Re: [PATCH v9 net-next 3/5] psp: add a new netdev event for dev unregister

[Daniel Zahka <daniel.zahka@gmail.com>]

On 3/31/26 5:51 PM, Wei Wang wrote:
> On Tue, Mar 31, 2026 at 6:30 AM Daniel Zahka <daniel.zahka@gmail.com> wrote:
>>
>> On 3/30/26 6:31 PM, Wei Wang wrote:
>>> +static bool psp_notifier_registered;
>>> +
>>> +/**
>>> + * psp_attach_netdev_notifier() - register netdev notifier on first use
>>> + *
>>> + * Register the netdevice notifier when the first device association
>>> + * is created. In many installations no associations will be created and
>>> + * the notifier won't be needed.
>>> + *
>>> + * Must be called without psd->lock held, due to lock ordering:
>>> + * rtnl_lock -> psd->lock (the notifier callback runs under rtnl_lock
>>> + * and takes psd->lock).
>>> + */
>>> +void psp_attach_netdev_notifier(void)
>>> +{
>>> +     if (READ_ONCE(psp_notifier_registered))
>>> +             return;
>>> +
>>> +     mutex_lock(&psp_devs_lock);
>>> +     if (!psp_notifier_registered) {
>>> +             if (!register_netdevice_notifier(&psp_netdev_notifier))
>>> +                     WRITE_ONCE(psp_notifier_registered, true);
>>> +     }
>>> +     mutex_unlock(&psp_devs_lock);
>>> +}
>> ...
>>> +int psp_device_get_locked_dev_assoc(const struct genl_split_ops *ops,
>>> +                                 struct sk_buff *skb, struct genl_info *info)
>>> +{
>>> +     psp_attach_netdev_notifier();
>>> +
>>> +     return __psp_device_get_locked(ops, skb, info, false);
>>> +}
>>
>>   From an AI review, but seems plausible to me:
>>
>> psp_device_get_locked_dev_assoc() will proceed even in the path where
>> register_netdevice_notifier() and psp_notifier_registered stays false.
>>
> This behavior is intended. In case register_netdevice_notifier() fails
> for some reason, this current dev_assoc will proceed but the next
> dev_assoc operation will try to register_netdevice_notifier() again.


That doesn't sound correct to me. If the notifier is not registered, but 
the dev-assoc command succeeds, then an entry can leak in the 
psd->assoc_dev_list during a NETDEV_UNREGISTER.