Hi Bjorn,
On Wednesday 05 April 2017 10:22 PM, Bjorn Helgaas wrote:
> On Wed, Apr 05, 2017 at 02:22:21PM +0530, Kishon Vijay Abraham I wrote:
>> Introduce a new EP core layer in order to support endpoint functions in
>> linux kernel. This comprises the EPC library (Endpoint Controller Library)
>> and EPF library (Endpoint Function Library). EPC library implements
>> functions specific to an endpoint controller and EPF library implements
>> functions specific to an endpoint function.
>> ...
>
>> +/**
>> + * pci_epf_linkup() - Notify the function driver that EPC device has
>> + * established a connection with the Root Complex.
>> + * @epf: the EPF device bound to the EPC device which has established
>> + * the connection with the host
>> + *
>> + * Invoke to notify the function driver that EPC device has established
>> + * a connection with the Root Complex.
>> + */
>> +void pci_epf_linkup(struct pci_epf *epf)
>> +{
>> + if (!epf->driver)
>> + dev_WARN(&epf->dev, "epf device not bound to driver\n");
>> +
>> + epf->driver->ops->linkup(epf);
>
> I don't understand what's going on here. We warn if epf->driver is
> NULL, but the next thing we do is dereference it.
>
> For NULL pointers that are symptoms of Linux defects, I usually prefer
> not to check at all so that a dereference generates an oops and we can
> debug the problem. For NULL pointers caused by user error, we would
> generally return an error that percolates up to the user.
>
> I haven't competely wrapped my head around this endpoint support, but
> I assume a NULL pointer here would be caused by user error, not
> necessarily a Linux defect. So why would we dereference a NULL
> pointer? And what happens when we do? Is this just going to oops an
> embedded Linux running inside the endpoint? Is that the correct
> behavior?
With the new configfs directory structure, this should be a kernel error.
However the EPF layer should be independent of how it's API's are used i.e
someone can create a new sysfs/configfs structure and the value of epf->driver
might be dependent on user actions.
I think I'd prefer not to dereference NULL pointers since we anyways have a
dev_WARN for debug. I'll resend this patch with return if epf->driver is NULL.
Thanks
Kishon
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