Re: [PATCH net v2] openvswitch: vport: fix race between linking and the device notifier

[Aaron Conole <aconole@redhat.com>]

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

> Sashiko reports that it is technically possible that we got the device
> reference, but by the time we're linking it to the OVS datapath, it
> may be already in the process of being deleted.  In this case if the
> notifier wins the race for RTNL, it will see that the device is not
> yet in the OVS datapath (ovs_netdev_get_vport() will fail in the
> dp_device_event()) and will do nothing.  Then the ovs_netdev_link()
> will take the RTNL and link the unregistering device to OVS datapath.
>
> Eventually, netdev_wait_allrefs_any() will re-broadcast the event and
> the device will be properly detached, but it will take at least a
> second before that happens, so it's not something we should rely on.
>
> Let's avoid linking the non-registered device in the first place.
>
> Note: As per documentation, RTNL doesn't protect the reg_state, but
> it actually does for all the state transitions we care about here,
> so it should not be necessary to use READ_ONCE or taking the instance
> lock.  We can still do that, but we have a few more places even in
> this file where the reg_state is accessed without those while under
> RTNL, and many more places like this across the kernel code, so it
> might make more sense to change all of them in a more centralized
> fashion in the future, if necessary.
>
> Fixes: ccb1352e76cf ("net: Add Open vSwitch kernel components.")
> Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
> ---

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