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 7542DC2B9F4 for ; Fri, 25 Jun 2021 17:18:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5CEEC60FD8 for ; Fri, 25 Jun 2021 17:18:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229630AbhFYRVD (ORCPT ); Fri, 25 Jun 2021 13:21:03 -0400 Received: from linux.microsoft.com ([13.77.154.182]:41730 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230073AbhFYRVB (ORCPT ); Fri, 25 Jun 2021 13:21:01 -0400 Received: from [192.168.254.32] (unknown [47.187.214.213]) by linux.microsoft.com (Postfix) with ESMTPSA id 9BC9120B6C50; Fri, 25 Jun 2021 10:18:39 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 9BC9120B6C50 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1624641520; bh=TlJDbyWbcxv6yECiCA1Zh3uMErfRQhw+ASy5p2fTu3I=; h=Subject:From:To:Cc:References:Date:In-Reply-To:From; b=CrdADwVSyqNrwBJyv8xrm6v9X6wDmgq6i2q8xRuFvz+Gc63/wsCWoB+33Npfd8vbT QU4fMD5jev7u/irVerfR8KSrwo1sVUUnKf6AbQGRKkfFJY95WFh3FtToYj/euqj8Zl UFoNtcjom/Aoi25ErD+v8uoGo5yK4awkmthZ6bHw= Subject: Re: [RFC PATCH v5 1/2] arm64: Introduce stack trace reliability checks in the unwinder From: "Madhavan T. Venkataraman" To: Mark Brown Cc: Mark Rutland , jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, jthierry@redhat.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210526214917.20099-1-madvenka@linux.microsoft.com> <20210526214917.20099-2-madvenka@linux.microsoft.com> <20210624144021.GA17937@C02TD0UTHF1T.local> <20210625155127.GC4492@sirena.org.uk> Message-ID: <2877744f-83ab-3f18-71e3-d406cfdd793d@linux.microsoft.com> Date: Fri, 25 Jun 2021 12:18:38 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 6/25/21 12:05 PM, Madhavan T. Venkataraman wrote: > > > On 6/25/21 10:51 AM, Mark Brown wrote: >> On Fri, Jun 25, 2021 at 10:39:57AM -0500, Madhavan T. Venkataraman wrote: >>> On 6/24/21 9:40 AM, Mark Rutland wrote: >> >>>> At a high-level, I'm on-board with keeping track of this per unwind >>>> step, but if we do that then I want to be abel to use this during >>>> regular unwinds (e.g. so that we can have a backtrace idicate when a >>>> step is not reliable, like x86 does with '?'), and to do that we need to >>>> be a little more accurate. >> >>> The only consumer of frame->reliable is livepatch. So, in retrospect, my >>> original per-frame reliability flag was an overkill. I was just trying to >>> provide extra per-frame debug information which is not really a requirement >>> for livepatch. >> >> It's not a requirement for livepatch but if it's there a per frame >> reliability flag would have other uses - for example Mark has mentioned >> the way x86 prints a ? next to unreliable entries in oops output for >> example, that'd be handy for people debugging issues and would have the >> added bonus of ensuring that there's more constant and widespread >> exercising of the reliability stuff than if it's just used for livepatch >> which is a bit niche. >> > > I agree. That is why I introduced the per-frame flag. > > So, let us try a different approach. > > First, let us get rid of the frame->reliable flag from this patch series. That flag > can be implemented when all of the pieces are in place for per-frame debug and tracking. > > For consumers such as livepatch that don't really care about per-frame stuff, let us > solve it more cleanly via the return value of unwind_frame(). > > Currently, the return value from unwind_frame() is a tri-state return value which is > somewhat confusing. > > 0 means continue unwinding > -error means stop unwinding. However, > -ENOENT means successful termination > Other values mean an error has happened. > > Instead, let unwind_frame() return one of 3 values: > > enum { > UNWIND_CONTINUE, > UNWIND_CONTINUE_WITH_ERRORS, > UNWIND_STOP, > }; > Sorry. I need to add one more value to this. So, the enum will be: enum { UNWIND_CONTINUE, UNWIND_CONTINUE_WITH_ERRORS, UNWIND_STOP, UNWIND_STOP_WITH_ERRORS, }; UNWIND_CONTINUE (what used to be a return value of 0) Continue with the unwind. UNWIND_CONTINUE_WITH_ERRORS (new return value) Errors encountered. But the errors are not fatal errors like stack corruption. UNWIND_STOP (what used to be -ENOENT) Successful termination of unwind. UNWIND_STOP_WITH_ERRORS (what used to be -EINVAL, etc) Unsuccessful termination. Sorry I missed this the last time. So, to reiterate: All consumers will stop unwinding when they see UNWIND_STOP and UNWIND_STOP_WITH_ERRORS. Debug type consumers can choose to continue when they see UNWIND_CONTINUE_WITH_ERRORS. Livepatch type consumers will only continue on UNWIND_CONTINUE. This way, my patch series does not have a dependency on the per-frame enhancements. Thanks! Madhavan