On Fri, 2017-12-08 at 10:54 +0800, Jason Wang wrote:
> Private destructor could be called when register_netdev() fail with
> rtnl lock held. This will lead deadlock in tun_free_netdev() who
> tries
> to hold rtnl_lock. Fixing this by switching to use spinlock to
> synchronize.
>
> Fixes: 96f84061620c ("tun: add eBPF based queue selection method")
> Reported-by: Eric Dumazet <eric.duma...@gmail.com>
> Cc: Eric Dumazet <eric.duma...@gmail.com>
> Cc: Willem de Bruijn <will...@google.com>
> Signed-off-by: Jason Wang <jasow...@redhat.com>
> ---
> drivers/net/tun.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 787cc35..f7ccd79 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2050,8 +2050,11 @@ static int __tun_set_steering_ebpf(struct
> tun_struct *tun,
> new->prog = prog;
> }
>
> - old = rtnl_dereference(tun->steering_prog);
> + spin_lock(&tun->lock);
> + old = rcu_dereference_protected(tun->steering_prog,
> + lock_is_held(&tun->lock));
> rcu_assign_pointer(tun->steering_prog, new);
> + spin_unlock(&tun->lock);
>
Hi Jason, thank you for the following up.
Have you tested this code path with lockdep enabled ?
My gut feeling is that you need spin_lock_bh() here.
Thanks
