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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 2FB7DC10DCE for ; Tue, 10 Mar 2020 23:14:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CEF0C2071B for ; Tue, 10 Mar 2020 23:14:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="X/tnX+GM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727506AbgCJXOX (ORCPT ); Tue, 10 Mar 2020 19:14:23 -0400 Received: from mail-yw1-f66.google.com ([209.85.161.66]:32847 "EHLO mail-yw1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726402AbgCJXOW (ORCPT ); Tue, 10 Mar 2020 19:14:22 -0400 Received: by mail-yw1-f66.google.com with SMTP id j186so285478ywe.0 for ; Tue, 10 Mar 2020 16:14:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=OqXVcwuo4+/NNHFG+y7HUy4xB5+imHtRO79dz1ss88k=; b=X/tnX+GMij5IAiKwrCbyuJyVadEau8r3RJMnZtxuYFRFkHOIqbtHxHuXTG+H3EZKVg QvVu7g1CAAphQ/Mq3pOPdvgfXUtTQW+Lsl9CycNUeNBVhHCmQNey1lv1hfbxAJVhQ/po R4eqCnHDQnYMWQm6yAoxlOcz+6x/ll04KJbPQDdWfCXV+VNiE8GUjr3YdGeohe48wOdB 8QdPEj/B/vaEX5suZJA98ncSCaa5YByCTSggPu71fwwgZs4BLUyIVLwBIFb03jIv2Tc9 sr64t3WSZYj3EUDjb4sqpHDcPl8yBR/sBzBT+Ro9bKxlTYde3epSXfHCdnGQHRyqwNNN wTLA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=OqXVcwuo4+/NNHFG+y7HUy4xB5+imHtRO79dz1ss88k=; b=akgXMzMJnk+BinxivkcNijWZCWP+YdyfE6oHqaN+PdX8YkOd7/9Cnj9CbljwxoFKFX E9iIfY/ScjhqDSlIKqNBD1/MBYbwZWZx2M7G9UK4/65NaviDH0TU1vhawPd7T4I61Hq+ KmXKuzUH2TZifO8rGDjF+6FMldl4xm37qA9u4Ge1zRvtBymB0FpbaYtifLSr+Mp4dbOf MPJW4Xm92DolRpucBg05cOOn2OohtNg+o0cUpNCvp/hFH7ea+DYKJXc979qXuMFRtBof fFlffj0zqnKNDsV3yoOLZT1TFKB+nKzoQcbIlcMXlMLCnhADN3L3TKHGuynn6+IHWjwF EjGg== X-Gm-Message-State: ANhLgQ3dHH0yQtqd4HZwncBLAnfXOeskKQbaQsN8IU8VqeI1knmhpG3/ njGzPGsMINck6yewVx4JXM0RCQzd X-Google-Smtp-Source: ADFU+vtPXE95cdQsKzrnis8v7rzKgd3vOk71HiB2zGdT1sFElj0s15X6USyJxbJdey2PV1dbgwkmkw== X-Received: by 2002:a81:4c8b:: with SMTP id z133mr208404ywa.344.1583882059696; Tue, 10 Mar 2020 16:14:19 -0700 (PDT) Received: from mail-yw1-f45.google.com (mail-yw1-f45.google.com. [209.85.161.45]) by smtp.gmail.com with ESMTPSA id y12sm5259508ywy.74.2020.03.10.16.14.18 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Mar 2020 16:14:18 -0700 (PDT) Received: by mail-yw1-f45.google.com with SMTP id t141so225194ywc.11 for ; Tue, 10 Mar 2020 16:14:18 -0700 (PDT) X-Received: by 2002:a81:ee0e:: with SMTP id l14mr211330ywm.354.1583882057981; Tue, 10 Mar 2020 16:14:17 -0700 (PDT) MIME-Version: 1.0 References: <20200309153435.32109-1-willemdebruijn.kernel@gmail.com> <20200310023528-mutt-send-email-mst@kernel.org> <20200310085437-mutt-send-email-mst@kernel.org> <20200310104024-mutt-send-email-mst@kernel.org> <20200310172833-mutt-send-email-mst@kernel.org> <20200310175627-mutt-send-email-mst@kernel.org> In-Reply-To: <20200310175627-mutt-send-email-mst@kernel.org> From: Willem de Bruijn Date: Tue, 10 Mar 2020 19:13:41 -0400 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH net] net/packet: tpacket_rcv: do not increment ring index on drop To: "Michael S. Tsirkin" Cc: Willem de Bruijn , Network Development , David Miller Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Mar 10, 2020 at 5:58 PM Michael S. Tsirkin wrote: > > On Tue, Mar 10, 2020 at 05:35:55PM -0400, Willem de Bruijn wrote: > > On Tue, Mar 10, 2020 at 5:30 PM Michael S. Tsirkin wrote: > > > > > > On Tue, Mar 10, 2020 at 11:38:16AM -0400, Willem de Bruijn wrote: > > > > On Tue, Mar 10, 2020 at 10:44 AM Michael S. Tsirkin wrote: > > > > > > > > > > On Tue, Mar 10, 2020 at 10:16:56AM -0400, Willem de Bruijn wrote: > > > > > > On Tue, Mar 10, 2020 at 8:59 AM Michael S. Tsirkin wrote: > > > > > > > > > > > > > > On Tue, Mar 10, 2020 at 08:49:23AM -0400, Willem de Bruijn wrote: > > > > > > > > On Tue, Mar 10, 2020 at 2:43 AM Michael S. Tsirkin wrote: > > > > > > > > > > > > > > > > > > On Mon, Mar 09, 2020 at 11:34:35AM -0400, Willem de Bruijn wrote: > > > > > > > > > > From: Willem de Bruijn > > > > > > > > > > > > > > > > > > > > In one error case, tpacket_rcv drops packets after incrementing the > > > > > > > > > > ring producer index. > > > > > > > > > > > > > > > > > > > > If this happens, it does not update tp_status to TP_STATUS_USER and > > > > > > > > > > thus the reader is stalled for an iteration of the ring, causing out > > > > > > > > > > of order arrival. > > > > > > > > > > > > > > > > > > > > The only such error path is when virtio_net_hdr_from_skb fails due > > > > > > > > > > to encountering an unknown GSO