Re: [PATCH net-next V2 3/3] tun: add eBPF based queue selection method

[Jason Wang]

On 2017å11æ01æ 00:45, Michael S. Tsirkin wrote:
> > +static void __tun_set_steering_ebpf(struct tun_struct *tun,
> > +				    struct bpf_prog *new)
> > +{
> > +	struct bpf_prog *old;
> > +
> > +	old = rtnl_dereference(tun->steering_prog);
> > +	rcu_assign_pointer(tun->steering_prog, new);
> > +
> > +	if (old) {
> > +		synchronize_net();
> > +		bpf_prog_destroy(old);
> > +	}
> > +}
> > +
> Is this really called under rtnl?

Yes it is __tun_chr_ioctl() will call rtnl_lock().

> If no then rtnl_dereference
> is wrong. If yes I'm not sure you can call synchronize_net
> under rtnl.

Are you worrying about the long wait? Looking at synchronize_net(), it does:

void synchronize_net(void)
{
ÂÂÂ might_sleep();
ÂÂÂ if (rtnl_is_locked())
ÂÂÂ ÂÂÂ synchronize_rcu_expedited();
ÂÂÂ else
ÂÂÂ ÂÂÂ synchronize_rcu();
}
EXPORT_SYMBOL(synchronize_net);

Thanks