Subject: Re:Re: [PATCH] powerpc: kernel: pci_dn: Add missing of_node_put() for of_get_xx API

From: "Liang He" <[email-masked]>
Date: Sat, 2 Jul 2022 05:36:50 +0800 (CST)

At 2022-07-02 03:47:22, "Tyrel Datwyler" <[email-masked]> wrote:
>On 7/1/22 06:17, Liang He wrote:
>> In pci_add_device_node_info(), we should use of_node_put() for the
>> reference 'parent' returned by of_get_parent() to keep refcount
>> balance.
>> 
>> Fixes: cca87d303c85 ("powerpc/pci: Refactor pci_dn")
>> Co-authored-by: Miaoqian Lin <[email-masked]>
>> Signed-off-by: Liang He <[email-masked]>
>> ---
>>  arch/powerpc/kernel/pci_dn.c | 1 +
>>  1 file changed, 1 insertion(+)
>> 
>> diff --git a/arch/powerpc/kernel/pci_dn.c b/arch/powerpc/kernel/pci_dn.c
>> index 938ab8838ab5..aa221958007e 100644
>> --- a/arch/powerpc/kernel/pci_dn.c
>> +++ b/arch/powerpc/kernel/pci_dn.c
>> @@ -330,6 +330,7 @@ struct pci_dn *pci_add_device_node_info(struct pci_controller *hose,
>>  	INIT_LIST_HEAD(&pdn->list);
>>  	parent = of_get_parent(dn);
>>  	pdn->parent = parent ? PCI_DN(parent) : NULL;
>NACK
>
>pdn->parent is now a long term reference so we should not do a put on parent
>until we pdn->parent is no longer valid.
>
>-Tyrel

Hi, Tyrel

Thanks for reviewing this code.

But I think there is some confusion about the of_get_parent() and I can confirm
my point when I check the 'pci_remove_device_node_info' function, which may be
a second bug.

In pci_remove_device_node_info(), I notice the comment, 'Drop the parent pci_dn's ref ...'.
However, of_get_parent() will increase the refcount of the parent, and then the
following of_node_put() will decrease the refcount, so, finally, there is no any change.

Back to this case, as the 'pdn->parent' is not the reference of parent device_node, it is
device_node's data, so I think it is better to keep the original meaning of refcounting, i.e,
add a of_node_put() to keep the refcount balance.

If I have some mis-understanding, please correct me.

Thanks,

Liang

>
>> +	of_node_put(parent);
>>  	if (pdn->parent)
>>  		list_add_tail(&pdn->list, &pdn->parent->child_list);
>>