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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6B8F8C433EF for ; Mon, 21 Mar 2022 16:00:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349603AbiCUQBo convert rfc822-to-8bit (ORCPT ); Mon, 21 Mar 2022 12:01:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241372AbiCUQBl (ORCPT ); Mon, 21 Mar 2022 12:01:41 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 28AFD496BD for ; Mon, 21 Mar 2022 09:00:14 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-239-DZcqY6ZCNM-Zxa3ztE6Iiw-1; Mon, 21 Mar 2022 16:00:10 +0000 X-MC-Unique: DZcqY6ZCNM-Zxa3ztE6Iiw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.32; Mon, 21 Mar 2022 16:00:11 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.033; Mon, 21 Mar 2022 16:00:10 +0000 From: David Laight To: 'Dan Carpenter' , Jakob Koschel CC: Joseph Qi , Mark Fasheh , Linux Kernel Mailing List , "ocfs2-devel@oss.oracle.com" , Joel Becker , Andrew Morton , "Geert Uytterhoeven" , Masahiro Yamada , Miguel Ojeda , Mike Rapoport , "Brian Johannesmeyer" , Cristiano Giuffrida , "Bos, H.J." Subject: RE: [PATCH] ocfs2: fix check if list iterator did find an element Thread-Topic: [PATCH] ocfs2: fix check if list iterator did find an element Thread-Index: AQHYPSvRVnhy0IZf6EGgy069JPLEqKzJ/HWg Date: Mon, 21 Mar 2022 16:00:10 +0000 Message-ID: <75180dd18a3f460891cd93f7fcb3aa1c@AcuMS.aculab.com> References: <20220319203106.2541700-1-jakobkoschel@gmail.com> <20220321135435.GL336@kadam> In-Reply-To: <20220321135435.GL336@kadam> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dan Carpenter > Sent: 21 March 2022 13:55 > On Mon, Mar 21, 2022 at 02:34:34PM +0100, Jakob Koschel wrote: > > >> @@ -556,11 +556,11 @@ static void *lockres_seq_start(struct seq_file *m, loff_t *pos) > > >> } > > >> } > > >> > > >> - list_for_each_entry(res, track_list, tracking) { > > >> - if (&res->tracking == &dlm->tracking_list) > > >> - res = NULL; > > >> - else > > >> - dlm_lockres_get(res); > > >> + list_for_each_entry(iter, track_list, tracking) { > > >> + if (&iter->tracking != &dlm->tracking_list) { > > This is an open coded version of: > > if (!list_entry_is_head(iter, &dlm->tracking_list, tracking)) { Doesn't list_for_each_entry() terminate before that happens? So this code is probably still horribly broken. My worry about bugs with these lists isn't really the code that uses list_for_each_entry() - they are fairly easy to locate, read and fix. The problem is all the other code that is scanning these list in other more obscure ways. It really isn't a list structure that is easy to use at all. It's only slight advantage is that you can unlink an item without knowing the list head. (Which can stop buggy code generating cross-linked lists.) Unless you actually need to traverse backwards the 'back pointer points to forwards pointer' list is much better. Even if you have to maintain a 'pointer to last' to get FIFO operation. The other option is to double-link the items into a loop and have a 'head' that points to the first item. Both these loops have 'pointer to items' to don't need container_of() and get better type checking from the compiler. David > > Ideally someone would come through with enough confidence to just delete > it but the second best option is to just make it readable... > > regards, > dan carpenter > > > >> + dlm_lockres_get(iter); > > >> + res = iter; > > >> + } > > >> break; > > >> } - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)