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Tue, 15 Apr 2025 10:33:57 -0700 (PDT) Date: Tue, 15 Apr 2025 10:33:55 -0700 From: Stanislav Fomichev To: Taehee Yoo Cc: davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, edumazet@google.com, andrew+netdev@lunn.ch, horms@kernel.org, almasrymina@google.com, asml.silence@gmail.com, dw@davidwei.uk, sdf@fomichev.me, skhawaja@google.com, simona.vetter@ffwll.ch, kaiyuanz@google.com, netdev@vger.kernel.org Subject: Re: [PATCH net] net: devmem: fix kernel panic when socket close after module unload Message-ID: References: <20250415092417.1437488-1-ap420073@gmail.com> Precedence: bulk X-Mailing-List: netdev@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: <20250415092417.1437488-1-ap420073@gmail.com> On 04/15, Taehee Yoo wrote: > Kernel panic occurs when a devmem TCP socket is closed after NIC module > is unloaded. > > This is Devmem TCP unregistration scenarios. number is an order. > (a)socket close (b)pp destroy (c)uninstall result > 1 2 3 OK > 1 3 2 (d)Impossible > 2 1 3 OK > 3 1 2 (e)Kernel panic > 2 3 1 (d)Impossible > 3 2 1 (d)Impossible > > (a) netdev_nl_sock_priv_destroy() is called when devmem TCP socket is > closed. > (b) page_pool_destroy() is called when the interface is down. > (c) mp_ops->uninstall() is called when an interface is unregistered. > (d) There is no scenario in mp_ops->uninstall() is called before > page_pool_destroy(). > Because unregister_netdevice_many_notify() closes interfaces first > and then calls mp_ops->uninstall(). > (e) netdev_nl_sock_priv_destroy() accesses struct net_device. > But if the interface module has already been removed, net_device > pointer is invalid, so it causes kernel panic. > > In summary, there are only 3 possible scenarios. > A. sk close -> pp destroy -> uninstall. > B. pp destroy -> sk close -> uninstall. > C. pp destroy -> uninstall -> sk close. > > Case C is a kernel panic scenario. > > In order to fix this problem, it makes netdev_nl_sock_priv_destroy() do > nothing if a module is already removed. > The mp_ops->uninstall() handles these instead. > > The netdev_nl_sock_priv_destroy() iterates binding->list and releases > them all with net_devmem_unbind_dmabuf(). > The net_devmem_unbind_dmabuf() has the below steps. > 1. Delete binding from a list. [..] > 2. Call _net_mp_close_rxq() for all rxq's bound to a binding. This should not happen in the (C) case, right? mp_dmabuf_devmem_uninstall removes the rxq from the xa. Can you explain more on why specifically the crash occurs? Are we missing some check in netdev_nl_sock_priv_destroy that makes sure the device is still alive?