From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net-next 3/3] tap: XDP support Date: Fri, 28 Jul 2017 07:05:03 +0300 Message-ID: <20170728070329-mutt-send-email-mst@kernel.org> 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=utf-8 Content-Transfer-Encoding: 8bit Cc: Jakub Kicinski , davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Jul 28, 2017 at 11:50:45AM +0800, Jason Wang wrote: > > > On 2017年07月28日 11:46, 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(). > > I suspect you need to sync RCU or something before that. > > __bpf_prog_put() will do call_rcu(), so looks like it was ok. > > Thanks True - I missed that. -- MST