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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 88D61C433E1 for ; Fri, 21 Aug 2020 21:39:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64CDF207DE for ; Fri, 21 Aug 2020 21:39:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726740AbgHUVj2 convert rfc822-to-8bit (ORCPT ); Fri, 21 Aug 2020 17:39:28 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:24982 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726187AbgHUVj2 (ORCPT ); Fri, 21 Aug 2020 17:39:28 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-221-Ovfv65qLMDOzSh5mErwndw-1; Fri, 21 Aug 2020 22:39:24 +0100 X-MC-Unique: Ovfv65qLMDOzSh5mErwndw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 21 Aug 2020 22:39:23 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 21 Aug 2020 22:39:23 +0100 From: David Laight To: 'Marcelo Ricardo Leitner' CC: "'linux-sctp@vger.kernel.org'" , "'netdev@vger.kernel.org'" Subject: RE: Use of genradix in sctp Thread-Topic: Use of genradix in sctp Thread-Index: AdZ1ckZAY2qe63tNS/O9MsxVdvHiSAALTAcAAANIG8AAkcwnAAADgzyw Date: Fri, 21 Aug 2020 21:39:23 +0000 Message-ID: <11eafe393bc640a8bbddf33d0e784901@AcuMS.aculab.com> References: <2ffb7752d3e8403ebb220e0a5e2cf3cd@AcuMS.aculab.com> <20200818213800.GJ906397@localhost.localdomain> <357ded60999a4957addb766a29431ad7@AcuMS.aculab.com> <20200821204636.GO3399@localhost.localdomain> In-Reply-To: <20200821204636.GO3399@localhost.localdomain> Accept-Language: en-GB, en-US Content-Language: 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: 0.001 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: 'Marcelo Ricardo Leitner' > Sent: 21 August 2020 21:47 ... > > 3) Defer the allocation until the stream is used. > > for outbound streams this could remove the extra buffer. > > This can be tricky. What should happen if it gets a packet on a stream > that it couldn't allocate, and then another on a stream that was > already allocated? Just a drop, it will retransmit and recover, and > then again.. While, OTOH, if the application requested such amount of > streams, it is likely going to use it. If not, that's an application > bug. You'd probably need to (effectively) drop the ethernet frame that contained the chunk. But the problem I see is that GFP flags are passed in. So there must me a path where the allocation can't sleep. Now allocating a couple of pages is fine but if the maximum is just over 300 for each of 'in' and 'out'. I can well imagine that is likely to fail. I suspect this happens because the remote system can (if my quick scan of the code is right) negotiate a much larger number on an active connection. I don't know what applications might be doing such things. But I can imagine someone will try to negotiate 64k-1 streams just because that is the maximum. And/or deciding to use stream 65535 for 'special' traffic. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)