On Wed, 2024-02-14 at 14:59 +0100, Marc Kleine-Budde wrote:
> From: Ziqi Zhao <astrajoan@xxxxxxxxx>
>
> The following 3 locks would race against each other, causing the
> deadlock situation in the Syzbot bug report:
>
> - j1939_socks_lock
> - active_session_list_lock
> - sk_session_queue_lock
>
> A reasonable fix is to change j1939_socks_lock to an rwlock, since in
> the rare situations where a write lock is required for the linked list
> that j1939_socks_lock is protecting, the code does not attempt to
> acquire any more locks. This would break the circular lock dependency,
> where, for example, the current thread already locks j1939_socks_lock
> and attempts to acquire sk_session_queue_lock, and at the same time,
> another thread attempts to acquire j1939_socks_lock while holding
> sk_session_queue_lock.
Just FYI, Eric recently did a great job removing most rwlock in
networking code, see commit 0daf07e52709 ("raw: convert raw sockets to
RCU").
I'm unsure if the same reasoning apply to can, but perhaps you could
consider converting this code to RCU for net-next.
Cheers,
Paolo
