update_userdata() takes target_list_lock to swap nt->userdata and nt->userdata_length, then frees the old buffer. Since commit 7eab73b18630 ("netconsole: convert to NBCON console infrastructure") that lock is also the console's device_lock, so writing a userdata value from configfs serialises against the printk core emitting messages. The buffer is immutable once published, which is what RCU is for. Move the string and its length into a single netcons_userdata object and publish it with rcu_replace_pointer(), freeing the old one with kfree_rcu(). New userdata design: 0) Unify the userdata fields into a struct netcons_userdata 1) update_userdata() no longer needs target_list_lock. 2) writers stay serialised by dynamic_netconsole_mutex. 3) reading userdata needs an RCU read lock. No functional change intended. Signed-off-by: Breno Leitao <leitao@debian.org> Reviewed-by: Gustavo Luiz Duarte <gustavold@gmail.com> Link: https://patch.msgid.link/20260810-netcons-userdata-rcu-v3-1-f65557f769ce@debian.org Signed-off-by: Paolo Abeni <pabeni@redhat.com>