: from linux.microsoft.com ([13.77.154.182]:58268 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230301AbhEURZR (ORCPT ); Fri, 21 May 2021 13:25:17 -0400 Received: from [192.168.254.32] (unknown [47.187.214.213]) by linux.microsoft.com (Postfix) with ESMTPSA id 8EB9020B7188; Fri, 21 May 2021 10:23:53 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 8EB9020B7188 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1621617834; bh=dsmQpGSpViASu2Lm8EpJourdT7RJuov0nXLCLji8uHw=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=iX33lxGgvBIWRLXPXT/y9uGoHbgKy27qqVfF/Y/wnHBeBjXJNYIeos5+GVAWP3c4Q +gy1NyQCSS/ip7vrI55Xbbx8vG19EyFK/FVXpzD08oKct5vo063qKdHzmLdR3FrefY H5O2mLHz3Ic11/fRCT5wM/jo4OLE5+vlG5gjbtIc= Subject: Re: [RFC PATCH v4 1/2] arm64: Introduce stack trace reliability checks in the unwinder To: Mark Brown Cc: mark.rutland@arm.com, jpoimboe@redhat.com, ardb@kernel.org, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <68eeda61b3e9579d65698a884b26c8632025e503> <20210516040018.128105-1-madvenka@linux.microsoft.com> <20210516040018.128105-2-madvenka@linux.microsoft.com> <20210521161117.GB5825@sirena.org.uk> From: "Madhavan T. Venkataraman" Message-ID: Date: Fri, 21 May 2021 12:23:52 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210521161117.GB5825@sirena.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/21/21 11:11 AM, Mark Brown wrote: > On Sat, May 15, 2021 at 11:00:17PM -0500, madvenka@linux.microsoft.com wrote: > >> Other reliability checks will be added in the future. > > ... > >> + frame->reliable = true; >> + > > All these checks are good checks but as you say there's more stuff that > we need to add (like your patch 2 here) so I'm slightly nervous about > actually setting the reliable flag here without even a comment. Equally > well there's no actual use of this until arch_stack_walk_reliable() gets > implemented so it's not like it's causing any problems and it gives us > the structure to start building up the rest of the checks. > OK. So how about changing the field from a flag to an enum that says exactly what happened with the frame? enum { FRAME_NORMAL = 0, FRAME_UNALIGNED, FRAME_NOT_ACCESSIBLE, FRAME_RECURSION, FRAME_GRAPH_ERROR, FRAME_INVALID_TEXT_ADDRESS, FRAME_UNRELIABLE_FUNCTION, FRAME_NUM_STATUS, } frame_status; struct stackframe { ... enum frame_status status; }; unwind_frame() { frame->status = FRAME_NORMAL; Then, for each situation, change the status appropriately. } Eventually, arch_stack_walk_reliable() could just declare the stack trace as unreliable if status != FRAME_NORMAL. Also, the caller can get an exact idea of why the stack trace failed. Is that acceptable? > The other thing I guess is the question of if we want to bother flagging > frames as unrelaible when we return an error; I don't see an issue with > it and it may turn out to make it easier to do something in the future > so I'm fine with that Initially, I thought that there is no need to flag it for errors. But Josh had a comment that the stack trace is indeed unreliable on errors. Again, the word unreliable is the one causing the problem. The above enum-based solution addresses Josh's comment as well. Let me know if this is good. Thanks! Madhavan