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

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

[Liang He]

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 <linmq006@gmail.com>
Signed-off-by: Liang He <windhl@126.com>
---
 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;
+	of_node_put(parent);
 	if (pdn->parent)
 		list_add_tail(&pdn->list, &pdn->parent->child_list);
 
-- 
2.25.1

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

[Tyrel Datwyler]

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 <linmq006@gmail.com>
> Signed-off-by: Liang He <windhl@126.com>
> ---
>  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parent is no longer valid.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

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

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

[Liang He]

At 2022-07-02 03:47:22, "Tyrel Datwyler" <tyreld@linux.ibm.com> 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 <linmq006@gmail.com>
>> Signed-off-by: Liang He <windhl@126.com>
>> ---
>>  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);
>> 

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

[Tyrel Datwyler]

On 7/1/22 12:47, Tyrel Datwyler 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 <linmq006@gmail.com>
>> Signed-off-by: Liang He <windhl@126.com>
>> ---
>>  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.

I withdraw my NACK. On closer inspection pdn->parent is a reference to the
parent struct pci_dn and not a reference to a parent struct device_node.

Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>

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

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

[Michael Ellerman]

On Fri, 1 Jul 2022 21:17:50 +0800, 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.
> 
> 

Applied to powerpc/next.

[1/1] powerpc: kernel: pci_dn: Add missing of_node_put() for of_get_xx API
      https://git.kernel.org/powerpc/c/110a1fcb6c4d55144d8179983a475f17a1d6f832

cheers