Re: [PATCH v2] once: Fix panic when module unload

[Hannes Frederic Sowa]

On Fri, Aug 6, 2021, at 10:21, Kefeng Wang wrote:
> DO_ONCE
> DEFINE_STATIC_KEY_TRUE(___once_key);
> __do_once_done
>   once_disable_jump(once_key);
>     INIT_WORK(&w->work, once_deferred);
>     struct once_work *w;
>     w->key = key;
>     schedule_work(&w->work);                     module unload
>                                                    //*the key is
> destroy*
> process_one_work
>   once_deferred
>     BUG_ON(!static_key_enabled(work->key));
>        static_key_count((struct static_key *)x)    //*access key, crash*
> 
> When module uses DO_ONCE mechanism, it could crash due to the above
> concurrency problem, we could reproduce it with link[1].
> 
> Fix it by add/put module refcount in the once work process.
> 
> [1] 
> https://lore.kernel.org/netdev/eaa6c371-465e-57eb-6be9-f4b16b9d7cbf@xxxxxxxxxx/
> 
> Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Reported-by: Minmin chen <chenmingmin@xxxxxxxxxx>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>

Acked-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>

Thanks,
Hannes