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Miller" , Eric Dumazet , Simon Horman , Shuah Khan , Sumit Semwal , Christian =?utf-8?B?S8O2bmln?= , Daniel Borkmann , Nikolay Aleksandrov , Tariq Toukan , Kaifeng Wang Subject: Re: [PATCH net v1 2/4] net: devmem: detach TX bindings on NETDEV_UNREGISTER Message-ID: References: <20261010025532.839559-1-almasrymina@google.com> <20261010025532.839559-3-almasrymina@google.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20261010025532.839559-3-almasrymina@google.com> On 10/10, Mina Almasry wrote: > TX devmem bindings (NETDEV_CMD_BIND_TX) have no bound RX queues, so > mp_dmabuf_devmem_uninstall() never runs when binding->dev or > binding->vdev unregisters. As a result, binding->dev and binding->vdev > dangle pointing to freed struct net_device memory, and the dma_buf > remains attached and mapped after device removal. > > Closing the netlink socket after netdev unregistration dereferences the > freed struct net_device in netdev_nl_sock_priv_destroy(): > > BUG: unable to handle page fault for address: ffff88824ca9b000 > Oops: Oops: 0000 [#1] SMP KASAN NOPTI > RIP: 0010:netdev_nl_sock_priv_destroy+0xbd/0x1e0 > Call Trace: > genl_release+0xf5/0x190 > netlink_release+0xd01/0x18d0 > __sock_release+0xb0/0x270 > sock_close+0x18/0x20 > > Add net_devmem_dev_unregister() called on NETDEV_UNREGISTER: > - When binding->dev (the physical DMA-capable device) unregisters, > erase the binding ID, clear both binding->dev and binding->vdev, wait > for in-flight RCU/TX readers via synchronize_net(), and unmap the > dma_buf under binding->lock. > - When only binding->vdev (virtual device) unregisters while > binding->dev lives, only clear binding->vdev so no new TX sends match > the virtual device while allowing in-flight TX packets on binding->dev > to finish DMA safely. > > Fixes: bd61848900bf ("net: devmem: Implement TX path") > Fixes: 1abe839b34ae ("net: devmem: support TX over NETMEM_TX_NO_DMA devices") > Cc: Kaiyuan Zhang > Cc: Stanislav Fomichev > Cc: Bobby Eshleman > Cc: Tariq Toukan > Cc: Kaifeng Wang > Signed-off-by: Mina Almasry > --- > net/core/devmem.c | 45 ++++++++++++++++++++++++++++++++++++++++++ > net/core/devmem.h | 5 +++++ > net/core/netdev-genl.c | 1 + > 3 files changed, 51 insertions(+) > > diff --git a/net/core/devmem.c b/net/core/devmem.c > index 5e4070b82df44..da7b3e8abaa13 100644 > --- a/net/core/devmem.c > +++ b/net/core/devmem.c > @@ -169,6 +169,51 @@ void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding) > percpu_ref_kill(&binding->ref); > } > > +void net_devmem_dev_unregister(struct net_device *dev) > +{ > + struct net_devmem_dmabuf_binding *binding; > + unsigned long xa_idx; > + [..] > + rcu_read_lock(); > + xa_for_each(&net_devmem_dmabuf_bindings, xa_idx, binding) { > + if (!percpu_ref_tryget(&binding->ref)) > + continue; > + rcu_read_unlock(); You use net_devmem_dmabuf_binding_put below but do not use net_devmem_dmabuf_binding_get here. Also, I feel like rcu_read_lock/rcu_read_unlock dance is confusing. bindings are not following rcu lifetimes. Can we race with __net_devmem_dmabuf_binding_free here? (xa_for_each returns a valid binding, then before we do try_get it gets kfree'd)