From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH net-next 3/3] tap: XDP support Date: Fri, 28 Jul 2017 17:11:38 +0200 Message-ID: <597B542A.7070704@iogearbox.net> References: <1501147533-12368-1-git-send-email-jasowang@redhat.com> <1501147533-12368-4-git-send-email-jasowang@redhat.com> <20170727201338.65d56b2a@cakuba.netronome.com> <7d1cb7bf-43c1-3993-be00-04e4676dd917@redhat.com> <20170728064603-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: Jakub Kicinski , davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: "Michael S. Tsirkin" , Jason Wang Return-path: In-Reply-To: <20170728064603-mutt-send-email-mst@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 07/28/2017 05:46 AM, Michael S. Tsirkin wrote: > On Fri, Jul 28, 2017 at 11:28:54AM +0800, Jason Wang wrote: >>>> + old_prog = rtnl_dereference(tun->xdp_prog); >>>> + if (old_prog) >>>> + bpf_prog_put(old_prog); >>>> + rcu_assign_pointer(tun->xdp_prog, prog); >>> Is this OK? Could this lead to the program getting freed and then >>> datapath accessing a stale pointer? I mean in the scenario where the >>> process gets pre-empted between the bpf_prog_put() and >>> rcu_assign_pointer()? >> >> Will call bpf_prog_put() after rcu_assign_pointer(). +1, good catch Jakub. > I suspect you need to sync RCU or something before that. No, see for example generic_xdp_install().