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 69F68C47076 for ; Fri, 21 May 2021 17:47:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 457DA61353 for ; Fri, 21 May 2021 17:47:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238434AbhEURsk (ORCPT ); Fri, 21 May 2021 13:48:40 -0400 Received: from linux.microsoft.com ([13.77.154.182]:33196 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235764AbhEURsi (ORCPT ); Fri, 21 May 2021 13:48:38 -0400 Received: from [192.168.254.32] (unknown [47.187.214.213]) by linux.microsoft.com (Postfix) with ESMTPSA id 8CCFC20B7188; Fri, 21 May 2021 10:47:14 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 8CCFC20B7188 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1621619235; bh=vp4bh6cnn5xgTCxdBL3ssrfVr3lmhjwR6/PPJY0zW0U=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=kmWtd/Guj2sJubHEiCjGimSMNVPfPbv4AqUu1tPkdEd4CsxXoa90nrgVdPZjS/egp YC33iOhW803pF5G2/4Q1+dg2zaO9Xb/n7G/Fassb1CBWUTXpav3DKhQeXov2oKVFx9 Isb1l0rFMw+VEm7kNqMo/GsWIH9O2llYHg3jzJkQ= 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> <20210521174242.GD5825@sirena.org.uk> From: "Madhavan T. Venkataraman" Message-ID: <26c33633-029e-6374-16e6-e9418099da95@linux.microsoft.com> Date: Fri, 21 May 2021 12:47:13 -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: <20210521174242.GD5825@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 12:42 PM, Mark Brown wrote: > On Fri, May 21, 2021 at 12:23:52PM -0500, Madhavan T. Venkataraman wrote: >> 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: > >>>> + 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 > >> OK. So how about changing the field from a flag to an enum that says exactly >> what happened with the frame? > > TBH I think the code is fine, or rather will be fine when it gets as far > as actually being used - this was more a comment about when we flip this > switch. > OK. >> Also, the caller can get an exact idea of why the stack trace failed. > > I'm not sure anything other than someone debugging things will care > enough to get the code out and then decode it so it seems like it'd be > more trouble than it's worth, we're unlikely to be logging the code as > standard. > OK. >>> 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. > > My understanding there is that arch_stack_walk_reliable() should be > returning an error if either the unwinder detected an error or if any > frame in the stack is flagged as unreliable so from the point of view of > users it's just looking at the error code, it's more that there's no > need for arch_stack_walk_reliable() to consider the reliability > information if an error has been detected and nothing else looks at the > reliability information. > > Like I say we may come up with some use for the flag in error cases in > future so I'm not opposed to keeping the accounting there. > So, should I leave it the way it is now? Or should I not set reliable = false for errors? Which one do you prefer? Josh, Are you OK with not flagging reliable = false for errors in unwind_frame()? Madhavan