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 617A1C433EF for ; Mon, 17 Jan 2022 09:20:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235559AbiAQJUU convert rfc822-to-8bit (ORCPT ); Mon, 17 Jan 2022 04:20:20 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:20702 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233695AbiAQJUU (ORCPT ); Mon, 17 Jan 2022 04:20:20 -0500 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-23-2CC5VzGtNxyVoTuySSDULQ-1; Mon, 17 Jan 2022 09:20:17 +0000 X-MC-Unique: 2CC5VzGtNxyVoTuySSDULQ-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 15.0.1497.28; Mon, 17 Jan 2022 09:20:16 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.028; Mon, 17 Jan 2022 09:20:16 +0000 From: David Laight To: 'Eric Dumazet' , "David S . Miller" , Jakub Kicinski CC: netdev , Eric Dumazet , syzbot , Ido Schimmel , "Jiri Pirko" Subject: RE: [PATCH v2 net] ipv4: update fib_info_cnt under spinlock protection Thread-Topic: [PATCH v2 net] ipv4: update fib_info_cnt under spinlock protection Thread-Index: AQHYCrfJGT15ZBxssEC1JYcw+v8Nsqxm75EQ Date: Mon, 17 Jan 2022 09:20:16 +0000 Message-ID: References: <20220116090220.2378360-1-eric.dumazet@gmail.com> In-Reply-To: <20220116090220.2378360-1-eric.dumazet@gmail.com> 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: netdev@vger.kernel.org From: Eric Dumazet > Sent: 16 January 2022 09:02 > > From: Eric Dumazet > > In the past, free_fib_info() was supposed to be called > under RTNL protection. > > This eventually was no longer the case. > > Instead of enforcing RTNL it seems we simply can > move fib_info_cnt changes to occur when fib_info_lock > is held. This probably ought to be a stable candidate. If an increment is lost due to the unlocked inc/dec it is possible for the count to wrap to -1 if all fib are deleted. That will cause the table size to be doubled on every allocate (until the count goes +ve again). Losing a decrement is less of a problem. You'd need to lose a lot of them for any ill effect. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)