Re: [PATCH net-next v3 1/2] netconsole: publish the userdata payload with RCU

[Gustavo Luiz Duarte]

On Mon, Aug 10, 2026 at 10:36 AM Breno Leitao <leitao@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>

Reviewed-by: Gustavo Luiz Duarte <gustavold@xxxxxxxxx>