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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 08860C2D0DB for ; Sat, 25 Jan 2020 10:25:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D2E222070A for ; Sat, 25 Jan 2020 10:25:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726612AbgAYKZe (ORCPT ); Sat, 25 Jan 2020 05:25:34 -0500 Received: from mga06.intel.com ([134.134.136.31]:18162 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726181AbgAYKZe (ORCPT ); Sat, 25 Jan 2020 05:25:34 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 25 Jan 2020 02:25:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,361,1574150400"; d="scan'208";a="400894449" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by orsmga005.jf.intel.com with ESMTP; 25 Jan 2020 02:25:07 -0800 Received: from andy by smile with local (Exim 4.93) (envelope-from ) id 1ivIcm-0003eG-Hz; Sat, 25 Jan 2020 12:25:08 +0200 Date: Sat, 25 Jan 2020 12:25:08 +0200 From: Andy Shevchenko To: James Bottomley Cc: Helge Deller , linux-parisc@vger.kernel.org Subject: Re: [PATCH v1] parisc: Use for_each_console() helper Message-ID: <20200125102508.GQ32742@smile.fi.intel.com> References: <20200124160739.65256-1-andriy.shevchenko@linux.intel.com> <1579883942.3001.14.camel@HansenPartnership.com> <20200124173846.GL32742@smile.fi.intel.com> <1579888788.3001.26.camel@HansenPartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1579888788.3001.26.camel@HansenPartnership.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org On Fri, Jan 24, 2020 at 09:59:48AM -0800, James Bottomley wrote: > On Fri, 2020-01-24 at 19:38 +0200, Andy Shevchenko wrote: > > On Fri, Jan 24, 2020 at 08:39:02AM -0800, James Bottomley wrote: > > > On Fri, 2020-01-24 at 18:07 +0200, Andy Shevchenko wrote: > > > > Replace open coded single-linked list iteration loop with > > > > for_each_console() > > > > helper in use. > > > > - while ((console = console_drivers) != NULL) > > > > - unregister_console(console_drivers); > > > > + for_each_console(console) > > > > + unregister_console(console); > > > > > > This is wrong. The old formulation iterates correctly in the face > > > of element removal. for_each_console is defined: > > > > > > #define for_each_console(con) \ > > > for (con = console_drivers; con != NULL; con = con->next) > > > > > > So it's not safe for any iteration that alters the list elements. > > > > Ah, I see. In this case we need to keep a pointer to the next > > element. Though, the original code assumes that console_drivers after > > unregistration will be promoted to the next element. Do we have this > > assumption solid? > > Yes, the original code simply removes the head until the list is empty. > That's a recognized way of emptying any list while letting the remove > code take care of the locking ... it works because parisc doesn't have > a braille console. By the way, consider this code from register_console() for_each_console(bcon) if (bcon->flags & CON_BOOT) unregister_console(bcon); It works based on assumption that next pointer of the just unregistered console is not damaged. So, My initial patch will work in the same way. -- With Best Regards, Andy Shevchenko