Re: [PATCH 5/6] OF: Utility helper functions for dynamic nodes

[Pantelis Antoniou <pantelis.antoniou@konsulko.com>]

Hi Ioan,

I'm going to let Grant answer that but the code in question doesn't look right.

On Jun 23, 2014, at 9:33 PM, Ioan Nicu wrote:

> Hi Pantelis,
> 
> On Mon, Jun 23, 2014 at 07:57:24PM +0300, ext Pantelis Antoniou wrote:
>> Hi Alexander,
>> 
>> On Jun 23, 2014, at 7:26 PM, Alexander Sverdlin wrote:
>> 
>>> Hello Pantelis!
>>> 
>>> On 22/06/14 11:40, ext Pantelis Antoniou wrote:
>>>> Introduce helper functions for working with the live DT tree,
>>>> all of them related to dynamically adding/removing nodes and
>>>> properties.
>>>> 
>>>> __of_copy_property() copies a property dynamically
>>>> __of_create_empty_node() creates an empty node
>>>> 
>>>> Bug fix about prop->len == 0 by Ionut Nicu <ioan.nicu.ext@nsn.com>
>>> 
>>> Are you sure about this? (see below...)
>>> 
> 
> Alexander is right, my fix was lost even though it's mentioned in this patch.
> 

I'm sorry, I didn't understand that the intention of the fix was to address
the issue below.

>>>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
>>>> ---
>> 
>> [snip]
>>>> +
>>>> +	if (prop->length > 0) {
>>>       ^^^^^^^^^^^^^^^^^^^^^
>>> Seems, that length==0 case will still produce value==NULL results,
>>> which will brake some checks in the kernel... Or am I missing something in
>>> the new version?
>>> 
>> 
>> prop->value will be set to NULL, and length will be set to zero (kzalloc).
>> This is a normal zero length property.
>> 
>> I don't know of any place in the kernel accessing the value if prop->length==0
>> 
> 
> We have a simple use case. We have an overlay which adds an interrupt controller.
> If you look in drivers/of/irq.c, in of_irq_parse_raw():
> 
> [...]
> 	/* Now start the actual "proper" walk of the interrupt tree */
> 	while (ipar != NULL) {
> 		/* Now check if cursor is an interrupt-controller and if it is
> 		 * then we are done
> 		 */
> 		if (of_get_property(ipar, "interrupt-controller", NULL) !=
> 				NULL) {
> 			pr_debug(" -> got it !\n");
> 			return 0;
> 		}
> [...]
> 
> A node is identified as an interrupt controller if it has a zero-length property
> called "interrupt-controller" but with a non-NULL value.
> 
> My proposed fix for this was to remove the if () condition. propn->value will be
> allocated with kmalloc(0) which returns ZERO_SIZE_PTR which is != NULL.
> 

If that's the case, the code in irq.c is wrong.

interrupt-controller is a bool property; the correct call to use is of_property_read_bool()
which returns true or false when the value is defined.

The use of of_get_property is a bug here. It is perfectly valid for a property to have a
NULL value when length = 0.

Regards

-- Pantelis

> 
>> 
>> [snip]
>> 
>>>> +
>>>> #endif /* _LINUX_OF_H */
>>>> 
>>> 
>>> -- 
>>> Best regards,
>>> Alexander Sverdlin.
>> 
>> Regards
>> 
>> -- Pantelis
>> 
> 
> Regards,
> Ionut Nicu