Re: [PATCH net 3/3] netdevsim: psp: rcu protect psp_dev reference

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

On 5/6/26 3:34 PM, Willem de Bruijn wrote:
> Daniel Zahka wrote
>>   static ssize_t
>> @@ -228,16 +237,23 @@ nsim_psp_rereg_write(struct file *file, const char __user *data, size_t count,
>>   		     loff_t *ppos)
>>   {
>>   	struct netdevsim *ns = file->private_data;
>> -	int err;
>> +	struct psp_dev *psd;
>> +	ssize_t ret;
>>   
>>   	mutex_lock(&ns->psp.rereg_lock);
>> -	__nsim_psp_uninit(ns);
>> +	__nsim_psp_uninit(ns, false);
>> +
>> +	psd = psp_dev_create(ns->netdev, &nsim_psp_ops, &nsim_psp_caps, ns);
>> +	if (IS_ERR(psd)) {
>> +		ret = PTR_ERR(psd);
>> +		goto out;
>> +	}
> Do you want to create the new device first and only delete the old
> state if that succeeds? To avoid a netdevsim in state without dev.
>
>>   
>> -	ns->psp.dev = psp_dev_create(ns->netdev, &nsim_psp_ops,
>> -				     &nsim_psp_caps, ns);
>> -	err = PTR_ERR_OR_ZERO(ns->psp.dev);
>> +	rcu_assign_pointer(ns->psp.dev, psd);
>> +	ret = count;
>> +out:
>>   	mutex_unlock(&ns->psp.rereg_lock);
>> -	return err ?: count;
>> +	return ret;
>>   }
>>   

Unfortunately, the way we have psp_dev_unregister() written, it would 
clear out the main_netdev->psp_dev field from the second 
psp_dev_create() call. I don't believe there is use case to do this in a 
real driver, so I'm not sure we need to change how the create/unregister 
paths work.