From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Ricardo Leitner Subject: tun issue after e0b46d0ee9c: tun: Use iovec iterators Date: Fri, 28 Nov 2014 17:25:27 -0200 Message-ID: <5478CC27.9040705@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev To: herbert@gondor.apana.org.au Return-path: Received: from mx1.redhat.com ([209.132.183.28]:33886 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750968AbaK1TZd (ORCPT ); Fri, 28 Nov 2014 14:25:33 -0500 Sender: netdev-owner@vger.kernel.org List-ID: Hi, I saw there are tun updates on Dave's queue but none seemed to handle this. I can't use current net-next (799d2fff1858004526ad75d66a5dd8a5cce6ad40) on a kvm hypervisor because tun got clogged somehow. Bisected down to: commit e0b46d0ee9c240c7430a47e9b0365674d4a04522 Author: Herbert Xu Date: Fri Nov 7 21:22:23 2014 +0800 tun: Use iovec iterators This patch removes the use of skb_copy_datagram_const_iovec in favour of the iovec iterator-based skb_copy_datagram_iter. tun interface, host drops 1 incoming packets from guest, shown at ip -s l l, and keeps like that forever. netstat -s didn't mention any checksum issue 12: vnet0: mtu 1500 qdisc pfifo_fast master virbr0 state UNKNOWN mode DEFAULT group default qlen 500 link/ether fe:54:00:10:3f:06 brd ff:ff:ff:ff:ff:ff RX: bytes packets errors dropped overrun mcast 0 0 0 1 0 0 TX: bytes packets errors dropped carrier collsns 2704 51 0 0 0 0 And tap interfaces go counting dropped++ every time: 20: tap0: mtu 1500 qdisc pfifo_fast master virbr0 state UNKNOWN mode DEFAULT group default qlen 500 link/ether fe:97:a4:a6:14:65 brd ff:ff:ff:ff:ff:ff RX: bytes packets errors dropped overrun mcast 0 0 0 16 0 0 TX: bytes packets errors dropped carrier collsns 1456 28 0 0 0 0 traffic capture on guest shows incoming and outgoing packets just fine, while on host, it shows no incoming packets at all. Tested with virtio_net and e1000. With: tun.c tun_get_user(): if (zerocopy) err = zerocopy_sg_from_iter(skb, from); else { err = skb_copy_datagram_from_iter(skb, 0, from, len); <- fails if (!err && msg_control) { struct ubuf_info *uarg = msg_control; uarg->callback(uarg, false); } } if (err) { tun->dev->stats.rx_dropped++; kfree_skb(skb); pr_err("%d %d %d %p\n", __LINE__, zerocopy, err, msg_control); return -EFAULT; } And net/core/datagram.c, skb_copy_datagram_from_iter(): if (copy > 0) { int ret; if (copy > len) copy = len; ret = copy_from_iter(skb->data + offset, copy, from); if (ret != copy) { pr_err("%d ret=%d copy=%d offset=%d len=%d\n", __LINE__, ret, copy, offset, len); goto fault; } I get, for tun interfaces: [ 75.435552] 506 ret=80 copy=90 offset=0 len=90 [ 75.435563] tun: 1124 0 -14 (null) [ 75.499528] 506 ret=80 copy=90 offset=0 len=90 [ 75.499540] tun: 1124 0 -14 (null) These were 1 drop on 1 interface each And for tap interfaces: [ 301.982639] 506 ret=80 copy=90 offset=0 len=90 [ 301.982649] tun: 1124 0 -14 (null) [ 301.988625] 506 ret=80 copy=90 offset=0 len=90 [ 301.988635] tun: 1124 0 -14 (null) [ 301.994762] 506 ret=80 copy=90 offset=0 len=90 [ 301.994773] tun: 1124 0 -14 (null) [ 302.229962] 506 ret=332 copy=342 offset=0 len=342 [ 302.229972] tun: 1124 0 -14 (null) [ 302.230621] 506 ret=332 copy=342 offset=0 len=342 [ 302.230627] tun: 1124 0 -14 (null) [ 302.239065] 506 ret=332 copy=342 offset=0 len=342 [ 302.239071] tun: 1124 0 -14 (null) It's returning 10 bytes less than the expected... ideas? I can provide more info if needed, it's easy to reproduce in here. Thanks, Marcelo