On 2017年11月01日 21:59, Michael S. Tsirkin wrote:
On Wed, Nov 01, 2017 at 09:02:03PM +0800, Jason Wang wrote:
On 2017年11月01日 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().
Is the call from tun_free_netdev under rtnl too?
Looks not, need hold rtnl_lock() in tun_free_netdev in next version.
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)
{
might_sleep();
if (rtnl_is_locked())
synchronize_rcu_expedited();
else
synchronize_rcu();
}
EXPORT_SYMBOL(synchronize_net);
Thanks
Not the wait - expedited is not a good thing to allow unpriveledged
userspace to do, it interrupts all VMs running on the same box.
Good point.
We could use a callback though the docs warn userspace can use that
to cause a DOS and needs to be limited.
Will do this in next version.
Thanks
