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

From: Kefeng Wang
Date: Sun Aug 08 2021 - 21:14:03 EST



On 2021/8/6 23:22, Hannes Frederic Sowa wrote:
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.

Thanks,
Hannes
.