type. > > > > > > > > > > > > > > > > > > > > Signed-off-by: Willem de Bruijn > > > > > > > > > > > > > > > > > > > > --- > > > > > > > > > > > > > > > > > > > > I wonder whether it should drop packets with unknown GSO types at all. > > > > > > > > > > This consistently blinds the reader to certain packets, including > > > > > > > > > > recent UDP and SCTP GSO types. > > > > > > > > > > > > > > > > > > Ugh it looks like you have found a bug. Consider a legacy userspace - > > > > > > > > > it was actually broken by adding USD and SCTP GSO. I suspect the right > > > > > > > > > thing to do here is actually to split these packets up, not drop them. > > > > > > > > > > > > > > > > In the main virtio users, virtio_net/tun/tap, the packets will always > > > > > > > > arrive segmented, due to these devices not advertising hardware > > > > > > > > segmentation for these protocols. > > > > > > > > > > > > > > Oh right. That's good then, sorry about the noise. > > > > > > > > > > > > Not at all. Thanks for taking a look! > > > > > > > > > > > > > > So the issue is limited to users of tpacket_rcv, which is relatively > > > > > > > > new. There too it is limited on egress to devices that do advertise > > > > > > > > h/w offload. And on r/x to GRO. > > > > > > > > > > > > > > > > The UDP GSO issue precedes the fraglist GRO patch, by the way, and > > > > > > > > goes back to my (argh!) introduction of the feature on the egress > > > > > > > > path. > > > > > > > > > > > > > > > > > > > > > > > > > > > The peer function virtio_net_hdr_to_skb already drops any packets with > > > > > > > > > > unknown types, so it should be fine to add an SKB_GSO_UNKNOWN type and > > > > > > > > > > let the peer at least be aware of failure. > > > > > > > > > > > > > > > > > > > > And possibly add SKB_GSO_UDP_L4 and SKB_GSO_SCTP types to virtio too. > > > > > > > > > > > > > > > > > > This last one is possible for sure, but for virtio_net_hdr_from_skb > > > > > > > > > we'll need more flags to know whether it's safe to pass > > > > > > > > > these types to userspace. > > > > > > > > > > > > > > > > Can you elaborate? Since virtio_net_hdr_to_skb users already returns > > > > > > > > -EINVAL on unknown GSO types and its callers just drop these packets, > > > > > > > > it looks to me that the infra is future proof wrt adding new GSO > > > > > > > > types. > > > > > > > > > > > > > > Oh I mean if we do want to add new types and want to pass them to > > > > > > > users, then virtio_net_hdr_from_skb will need to flag so it > > > > > > > knows whether that will or won't confuse userspace. > > > > > > > > > > > > I'm not sure how that would work. Ignoring other tun/tap/virtio for > > > > > > now, just looking at tpacket, a new variant of socket option for > > > > > > PACKET_VNET_HDR, for every new GSO type? > > > > > > > > > > Maybe a single one with a bitmap of legal types? > > > > > > > > > > > In practice the userspace I'm aware of, and any sane implementation, > > > > > > will be future proof to drop and account packets whose type it cannot > > > > > > process. So I think we can just add new types. > > > > > > > > > > Well if packets are just dropped then userspace breaks right? > > > > > > > > It is an improvement over the current silent discard in the kernel. > > > > > > > > If it can count these packets, userspace becomes notified that it > > > > should perhaps upgrade or use ethtool to stop the kernel from > > > > generating certain packets. > > > > > > > > Specifically for packet sockets, it wants to receive packets as they > > > > appear "on the wire". It does not have to drop these today even, but > > > > can easily parse the headers. > > > > > > > > For packet sockets at least, I don't think that we want transparent > > > > segmentation. > > > > > > Well it's GSO is in the way then it's no longer "on the wire", right? > > > Whether we split these back to individual skbs or we don't > > > it's individual packets that are on the wire. GSO just allows > > > passing them to the application in a more efficient way. > > > > Not entirely. With TSO enabled, packet sockets will show the TCP TSO > > packets, not the individual segment on the wire. > > But nothing breaks if it shows a segment on the wire while linux > processes packets in batches, right? It's just some extra info that > an app can't handle, so we hide it from the app... I don't entirely follow. Are we on the same page here and agree that we should just show the GSO packet to userspace?