Re: [PATCH v2] wireguard: device: use exit_rtnl callback instead of manual rtnl_lock in pre_exit

Jason A. Donenfeld
2026-04-14T13:28:56Z

Hi Shardul,

On Mon, Apr 13, 2026 at 5:13 PM Shardul Bankar
<shardul.b@mpiricsoftware.com> wrote:
>
> wg_netns_pre_exit() manually acquires rtnl_lock() inside the
> pernet .pre_exit callback. This causes a hung task when another
> thread holds rtnl_mutex - the cleanup_net workqueue (or the
> setup_net failure rollback path) blocks indefinitely in
> wg_netns_pre_exit() waiting to acquire the lock.
>
> Convert to .exit_rtnl, introduced in commit 7a60d91c690b ("net:
> Add ->exit_rtnl() hook to struct pernet_operations."), where the
> framework already holds RTNL and batches all callbacks under a
> single rtnl_lock()/rtnl_unlock() pair, eliminating the contention
> window.
>
> The rcu_assign_pointer(wg->creating_net, NULL) is safe to move
> from .pre_exit to .exit_rtnl (which runs after synchronize_rcu())
> because all RCU readers of creating_net either use maybe_get_net()
> - which returns NULL for a dying namespace with zero refcount - or
> access net->user_ns which remains valid throughout the entire
> ops_undo_list sequence.
>
> Reported-by: syzbot+f2fbf7478a35a94c8b7c@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?id=cb64c22a492202ca929e18262fdb8cb89e635c70
> Signed-off-by: Shardul Bankar <shardul.b@mpiricsoftware.com>

Thanks. Applied to the wireguard tree, and also added the missing
__net_exit and __read_mostly annotations in the process.

Jason