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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: Andrea Parri , Kuniyuki Iwashima , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next v2] rtnetlink: comment the RCU waits in unregister paths Date: Thu, 15 Oct 2026 10:17:16 +0200 Message-ID: <20261015081723.404990-1-parri.andrea@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit rtnl_unregister_all() and rtnl_af_unregister() wait for RCU readers before tearing down what those readers use, but do not say which readers they are waiting for. A missing wait is then easy to overlook: rtnl_link_unregister() lacked its synchronize_rcu() until commit 3b70edea393d ("rtnetlink: wait for RCU readers in rtnl_link_unregister()"). Add a comment to both waits, naming the readers each one waits for. Suggested-by: Eric Dumazet Link: https://lore.kernel.org/CAL4WiioFMQN4troVjQjCmE6Z9kwwb95SnoEupjD=PPSK6Q5f6w@mail.gmail.com Assisted-by: LLM Signed-off-by: Andrea Parri --- v2: - Drop the comments on synchronize_srcu(), its argument already names the readers (Kuniyuki) - Name rtnetlink_rcv_msg() and try_module_get() in the rtnl_unregister_all() comment (Kuniyuki) - Mention the rtnl_af_ops walkers that do not take ops->srcu in the rtnl_af_unregister() comment v1: https://lore.kernel.org/20261008124423.11543-1-parri.andrea@gmail.com net/core/rtnetlink.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index 15bffafbf0a9c..d73dbc2c8ba0d 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -526,6 +526,9 @@ void rtnl_unregister_all(int protocol) } rtnl_unlock(); + /* Wait for rtnl_get_link() calls that rtnetlink_rcv_msg() makes + * under RCU, before try_module_get(). + */ synchronize_net(); kfree(tab); @@ -843,6 +846,9 @@ void rtnl_af_unregister(struct rtnl_af_ops *ops) list_del_rcu(&ops->list); spin_unlock(&rtnl_af_ops_lock); + /* Wait for rtnl_af_ops walkers that invoke callbacks without + * ops->srcu, and for rtnl_af_lookup() readers not yet holding it. + */ synchronize_rcu(); synchronize_srcu(&ops->srcu); cleanup_srcu_struct(&ops->srcu); -- 2.53.0