From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751459AbeCNTol (ORCPT ); Wed, 14 Mar 2018 15:44:41 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:39480 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750779AbeCNToj (ORCPT ); Wed, 14 Mar 2018 15:44:39 -0400 Date: Wed, 14 Mar 2018 14:44:36 -0500 From: Josh Poimboeuf To: Joe Lawrence Cc: Petr Mladek , Jiri Kosina , Miroslav Benes , Jessica Yu , Nicolai Stange , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] livepatch: Initialize shadow variables by init function safely Message-ID: <20180314194436.fl5xro6aixroqzxk@treble> References: <20180313155448.1998-1-pmladek@suse.com> <20180313155448.1998-2-pmladek@suse.com> <20180314192702.h6fvqoo7myt426ww@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180314192702.h6fvqoo7myt426ww@redhat.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 14, 2018 at 03:27:02PM -0400, Joe Lawrence wrote: > On Tue, Mar 13, 2018 at 04:54:47PM +0100, Petr Mladek wrote: > > The existing API allows to pass a sample data to initialize the shadow > > data. It works well when the data are position independent. But it fails > > miserably when we need to set a pointer to the shadow structure itself. > > > > Unfortunately, we might need to initialize the pointer surprisingly > > often because of struct list_head. It is even worse because the list > > might be hidden in other common structures, for example, struct mutex, > > struct wait_queue_head. > > > > This patch makes the API more safe. A custom init function and data > > are passed to klp_shadow_*alloc() functions instead of the sample data. > > Yup, this looks kinda familiar, I remember tinkering with the same idea > last year [1] before settling on the simpler API. > > [1] https://github.com/torvalds/linux/compare/master...joe-lawrence:shadow_variables_v2_c > > > Note that the init_data are not longer a template for the shadow->data. > > It might point to any data that might be necessary when the init > > function is called. > > I'm not opposed to changing the API, but I was wondering if you had > thought about expanding it as an alternative? > > When working on this last summer, I remember holding onto to some less > than intuitive naming conventions so that I could support a basic API > and an extended API with bells and whistles like this patchset > implements. It didn't seem too difficult to layer the basic API ontop > of one like this (see [1] for example), so maybe that's an option to > keep basic shadow variable usage a little simpler. /two cents I like Petr's new API. It's not a big deal to just pass a couple of NULLs if you don't need the callback. And I prefer fewer functions anyway -- maybe it's my functionitis allergies acting up again. > Perhaps shadow variables are another candidate for some kind of > kselftest? Indeed! -- Josh