Re: [PATCH net v2 1/2] openvswitch: vport: fix self-deadlock on release of tunnel ports

[Aaron Conole <aconole@redhat.com>]

Ilya Maximets <i.maximets@ovn.org> writes:

> vports are used concurrently and protected by RCU, so netdev_put()
> must happen after the RCU grace period.  So, either in an RCU call or
> after the synchronize_net().  The rtnl_delete_link() must happen under
> RTNL and so can't be executed in RCU context.  Calling synchronize_net()
> while holding RTNL is not a good idea for performance and system
> stability under load in general, so calling netdev_put() in RCU call
> is the right solution here.
>
> However,
> when the device is deleted, rtnl_unlock() will call netdev_run_todo()
> and block until all the references are gone.  In the current code this
> means that we never reach the call_rcu() and the vport is never freed
> and the reference is never released, causing a self-deadlock on device
> removal.
>
> Fix that by moving the rcu_call() before the rtnl_unlock(), so the
> scheduled RCU callback will be executed when synchronize_net() is
> called from the rtnl_unlock()->netdev_run_todo() while the RTNL itself
> is already released.
>
> Fixes: 6931d21f87bc ("openvswitch: defer tunnel netdev_put to RCU release")
> Cc: stable@vger.kernel.org
> Acked-by: Eelco Chaudron <echaudro@redhat.com>
> Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
> ---

Acked-by: Aaron Conole <aconole@redhat.com>