From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966171AbdADLHy (ORCPT ); Wed, 4 Jan 2017 06:07:54 -0500 Received: from mail.free-electrons.com ([62.4.15.54]:55166 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965015AbdADLHx (ORCPT ); Wed, 4 Jan 2017 06:07:53 -0500 Date: Wed, 4 Jan 2017 12:07:50 +0100 From: Alexandre Belloni To: Julia Lawall Cc: Russell King - ARM Linux , Kees Cook , andrew@lunn.ch, Jason Cooper , rtc-linux@googlegroups.com, a.zummo@towertech.it, LKML , "linux-arm-kernel@lists.infradead.org" , gregory.clement@free-electrons.com, Bhumika Goyal , sebastian.hesselbarth@gmail.com Subject: Re: [PATCH] rtc: armada38x: add __ro_after_init to armada38x_rtc_ops Message-ID: <20170104110750.dtu54t74qkuuvkvq@piout.net> References: <1482751862-18699-1-git-send-email-bhumirks@gmail.com> <20170102140654.GF14217@n2100.armlinux.org.uk> <20170103213118.GM14217@n2100.armlinux.org.uk> <20170103215421.GN14217@n2100.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20161126 (1.7.1) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/01/2017 at 11:57:00 +0100, Julia Lawall wrote : > > > On Tue, 3 Jan 2017, Russell King - ARM Linux wrote: > > > On Tue, Jan 03, 2017 at 09:31:18PM +0000, Russell King - ARM Linux wrote: > > > On Tue, Jan 03, 2017 at 01:18:29PM -0800, Kees Cook wrote: > > > > On Mon, Jan 2, 2017 at 6:06 AM, Russell King - ARM Linux > > > > wrote: > > > > > On Mon, Dec 26, 2016 at 05:01:02PM +0530, Bhumika Goyal wrote: > > > > >> The object armada38x_rtc_ops of type rtc_class_ops structure is not > > > > >> modified after getting initialized by armada38x_rtc_probe. Apart from > > > > >> getting referenced in init it is also passed as an argument to the function > > > > >> devm_rtc_device_register but this argument is of type const struct > > > > >> rtc_class_ops *. Therefore add __ro_after_init to its declaration. > > > > > > > > > > What I'd prefer here is for the structure to be duplicated, with one > > > > > copy having the alarm methods and one which does not. Both can then > > > > > be made "const" (so placed into the read-only section at link time) > > > > > and the probe function select between the two. > > > > > > > > > > I think that's a cleaner and better solution, even though it's > > > > > slightly larger. > > > > > > > > > > I'm not a fan of __ro_after_init being used where other solutions are > > > > > possible. > > > > > > > > Can the pointer that points to the struct rtc_class_ops be made ro_after_init? > > > > > > It's passed into the RTC core code, and probably stored in some dynamically > > > allocated object, so probably no. It's the same class of problem as every > > > file_operations pointer in the kernel, or the thousand other operations > > > structure pointers that a running kernel has. > > I'm not sure to understand the question and the response. A quick check > with grep suggests that most rtc_class_ops pointers are already const. > There seem to be just some instances in specific drivers that are not. > The question was whether the point to the rtc_class_ops could be made __ro_after_init. And Russell is right, it is pointed to by the ops pointer in a struct rtc_device and that struct is dynamically allocated in rtc_device_register(). -- Alexandre Belloni, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com