From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: single process receives own frames due to PACKET_MMAP Date: Tue, 07 Jan 2014 16:26:12 +0100 Message-ID: <52CC1C94.2060808@redhat.com> References: <52B4465E.2090904@aimvalley.nl> <52CB34F9.6020906@aimvalley.nl> <52CBC991.8030701@redhat.com> <20140107110609.74f71979@redhat.com> <52CBFE13.8@aimvalley.nl> <20140107150938.1058b358@redhat.com> <52CC1A61.5080205@aimvalley.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Jesper Dangaard Brouer , netdev@vger.kernel.org, David Miller , uaca@alumni.uv.es To: Norbert van Bolhuis Return-path: Received: from mx1.redhat.com ([209.132.183.28]:27768 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751057AbaAGP1Z (ORCPT ); Tue, 7 Jan 2014 10:27:25 -0500 In-Reply-To: <52CC1A61.5080205@aimvalley.nl> Sender: netdev-owner@vger.kernel.org List-ID: On 01/07/2014 04:16 PM, Norbert van Bolhuis wrote: > On 01/07/14 15:09, Jesper Dangaard Brouer wrote: >> On Tue, 07 Jan 2014 14:16:03 +0100 >> Norbert van Bolhuis wrote: >>> On 01/07/14 11:06, Jesper Dangaard Brouer wrote: >>>> On Tue, 07 Jan 2014 10:32:01 +0100 >>>> Daniel Borkmann wrote: >>>> >>>>> On 01/06/2014 11:58 PM, Norbert van Bolhuis wrote: >>>>>> >> [...] >>>>> >>>>>> I'd say it makes no sense to make the same process receive its >>>>>> own transmitted frames on that same interface (unless its lo). >>>> >>>> Have you setup: >>>> ring->s_ll.sll_protocol = 0 >>>> >>>> This is what I did in trafgen to avoid this problem. >>>> >>>> See line 55 in netsniff-ng/ring.c: >>>> https://github.com/borkmann/netsniff-ng/blob/c3602a995b21e8133c7f4fd1fb1e7e21b6a844f1/ring.c#L55 >>>> >>>> Commit: >>>> https://github.com/borkmann/netsniff-ng/commit/c3602a995b21e8133c7f4fd1fb1e7e21b6a844f1 >>>> >>> >>> >>> No I did not do that, I was checking my code against netsniff-ng-0.5.8-rc4. >>> >>> But I just tried it, I believe I do the same as netsniff-ng-0.5.8-rc5, but it doesn't >>> work for me. Maybe because I have an old FC14 system (kernel 2.6.35.14-106.fc14.x86_64). >>> >>> So I tried to see whether netsniff-ng-0.5.8-rc5/trafgen still makes the >>> kernel call packet_rcv() on my FC14 system. So I build and run it, but I'm not sure >>> how to (easily) check that. >> >> The easiest way is to: >> cat /proc/net/ptype >> And look if someone registered a proto handler/function: packet_rcv (or tpacket_rcv). >> >> The more exact method is, to run "perf record -a -g" and then look (at >> the result with "perf report") for a lock contention, and "expand" the >> spin_lock and see if packet_rcv() is calling this spin lock. >> > > > I checked the easy way. > Even on my old FC14 system the "protocol=0 patch" seems to make a difference > for trafgen. > Without the patch I see for each CPU in use by trafgen a "packet_rcv entry" in > /proc/net/ptype. > With the patch I see no additional "packet_rcv entry". Yes, that is expected behaviour. ;-) See more below. > It could be my Appl is wrong or maybe the "protocol=0 patch" does not help. > I think the latter, afterall my Appl has, unlike trafgen, another RX > (AF_PACKET) socket. > > >> >>> In anyway, Wireshark does capture the trafgen generated >>> frames, does that say anything ? >> >> Be careful not to start a wireshark/tcpdump, at the sametime, as this >> will slow you down. >> >>> In the future, I can at least use PACKET_QDISC_BYPASS as a "workaround". >> >> And in the future with PACKET_QDISC_BYPASS, your wireshark will not >> catch these packets, remember that. >> > > > Yes, this is why I would love to see the "protocol=0 patch" work for my Appl. > > So I will try my Appl with the latest net-next kernel to see if that makes > it work. Hopefully I can find some time in the next coming days, I will keep > you informed. As long as there's at least one single PF_PACKET receive socket open and you do not make use of PACKET_QDISC_BYPASS on your tx socket, then those packets go back the dev_queue_xmit_nit() path, even if your tx socket uses protocol=0. If you make use of PACKET_QDISC_BYPASS [1] for your particular tx socket, then packets generated by that socket will not hit the dev_queue_xmit_nit() path back to other possible rx listeners that are present on your system (w/ the side-effects for tx as described in [1]). [1] Documentation/networking/packet_mmap.txt +960 > --- > Norbert