From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934258AbdKBDYY (ORCPT ); Wed, 1 Nov 2017 23:24:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40350 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751428AbdKBDYX (ORCPT ); Wed, 1 Nov 2017 23:24:23 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 44654859FA Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jasowang@redhat.com Subject: Re: [PATCH net-next V2 3/3] tun: add eBPF based queue selection method To: Alexei Starovoitov , "Michael S. Tsirkin" Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, willemdebruijn.kernel@gmail.com, tom@herbertland.com, Daniel Borkmann References: <1509445938-4345-1-git-send-email-jasowang@redhat.com> <1509445938-4345-4-git-send-email-jasowang@redhat.com> <20171031184002-mutt-send-email-mst@kernel.org> <43c86606-2911-768d-704f-8b25e04cb47b@redhat.com> <20171101150458-mutt-send-email-mst@kernel.org> <20171101191213.2h5rlawpbnqtq662@ast-mbp> From: Jason Wang Message-ID: <673b759a-cc35-e5db-4dd4-9677ab40d2a0@redhat.com> Date: Thu, 2 Nov 2017 11:24:16 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171101191213.2h5rlawpbnqtq662@ast-mbp> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 02 Nov 2017 03:24:23 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017年11月02日 03:12, Alexei Starovoitov wrote: > On Wed, Nov 01, 2017 at 03:59:48PM +0200, Michael S. Tsirkin wrote: >> On Wed, Nov 01, 2017 at 09:02:03PM +0800, Jason Wang wrote: >>> >>> On 2017年11月01日 00:45, Michael S. Tsirkin wrote: >>>>> +static void __tun_set_steering_ebpf(struct tun_struct *tun, >>>>> + struct bpf_prog *new) >>>>> +{ >>>>> + struct bpf_prog *old; >>>>> + >>>>> + old = rtnl_dereference(tun->steering_prog); >>>>> + rcu_assign_pointer(tun->steering_prog, new); >>>>> + >>>>> + if (old) { >>>>> + synchronize_net(); >>>>> + bpf_prog_destroy(old); >>>>> + } >>>>> +} >>>>> + >>>> Is this really called under rtnl? >>> Yes it is __tun_chr_ioctl() will call rtnl_lock(). >> Is the call from tun_free_netdev under rtnl too? >> >>>> If no then rtnl_dereference >>>> is wrong. If yes I'm not sure you can call synchronize_net >>>> under rtnl. >>>> >>> Are you worrying about the long wait? Looking at synchronize_net(), it does: >>> >>> void synchronize_net(void) >>> { >>>     might_sleep(); >>>     if (rtnl_is_locked()) >>>         synchronize_rcu_expedited(); >>>     else >>>         synchronize_rcu(); >>> } >>> EXPORT_SYMBOL(synchronize_net); >>> >>> Thanks >> Not the wait - expedited is not a good thing to allow unpriveledged >> userspace to do, it interrupts all VMs running on the same box. >> >> We could use a callback though the docs warn userspace can use that >> to cause a DOS and needs to be limited. > the whole __tun_set_steering_ebpf() looks odd to me. > There is tun_attach_filter/tun_detach_filter pattern > that works for classic BPF. Why for eBPF this strange > synchronize_net() is there? > I'm not sure I get the question. eBPF here is used to do queue selection, so we could not reuse socket filter (tun_detach_filter use call_rcu()). cBPF could be used here, but I'm not quite sure it's worth to support it. And I agree we should use call_rcu() here. Hope this answer your question. Thanks