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Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, eric.dumazet@gmail.com, Nikolay Aleksandrov , Ido Schimmel Subject: Re: [PATCH net-next] net: bridge: remove stale rcu_barrier() in br_multicast_dev_del() In-Reply-To: <20260519095540.2643318-1-edumazet@google.com> (Eric Dumazet's message of "Tue, 19 May 2026 09:55:40 +0000") References: <20260519095540.2643318-1-edumazet@google.com> Date: Tue, 19 May 2026 12:52:23 +0200 Message-ID: <87cxyroemw.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Tue, May 19, 2026 at 09:55 AM GMT, Eric Dumazet wrote: > This rcu_barrier() came from a time call_rcu() calls were used in > net/bridge/br_multicast.c. > > Now kfree_rcu() is there, we can remove this problematic rcu_barrier() > which causes extreme RTNL pressure in many syzbot reports. > > INFO: task syz-executor:77945 is blocked on a mutex likely owned by task kworker/u1024:5:36537. > task:kworker/u1024:5 state:D stack:24616 pid:36537 tgid:36537 ppid:2 task_flags:0x4208060 flags:0x00080000 last_sleep:612797637337 > Workqueue: netns cleanup_net > Call Trace: > > [] context_switch+0xf2a/0x1730 kernel/sched/core.c:6483 > [] __schedule+0x1133/0x43a0 kernel/sched/core.c:8411 > [] __schedule_loop kernel/sched/core.c:8514 [inline] > [] schedule+0xab/0x260 kernel/sched/core.c:8529 > [] schedule_timeout+0xc3/0x2b0 kernel/time/sleep_timeout.c:75 > [] do_wait_for_common kernel/sched/completion.c:100 [inline] > [] __wait_for_common kernel/sched/completion.c:121 [inline] > [] wait_for_common kernel/sched/completion.c:132 [inline] > [] wait_for_completion+0x2c7/0x5d0 kernel/sched/completion.c:153 > [] rcu_barrier+0x49f/0x620 kernel/rcu/tree.c:3888 > [] br_multicast_dev_del+0x303/0x350 net/bridge/br_multicast.c:4459 > [] br_dev_uninit+0x1c/0x40 net/bridge/br_device.c:157 > [] unregister_netdevice_many_notify+0x1c1c/0x2300 net/core/dev.c:12599 > [] ops_exit_rtnl_list net/core/net_namespace.c:187 [inline] > [] ops_undo_list+0x3d3/0x940 net/core/net_namespace.c:248 > > Signed-off-by: Eric Dumazet > --- Reviewed-by: Jakub Sitnicki