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a9560343d4
update_userdata() takes target_list_lock to swap nt->userdata and
nt->userdata_length, then frees the old buffer. Since commit
7eab73b186 ("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>