From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zoltan Kiss Subject: Re: [3.15-rc3] Bisected: xen-netback mangles packets between two guests on a bridge since merge of "TX grant mapping with SKBTX_DEV_ZEROCOPY instead of copy" series. Date: Thu, 1 May 2014 16:16:51 +0100 Message-ID: <53626563.8010404@citrix.com> References: <395225650.20140430124506@eikelenboom.it> <536250F9.7060405@citrix.com> <1967602892.20140501160513@eikelenboom.it> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: Ian Campbell , "David S. Miller" , , To: Sander Eikelenboom Return-path: Received: from smtp02.citrix.com ([66.165.176.63]:55778 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754082AbaEAPQ7 (ORCPT ); Thu, 1 May 2014 11:16:59 -0400 In-Reply-To: <1967602892.20140501160513@eikelenboom.it> Sender: netdev-owner@vger.kernel.org List-ID: On 01/05/14 15:05, Sander Eikelenboom wrote: > > Thursday, May 1, 2014, 3:49:45 PM, you wrote: > >> On 30/04/14 11:45, Sander Eikelenboom wrote: >>> Another point would be: what *correctness* testing is actually done on the xen-net* patches ? >> I can speak only about my patches: I have manually tested them for the >> usecases where they likely to make a difference, plus they went through >> Xenserver's full test suite several times. > > I think Paul's patches for 3.14 also went through this testsuite fine, however > it did have a bug in it. Does this testsuite include a test which causes a > diverse pattern of frags (for both tx and rx case) ? Unfortunately these tests doesn't directly try with various skb layouts, but it depends on the sending application/kernel what kind of packet they feed in to netback/netfront. I was always thinking we should create a testing facility where we can generate various different skb's and feed them in at an arbitrary part of the networking stack. Or does such thing already exist? > > >>> As i suspect this is again about fragmented packets .. that doesn't seem to be included in any test case while it actually seems to be a case which is hard to get right... >> Beware, there are frags and frag_list which are two entirely different >> things with confusing names. In netback case, frags are used to pass >> through large packets for a long time. frag_list is used only since my >> grant mapping patches, to handle older guests (see comment in >> include/xen/interface/io/netif.h for XEN_NETIF_NR_SLOTS_MIN) > > Ah ok .. it's not about the frags in the packets being handled, but the frag > mechanism is supposed to be used internally ? Yes, the skb on the frag_list should contain no linear data but that extra frag the guest sent to netback. After the grant operations are done, xenvif_handle_frag_list coalesce the frags and that extra skb into brand new, PAGE_SIZE frags. > > If so .. there is at least something wrong in the "older guest" detection, > because both dom0 and PV guests are running the same 3.15-rc3 kernel. That seems very odd ... Can you check ethtool -S vifX.Y in Dom0? tx_frag_overflow will count the packets with too many frags