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Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Alex Shi , Yanteng Si , Dongliang Mu , Michael Chan , Pavan Chebbi , Joshua Washington , Harshitha Ramamurthy , Saeed Mahameed , Tariq Toukan , Mark Bloch , Leon Romanovsky , Alexander Duyck , kernel-team@meta.com, Daniel Borkmann , Nikolay Aleksandrov , Shuah Khan , dw@davidwei.uk, sdf.kernel@gmail.com, mohsin.bashr@gmail.com, willemb@google.com, jiang.kun2@zte.com.cn, xu.xin16@zte.com.cn, wang.yaxin@zte.com.cn, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, Stanislav Fomichev , Mina Almasry , Bobby Eshleman Subject: Re: [PATCH net-next v3 3/8] net: devmem: support TX over NETMEM_TX_NO_DMA devices Message-ID: References: <20260507-tcp-dm-netkit-v3-0-52821445867c@meta.com> <20260507-tcp-dm-netkit-v3-3-52821445867c@meta.com> <20260508134717.4ef87ab6@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260508134717.4ef87ab6@kernel.org> On Fri, May 08, 2026 at 01:47:17PM -0700, Jakub Kicinski wrote: > On Thu, 07 May 2026 19:27:48 -0700 Bobby Eshleman wrote: > > + /* Virtual device (e.g. netkit) the user called bind-tx on. Must be > > + * NETMEM_TX_NO_DMA. > > + */ > > + struct net_device *vdev; > > AI keeps complaining that we don't hold a reference to this dev which > I think is fine, we're just comparing pointers. Could we maybe make this > a void pointer and mention in the comment that we treat it as "best > effort cookie" (better phrasing welcome). > > Or we should wipe these vdev pointers when vdevs disappear, not sure > how hard that'd be (or whether it's worth the extra state). My guess is this would probably be the simplest way? diff --git a/net/core/devmem.c b/net/core/devmem.c index 644c286b778f..e28fae14c687 100644 --- a/net/core/devmem.c +++ b/net/core/devmem.c @@ -533,3 +533,38 @@ static const struct memory_provider_ops dmabuf_devmem_ops = { .nl_fill = mp_dmabuf_devmem_nl_fill, .uninstall = mp_dmabuf_devmem_uninstall, }; + +static int net_devmem_netdev_event(struct notifier_block *nb, + unsigned long event, void *ptr) +{ + struct net_device *dev = netdev_notifier_info_to_dev(ptr); + struct net_devmem_dmabuf_binding *binding; + unsigned long id; + + if (event != NETDEV_UNREGISTER) + return NOTIFY_DONE; + + xa_for_each(&net_devmem_dmabuf_bindings, id, binding) { + if (!net_devmem_dmabuf_binding_get(binding)) + continue; + mutex_lock(&binding->lock); + if (READ_ONCE(binding->vdev) == dev) { + ASSERT_EXCLUSIVE_WRITER(binding->vdev); + WRITE_ONCE(binding->vdev, NULL); + } + mutex_unlock(&binding->lock); + net_devmem_dmabuf_binding_put(binding); + } + + return NOTIFY_DONE; +} + +static struct notifier_block net_devmem_netdev_nb = { + .notifier_call = net_devmem_netdev_event, +}; + +static int __init net_devmem_init(void) +{ + return register_netdevice_notifier(&net_devmem_netdev_nb); +} +subsys_initcall(net_devmem_init); I'm open to either approach. The void* + comment is good too, IMHO. For the notifier, I'd probably want to add a test too ensure sendmsg() kicks back after the device is removed. Best, Bobby